Merge branch 'serhei/bpf_asm' -- kernel_string() tapset and experimental bpf assembler

[systemtap.git] / NEWS

* What's new in version 4.1

- Runtime/tapsets were ported to include up to kernel version PRERELEASE



* What's new in version 4.0, 2018-10-13

- Runtime/tapsets were ported to include up to kernel version 4.19-rc

- A new network service, stap-exporter, is included.  It glues
  systemtap and the web.  It allows a prometheus (or compatible
  systems such as pcp) to consume metrics exported by systemtap
  scripts.  Some tapset macros/functions are available to make it
  easier to write such scripts.  See the stap-exporter(8) man page and
  the systemd service.

- When a systemtap module is loaded, the name of the original stap script
  is now printed to dmesg by the kernel runtime.

- On some Fedora kernels, the information necessary to automatically
  engage in SecureBoot module signing is hidden from systemtap.
  Setting the $SYSTEMTAP_SIGN environment variable forces it on.
  A running stap-server instance will also be needed.

- Embedded-C functions marked /* guru */ may now be invoked from other
  tapset probes / functions, while still being invalid for normal call
  from an unprivileged user script.

- The syscall tapset is now updated to work on kernel 4.17+.
  Additionally, the tapset now includes an automatic fallback alias to
  the sys_enter / sys_exit kernel tracepoints, if no other
  kprobe-based mechanism is found.  These changes have brought
  unavoidable consequences.  Raw $target variables for the syscall
  arguments and return probes (e.g. @entry($fd), $return, returnval())
  may not longer be relied upon. Instead, use the variables defined by
  the tapset aliases.  For example:
  
     % stap -L syscall.read
     syscall.read name:string fd:long buf_uaddr:long count:long argstr:string
     % stap -L syscall.read.return
     syscall.read.return name:string retval:long retstr:string
     
  to see the available variables for that syscall.  See
  [man stapprobes] for further details.  returnval() in particular is
  being deprecated soon; use retval in syscall.*.return probes instead.

- New script language operators @kderef/@uderef and @kregister/@uregister
  were added.
  @kderef/@uderef (size,address) can be used to dereference integers and
  @kregister/@uregister (dwarf#) can be used to access register values.

- A systemd service file has been added for systemtap.service (which
  runs a configurable set of scripts automatically on system
  startup). The existing /etc/init.d/systemtap init script has been
  moved to a new utility command 'systemtap-service' which preserves
  functionality such as configuring onboot systemtap scripts via
  dracut. See systemtap-service(8) for details.

- The eBPF backend's string support has been improved. Strings
  can now be stored in variables, passed as function arguments,
  and stored as array keys and values.

- The 3rd operand of the ternary operator '?:' in the script language
  now binds tighter than the binary assignment operators like '=' and
  '+=', just like the C language. The original operator precedence can
  be restored by the '--compatible 3.3' option.

- The script language now supports the use of bare 'return' statements
  (without any return values) inside functions which do not return any
  values. A trailing semicolon is recommended for such return
  statements to avoid any potential ambiguity. The parser treats a
  following semicolon (';') or a closing curly bracket ('}') as a
  terminator for such bare return statements.

- Parentheses after unary '&' with a target-symbol expression is
  now accepted in the script language.

- Tapset functions register() and u_register() now support 8-bit
  x86 register names "ah", "al", "bh", "bl", "ch", "cl", "dh", and
  "dl" on both x86_64 and i386. And 16-bit x86 registers are now
  truly read as 16-bit integers instead of as 32-bit ones.

- The experimental ftrace ring buffer mechanism (STP_USE_RING_BUFFER)
  has been deprecated and may be removed in future versions.

* What's new in version 3.3, 2018-06-08

- A new "stap --example FOO.stp" mode searches the example scripts
  distributed with systemtap for a file named FOO.stp, so its whole
  path does not need to be typed in.

- Systemtap's runtime has learned to deal with several of the
  collateral damage from kernel hardening after meltdown/spectre,
  including more pointer hiding and relocation.  The kptr_restrict
  procfs flag is forced on if running on a new enough kernel.

- The "stap --sysroot /PATH" option has received a revamp, so it
  works much better against cross-compiled environments.

- The eBPF backend has learned to perform loops - at least in the
  userspace "begin/end" probe contexts, so one can iterate across BPF
  arrays for reporting.  (The linux kernel eBPF interpreter precludes
  loops and string processing.)  It can also handle much larger probe
  handler bodies, with a smarter register spiller/allocator.

- The eBPF backend now supports uprobes, perf counter, timer, and
  tracepoint probes.

- An rpm macro %_systemtap_tapsetdir is now defined, to make it
  easier for third party packages to add .stp files into the standard
  tapset.

- Several low level locking-related fixes were added to the runtime
  that used uprobes/tracepoint apis, in order to work more reliably on
  rt kernels and on high-cpu-count machines.

- Runtime/tapsets were ported to include up to kernel version 4.16.
  (The syscall tapsets are broken on kernel 4.17-rc, and will be fixed
  in a next release coming soon; PR23160.)

- Add new built-in tapset function abort() which is similar to exit(),
  but it aborts the current probe handler (and any function calls in
  it) immediately instead of waiting for its completion. Probe handlers
  already running on *other* CPU cores, however, will still continue
  to their completion. Unlike error(), abort() cannot be caught by
  try {...} catch {...}. Similar to exit(), abort() yeilds the zero
  process exit code. It works with both the kernel and dyninst runtimes.
  This function can be disabled by the '--compatible 3.3' option.

* What's new in version 3.2, 2017-10-18

- SystemTap now includes an extended Berkeley Packet Filter (eBPF)
  backend. This experimental backend does not use kernel modules
  and instead produces eBPF programs that are verified by the kernel
  and executed by an in-kernel virtual machine. Select this backend
  with the new stap option '--runtime=bpf'. For example:

    stap --runtime=bpf -e \
      'probe kernel.function("sys_open") { printf("hi from stapbpf!\n") }'

  Please see the stapbpf(8) man page for more information.

- The regular expression engine now supports extraction of the matched
  string and subexpressions using the matched() tapset function:
  
      if ("regexculpicator" =~ "reg(ex.*p).*r") log(matched(1))
   -> exculp

- The translator produces better diagnostics for common/annoying case
  of missing debuginfo that blocks use of context $variables. 

- "stap -k" build trees in $TMPDIR now also include a preprocessed .i form
  of the generated module .c code, for problem diagnostics purposes.

- The syscall.execve probes now provide a decoded env_str string vector,
  just like the argument vector. Because of this, the unused
  __count_envp() and __count_compat_evenp() functions have been
  deprecated.

- The task_exe_file() Function has been deprecated and replaced by the
  current_exe_file() function.

- A new probe alias input.char allows scripts to access input from stdin
  during runtime.

* What's new in version 3.1, 2017-02-17

- Systemtap now needs C++11 to build.

- Syscall and nd_syscall tapsets have been merged in a way that either
  dwarf-based, or non-dwarf probe gets automatically used based on
  debuginfo availability (e.g. probe syscall.open).

  To force use the dwarf based probe, a dw_syscall has been introduced
  (e.g. probe dw_syscall.open) and the non-dwarf syscall probes were
  left untouched (e.g. nd_syscall.open).

- The syscall tapset files have been reorganized in a way that original
  big tapset files carrying many syscall probes were split into smaller
  'sysc_' prefixed tapset files.  This should reduce the syscall tapset
  maintenance burden.

- The powerpc variant of syscall.compat_sysctl got deprecated on favor of
  syscall.sysctl32. This aligns the syscall to its respective nd_syscall and
  to ia64/s390/x86_64 variants too.

- The syscall.compat_pselect7a (this was actually a typo, but still available
  for compatibility purposes with --compatible 1.3) has beed deprecated.

- The 'description_auddr' convenience variable of syscall.add_key has been
  deprecated.

- Support has been added for probing python 2 and 3 functions using a
  custom python helper module. Python function probes can target
  function entry, returns, or specific line numbers.

      probe python2.module("myscript").function("foo")
         { println($$parms) }

  To run with the custom python helper module, you'd use python's '-m'
  option like the following:
  
      stap myscript.stp -c "python -m HelperSDT myscript.py"

- Java method probes now convert all types of java parameters to
  strings using the java toString() method before passing them to
  systemtap probes; new argN variables copy them into string
  variables.  Previously, only numeric types were passed, and only by
  casting to integers.  The previous behaviour is available with
  --compatible=3.0 .

  3.1:  probe java(...).class(...).method(...) { printf("%s", arg1) }
  3.0:  probe java(...).class(...).method(...) { printf("%d", $arg1) }

- An older defensive measure to suppress kernel kprobes optimizations
  since the 3.x era has been disabled for recent kernels.  This improves
  the performance of kernel function probes.  In case of related problems,
  please report and work around with:
  # echo 0 > /proc/sys/debug/kprobes-optimization

- Context variables in .return probes should be accessed with @entry($var)
  rather than $var, to make it clear that entry-time snapshots are being
  used.  The latter construct now generates a warning.  Availability testing
  with either @defined(@entry($var)) or @defined($var) works.

- Tapsets containing process probes may now be placed in the special
  $prefix/share/systemtap/tapset/PATH/ directory to have their process parameter
  prefixed with the location of the tapset. For example,

  process("foo").function("NAME") expands to process("/usr/bin/foo").function("NAME")
  when placed in $prefix/share/systemtap/tapset/PATH/usr/bin/

  This is intended to help write more reusable tapsets for userspace binaries.

- The implementation of "var <<< X" for each aggregate variable is now
  specially compiled to compute only the script-requested @op(var) values,
  not all potential ones.  This speeds up the <<< operations.

- Systemtap now warns if script arguments given on the command line are unused,
  instead of mentioned by the script with $n/@n.

- Netfilter tapsets now provide variables data_hex and data_str to display packet
  contents in hexadecimal and ASCII respectively.

- Translator now accepts new @const() operator for convenient expressing
  constants in tapset code, or guru-mode scripts. See stap(1) for details.

- New -T option allows the script to be terminated after a specified number
  of seconds. This is a shortcut for adding the probe, timer {exit()}.

- New installcheck-parallel testsuite feature allows running the tests in
  parallel in order to save time.  See testsuite/README for details.

- New tapset functions set_user_string(), set_user_string_n(), set_user_long()
  set_user_int(), set_user_short(), set_user_char() and set_user_pointer() to
  write a value of specified type directly to a user space address.

- New tapset functions user_buffer_quoted(), user_buffer_quoted_error(), 
  kernel_buffer_quoted(), and kernel_buffer_quoted_error() to print a
  buffer of an exact length.  These functions can handle '\0' characters
  as well.  

- New statistics @variance() operator using the Welford's online algorithm
  for per-cpu computation, and the Total Variance formula authored by
  Niranjan Kamat and Arnab Nandi from the Ohio State University for the
  cross-cpu aggregation.

- New command within interactive mode, sample.  Allows you to search through
  all included example scripts to load for further editing or running.  Sample
  and example scripts have been moved to /usr/share/systemtap/examples.  A
  symlink in the former location under $docdir links to it.

* What's new in version 3.0, 2016-03-27

- The new experimental "interactive" mode, specified by "stap -i",
  drops you into a command-line prompt where you can build up a script,
  run it, edit it, run it again, etc. Type "help" for a list of commands.

- New experimental --monitor[=INTERVAL] option similar to unix "top". This
  allows users to see statistics about the running module(uptime, module name,
  invoker uid, memory sizes, global variables, and the current probe list
  along with their statistics).

  An interface is also provided to allow control over the running
  module(resetting global variables, sorting the list of probes, deactivating
  and reactivating probes).

- The performance of associative arrays have been dramatically
  improved, especially for densely filled tables and for multiple
  indexes.  The hash tables behind these arrays is now sized as a
  function of the array maximum size with an optional MAPHASHBIAS
  space/time tradeoff knob.

- Add macros @prints to print a scalar aggregate variable, @prints[1-9]
  to print an array aggregate (of given index-arity), formatted similarly
  to the automatic printing of written-only global variables.

  global a, b
  probe oneshot { a <<< 1; b[tid()] <<< 2 }
  probe end { @prints(a); @prints1(b) }

- Functions may now be overloaded during module runtime using the "next"
  statement in script functions and STAP_NEXT macro for embedded-C functions.
  They may also be overloaded by number of parameters during compile time.
  For example,

  Runtime overloading:
    function f() { if (condition) next; print("first function") }
    function f() %{ STAP_NEXT; print("second function") %}
    function f() { print("third function") }

  For the given functions above, a functioncall f(), will execute the body of the
  third function if condition evaluates to true and print "third function".
  Note that the second function is unconditionally nexted.

  Parameter overloading:
    function g() { print("first function") }
    function g(x) { print("second function") }
    g() -> "first function"
    g(1) -> "second function"

  Note that runtime overloading does not occur in the above example as the number
  of parameters of the functions differ. The use of a next statement inside a function
  while no more overloads remain will trigger a runtime exception. The function
  candidates are selected at compile time and is determined by the number of arguments
  provided for the functioncall.

- Add Czech version of manual pages.

- The stap compile server will log the stap client's options that are passed
  to the server. The options that get logged on the server will include the
  script name or the -e script, depending on which is used by the client.

- Embedded-C functions and blocks may now access script level global variables
  using the STAP_GLOBAL_GET_* and STAP_GLOBAL_SET_* macros.

  To read or write the script global var, the /* pragma:read:var */ or
  /* pragma:write:var */ marker must be placed in the embedded-C function or block.
  The written type must match the type inferred at script level.

  Scalars:
    STAP_GLOBAL_SET_var(STAP_GLOBAL_GET_var()+1) -> increments script global var by 1
    STAP_GLOBAL_SET_var("hello")

  Associative arrays:
    STAP_GLOBAL_GET_var(index-1, ..., index-n)
    STAP_GLOBAL_SET_var(index-1, ..., index-n, new value)

- Probe point brace expansion is now supported to improve brevity in
  specifying probe points. For example,

  process.{function("a"), function("b").{call,return}}
  => process.function("a"), process.function("b").call, process.function("b").return

  process.{function("*").callees,plt}?
  => process.function("*").callees?, process.plt?

  {kernel,module("nfs")}.function("nfs*")!
  => kernel.function("nfs*")!, module("nfs").function("nfs*")!

- Profiling timers at arbitrary frequencies are now provided and perf probes
  now support a frequency field as an alternative to sampling counts.

  probe timer.profile.freq.hz(N)
  probe perf.type(N).config(M).hz(X)

  The specified frequency is only accurate up to around 100hz. You may
  need to provide a higher value to achieve the desired rate.

- Added support for private global variables and private functions. The scope
  of these is limited to the tapset file they are defined in (PR19136).

- New tapset function string_quoted() to quote and \-escape general strings.
  String $context variables that are pretty-printed are now processed with
  such a quotation engine, falling back to a 0x%x (hex pointer) on errors.

- Functions get_mmap_args() and get_32mmap_args() got deprecated.

* What's new in version 2.9, 2015-10-08

- SystemTap now uses symbols from /proc/kallsyms when kernel debuginfo is not
  available.

- New --prologue-searching[=WHEN] option has been added to stap with '-P' being
  its short counterpart.  Using --prologue-searching=never turns prologue
  searching deliberately off working around issue of int_arg() returning wrong
  value when a 32-bit userspace binary having debug info is being probed with
  active prologue searching (PR18649).

- The powerpc variant of nd_syscall.compat_sysctl got deprecated on favor of
  nd_syscall.sysctl32. This aligns the nd_syscall to its respective syscall and
  to ia64/s390/x86_64 variants too.

- New tapset function assert(expression, msg) has been added.

- Embedded-C functions may now use the new STAP_PRINTF(fmt, ...)
  macro for output.

- New tapset functions fullname_struct_path and fullname_struct_nameidata
  resolve full path names from internal kernel struct pointers.
  
- New tapset functions arch_bytes() and uarch_bytes() to obtain address size
  for kernel and user space respectively.

- New tapset function switch_file() allows control over rotation
  of output files.

- The [nd_]syscall tapset got autodocumented. Related paragraph got added to PDF
  and HTML tapset reference. Also a new tapset::syscall 3stap man page got added.

- Embedded-C functions with parameter arity-0 can now be marked with
  the /* stable */ /* pure */ pragmas, if (roughly speaking) the
  function is side-effect-free and idempotent.  The translator may
  execute these speculatively and have their results memoized.  This
  lets probes with multiple calls to such functions run faster. 
  
  Context variable ($foo) getter functions (in non-guru mode), and
  numerous tapset functions are now marked as /* stable */ /* pure */.
  Several example scripts have been modified to eschew explicit
  memoization.

- Callee probe points now support '.return' and '.call' suffix.
  For example,

    process("proc").function("foo").callee("bar").return

  will fire upon returning from bar when called by foo.

    process("proc").function("foo").callee("bar").call

  will only fire for non-inlined callees.

- The following tapset variables and functions are deprecated in
  version 2.9:
  - The '__int32_compat' library macro got deprecated in favor of
    new '__compat_long' library macro.
  - The 'uargs' convenience variable of the 'seccomp' syscall probe
    got deprecated in favor of new 'uargs_uaddr' variable.

- SystemTap has reduced its memory consumption by using interned_strings (a
  wrapper for boost::string_ref) in place of std::string instances. The change
  is to reduce the number of duplicate strings created by replacing them with
  interned_strings which act like pointers to existing strings.

  For the implementation of interned_string, see stringtable.h

* What's new in version 2.8, 2015-06-17

- SystemTap has improved support for probing golang programs. Work has been
  done to be able to handle DWARF information, reporting file names, line
  numbers, and column numbers, and tolerance of odd characters in symbol names.

- The function::*, probe::* and new macro::* man pages cross-references the
  enclosing tapset::* man page. For example:

  function::pn(3stap) mentions tapset::pn(3stap) in the SEE ALSO section

- New stapref(1) man page provides a reference for the scripting language. The
  stapref page contains an overview of the features available in the language,
  such as keywords, data types, operators and more.

- The @task macro performs the very common @cast to a task_struct.

  The embedded-C bodies of task_current() and pid2task() are now wrapped
  by @task, which gives them a debuginfo type on the return value.  With
  autocast type propagation, this removes the need for any explicit @cast
  in many places.

  Other places which take untyped task pointers as parameters, for
  instance, now use @task as well to simplify their code.

- New namespace-aware tapset functions [task_]ns_*() and ia new option
  --target-namespaces=PID to denote a target set of namespaces corresponding to
  the PID's namespaces. The namespace-aware tapsets will return values
  relative to the target namespaces if specified, or the stap process' namespaces.

- Netfilter probes now attempt to decode Spanning Tree Protocol packets
  into local variables: probe netfilter.bridge.*, br_* variables,
  stp_dump.stp sample script.

- Colorization of error string tokens is made more robust, especially
  in presence of $N/@N substitution.

- The following tapset variables and functions are deprecated in
  version 2.8:
  - The 'hostname_uaddr' variable in the syscall.setdomainname and
    nd_syscall.setdomainname probe aliases have been deprecated in
    favor of the new 'domainname_uaddr' variable.
  - The 'fd' and 'fd_str' variables in the syscall.execveat and
    nd_syscall.execveat probe aliases have been deprecated in favor of
    the new 'dirfd' and 'dirfd_str' variables.

* What's new in version 2.7, 2015-02-18

- Some systemtap sample scripts are now identified with the "_best" keyword,
  because they are generally useful or educational.  They are now promoted
  within the generated index files.

- Passing strings to and from functions has become faster due to optimization
  (passing some strings by reference instead of by value/copy).  It may
  be disabled by using the unoptimize flag (-u).

  To make embedded-C functions eligible for the same optimization, use the pragma
  /* unmodified-fnargs */ to indicate that the function body will not modify
  the function arguments.  Remember to use MAXSTRINGLEN for string length,
  rather than sizeof(string_arg) (which might now be a pointer).

- SystemTap now allows .function probes to be specified by their full function
  name, file, and declaration line number. Use the .statement probe to probe a
  specific line number.

- Tracepoint probes can now also be specified by the target subsystem. For
  example, the following are all supported:

  probe kernel.trace("sched:sched_switch") --> probe sched_switch found in the
                                               sched subsystem
  probe kernel.trace("sched:*") --> probe all tracepoints in sched subsystem

  As a result, tapset functions such as pn() will now return a different string
  than before. To retain the previous behaviour, use '--compatible=2.6'.

- The following functions are deprecated in release 2.7:
  - _adjtx_mode_str(), _statfs_f_type_str(), _waitid_opt_str(),
    _internal_wait_opt_str(), and _epoll_events_str().

- New tapset functions [u]symfileline(), [u]symfile() and [u]symline() will
  return a string containing the specified portion of the filename:linenumber
  match from a given address.

  Using these functions may result in large generated modules from stored
  address->file:line information.

* What's new in version 2.6, 2014-09-05

- SystemTap now supports on-the-fly arming/disarming of certain probe types:
  kprobes, uprobes, and timer.*s(NUM) probes. For example, this probe

  probe kernel.function("vfs_read") if (i > 4) { ... }

  will automatically register/unregister the associated kprobe on vfs_read
  whenever the value of the condition changes (as some probe handler
  modifies 'i').  This allows us to avoid probe overhead when we're not
  interested.  If the arming capability is not relevant/useful, nest the
  condition in the normal probe handler:

  probe kernel.function("vfs_read") { if (i > 4) { ... } }

- statement("*@file:NNN").nearest probes now available to let systemtap
  translate probe to nearest probe-able line to one given if necessary

- process("PATH").library("PATH").plt("NAME").return probes are now supported.

- SystemTap now supports SDT probes with operands that refer to symbols.

- While in listing mode (-l/-L), probes printed are now more consistent
  and precise.

- Statement probes now support enumerated linenos to probe discontiguous
  linenos using the form:

  process.statement("foo@file.c:3,5-7,9")

- Statement counting is now suppressed in the generated c code for probes that
  are non-recursive and loop-free. Statement counting can be turned back on in
  unoptimize mode (-u).

- SystemTap now asserts that the PID provided for a process probe corresponds
  to a running process.

- DWARF process probes can be bound to a specific process using the form:

  process(PID).function("*")

- SystemTap now accepts additional scripts through the new -E SCRIPT option.
  There still needs to be a main script specified through -e or file in order
  to provide an additional script. This makes it feasible to have scripts in
  the $HOME/.systemtap/rc file.  For example:

  -E 'probe begin, end, error { log("systemtap script " . pn()) }'
  -E 'probe timer.s(30) { error ("timeout") }

  The -E SCRIPT option can also be used in listing mode (-l/-L), such that
  probe points for the additional scripts will not listed, but other parts of
  the script are still available, such as macros or aliases.

- SystemTap now supports array slicing within foreach loop conditions, delete
  statements and membership tests. Wildcards are represented by "*". Examples
  of the expressions are:

  foreach ([a,b,c] in val[*,2,*])
  delete val[*, 2, *]
  [*, 2, *] in val

- Integer expressions which are derived from DWARF values, like context $vars,
  @cast, and @var, will now carry that type information into subsequent reads.
  Such expressions can now use "->" and "[]" operators, as can local variables
  which were assigned such values.

  foo = $param->foo; printf("x:%d y:%d\n", foo->x, foo->y)
  printf("my value is %d\n", ($type == 42 ? $foo : $bar)->value)
  printf("my parent pid is %d\n", task_parent(task_current())->tgid)

* What's new in version 2.5, 2014-04-30

- Systemtap now supports backtracing through its own, invoking module.

- Java probes now support backtracing using the print_java_backtrace()
  and sprint_java_backtrace() functions.

- Statement probes (e.g. process.statement) are now faster to resolve,
  more precise, and work better with inlined functions.

- New switches have been added to help inspect the contents of installed
  library files:

  stap --dump-functions --> list all library functions and their args
  stap --dump-probe-aliases --> list all library probe aliases

- The heuristic algorithms used to search for function-prologue
  endings were improved, to cover more optimization (or
  lack-of-optimization, or incorrect-debuginfo) cases.  These
  heuristics are necessary to find $context parameters for some
  function-call/entry probes.  We recommend programs be built with
  CFLAGS+=-grecord-gcc-switches to feed information to the heuristics.

- The stap --use-server option now more correctly supports address:port
  type parametrization, for manual use in the absence of avahi.

- A new probe alias "oneshot" allows a single quick script fragment to run,
  then exit.

- The argv tapset now merges translate-time and run-time positional
  arguments, so all of these work:

  stap -e 'probe oneshot {println(argv[1]," ",argv[2])}' hello world

  stap -e 'probe oneshot {println(argv[1]," ",argv[2])}' \
       -G argv_1=hello -G argv_2=world

  staprun hello.ko argv_1=hello argv_2=world

- SystemTap now falls back on the symbol table for probing
  functions in processes if the debuginfo is not available.

- SystemTap now supports a %( guru_mode == 0 /* or 1 */ %)
  conditional for making dual-use scripts.

- SystemTap now supports UEFI/SecureBoot systems, via
  machine-owner-keys maintained by a trusted stap-server on the
  network.  (Key enrollment requires a one-time reboot and BIOS
  conversation.)
  https://sourceware.org/systemtap/wiki/SecureBoot

- SystemTap now reports more accurate and succinct errors on type
  mismatches.

- Embedded-C functions may use STAP_RETURN(value) instead of the
  more wordy STAP_RETVALUE assignment followed by a "goto out".
  The macro supports numeric or string values as appropriate.
  STAP_ERROR(...) is available to return with a (catchable) error.

- Some struct-sockaddr fields are now individually decoded for
  socket-related syscalls:
  probe syscall.connect { println (uaddr_af, ":", uaddr_ip) }

- The documentation for the SystemTap initscript service and the
  SystemTap compile-server service have been completely converted from
  README files to man pages (see systemtap(8) and stap-server(8)).

- SystemTap is now capable of inserting modules early during the boot
  process on dracut-based systems. See the 'onboot' command in
  systemtap(8) for more information.

- DWARF probes can now use the '.callee[s]' variants, which allow more
  precise function probing. For example, the probe point

    process("myproc").function("foo").callee("bar")

  will fire upon entering bar() from foo(). A '.callees' probe will
  instead place probes on all callees of foo().
    Note that this also means that probe point wildcards should be used
  with more care. For example, use signal.*.return rather than
  signal.*.*, which would also match '.callees'. See stapprobes(3stap)
  for more info. This feature requires at least GCC 4.7.

- A few new functions in the task_time tapsets, as well as a new tapset
  function task_ancestry(), which prints out the parentage of a process.

- The kprocess.exec probe has been updated to use syscall.execve, which
  allows access to the new process' arguments (through the new 'argstr'
  or 'args' variables) as well as giving better support across kernel
  versions. Note also that the 'filename' variable now holds the
  filename (quoted), or the address (unquoted) if it couldn't be
  retrieved.

- The [s]println() function can now be called without any arguments to
  simply print a newline.

- Suggestions are now provided when markers could not be resolved. For
  example, process("stap").mark("benchmart") will suggest 'benchmark'.

- SystemTap colors can now be turned off by simply setting
  SYSTEMTAP_COLORS to be empty, rather than having to make it invalid.

- There is a new context tapset function, pnlabel(), which returns the
  name of the label which fired.

- The following tapset variables and functions are deprecated in
  release 2.5:
  - The 'clone_flags', 'stack_start', 'stack_size',
    'parent_tid_uaddr', and 'child_tid_uaddr' variables in the
    'syscall.fork' and 'nd_syscall.fork' probe aliases. 
  - The '_sendflags_str()' and '_recvflags_str()' functions have been
    deprecated in favor of the new '_msg_flags_str()' function.
  - The 'flags' and 'flags_str' variables in the 'syscall.accept' and
    'nd_syscall.accept' probe alias.
  - The 'first', 'second', and 'uptr_uaddr' variables in the
    'syscall.compat_sys_shmctl', and 'nd_syscall.compat_sys_shmctl'
    probe aliases have been deprecated in favor of the new 'shmid',
    'cmd', and 'buf_uaddr' variables.

* What's new in version 2.4, 2013-11-06

- Better suggestions are given in many of the semantic errors in which
  alternatives are provided. Additionally, suggestions are now provided
  when plt and trace probes could not be resolved. For example,
  kernel.trace("sched_siwtch") will suggest 'sched_switch'.

- SystemTap is now smarter about error reporting. Errors from the same
  source are considered duplicates and suppressed. A message is
  displayed on exit if any errors/warnings were suppressed.

- Statistics aggregate typed objects are now implemented locklessly,
  if the translator finds that they are only ever read (using the
  foreach / @count / etc. constructs) in a probe-begin/end/error.

- SystemTap now supports probing inside virtual machines using the
  libvirt and unix schemes, e.g.

      stap -ve 'probe timer.s(1) { printf("hello!\n") }' \
         --remote=libvirt://MyVirtualMachine

  Virtual machines managed by libvirt can be prepared using stapvirt.
  See stapvirt(1) and the --remote option in stap(1) for more details.

- Systemtap now checks for and uses (when available) the .gnu_debugdata
  section which contains a subset of debuginfo, useful for backtraces
  and function probing

- SystemTap map variables are now allocated with vmalloc() instead of
  with kmalloc(), which should cause memory to be less fragmented.

- Although SystemTap itself requires elfutils 0.148+, staprun only
  requires elfutils 0.142+, which could be useful with the
  '--disable-translator' configure switch.

- Under FIPS mode (/proc/sys/crypto/fips_enabled=1), staprun will
  refuse to load systemtap modules (since these are not normally
  signed with the kernel's build-time keys).  This protection may
  be suppressed with the $STAP_FIPS_OVERRIDE environment variable.

- The stap-server client & server code now enable all SSL/TLS
  ciphers rather than just the "export" subset.

- For systems with in-kernel utrace, 'process.end' and 'thread.end'
  probes will hit before the target's parent process is notified of
  the target's death. This matches the behavior of newer kernels
  without in-kernel utrace.

* What's new in version 2.3, 2013-07-25

- More context-accessing functions throw systemtap exceptions upon a
  failure, whereas in previous versions they might return non-error
  sentinel values like "" or "<unknown>".  Use try { } / catch { }
  around these, or new wrapper functions such as user_string_{n_}quoted()
  that internally absorb exceptions.

- java("org.my.MyApp") probes are now restricted to pre-existing jvm pid's with
  a listing in jps -l output to avoid recursive calls

- The tapset [nd_]syscall.semop parameter tsops_uaddr is renamed sops_uaddr for
  consistency with [nd_]syscall.semtimedop.

- The udp.stp tapset adds some ip-address/port variables.

- A new guru-mode-only tapset function raise() is available to send signals
  to the current task.

- Support for the standard Posix ERE named character classes has been
  added to the regexp engine, e.g. [:digit:], [:alpha:], ...

- A substantial internal overhaul of the regexp engine has resulted in
  correct behaviour on further obscure edge cases. The regexp engine
  now implements the ERE standard and correctly passes the testsuite
  for the glibc regexp engine (minus portions corresponding to
  unimplemented features -- i.e. subexpression capture and reuse).

- Alternative functions are now suggested when function probes could not be
  resolved. For example, kernel.function("vfs_reads") will suggest vfs_read.
  Other probes for which suggestions are made are module.function,
  process.function, and process.library.function.

- Has life been a bit bland lately? Want to spice things up? Why not write a
  few faulty probes and feast your eyes upon the myriad of colours adorning
  your terminal as SystemTap softly whispers in your ear... 'parse error'.
  Search for '--color' in 'man stap' for more info.

- The following tapset functions are deprecated in release 2.3:
  'stap_NFS_CLIENT', '__getfh_inode', '_success_check',
  '_sock_prot_num', '_sock_fam_num', '_sock_state_num',
  '_sock_type_num', and '_sock_flags_num'.

* What's new in version 2.2.1, 2013-05-16
* What's new in version 2.2, 2013-05-14

- Experimental support has been added for probing Java methods using
  Byteman 2.0 as a backend. Java method probes can target method entries,
  returns, or specific statements in the method as specified by line number.

      probe java("org.my.MyApp").class("^java.lang.Object").method("foo(int)")
         { println($$parms) }

  See java/README for information on how to set up Java/Byteman
  functionality.  Set env STAPBM_VERBOSE=yes for more tracing. 

- The stap -l output and pn() tapset function's return value may be slightly
  different for complicated web of wildcarded/aliased probes.

- The dyninst backend has improved in several aspects:

  - Setting custom values for global variables is now supported, both
    with -G when compiling a script, and from the stapdyn command line
    when loading a precompiled module.

  - A high-performance shared-memory-based transport is used for
    trace data.

- A systemd service file and tmpfile have been added to allow
  systemtap-server to be managed natively by systemd.

- Due to the removal of register_timer_hook in recent kernels, the
  behaviour of timer.profile has been changed slightly. This probe is
  now an alias which uses the old mechanism where possible, but falls
  back to perf.sw.cpu_clock or another mechanism when the kernel timer
  hook is not available.

  To require the kernel timer hook mechanism in your script, use
  timer.profile.tick instead of timer.profile.

- The following tapset variables are deprecated in release 2.2:
  - The 'origin' variables in the 'generic.fop.llseek',
    'generic.fop.llseek.return', and 'nfs.fop.llseek' probes. The
    'origin' variable has been replaced by the 'whence' variable.
  - The 'page_index' variable in the 'vfs.block_sync_page' and
    'vfs.buffer_migrate_page' probe aliases.
  - The 'write_from' and 'write_upto' variables in the
    '_vfs.block_prepare_write' and '_vfs.block_prepare_write.return'
    probe aliases.
  - The 'regs' variable in the 'syscall.sigaltstack',
    'nd_syscall.sigaltstack', 'syscall.fork', and 'nd_syscall.fork'
    probe aliases.
  - The 'first', 'second', 'third', and 'uptr_uaddr' variables in the
    'syscall.compat_sys_shmat' and 'nd_syscall.compat_sys_shmat' probe
    aliases.

- The following tapset functions are deprecated in release 2.2:
  'ppos_pos', '_dev_minor', and '_dev_major'

- The folowing tapset functions used to return error strings instead
  of raising an error. The original behavior is deprecated in release
  2.2.

  'ctime', 'probemod', 'modname'

* What's new in version 2.1, 2013-02-13

- EMACS and VIM editor modes for systemtap source files are included / updated.

- The translator now eliminates duplicate tapset files between its
  preferred directory (as configured during the build with --prefix=/
  or specified with the -I /path option), and files it may find under
  $XDG_DATA_DIRS.  This should eliminate a class of conflicts between
  parallel system- and hand-built systemtap installations.

- The translator accepts a --suppress-time-limits option, which defeats
  time-related constraints, to allows probe handlers to run for indefinite
  periods.  It requires the guru mode (-g) flag to work.  Add the earlier
  --suppress-handler-errors flag for a gung-ho "just-keep-going" attitude.

- Perf event probes may now be read on demand. The counter probe is
  defined using the counter-name part: 
  probe perf.type(0).config(0).counter("NAME").  The counter is
  read in a user space probe using @perf("NAME"), e.g.
   process("PROCESS").statement("func@file") {stat <<< @perf("NAME")} 

- Perf event probes may now be bound to a specific task using the
  process-name part:  probe perf.type(0).config(0).process("NAME") { }
  If the probed process name is not specified, then it is inferred
  from the -c CMD argument.  

- Some error messages and warnings now refer to additional information
  that is found in man pages.  These are generally named
  error::FOO or warning::BAR (in the 7stap man page section)
  and may be read via
     % man error::FOO
     % man warning::BAR

- The dyninst backend has improved in several aspects:
  - The runtime now allows much more concurrency when probing multithreaded
    processes, and will also follow probes across forks.
  - Several new probe types are now supported, including timers, function
    return, and process.begin/end and process.thread.begin/end.
  - Semaphores for SDT probes are now set properly.
  - Attaching to existing processes with -x PID now works.

- The foreach looping construct can now sort aggregate arrays by the user's
  choice of aggregating function.  Previously, @count was implied.  e.g.:
     foreach ([x,y] in array @sum +) { println(@sum(array[x,y])) } 

- Proof of concept support for regular expression matching has been added:
     if ("aqqqqqb" =~ "q*b") { ... }
     if ("abc" !~ "q*b") { ... }

  The eventual aim is to support roughly the same functionality as
  the POSIX Extended Regular Expressions implemented by glibc.
  Currently missing features include extraction of the matched string
  and subexpressions, and named character classes ([:alpha:], [:digit:], &c).

  Special thanks go to the re2c project, whose public domain code this
  functionality has been based on. For more info on re2c, see:
     http://sourceforge.net/projects/re2c/

- The folowing tapset variables are deprecated in release 2.1 and will
  be removed in release 2.2:
  - The 'send2queue' variable in the 'signal.send' probe.
  - The 'oldset_addr' and 'regs' variables in the 'signal.handle' probe.

- The following tapset probes are deprecated in release 2.1 and will
  be removed in release 2.2:
  - signal.send.return
  - signal.handle.return

* What's new in version 2.0, 2012-10-09

- Systemtap includes a new prototype backend, which uses Dyninst to instrument
  a user's own processes at runtime. This backend does not use kernel modules,
  and does not require root privileges, but is restricted with respect to the
  kinds of probes and other constructs that a script may use.

  Users from source should configure --with-dyninst and install a
  fresh dyninst snapshot such as that in Fedora rawhide.  It may be
  necessary to disable conflicting selinux checks; systemtap will advise.

  Select this new backend with the new stap option --runtime=dyninst
  and a -c target process, along with normal options. (-x target
  processes are not supported in this prototype version.) For example:

    stap --runtime=dyninst -c 'stap -l begin' \
      -e 'probe process.function("main") { println("hi from dyninst!") }'

- To aid diagnosis, when a kernel panic occurs systemtap now uses
  the panic_notifier_list facility to dump a summary of its trace
  buffers to the serial console.

- The systemtap preprocessor now has a simple macro facility as follows:

    @define add(a,b) %( ((@a)+(@b)) %)
    @define probegin(x) %(
       probe begin {
         @x
       }
    %)

    @probegin( foo = @add(40, 2); print(foo) ) 

  Macros defined in the user script and regular tapset .stp files are
  local to the file. To get around this, the tapset library can define
  globally visible 'library macros' inside .stpm files. (A .stpm file
  must contain a series of @define directives and nothing else.)

  The status of the feature is experimental; semantics of macroexpansion
  may change (unlikely) or expand in the future.

- Systemtap probe aliases may be used with additional suffixes
  attached. The suffixes are passed on to the underlying probe
  point(s) as shown below:

    probe foo = bar, baz { }
    probe foo.subfoo.option("gronk") { }
    // expands to: bar.subfoo.option("gronk"), baz.subfoo.option("gronk")

  In practical terms, this allows us to specify additional options to
  certain tapset probe aliases, by writing e.g.
    probe syscall.open.return.maxactive(5) { ... }

- To support the possibility of separate kernel and dyninst backends,
  the tapsets have been reorganized into separate folders according to
  backend. Thus kernel-specific tapsets are located under linux/, the
  dyninst-specific ones under dyninst/

- The backtrace/unwind tapsets have been expanded to allow random
  access to individual elements of the backtrace. (A caching mechanism
  ensures that the backtrace computation run at most once for each
  time a probe fires, regardless of how many times or what order the
  query functions are called in.) New tapset functions are:
    stack/ustack - return n'th element of backtrace
    callers/ucallers - return first n elements of backtrace
    print_syms/print_usyms - print full information on a list of symbols
    sprint_syms/sprint_usyms - as above, but return info as a string

  The following existing functions have been superseded by print_syms()
  et al.; new scripts are recommended to avoid using them:
      print_stack()
      print_ustack()
      sprint_stack()
      sprint_ustack()

- The probefunc() tapset function is now myproc-unprivileged, and can
  now be used in unprivileged scripts for such things as profiling in
  userspace programs. For instance, try running
  systemtap.examples/general/para-callgraph.stp in unprivileged mode
  with a stapusr-permitted probe.  The previous implementation of
  probefunc() is available with "stap --compatible=1.8".

- Preprocessor conditional to vary code based on script privilege level:
  unprivileged -- %( systemtap_privilege == "stapusr" %? ... %)
  privileged   -- %( systemtap_privilege != "stapusr" %? ... %)
  or, alternately %( systemtap_privilege == "stapsys"
                  || systemtap_privilege == "stapdev" %? ... %)

- To ease migration to the embedded-C locals syntax introduced in 1.8
  (namely, STAP_ARG_* and STAP_RETVALUE), the old syntax can now be
  re-enabled on a per-function basis using the /* unmangled */ pragma:

    function add_foo:long(a:long, b:long) %{ /* unmangled */
      THIS->__retvalue = THIS->a + STAP_ARG_b;
    %}

  Note that both the old and the new syntax may be used in an
  /* unmangled */ function. Functions not marked /* unmangled */
  can only use the new syntax.

- Adjacent string literals are now glued together irrespective of
  intervening whitespace or comments:
    "foo " "bar" --> "foo bar"
    "foo " /* comment */ "bar" --> "foo bar"
  Previously, the first pair of literals would be glued correctly,
  while the second would cause a syntax error.

* What's new in version 1.8, 2012-06-17

- staprun accepts a -T timeout option to allow less frequent wake-ups
  to poll for low-throughput output from scripts.

- When invoked by systemtap, the kbuild $PATH environment is sanitized
  (prefixed with /usr/bin:/bin:) in an attempt to exclude compilers
  other than the one the kernel was presumed built with.

- Printf formats can now use "%#c" to escape non-printing characters.

- Pretty-printed bitfields use integers and chars use escaped formatting
  for printing.

- The systemtap compile-server and client now support IPv6 networks.
  - IPv6 addresses may now be specified on the --use-server option and will
    be displayed by --list-servers, if the avahi-daemon service is running and
    has IPv6 enabled.
  - Automatic server selection will automatically choose IPv4 or IPv6 servers
    according to the normal server selection criteria when avahi-daemon is
    running. One is not preferred over the other.
  - The compile-server will automatically listen on IPv6 addresses, if
    available.
  - To enable IPv6 in avahi-daemon, ensure that /etc/avahi/avahi-daemon.conf
    contains an active "use-ipv6=yes" line. After adding this line run
    "service avahi-daemon restart" to activate IPv6 support.
  - See man stap(1) for details on how to use IPv6 addresses with the
    --use-server option.

- Support for DWARF4 .debug_types sections (for executables and shared
  libraries compiled with recent GCC's -gdwarf-4 / -fdebug-types-section).
  PR12997.  SystemTap now requires elfutils 0.148+, full .debug_types support
  depends on elfutils 0.154+.

- Systemtap modules are somewhat smaller & faster to compile.  Their
  debuginfo is now suppressed by default; use -B CONFIG_DEBUG_INFO=y to
  re-enable.

- @var now an alternative language syntax for accessing DWARF variables
  in uprobe and kprobe handlers (process, kernel, module). @var("somevar")
  can be used where $somevar can be used. The @var syntax also makes it
  possible to access non-local, global compile unit (CU) variables by
  specifying the CU source file as follows @var("somevar@some/src/file.c").
  This will provide the target variable value of global "somevar" as defined
  in the source file "some/src/file.c". The @var syntax combines with all
  normal features of DWARF target variables like @defined(), @entry(),
  [N] array indexing, field access through ->, taking the address with
  the & prefix and shallow or deep pretty printing with a $ or $$ suffix.

- Stap now has resource limit options:
    --rlimit-as=NUM
    --rlimit-cpu=NUM
    --rlimit-nproc=NUM
    --rlimit-stack=NUM
    --rlimit-fsize=NUM
  All resource limiting has been moved from the compile server to stap
  itself. When running the server as "stap-server", default resource
  limit values are specified in ~stap-server/.systemtap/rc.

- Bug CVE-2012-0875 (kernel panic when processing malformed DWARF unwind data)
  is fixed.

- The systemtap compile-server now supports multiple concurrent connections.
  Specify the desired maximum number of concurrent connections with
  the new stap-server/stap-serverd --max-threads option. Specify a
  value of '0' to tell the server not to spawn any new threads (handle
  all connections serially in the main thread). The default value is
  the number of processor cores on the host.

- The following tapset functions are deprecated in release 1.8 and will be
  removed in release 1.9:
      daddr_to_string()

- SystemTap now mangles local variables to avoid collisions with C
  headers included by tapsets. This required a change in how
  embedded-C functions access local parameters and the return value slot.

  Instead of THIS->foo in an embedded-C function, please use the newly
  defined macro STAP_ARG_foo (substitute the actual name of the
  argument for 'foo'); instead of THIS->__retvalue, use the newly
  defined STAP_RETVALUE. All of the tapsets and test cases have been
  adapted to use this new notation.

  If you need to run code which uses the old THIS-> notation, run stap
  with the --compatible=1.7 option.

- There is updated support for user-space probing against kernels >=
  3.5, which have no utrace but do have the newer inode-uprobes work
  by Srikar Dronamraju and colleagues.  For kernels < 3.5, the
  following 3 sets of kernel patches would need to be backported to
  your kernel to use this preliminary user-space probing support:

  - inode-uprobes patches:
    - 2b144498350860b6ee9dc57ff27a93ad488de5dc
    - 7b2d81d48a2d8e37efb6ce7b4d5ef58822b30d89
    - a5f4374a9610fd7286c2164d4e680436727eff71
    - 04a3d984d32e47983770d314cdb4e4d8f38fccb7
    - 96379f60075c75b261328aa7830ef8aa158247ac
    - 3ff54efdfaace9e9b2b7c1959a865be6b91de96c
    - 35aa621b5ab9d08767f7bc8d209b696df281d715
    - 900771a483ef28915a48066d7895d8252315607a
    - e3343e6a2819ff5d0dfc4bb5c9fb7f9a4d04da73
  - exec tracepoint kernel patch:
    - 4ff16c25e2cc48cbe6956e356c38a25ac063a64d
  - task_work_add kernel patches:
    - e73f8959af0439d114847eab5a8a5ce48f1217c4
    - 4d1d61a6b203d957777d73fcebf19d90b038b5b2
    - 413cd3d9abeaef590e5ce00564f7a443165db238
    - dea649b8ac1861107c5d91e1a71121434fc64193
    - f23ca335462e3c84f13270b9e65f83936068ec2c

* What's new in version 1.7, 2012-02-01

- Map inserting and deleting is now significantly faster due to
  improved hashing and larger hash tables. The hashes are also
  now randomized to provide better protection against deliberate
  collision attacks.

- Formatted printing is faster by compiling the formatting directives
  to C code rather than interpreting at run time.

- Systemtap loads extra command line options from $SYSTEMTAP_DIR/rc
  ($HOME/.systemtap/rc by default) before the normal argc/argv.  This
  may be useful to activate site options such as --use-server or
  --download-debuginfo or --modinfo.

- The stap-server has seen many improvements, and is no longer considered
  experimental.

- The stap-server service (initscript) now supports four new options:
    -D MACRO[=VALUE]
    --log LOGFILE
    --port PORT-NUMBER
    --SSL CERT-DATABASE
  These allow the specification of macro definitions to be passed to stap
  by the server, the location of the log file, network port number and
  NSS certificate database location respectively. These options are also
  supported within individual server configuration files. See stap-server
  and initscript/README.stap-server for details.  The stap-server is no
  longer activated by default.

- process("PATH").[library("PATH")].function("NAME").exported probes are now
  supported to filter function() to only exported instances.

- The translator supports a new --suppress-handler-errors option, which
  causes most runtime errors to be turned into quiet skipped probes.  This
  also disables the MAXERRORS and MAXSKIPPED limits.

- Translator warnings have been standardized and controlled by the -w / -W
  flags.

- The translator supports a new --modinfo NAME=VALUE option to emit additional
  MODULE_INFO(n,v) macros into the generated code.

- There is no more fixed maximum number of VMA pages that will be tracked
  at runtime. This reduces memory use for those scripts that don't need any,
  or only limited target process VMA tracking and allows easier system
  wide probes inspecting shared library variables and/or user backtraces.
  stap will now silently ignore -DTASK_FINDER_VMA_ENTRY_ITEMS.

- The tapset functions remote_id() and remote_uri() identify the member of a
  swarm of "stap --remote FOO --remote BAR baz.stp" concurrent executions.

- Systemtap now supports a new privilege level and group, "stapsys", which
  is equivalent to the privilege afforded by membership in the group "stapdev",
  except that guru mode (-g) functionality may not be used. To support this, a
  new option, --privilege=[stapusr|stapsys|stapdev] has been added.
  --privilege=stapusr is equivalent to specifying the existing --unprivileged
  option. --privilege=stapdev is the default. See man stap(1) for details.

- Scripts that use kernel.trace("...") probes compile much faster.

- The systemtap module cache is cleaned less frequently, governed by the
  number of seconds in the $SYSTEMTAP_DIR/cache/cache_clean_interval_s file.

- SDT can now define up to 12 arguments in a probe point.

- Parse errors no longer generate a cascade of false errors.  Instead, a
  parse error skips the rest of the current probe or function, and resumes
  at the next one.  This should generate fewer and better messages.

- Global array wrapping is now supported for both associative and statistics typed
  arrays using the '%' character to signify a wrapped array. For example,
  'global foo%[100]' would allow the array 'foo' to be wrapped if more than 100
  elements are inserted.

- process("PATH").library("PATH").plt("NAME") probes are now supported.
  Wildcards are supported in the plt-name part, to refer to any function in the
  program linkage table which matches the glob pattern and the rest of the
  probe point.

- A new option, --dump-probe-types, will dump a list of supported probe types.
  If --unprivileged is also specified, the list will be limited to probe types
  which are available to unprivileged users.

- Systemtap can now automatically download the required debuginfo
  using abrt. The --download-debuginfo[=OPTION] can be used to
  control this feature. Possible values are: 'yes', 'no', 'ask',
  and a positive number representing the timeout desired. The 
  default behavior is to not automatically download the debuginfo.

- The translator has better support for probing C++ applications by
  better undertanding of compilation units, nested types, templates,
  as used in probe point and @cast constructs.

- On 2.6.29+ kernels, systemtap can now probe kernel modules that
  arrive and/or depart during the run-time of a session.  This allows
  probing of device driver initialization functions, which had formerly been
  blacklisted.

- New tapset functions for cpu_clock and local_clock access were added.

- There is some limited preliminary support for user-space probing
  against kernels such as linux-next, which have no utrace but do have
  the newer inode-uprobes work by Srikar Dronamraju and colleagues.

- The following probe types are deprecated in release 1.7 and will be
  removed in release 1.8:
      kernel.function(number).inline
      module(string).function(number).inline
      process.function(number).inline
      process.library(string).function(number).inline
      process(string).function(number).inline
      process(string).library(string).function(number).inline

- The systemtap-grapher is deprecated in release 1.7 and will be removed in
  release 1.8.

- The task_backtrace() tapset function was deprecated in 1.6 and has been
  removed in 1.7.

- MAXBACKTRACE did work in earlier releases, but has now been documented
  in the stap 1 manual page.

- New tapset function probe_type(). Returns a short string describing
  the low level probe handler type for the current probe point.

- Both unwind and symbol data is now only collected and emitted for
  scripts actually using backtracing or function/data symbols.
  Tapset functions are marked with /* pragma:symbols */ or
  /* pragma:unwind */ to indicate they need the specific data.

- Kernel backtraces can now be generated for non-pt_regs probe context
  if the kernel support dump_trace(). This enables backtraces from
  certain timer probes and tracepoints.

- ubacktrace() should now also work for some kernel probes on x86 which can
  use the dwarf unwinder to recover the user registers to provide
  more accurate user backtraces.

- For s390x the systemtap runtime now properly splits kernel and user
  addresses (which are in separate address spaces on that architecture)
  which enable user space introspection.

- ppc and s390x now supports user backtraces through the DWARF unwinder.

- ppc now handles function descriptors as symbol names correctly.

- arm support kernel backtraces through the DWARF unwinder.

- arm now have a uprobes port which enables user probes. This still
  requires some kernel patches (user_regsets and tracehook support for
  arm).

- Starting in release 1.7, these old variables will be deprecated:
  - The 'pid' variable in the 'kprocess.release' probe has been
    deprecated in favor of the new 'released_pid' variable.
  - The 'args' variable in the
    '_sunrpc.clnt.create_client.rpc_new_client_inline' probe has been
    deprecated in favor of the new internal-only '__args' variable.

- Experimental support for recent kernels without utrace has been
  added for the following probe types: 

    process(PID).begin
    process("PATH").begin
    process.begin
    process(PID).thread.begin
    process("PATH").thread.begin
    process.thread.begin
    process(PID).end
    process("PATH").end
    process.end
    process(PID).thread.end
    process("PATH").thread.end
    process.thread.end
    process(PID).syscall
    process("PATH").syscall
    process.syscall
    process(PID).syscall.return
    process("PATH").syscall.return 
    process.syscall.return

- staprun disables kprobe-optimizations in recent kernels, as problems
  were found.  (PR13193)

* What's new in version 1.6, 2011-07-25

- Security fixes for CVE-2011-2503: read instead of mmap to load modules,
  CVE-2011-2502: Don't allow path-based auth for uprobes

- The systemtap compile-server no longer uses the -k option when calling the
  translator (stap). As a result, the server will now take advantage of the
  module cache when compiling the same script more than once. You may observe
  an improvement in the performance of the server in this situation.

- The systemtap compile-server and client now each check the version of the
  other, allowing both to adapt when communicating with a down-level
  counterpart. As a result, all version of the client can communicate
  with all versions of the server and vice-versa. Client will prefer newer
  servers when selecting a server automatically.

- SystemTap has improved support for the ARM architecture.  The
  kread() and kwrite() operations for ARM were corrected allowing many
  of the tapsets probes and function to work properly on the ARM
  architecture.

- Staprun can now rename the module to a unique name with the '-R' option before 
  inserting it. Systemtap itself will also call staprun with '-R' by default. 
  This allows the same module to be inserted more than once, without conflicting 
  duplicate names.

- Systemtap error messages now provide feedback when staprun or any other
  process fails to launch.  This also specifically covers when the user 
  doesn't have the proper permissions to launch staprun.

- Systemtap will now map - to _ in module names.  Previously, 
  stap -L 'module("i2c-core").function("*")' would be empty.  It now returns
  a list had stap -L 'module("i2c_core").function("*") been specified.

- Systemtap now fills in missing process names to probe points, to
  avoid having to name them twice twice:
  % stap -e 'probe process("a.out").function("*") {}' -c 'a.out ...'
  Now the probed process name is inferred from the -c CMD argument.
  % stap -e 'probe process.function("*") {}' -c 'a.out ...'

- stap -L 'process("PATH").syscall' will now list context variables

- Depends on elfutils 0.142+.

- Deprecated task_backtrace:string (task:long). This function will go
  away after 1.6. Please run your scripts with stap --check-version.

* What's new in version 1.5, 2011-05-23

- Security fixes for CVE-2011-1781, CVE-2011-1769: correct DW_OP_{mod,div}
  division-by-zero bug

- The compile server and its related tools (stap-gen-ert, stap-authorize-cert,
   stap-sign-module) have been re-implemented in C++. Previously, these
   components were a mix of bash scripts and C code. These changes should be
   transparent to the end user with the exception of NSS certificate database
   password prompting (see below). The old implementation would prompt more
   than once for the same password in some situations.
  
- eventcount.stp now allows for event counting in the format of
  'stap eventcount.stp process.end syscall.* ...', and also reports
  corresponding event tid's.

- Systemtap checks that the build-id of the module being probed matches the
  build-id saved in the systemtap module.  Invoking systemtap with
  -DSTP_NO_BUILDID_CHECK will bypass this build-id runtime verification.  See
  man ld(1) for info on --build-id.

- stapio will now report if a child process has an abnormal exit along with
  the associated status or signal.

- Compiler optimization may sometimes result in systemtap not being able to
  access a user-space probe argument.  Compiling the application with
  -DSTAP_SDT_ARG_CONSTRAINT=nr will force the argument to be an immediate or
  register value which should enable systemtap to access the argument.

- GNU Gettext has now been intergrated with systemtap.  Our translation
  page can be found at http://www.transifex.net/projects/p/systemtap/ .
  "make update-po" will generate the necessary files to use translated
  messages.  Please refer to the po/README file for more info and 
  please consider contributing to this I18N effort!

- The new addr() function returns the probe's instruction pointer.

- process("...").library("...") probes are now supported.  Wildcards
  are supported in the library-name part, to refer to any shared
  library that is required by process-name, which matches the glob
  pattern and the rest of the probe point.

- The "--remote USER@HOST" functionality can now be specified multiple times
  to fan out on multiple targets.  If the targets have distinct kernel and
  architecture configurations, stap will automatically build the script
  appropriately for each one.  This option is also no longer considered
  experimental.

- The NSS certificate database generated for use by the compile server is now
  generated with no password. Previously, a random password was generated and
  used to access the database. This change should be transparent to most users.
  However, if you are prompted for a password when using systemtap, then
  running $libexecdir/stap-gen-cert should correct the problem.

- The timestamp tapset includes jiffies() and HZ() for lightweight approximate
  timekeeping.

- A powerful new command line option --version has been added.

- process.mark now supports $$parms for reading probe parameters.

- A new command line option, --use-server-on-error[=yes|no] is available
  for stap.  It instructs stap to retry compilation of a script using a
  compile server if it fails on the local host.  The default setting
  is 'no'.

- The following deprecated tools have been removed:
      stap-client
      stap-authorize-server-cert
      stap-authorize-signing-cert
      stap-find-or-start-server
      stap-find-servers
  Use the --use-server, --trust-server and --list-servers options of stap
  instead.

* What's new in version 1.4, 2011-01-17

- Security fixes for CVE-2010-4170, CVE-2010-4171: staprun module
  loading/unloading

- A new /* myproc-unprivileged */ marker is now available for embedded C
  code and and expressions. Like the /* unprivileged */ marker, it makes
  the code or expression available for use in unprivileged mode (see
  --unprivileged). However, it also automatically adds a call to
  assert_is_myproc() to the code or expression, thus, making it available
  to the unprivileged user only if the target of the current probe is within
  the user's own process.

- The experimental "--remote USER@HOST" option will run pass 5 on a given
  ssh host, after building locally (or with --use-server) for that target.

- Warning messages from the script may now be suppressed with the stap
  and/or staprun -w option.  By default, duplicate warning messages are
  suppressed (up to a certain limit).  With stap --vp 00002 and above,
  the duplicate elimination is defeated.

- The print_ubacktrace and usym* functions attempt to print the full
  path of the user-space binaries' paths, instead of just the basename.
  The maximum saved path length is set by -DTASK_FINDER_VMA_ENTRY_PATHLEN,
  default 64.  Warning messages are produced if unwinding fails due to
  a missing 'stap -d MODULE' option, providing preloaded unwind data.

- The new tz_ctime() tapset function prints times in the local time zone.

- More kernel tracepoints are accessible to the kernel.trace("...") mechanism,
  if kernel source trees or debuginfo are available.  These formerly "hidden"
  tracepoints are those that are declared somewhere other than the usual
  include/linux/trace/ headers, such as xfs and kvm.

- debuginfo-based process("...").function/.statement/.mark probes support
  wildcards in the process-name part, to refer to any executable files that
  match the glob pattern and the rest of the probe point.

- The -t option now displays information per probe-point rather than a summary
  for each probe.  It also now shows the derivation chain for each probe-point.

- A rewrite of the sys/sdt.h header file provides zero-cost startup (few or
  no ELF relocations) for the debuginfo-less near-zero-cost runtime probes.
  Binaries compiled with earlier sdt.h versions remain supported.  The
  stap -L (listing) option now lists parameters for sys/sdt.h markers.

- The implementation of the integrated compile-server client has been
  extended.
  o --use-server now accepts an argument representing a particular server and
    may be specified more than once.
  o --list-servers now accepts an expanded range of arguments.
  o a new --trust-servers option has been added to stap to replace several
    old certificate-management scripts.
  o The following tools are now deprecated and will be removed in release 1.5:
      stap-client
      stap-authorize-server-cert
      stap-authorize-signing-cert
      stap-find-or-start-server
      stap-find-servers
  See man stap(1) for complete details.

- The compile-server now returns the uprobes.ko to the client when it is
  required by the script being compiled. The integrated compile-server client
  now makes it available to be loaded by staprun. The old (deprecated)
  stap-client does not do this.

- process probes with scripts as the target are recognized by stap and the
  interpreter would be selected for probing.

- Starting in release 1.5, these old variables/functions will be deprecated
  and will only be available when the '--compatible=1.4' flag is used:

  - In the 'syscall.add_key' probe, the 'description_auddr' variable
    has been deprecated in favor of the new 'description_uaddr'
    variable.
  - In the 'syscall.fgetxattr', 'syscall.fsetxattr',
    'syscall.getxattr', 'syscall.lgetxattr', and
    'syscall.lremovexattr' probes, the 'name2' variable has been
    deprecated in favor of the new 'name_str' variable.
  - In the 'nd_syscall.accept' probe the 'flag_str' variable
    has been deprecated in favor of the new 'flags_str' variable.
  - In the 'nd_syscall.dup' probe the 'old_fd' variable has been
    deprecated in favor of the new 'oldfd' variable.
  - In the 'nd_syscall.fgetxattr', 'nd_syscall.fremovexattr',
    'nd_syscall.fsetxattr', 'nd_syscall.getxattr', and
    'nd_syscall.lremovexattr' probes, the 'name2' variable has been 
    deprecated in favor of the new 'name_str' variable.
  - The tapset alias 'nd_syscall.compat_pselect7a' was misnamed.  It should
    have been 'nd_syscall.compat_pselect7' (without the trailing 'a').
  - The tapset function 'cpuid' is deprecated in favor of the better known 
    'cpu'.
  - In the i386 'syscall.sigaltstack' probe, the 'ussp' variable has
    been deprecated in favor of the new 'uss_uaddr' variable.
  - In the ia64 'syscall.sigaltstack' probe, the 'ss_uaddr' and
    'oss_uaddr' variables have been deprecated in favor of the new
    'uss_uaddr' and 'uoss_uaddr' variables.
  - The powerpc tapset alias 'syscall.compat_sysctl' was deprecated
    and renamed 'syscall.sysctl32'.
  - In the x86_64 'syscall.sigaltstack' probe, the 'regs_uaddr'
    variable has been deprecated in favor of the new 'regs' variable.

* What's new in version 1.3, 2010-07-21

- The uprobes kernel module now has about half the overhead when probing
  NOPs, which is particularly relevant for sdt.h markers.

- New stap option -G VAR=VALUE allows overriding global variables
  by passing the settings to staprun as module options.

- The tapset alias 'syscall.compat_pselect7a' was misnamed.  It should
  have been 'syscall.compat_pselect7' (without the trailing 'a').
  Starting in release 1.4, the old name will be deprecated and
  will only be available when the '--compatible=1.3' flag is used.

- A new procfs parameter .umask(UMASK) which provides modification of
  file permissions using the proper umask value.  Default file
  permissions for a read probe are 0400, 0200 for a write probe, and
  0600 for a file with a read and write probe.

- It is now possible in some situations to use print_ubacktrace() to
  get a user space stack trace from a kernel probe point. e.g. for
  user backtraces when there is a pagefault:
  $ stap -d /bin/sort --ldd -e 'probe vm.pagefault {
      if (pid() == target()) {
         printf("pagefault @0x%x\n", address); print_ubacktrace();
      } }' -c /bin/sort
  [...]
  pagefault @0x7fea0595fa70
   0x000000384f07f958 : __GI_strcmp+0x12b8/0x1440 [libc-2.12.so]
   0x000000384f02824e : __gconv_lookup_cache+0xee/0x5a0 [libc-2.12.so]
   0x000000384f021092 : __gconv_find_transform+0x92/0x2cf [libc-2.12.so]
   0x000000384f094896 : __wcsmbs_load_conv+0x106/0x2b0 [libc-2.12.so]
   0x000000384f08bd90 : mbrtowc+0x1b0/0x1c0 [libc-2.12.so]
   0x0000000000404199 : ismbblank+0x39/0x90 [sort]
   0x0000000000404a4f : inittables_mb+0xef/0x290 [sort]
   0x0000000000406934 : main+0x174/0x2510 [sort]
   0x000000384f01ec5d : __libc_start_main+0xfd/0x1d0 [libc-2.12.so]
   0x0000000000402509 : _start+0x29/0x2c [sort]
  [...]

- New tapset functions to get a string representation of a stack trace:
  sprint_[u]backtrace() and sprint_[u]stack().

- New tapset function to get the module (shared library) name for a
  user space address umodname:string(long). The module name will now
  also be in the output of usymdata() and in backtrace addresses even
  when they were not given with -d at the command line.

- Kernel backtraces are now much faster (replaced a linear search
  with a binary search).

- A new integrated compile-server client is now available as part of stap.

  o 'stap --use-server ...' is equivalent to 'stap-client ...'
  o 'stap --list-servers' is equivalent to 'stap-find-servers'
  o 'stap --list-servers=online' is equivalent to 'stap-find-servers --all'
  o stap-client and its related tools will soon be deprecated.
  o the nss-devel and avahi-devel packages are required for building stap with
    the integrated client (checked during configuration).
  o nss and avahi are required to run the integrated client.

- A new operator @entry is available for automatically saving an expression
  at entry time for use in a .return probe.
   probe foo.return { println(get_cycles() - @entry(get_cycles())) }

- Probe $target variables and @cast() can now use a suffix to print complex
  data types as strings.  Use a single '$' for a shallow view, or '$$' for a
  deeper view that includes nested types.  For example, with fs_struct:
   $fs$ : "{.users=%i, .lock={...}, .umask=%i,
            .in_exec=%i, .root={...}, .pwd={...}}"
   $fs$$ : "{.users=%i, .lock={.raw_lock={.lock=%u}}, .umask=%i, .in_exec=%i,
             .root={.mnt=%p, .dentry=%p}, .pwd={.mnt=%p, .dentry=%p}}"

- The <sys/sdt.h> user-space markers no longer default to an implicit
  MARKER_NAME_ENABLED() semaphore check for each marker.  To check for
  enabled markers use a .d declaration file, then:
     if (MARKER_NAME_ENABLED()) MARKER_NAME()

- Hyphenated <sys/sdt.h> marker names such as process(...).mark("foo-bar")
  are now accepted in scripts.  They are mapped to the double-underscore
  form ("foo__bar").

- More robust <sys/sdt.h> user-space markers support is included.  For
  some platforms (x86*, ppc*), this can let systemtap probe the markers
  without debuginfo.  This implementation also supports preserving
  the "provider" name associated with a marker:
    probe process("foo").provider("bar").mark("baz") to match
    STAP_PROBE<n>(bar, baz <...>)
  (Compile with -DSTAP_SDT_V1 to revert to the previous implementation.
  Systemtap supports pre-existing or new binaries using them.)

- Embedded-C may be used within expressions as values, when in guru mode:
     num = %{ LINUX_VERSION_CODE %}               // int64_t
     name = %{ /* string */ THIS_MODULE->name %}  // const char*
     printf ("%s %x\n", name, num)
  The usual /* pure */, /* unprivileged */, and /* guru */ markers may be used 
  as with embedded-C functions.

- By default the systemtap-runtime RPM builds now include a shared
  library, staplog.so, that allows crash to extract systemtap data from
  a vmcore image.

- Iterating with "foreach" can now explicitly save the value for the loop.
     foreach(v = [i,j] in array)
       printf("array[%d,%s] = %d\n", i, j, v /* array[i,j] */)

- The new "--ldd" option automatically adds any additional shared
  libraries needed by probed or -d-listed userspace binaries to the -d
  list, to enable symbolic backtracing through them.  Similarly, the
  new "--all-modules" option automatically adds any currently loaded
  kernel modules (listed in /proc/modules) to the -d list.

- A new family of set_kernel_* functions make it easier for gurus to write
  new values at arbitrary memory addresses.

- Probe wildcards can now use '**' to cross the '.' separator.
     $ stap -l 'sys**open'
     syscall.mq_open
     syscall.open

- Backward compatibility flags (--compatible=VERSION, and matching
  script preprocessing predicate %( systemtap_v CMP "version" %)
  and a deprecation policy are being introduced, in case future
  tapset/language changes break valid scripts.

* What's new in version 1.2, 2010-03-22

- Prototype support for "perf events", where the kernel supports the
  2.6.33 in-kernel API.  Probe points may refer to low-level 
  perf_event_attr type/config numbers, or to a number of aliases
  defined in the new perf.stp tapset:
     probe perf.sw.cpu_clock, perf.type(0).config(4) { }

- Type-casting can now use multiple headers to resolve codependencies.
     @cast(task, "task_struct",
           "kernel<linux/sched.h><linux/fs_struct.h>")->fs->umask

- Tapset-related man pages have been renamed.  'man -k 3stap' should show
  the installed list, which due to prefixing should no longer collide over
  ordinary system functions.

- User space marker arguments no longer use volatile if the version of gcc,
  which must be at least 4.5.0, supports richer DWARF debuginfo.  Use cflags
  -DSTAP_SDT_VOLATILE=volatile or -DSTAP_SDT_VOLATILE= when building
  the sys/sdt.h application to override this one way or another.

- A new construct for error handling is available.  It is similar to c++
  exception catching, using try and catch as new keywords.  Within a handler
  or function, the following is valid and may be nested:
     try { /* arbitrary statements */ }
     catch (er) { /* e.g. println("caught error ", er) */ }

- A new command line flag '-W' forces systemtap to abort translation of
  a script if any warnings are produced.  It is similar to gcc's -Werror.
  (If '-w' is also supplied to suppress warnings, it wins.)

- A new predicate @defined is available for testing whether a
  particular $variable/expression is resolvable at translate time:
  probe foo { if (@defined($bar)) log ("$bar is available here") }

- Adjacent string literals are glued together, making this
  construct valid:
     probe process("/usr" @1 "/bin").function("*") { ... }

- In order to limit potential impact from future security problems, 
  the stap-server process does not permit its being launched as root.

- On recent kernels, for some architectures/configurations, hardware
  breakpoint probes are supported.  The probe point syntax is:

     probe kernel.data(ADDRESS).write
     probe kernel.data(ADDRESS).length(LEN).write
     probe kernel.data("SYMBOL_NAME").write

* What's new in version 1.1, 2010-01-15

- New tracepoint based tapset for memory subsystem.

- The loading of signed modules by staprun is no longer allowed for
  ordinary, unprivileged users.  This means that only root, members of
  the group 'stapdev' and members of the group 'stapusr' can load
  systemtap modules using staprun, stap or stap-client.  The minimum
  privilege required to run arbitrary --unprivileged scripts is now
  'stapusr' membership.

- The stap-server initscript is available. This initscript allows you
  to start systemtap compile servers as a system service and to manage
  these servers as a group or individually. The stap-server initscript
  is installed by the systemtap-server rpm.  The build directory for
  the uprobes module (/usr/share/systemtap/runtime/uprobes) is made
  writable by the 'stap-server' group. All of the files generated when
  building the uprobes module, including the digital signature, are
  also writable by members of stap-server.

  See initscript/README.stap-server for details.

- Some of the compile server client, server and certificate management
  tools have been moved from $bindir to $libexecdir/systemtap.
  You should use the new stap-server script or the stap-server initscript
  for server management where possible. The stap-server script provides the same
  functionality as the stap-server initscript except that the servers are
  run by the invoking user by default as opposed to servers started by the
  stap-server initscript which are run by the user stap-server
  by default. See stap-server(8) for more information.

  You may continue to use these tools by adding $libexecdir/systemtap to
  your path. You would need to do this, for example, if you are not root,
  you want to start a compile server and you are not running systemtap from a
  private installation. In this case you still need to use stap-start-server.

- Any diagnostic output line that starts with "ERROR", as in
  error("foo"), will promote a "Pass 5: run failed", and the return
  code is 1.

- Systemtap now warns about global variables being referenced from other
  script files.  This aims to protect against unintended local-vs-global 
  namespace collisions such as:

     % cat some_tapset.stp
     probe baz.one = bar { foo = $foo; bar = $bar }
     % cat end_user_script.stp
     global foo # intended to be private variable
     probe timer.s(1) { foo ++ }
     probe baz.* { println(foo, pp()) }
     % stap end_user_script.stp
     WARNING: cross-file global variable reference to foo from some_tapset.stp

- Preprocessor conditional for kernel configuration testing:
  %( CONFIG_foo == "y" %? ... %) 

- ftrace(msg:string) tapset function to send strings to the system-wide
  ftrace ring-buffer (if any).

- Better support for richer DWARF debuginfo output from GCC 4.5
  (variable tracking assignments). Kernel modules are now always resolved
  against all their dependencies to find any info referring to missing
  symbols. DW_AT_const_value is now supported when no DW_AT_location
  is available.

* What's new in verson 1.0, 2009-09-22

- process().mark() probes now use an enabling semaphore to reduce the
  computation overhead of dormant probes.

- The function spec for dwarf probes now supports C++ scopes, so you can
  limit the probes to specific namespaces or classes.  Multiple scopes
  can be specified, and they will be matched progressively outward.
      probe process("foo").function("std::vector<*>::*") { }
      probe process("foo").function("::global_function") { }

- It is now possible to cross-compile systemtap scripts for foreign
  architectures, using the new '-a ARCH' and '-B OPT=VALUE' flags.
  For example, put arm-linux-gcc etc. into your $PATH, and point
  systemtap at the target kernel build tree with:
     stap -a arm -B CROSS_COMPILE=arm-linux- -r /build/tree  [...]
  The -B option is passed to kbuild make.  -r identifies the already
  configured/built kernel tree and -a its architecture (kbuild ARCH=...).
  Systemtap will infer -p4.

- Cross compilation using the systemtap client and server
  - stap-start-server now accepts the -r, -R, -I, -B and -a options in
    order to start a cross compiling server. The server will correctly
    advertise itself with respect to the kernel release and architecture
    that it compiles for.
  - When specified on stap-client, the -r and -a options will be
    considered when searching for a suitable server.

- When using the systemtap client and server udp port 5353 must be open
  in your firewall in order for the client to find servers using
  avahi-browse.  Also the systemtap server will choose a random port in
  the range 1024-63999 for accepting ssl connections.

- Support for unprivileged users:
  ***********************************************************************
  * WARNING!!!!!!!!!!                                                   *
  * This feature is EXPERIMENTAL at this time and should be used with   *
  * care. This feature allows systemtap kernel modules to be loaded by  *
  * unprivileged users. The user interface and restrictions will change *
  * as this feature evolves.                                            *
  ***********************************************************************
  - Systemtap modules generated from scripts which use a restricted
    subset of the features available may be loaded by staprun for
    unprivileged users. Previously, staprun would load modules only for
    root or for members of the groups stapdev and stapusr.
  - Using the --unprivileged option on stap enables translation-time
    checking for use by unprivileged users (see restrictions below).
  - All modules deemed suitable for use by unprivileged users will be
    signed by the systemtap server when --unprivileged is specified on
    stap-client. See module signing in release 0.9.8 and stap-server in
    release 0.9 below.
  - Modules signed by trusted signers (servers) and verified by staprun
    will be loaded by staprun regardless of the user's privilege level.
  - The system administrator asserts the trustworthiness of a signer
    (server) by running stap-authorize-signing-cert <cert-file> as root,
    where the <cert-file> can be found in
    ~<user>/.systemtap/ssl/server/stap.cert for servers started by
    ordinary users and in $sysconfdir/systemtap/ssl/server/stap.cert for
    servers started by root.
  - Restrictions are intentionally strict at this time and may be
    relaxed in the future:
     - probe points are restricted to:
         begin, begin(n), end, end(n), error, error(n), never,
         timer.{jiffies,s,sec,ms,msec,us,usec,ns,nsec}(n)*, timer.hz(n),
         process.* (for processes owned by the user).
     - use of embedded C code is not allowed.
     - use of tapset functions is restricted.
       - some tapset functions may not be used at all. A message will be
         generated at module compilation time.
       - some actions by allowed tapset functions may only be performed
         in the context of the user's own process. A runtime fault will
         occur in these situations, for example, direct memory access.
       - The is_myproc() tapset function has been provided so that
         tapset writers for unprivileged users can check that the
         context is of the users own process before attempting these
         actions.
     - accessing the kernel memory space is not allowed.
     - The following command line options may not be used by stap-client
       -g, -I, -D, -R, -B
     - The following environment variables are ignored by stap-client:
       SYSTEMTAP_RUNTIME, SYSTEMTAP_TAPSET, SYSTEMTAP_DEBUGINFO_PATH
  - nss and nss-tools are required to use this feature.

- Support output file switching by SIGUSR2. Users can command running
  stapio to switch output file by sending SIGUSR2.

- Memory consumption for scripts involving many uprobes has been
  dramatically reduced.

- The preprocessor now supports || and && in the conditions.
  e.g. %( arch == "x86_64" || arch == "ia64" %: ... %)

- The systemtap notion of "architecture" now matches the kernel's, rather
  than that of "uname -m".  This means that 32-bit i386 family are all
  known as "i386" rather than "i386" or "i686"; "ppc64" as "powerpc";
  "s390x" as "s390", and so on.  This is consistent between the new
  "-a ARCH" flag and the script-level %( arch ... %) conditional.

- It is now possible to define multiple probe aliases with the same name.
  A probe will expand to all matching aliases.
    probe foo = bar { }
    probe foo = baz { }
    probe foo { } # expands twice, once to bar and once to baz

- A new experimental transport mechanism, using ftrace's ring_buffer,
  has been added.  This may become the default transport mechanism in
  future versions of systemtap.  To test this new transport mechanism,
  define 'STP_USE_RING_BUFFER'.

- Support for recognizing DW_OP_{stack,implicit}_value DWARF expressions
  as emitted by GCC 4.5.

* What's new in version 0.9.9, 2009-08-04

- Systemwide kernel .function.return (kretprobe) maxactive defaults may
  be overridden with the -DKRETACTIVE=nnn parameter.

- Translation pass 2 is significantly faster by avoiding unnecessary
  searching through a kernel build/module directory tree.

- When compiled against elfutils 0.142 systemtap now handles the new
  DW_OP_call_frame_CFA generated by by GCC.

- uprobes and ustack() are more robust when used on applications that
  depend on prelinked/separate debuginfo shared libraries.

- User space PROBE marks are not always found with or without separate
  debuginfo. The .probes section itself is now always put in the main
  elf file and marked as allocated. When building pic code the section
  is marked writable. The selinux memory check problems seen with
  programs using STAP_PROBES is fixed.

- statement() probes can now override "address not at start of statement"
  errors in guru mode. They also provide alternative addresses to use
  in non-guru mode.

- The stapgraph application can generate graphs of data and events
  emitted by systemtap scripts in real time.  Run "stapgraph
  testsuite/systemtap.examples/general/grapher.stp" for an example of
  graphing the system load average and keyboard events.
  
- Dwarf probes now show parameters and local variables in the verbose
  listing mode (-L).

- Symbol aliases are now resolved to their canonical dwarf names.  For
  example, probing "malloc" in libc resolves to "__libc_malloc".

- The syntax for dereferencing $target variables and @cast() gained new
  capabilities:
  - Array indexes can now be arbitrary numeric expressions.
  - Array subscripts are now supported on pointer types.
  - An '&' operator before a @cast or $target returns the address of the
    final component, especially useful for nested structures.

- For reading all probe variables, kernel.mark now supports $$vars and
  $$parms, and process.syscall now supports $$vars.

- The SNMP tapset provides probes and functions for many network
  statistics.  See stapprobes.snmp(3stap) for more details.

- The dentry tapset provides functions to map kernel VFS directory entries
  to file or full path names: d_path(), d_name() and reverse_path_walk().

- SystemTap now has userspace markers in its own binaries, and the stap
  tapset provides the available probepoints and local variables.

- Miscellaneous new tapset functions:
  - pgrp() returns the process group ID of the current process
  - str_replace() performs string replacement

* What's new in version 0.9.8, 2009-06-11

- Miscellaneous new tapset functions:
  - sid() returns the session ID of the current process
  - stringat() indexes a single character from a string.

- Using %M in print formats for hex dumps can now print entire buffers,
  instead of just small numbers.

- Dwarfless syscalls: The nd_syscalls tapset is now available to probe
  system calls without requiring kernel debugging information.  All of
  the same probepoints in the normal syscalls tapset are available with
  an "nd_" prefix, e.g. syscall.open becomes nd_syscall.open.  Most
  syscall arguments are also available by name in nd_syscalls.

- Module signing: If the appropriate nss libraries are available on your
  system, stap-server will sign each compiled module using a self-generated
  certificate.  This is the first step toward extending authority to
  load certain modules to unprivileged users. For now, if the system
  administrator adds a certificate to a database of trusted signers
  (stap-authorize-signing-cert), modules signed using that certificate
  will be verified by staprun against tampering.  Otherwise, you should
  notice no difference in the operation of stap or staprun.

* What's new in version 0.9.7, 2009-04-23

- @cast can now determine its type information using an explicit header
  specification.  For example:
    @cast(tv, "timeval", "<sys/time.h>")->tv_sec
    @cast(task, "task_struct", "kernel<linux/sched.h>")->tgid

- The overlapping process.* tapsets are now separated.  Those probe points
  documented in stapprobes(3stap) remain the same.  Those that were formerly
  in stapprobes.process(3stap) have been renamed to kprocess, to reflect
  their kernel perspective on processes.

- The --skip-badvars option now also suppresses run-time error
  messages that would otherwise result from erroneous memory accesses.
  Such accesses can originate from $context expressions fueled by
  erroneous debug data, or by kernel_{long,string,...}() tapset calls.

- New probes kprobe.function(FUNCTION) and kprobe.function(FUNCTION).return
  for dwarfless probing. These postpone function address resolution to
  run-time and use the kprobe symbol-resolution mechanism.
  Probing of absolute statements can be done using the
  kprobe.statement(ADDRESS).absolute construct.

- EXPERIMENTAL support for user process unwinding. A new collection of
  tapset functions have been added to handle user space backtraces from
  probe points that support them (currently process and timer probes -
  for timer probes test whether or not in user space first with the
  already existing user_mode() function). The new tapset functions are:
    uaddr - User space address of current running task.
    usymname - Return the symbol of an address in the current task.
    usymdata - Return the symbol and module offset of an address.
    print_ustack - Print out stack for the current task from string.
    print_ubacktrace - Print stack back trace for current task.
    ubacktrace - Hex backtrace of current task stack.
  Please read http://sourceware.org/ml/systemtap/2009-q2/msg00364.html
  on the current restrictions and possible changes in the future and
  give feedback if you want to influence future developments.

* What's new in version 0.9.5, 2009-03-27

- New probes process().insn and process().insn.block that allows
  inspection of the process after each instruction or block of
  instructions executed. So to count the total number of instructions
  a process executes during a run do something like:
    $ stap -e 'global steps; probe process("/bin/ls").insn {steps++}
               probe end {printf("Total instructions: %d\n", steps);}' \
           -c /bin/ls
  This feature can slow down execution of a process somewhat.

- Systemtap probes and function man pages extracted from the tapsets
  are now available under 3stap. To show the page for probe vm.pagefault
  or the stap function pexecname do:
    $ man 3stap vm.pagefault
    $ man 3stap pexecname

- Kernel tracepoints are now supported for probing predefined kernel
  events without any debuginfo.  Tracepoints incur less overhead than
  kprobes, and context parameters are available with full type
  information.  Any kernel 2.6.28 and later should have defined
  tracepoints.  Try the following to see what's available:
    $ stap -L 'kernel.trace("*")'

- Typecasting with @cast now supports modules search paths, which is
  useful in case there are multiple places where the type definition
  may be found.  For example:
    @cast(sdev, "scsi_device", "kernel:scsi_mod")->sdev_state

- On-file flight recorder is supported. It allows stap to record huge
  trace log on the disk and to run in background.
  Passing -F option with -o option runs stap in background mode. In this
  mode, staprun is detached from console, and stap itself shows staprun's
  pid and exits.
  Specifying the max size and the max number of log files are also available
  by passing -S option. This option has one or two arguments seperated by
  a comma. The first argument is the max size of a log file in MB. If the
  size of a log file exceeds it, stap switches to the next log file
  automatically. The second is how many files are kept on the disk. If the
  number of log files exceeds it, the oldest log file is removed
  automatically. The second argument can be omitted.

  For example, this will record output on log files each of them is smaller
  than 1024MB and keep last 3 logs, in background.
    % stap -F -o /tmp/staplog -S 1024,3 script.stp

- In guru mode (-g), the kernel probing blacklist is disabled, leaving 
  only a subset - the kernel's own internal kprobe blacklist - to attempt
  to filter out areas unsafe to probe.  The differences may be enough to
  probe more interrupt handlers.

- Variables unavailable in current context may be skipped by setting a 
  session level flag with command line option --skip-badvars now available.
  This replaces any dwarf $variable expressions that could not be resolved
  with literal numeric zeros, along with a warning message.

- Both kernel markers and kernel tracepoint support argument listing
  through stap -L 'kernel.mark("*")' or stap -L 'kernel.trace("*")'

- Users can use -DINTERRUPTIBLE=0 to prevent interrupt reentrancy in
  their script, at the cost of a bit more overhead to toggle the
  interrupt mask.

- Added reentrancy debugging. If stap is run with the arguments
  "-t -DDEBUG_REENTRANCY", additional warnings will be printed for
  every reentrancy event, including the probe points of the
  resident and interloper probes.

- Default to --disable-pie for configure.
  Use --enable-pie to turn it back on.

- Improved sdt.h compatibility and test suite for static dtrace
  compatible user space markers.

- Some architectures now use syscall wrappers (HAVE_SYSCALL_WRAPPERS).
  The syscall tapset has been enhanced to take care of the syscall
  wrappers in this release.

- Security fix for CVE-2009-0784: stapusr module-path checking race.

* What's new in version 0.9, 2009-02-19

- Typecasting is now supported using the @cast operator.  A script can
  define a pointer type for a "long" value, and then access type members
  using the same syntax as with $target variables.  For example, this will
  retrieve the parent pid from a kernel task_struct:
    @cast(pointer, "task_struct", "kernel")->parent->pid

- process().mark() probes are now possible to trace static user space
  markers put in programs with the STAP_PROBE macro using the new
  sys/sdt.h include file. This also provides dtrace compatible markers
  through DTRACE_PROBE and an associated python 'dtrace' script that
  can be used in builds based on dtrace that need dtrace -h or -G
  functionality.

- For those that really want to run stap from the build tree there is
  now the 'run-stap' script in the top-level build directory that sets
  up the SYSTEMTAP_TAPSET, SYSTEMTAP_RUNTIME, SYSTEMTAP_STAPRUN, and
  SYSTEMTAP_STAPIO environment variables (installing systemtap, in a
  local prefix, is still recommended for common use).

- Systemtap now comes with a new Beginners Guide that walks the user
  through their first steps setting up stap, understanding how it all
  works, introduces some useful scripts and describes some common
  pitfalls.  It isn't created by default since it needs a Publican
  setup, but full build instructions can be found in the wiki:
  http://sourceware.org/systemtap/wiki/PublicanQuikHowto
  An online version can be found at:
  http://sourceware.org/systemtap/SystemTap_Beginners_Guide.pdf

- Standard tapsets included with Systemtap were modified to include
  extractable documentation information based on the kernel-doc
  infrastructure. When configured --enabled-docs a HTML and PDF
  version of the Tapset Reference Manual is produced explaining probes
  defined in each tapset.

- The systemtap client and compile server are now available.
  These allow you to compile a systemtap module on a host other than
  the one which it will be run, providing the client and server
  are compatible. Other than using a server for passes 1 through
  4, the client behaves like the 'stap' front end itself. This
  means, among other things, that the client will automatically
  load the resulting module on the local host unless -p[1234]
  was specified.  See stap-server(8) for more details.
  The client/server now use SSL for network connection security and
  for signing.

  The systemtap client and server are prototypes only. Interfaces, options
  and usage may change at any time.

- function("func").label("label") probes are now supported to allow matching
  the label of a function.

- Systemtap initscript is available. This initscript allows you to run
  systemtap scripts as system services (in flight recorder mode) and
  control those scripts individually.
  See README.systemtap for details.

- The stap "-r DIR" option may be used to identify a hand-made kernel
  build directory.  The tool determines the appropriate release string
  automatically from the directory.

- Serious problems associated with user-space probing in shared libraries
  were corrected, making it now possible to experiment with probe shared
  libraries.  Assuming dwarf debugging information is installed, use this
  twist on the normal syntax:

    probe process("/lib64/libc-2.8.so").function("....") { ... }

  This would probe all threads that call into that library.  Running
  "stap -c CMD" or "stap -x PID" naturally restricts this to the target
  command+descendants only.  $$vars etc. may be used.

- For scripts that sometimes terminate with excessive "skipped" probes,
  rerunning the script with "-t" (timing) will print more details about
  the skippage reasons.

- Symbol tables and unwind (backtracing) data support were formerly
  compiled in for all probed modules as identified by the script
  (kernel; module("name"); process("file")) plus those listed by the
  stap "-d BINARY" option.  Now, this data is included only if the systemtap
  script uses tapset functions like probefunc() or backtrace() that require
  such information.  This shrinks the probe modules considerably for the rest.

- Per-pass verbosity control is available with the new "--vp {N}+" option.
  "stap --vp 040" adds 4 units of -v verbosity only to pass 2.  This is useful
  for diagnosing errors from one pass without excessive verbosity from others.

- Most probe handlers now run with interrupts enabled, for improved
  system responsiveness and less probing overhead.  This may result
  in more skipped probes, for example if a reentrant probe handler
  is attempted from within an interrupt handler.  It may also make the
  systemtap overload detection facility more likely to be triggered, as
  interrupt handlers' run time would be included in the self-assessed
  overhead of running probe handlers.

* What's new in version 0.8, 2008-11-13

- Cache limiting is now available.  If the compiled module cache size is
  over a limit specified in the $SYSTEMTAP_DIR/cache/cache_mb_limit file,
  some old cache entries will be unlinked.  See man stap(1) for more.

- Error and warning messages are now followed by source context displaying
  the erroneous line/s and a handy '^' in the following line pointing to the
  appropriate column.

- A bug reporting tool "stap-report" is now available which will quickly
  retrieve much of the information requested here: 
  http://sourceware.org/systemtap/wiki/HowToReportBugs

- The translator can resolve members of anonymous structs / unions:
    given            struct { int foo; struct { int bar; }; } *p;
    this now works:  $p->bar

- The stap "-F" flag activates "flight recorder" mode, which consists of
  translating the given script as usual, but implicitly launching it into
  the background with staprun's existing "-L" (launch) option.  A user
  can later reattach to the module with "staprun -A MODULENAME".

- Additional context variables are available on user-space syscall probes.
  - $argN ($arg1, $arg2, ... $arg6) in process(PATH_OR_PID).syscall
    gives you the argument of the system call.
  - $return in process(PATH_OR_PID).syscall.return gives you the return
    value of the system call.

- Target process mode (stap -c CMD or -x PID) now implicitly restricts all
  "process.*" probes to the given child process.  (It does not affect
  kernel.* or other probe types.)  The CMD string is normally run directly,
  rather than via a /bin/sh -c subshell, since then utrace/uprobe probes
  receive a fairly "clean" event stream.  If metacharacters like
  redirection operators were present in CMD, then "sh -c CMD" is still
  used, and utrace/uprobe probes will receive events from the shell.

     % stap -e 'probe process.syscall, process.end {
                   printf("%s %d %s\n", execname(), pid(), pp())}'\
            -c ls
     ls 2323 process.syscall 
     ls 2323 process.syscall 
     ls 2323 process.end

- Probe listing mode is improved: "-L" lists available script-level variables

     % stap -L 'syscall.*open*'
     syscall.mq_open name:string name_uaddr:long filename:string mode:long u_attr_uaddr:long oflag:long argstr:string
     syscall.open name:string filename:string flags:long mode:long argstr:string
     syscall.openat name:string filename:string flags:long mode:long argstr:string

- All user-space-related probes support $PATH-resolved executable
  names, so

     probe process("ls").syscall {}
     probe process("./a.out").syscall {}

  work now, instead of just

     probe process("/bin/ls").syscall {}
     probe process("/my/directory/a.out").syscall {}

- Prototype symbolic user-space probing support:

     # stap -e 'probe process("ls").function("*").call {
                   log (probefunc()." ".$$parms)
                }' \
            -c 'ls -l'

  This requires:
  - debugging information for the named program
  - a version of utrace in the kernel that is compatible with the "uprobes"
    kernel module prototype.  This includes RHEL5 and older Fedora, but not
    yet current lkml-track utrace; a "pass 4a"-time build failure means
    your system cannot use this yet.

- Global variables which are written to but never read are now
  automatically displayed when the session does a shutdown.  For example:

      global running_tasks
      probe timer.profile {running_tasks[pid(),tid()] = execname()}
      probe timer.ms(8000) {exit()}

- A formatted string representation of the variables, parameters, or local
  variables at a probe point is now supported via the special $$vars,
  $$parms, and $$locals context variables, which expand to a string
  containing a list "var1=0xdead var2=0xbeef var3=?".  (Here, var3 exists
  but is for some reason unavailable.)  In return probes only, $$return
  expands to an empty string for a void function, or "return=0xf00".


* What's new in version 0.7, 2008-07-15

- .statement("func@file:*") and .statement("func@file:M-N") probes are now
  supported to allow matching a range of lines in a function.  This allows
  tracing the execution of a function.

- Scripts relying on probe point wildcards like "syscall.*" that expand
  to distinct kprobes are processed significantly faster than before.

- The vector of script command line arguments is available in a
  tapset-provided global array argv[].  It is indexed 1 ... argc,
  another global.  This can substitute for of preprocessor
  directives @NNN that fail at parse time if there are not
  enough arguments.

      printf("argv: %s %s %s", argv[1], argv[2], argv[3])

- .statement("func@file+line") probes are now supported to allow a
  match relative to the entry of the function incremented by line
  number.  This allows using the same systemtap script if the rest
  of the file.c source only changes slightly.

- A probe listing mode is available.
  % stap -l vm.*
  vm.brk
  vm.mmap
  vm.munmap
  vm.oom_kill
  vm.pagefault
  vm.write_shared

- More user-space probe types are added:

  probe process(PID).begin { }
  probe process("PATH").begin { }
  probe process(PID).thread.begin { }
  probe process("PATH").thread.begin { }
  probe process(PID).end { }
  probe process("PATH").end { }
  probe process(PID).thread.end { }
  probe process("PATH").thread.end { }
  probe process(PID).syscall { }
  probe process("PATH").syscall { }
  probe process(PID).syscall.return { }
  probe process("PATH").syscall.return { }

- Globals now accept ; terminators

  global odds, evens;
  global little[10], big[5];

* What's new in version 0.6, 2007-12-15

- A copy of the systemtap tutorial and language reference guide
  are now included.

- There is a new format specifier, %m, for the printf family of
  functions.  It functions like %s, except that it does not stop when
  a nul ('\0') byte is encountered.  The number of bytes output is
  determined by the precision specifier.  The default precision is 1.
  For example:

      printf ("%m", "My String") // prints one character: M
      printf ("%.5", myString)   // prints 5 bytes beginning at the start
                                 // of myString

- The %b format specifier for the printf family of functions has been enhanced
  as follows:

  1) When the width and precision are both unspecified, the default is %8.8b.
  2) When only one of the width or precision is specified, the other defaults
     to the same value.  For example, %4b == %.4b == %4.4b
  3) Nul ('\0') bytes are used for field width padding.  For example,

     printf ("%b", 0x1111deadbeef2222) // prints all eight bytes
     printf ("%4.2b", 0xdeadbeef)      // prints  \0\0\xbe\xef

- Dynamic width and precision are now supported for all printf family format
  specifiers.  For example:

     four = 4
     two = 2
     printf ("%*.*b", four, two, 0xdeadbbeef) // prints  \0\0\xbe\xef
     printf ("%*d", four, two)                // prints  <space><space><space>2

- Preprocessor conditional expressions can now include wildcard style
  matches on kernel versions.
  %( kernel_vr != "*xen" %? foo %: bar %)

- Prototype support for user-space probing is showing some progress.
  No symbolic notations are supported yet (so no probing by function names,
  file names, process names, and no access to $context variables), but at
  least it's something:

    probe process(PID).statement(ADDRESS).absolute { }

  This will set a uprobe on the given process-id and given virtual address.
  The proble handler runs in kernel-space as usual, and can generally use
  existing tapset functions.

- Crash utility can retrieve systemtap's relay buffer from a kernel dump
  image by using staplog which is a crash extension module. To use this
  feature, type commands as below from crash(8)'s command line:

    crash> extend staplog.so
    crash> help systemtaplog

  Then, you can see more precise help message.

- You can share a relay buffer amoung several scripts and merge outputs from
  several scripts by using "-DRELAY_HOST" and "-DRELAY_GUEST" options.
  For example:

    # run a host script
    % stap -ve 'probe begin{}' -o merged.out -DRELAY_HOST &
    # wait until starting the host.
    % stap -ve 'probe begin{print("hello ");exit()}' -DRELAY_GUEST
    % stap -ve 'probe begin{print("world\n");exit()}' -DRELAY_GUEST

  Then, you'll see "hello world" in merged.out.

- You can add a conditional statement for each probe point or aliase, which
  is evaluated when the probe point is hit. If the condition is false, the
  whole probe body(including aliases) is skipped. For example:

    global switch = 0;
    probe syscall.* if (switch) { ... }
    probe procfs.write {switch = strtol($value,10)} /* enable/disable ctrl */

- Systemtap will warn you if your script contains unused variables or
  functions.  This is helpful in case of misspelled variables.  If it
  doth protest too much, turn it off with "stap -w ...".

- You can add error-handling probes to a script, which are run if a
  script was stopped due to errors.  In such a case, "end" probes are
  not run, but "error" ones are.

    probe error { println ("oops, errors encountered; here's a report anyway")
                  foreach (coin in mint) { println (coin) } }

- In a related twist, one may list probe points in order of preference,
  and mark any of them as "sufficient" beyond just "optional".  Probe
  point sequence expansion stops if a sufficient-marked probe point has a hit.
  This is useful for probes on functions that may be in a module (CONFIG_FOO=m)
  or may have been compiled into the kernel (CONFIG_FOO=y), but we don't know
  which.  Instead of

    probe module("sd").function("sd_init_command") ? ,
          kernel.function("sd_init_command") ? { ... }

  which might match neither, now one can write this:

    probe module("sd").function("sd_init_command") ! , /* <-- note excl. mark */
          kernel.function("sd_init_command")  { ... }

- New security model.  To install a systemtap kernel module, a user
  must be one of the following: the root user; a member of the
  'stapdev' group; or a member of the 'stapusr' group.  Members of the
  stapusr group can only use modules located in the
  /lib/modules/VERSION/systemtap directory (where VERSION is the
  output of "uname -r").

- .statement("...@file:line") probes now apply heuristics to allow an
  approximate match for the line number.  This works similarly to gdb,
  where a breakpoint placed on an empty source line is automatically
  moved to the next statement.  A silly bug that made many $target
  variables inaccessible to .statement() probes was also fixed.

- LKET has been retired.  Please let us know on <systemtap@sourceware.org>
  if you have been a user of the tapset/tools, so we can help you find
  another way.

- New families of printing functions println() and printd() have been added.
  println() is like print() but adds a newline at the end;
  printd() is like a sequence of print()s, with a specified field delimiter.

* What's new since version 0.5.14?, 2007-07-03

- The way in which command line arguments for scripts are substituted has
  changed.  Previously, $1 etc. would interpret the corresponding command
  line argument as an numeric literal, and @1 as a string literal.  Now,
  the command line arguments are pasted uninterpreted wherever $1 etc.
  appears at the beginning of a token.  @1 is similar, but is quoted as
  a string.  This change does not modify old scripts, but has the effect
  of permitting substitution of arbitrary token sequences.

  # This worked before, and still does:
  % stap -e 'probe timer.s($1) {}'        5
  # Now this also works:
  % stap -e 'probe syscall.$1 {log(@1)}'  open
  # This won't crash, just signal a recursion error:
  % stap -e '$1'                          '$1'
  # As before, $1... is recognized only at the beginning of a token
  % stap -e 'probe begin {foo$1=5}'

* What's new since version 0.5.13?, 2007-03-26

- The way in which systemtap resolves function/inline probes has changed:
   .function(...) - now refers to all functions, inlined or not
   .inline(...)   - is deprecated, use instead:
   .function(...).inline - filters function() to only inlined instances
   .function(...).call - filters function() to only non-inlined instances
   .function(...).return - as before, but now pairs best with .function().call
   .statement() is unchanged.

* What's new since version 0.5.12?, 2007-01-01

- When running in -p4 (compile-only) mode, the compiled .ko file name
  is printed on standard output.

- An array element with a null value such as zero or an empty string
  is now preserved, and will show up in a "foreach" loop or "in" test.
  To delete such an element, the scripts needs to use an explicit
  "delete array[idx]" statement rather than something like "array[idx]=0".

- The new "-P" option controls whether prologue searching heuristics
  will be activated for function probes.  This was needed to get correct
  debugging information (dwarf location list) data for $target variables.
  Modern compilers (gcc 4.1+) tend not to need this heuristic, so it is
  no longer default.  A new configure flag (--enable-prologues) restores
  it as a default setting, and is appropriate for older compilers (gcc 3.*).

- Each systemtap module prints a one-line message to the kernel informational
  log when it starts.  This line identifies the translator version, base
  address of the probe module, a broken-down memory consumption estimate, and
  the total number of probes.  This is meant as a debugging / auditing aid.

- Begin/end probes are run with interrupts enabled (but with
  preemption disabled).  This will allow begin/end probes to be
  longer, to support generating longer reports.

- The numeric forms of kernel.statement() and kernel.function() probe points
  are now interpreted as relocatable values - treated as relative to the
  _stext symbol in that kernel binary.  Since some modern kernel images
  are relocated to a different virtual address at startup, such addresses
  may shift up or down when actually inserted into a running kernel.

     kernel.statement(0xdeadbeef): validated, interpreted relative to _stext,
                                   may map to 0xceadbeef at run time.

  In order to specify unrelocated addresses, use the new ".absolute"
  probe point suffix for such numeric addresses.  These are only
  allowed in guru mode, and provide access to no $target variables.
  They don't use debugging information at all, actually.

     kernel.statement(0xfeedface).absolute: raw, unvalidated, guru mode only

* What's new since version 0.5.10?, 2006-10-19

- Offline processing of debugging information, enabling general
  cross-compilation of probe scripts to remote hosts, without
  requiring identical module/memory layout.  This slows down
  compilation/translation somewhat.

- Kernel symbol table data is loaded by staprun at startup time
  rather than compiled into the module.

- Support the "limit" keyword for foreach iterations:
    foreach ([x,y] in ary limit 5) { ... }
  This implicitly exits after the fifth iteration.  It also enables
  more efficient key/value sorting.

- Support the "maxactive" keyword for return probes:
    probe kernel.function("sdfsdf").maxactive(848) { ... }
  This allows up to 848 concurrently outstanding entries to
  the sdfsdf function before one returns.  The default maxactive
  number is smaller, and can result in missed return probes.

- Support accessing of saved function arguments from within
  return probes.  These values are saved by a synthesized
  function-entry probe.

- Add substantial version/architecture checking in compiled probes to
  assert correct installation of debugging information and correct
  execution on a compatible kernel.

- Add probe-time checking for sufficient free stack space when probe
  handlers are invoked, as a safety improvement.

- Add an optional numeric parameter for begin/end probe specifications,
  to order their execution.
     probe begin(10) { } /* comes after */ probe begin(-10) {}

- Add an optional array size declaration, which is handy for very small
  or very large ones.
     global little[5], big[20000]

- Include some example scripts along with the documentation.

- Change the start-time allocation of probe memory to avoid causing OOM
  situations, and to abort cleanly if free kernel memory is short.

- Automatically use the kernel DWARF unwinder, if present, for stack
  tracebacks.

- Many minor bug fixes, performance, tapset, and error message
  improvements.