add an option, let the systemtap doesn't check whether the probe point is at the start of an assembly instruction

[peng yu <yupeng0921 at gmail dot com>]

Hi, list.

I found systemtap verify whether a raw address matches the beginning
of a statement. Systemtap use this method to check whether the address
is at the start of an assembly instruction. But sometimes, I really
need to probe an address which is not at the start of a statement. For
example, below is a piece of disassemble instructions:

/usr/src/debug/kernel-2.6.18/linux-2.6.18.i686/arch/i386/mm/highmem.c: 70
0xc041df94 <kunmap_atomic+64>:  mov    0xc079d24c,%eax
0xc041df99 <kunmap_atomic+69>:  lea    0x0(,%ecx,8),%edx
0xc041dfa0 <kunmap_atomic+76>:  sub    %edx,%eax

I want to see the value in eax before "sub %edx, %eax" and after "mov
0xc079d24c,%eax", but systemtap forbid me to probe the address
"0xc041df99". I think it is useful if the stap command can accept a
new cmdline option,  let it don't do the address valid check. So such
systemtap script can work: "probe kernel.statement(0xc041df99)".

Below is a patch, I test it on the systemtap-1.8, after apply the
patch, we can use a '-i' option when call stap command, let the
systemtap don't do the address valid check.

diff -Nurp systemtap-1.8.ori/cmdline.h systemtap-1.8/cmdline.h
--- systemtap-1.8.ori/cmdline.h	2012-07-16 12:06:02.911200148 +0800
+++ systemtap-1.8/cmdline.h	2012-07-16 12:08:20.137189928 +0800
@@ -58,7 +58,7 @@ enum {

 // NB: when adding new options, consider very carefully whether they
 // should be restricted from stap clients (after --client-options)!
-#define STAP_SHORT_OPTIONS "hVvtp:I:e:o:R:r:a:m:kgPc:x:D:bs:uqwl:d:L:FS:B:WG:"
+#define STAP_SHORT_OPTIONS "hVvtp:I:e:o:R:r:a:m:kgPc:x:D:bs:uqwl:d:L:FS:B:WG:i"

 #define OWE5 "tter"
 #define OWE1 "uild-"
diff -Nurp systemtap-1.8.ori/session.cxx systemtap-1.8/session.cxx
--- systemtap-1.8.ori/session.cxx	2012-07-16 12:06:02.910188209 +0800
+++ systemtap-1.8/session.cxx	2012-07-16 12:08:20.136188467 +0800
@@ -105,6 +105,7 @@ systemtap_session::systemtap_session ():
   listing_mode = false;
   listing_mode_vars = false;
   dump_probe_types = false;
+  ignore_address_check = false;

 #ifdef ENABLE_PROLOGUES
   prologue_searching = true;
@@ -844,6 +845,11 @@ systemtap_session::parse_cmdline (int ar
           kbuildflags.push_back (string (optarg));
 	  break;

+        case 'i':
+          server_args.push_back (string ("-") + (char)grc);
+          ignore_address_check = true;
+          break;
+
 	case LONG_OPT_VERSION:
 	  version ();
 	  exit (0);
diff -Nurp systemtap-1.8.ori/session.h systemtap-1.8/session.h
--- systemtap-1.8.ori/session.h	2012-07-16 12:06:03.053189385 +0800
+++ systemtap-1.8/session.h	2012-07-16 12:08:20.276189957 +0800
@@ -179,6 +179,7 @@ public:
   bool unoptimized;
   bool suppress_warnings;
   bool panic_warnings;
+  bool ignore_address_check;
   int buffer_size;
   bool prologue_searching;
   bool tapset_compile_coverage;
diff -Nurp systemtap-1.8.ori/tapsets.cxx systemtap-1.8/tapsets.cxx
--- systemtap-1.8.ori/tapsets.cxx	2012-07-16 12:06:03.031191674 +0800
+++ systemtap-1.8/tapsets.cxx	2012-07-16 12:08:20.255189907 +0800
@@ -1400,7 +1400,7 @@ query_addr(Dwarf_Addr addr, dwarf_query
       // is at the start of an assembly instruction.  Mark probes are in the
       // middle of a macro and thus not strictly at a statement beginning.
       // Guru mode may override this check.
-      if (!q->has_mark && (!address_line || address_line.addr() != addr))
+      if (!q->has_mark && !dw.sess.ignore_address_check &&
(!address_line || address_line.addr() != addr))
         {
           stringstream msg;
           msg << _F("address %#" PRIx64 " does not match the
beginning of a statement",