[Bug translator/11346] New: @defined() with '--skip-badvars' doesn't work correctly

["dsmith at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

On kernel 2.6.31.12-174.2.22.fc12.x86_64, assume the following script:

====
probe kernel.function("SyS_getxattr").call !,                                   
      kernel.function("sys_getxattr").call                                      
{                                                                               
        path = user_string(@defined($foo) ? $foo : $pathname)                   
        printf("getxattr: %s\n", path)                                          
}                                                                               
====

When run, you'll get this:

====
#  stap -v -p2 ../defined1.stp
Pass 1: parsed user script and 65 library script(s) using
48504virt/19368res/1656shr kb, in 140usr/40sys/180real ms.
# functions
_dwarf_tvar_get_pathname_2:long ()
%{
#define fetch_register k_fetch_register
#define store_register k_store_register
{
  {
    uint64_t addr;
    { // DWARF expression: 0x55
    { uint64_t value = fetch_register (5); addr = value; }
    }
    THIS->__retvalue = addr;
  }
  goto out;
if (0) goto deref_fault;
deref_fault:
  goto out;
}
/* pure *//* unprivileged */
#undef fetch_register

#undef store_register
%}
user_string:string (addr:long)
return user_string2(addr, "<unknown>")
user_string2:string (addr:long, err_msg:string)
%{ /* pure */ /* unprivileged */
  assert_is_myproc();
  if (_stp_strncpy_from_user (THIS->__retvalue, 
        (const char __user*) (uintptr_t) THIS->addr,
        MAXSTRINGLEN) < 0)
    strlcpy (THIS->__retvalue, THIS->err_msg, MAXSTRINGLEN);
%}
# probes
kernel.function("sys_getxattr@fs/xattr.c:348").call /* pc=_stext+0x11e167 */ /*
<- kernel.function("SyS_getxattr").call!,kernel.function("sys_getxattr").call */
  # locals
  path:string
{
(path) = (user_string(_dwarf_tvar_get_pathname_2()))
printf("getxattr: %s\\n", path)
}
Pass 2: analyzed script: 1 probe(s), 3 function(s), 0 embed(s), 0 global(s)
using 185792virt/116112res/74748shr kb, in 600usr/620sys/1227real ms.
====

Notice how the line:
    path = user_string(@defined($foo) ? $foo : $pathname)
got replaced by:
    (path) = (user_string(_dwarf_tvar_get_pathname_2()))

This looks reasonable.

Now run the same stap command again, but add '--skip-badvars':

====
# stap --skip-badvars -v -p2 ../defined1.stp
Pass 1: parsed user script and 65 library script(s) using
48504virt/19368res/1656shr kb, in 130usr/40sys/171real ms.
WARNING: Bad $context variable being substituted with literal 0: identifier
'$foo' at ../defined1.stp:5:37
 source:         path = user_string(@defined($foo) ? $foo : $pathname)
                                             ^
# functions
user_string:string (addr:long)
return user_string2(addr, "<unknown>")
user_string2:string (addr:long, err_msg:string)
%{ /* pure */ /* unprivileged */
  assert_is_myproc();
  if (_stp_strncpy_from_user (THIS->__retvalue, 
        (const char __user*) (uintptr_t) THIS->addr,
        MAXSTRINGLEN) < 0)
    strlcpy (THIS->__retvalue, THIS->err_msg, MAXSTRINGLEN);
%}
# probes
kernel.function("sys_getxattr@fs/xattr.c:348").call /* pc=_stext+0x11e167 */ /*
<- kernel.function("SyS_getxattr").call!,kernel.function("sys_getxattr").call */
  # locals
  path:string
{
(path) = (user_string(0))
printf("getxattr: %s\\n", path)
}
Pass 2: analyzed script: 1 probe(s), 2 function(s), 0 embed(s), 0 global(s)
using 185792virt/116108res/74748shr kb, in 500usr/570sys/1074real ms.
====

Notice the new warning we get:

  WARNING: Bad $context variable being substituted with literal 0: identifier
'$foo' at ../defined1.stp:5:37
   source:         path = user_string(@defined($foo) ? $foo : $pathname)

Notice how the line:
    path = user_string(@defined($foo) ? $foo : $pathname)
got replaced by:
    (path) = (user_string(0))

This replacement is wrong.

-- 
           Summary: @defined() with '--skip-badvars' doesn't work correctly
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: dsmith at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=11346

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