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CONTRIB: trace: try to display the function's return value on exit

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On x86_64, when gcc instruments functions and compiles at -O0, it saves
the function's return value in register rbx before calling the trace
callback. It provides a nice opportunity to display certain useful
values (flags, booleans etc) during trace sessions. It's absolutely
not guaranteed that it will always work but it provides a considerable
help when it does so it's worth activating it. When building on a
different architecture, the value 0 is always reported as the return
value. On x86_64 with optimizations (-O), the RBX register will not
necessarily match and random values will be reported, but since it's
not the primary target it's not a problem.
This commit is contained in:
Willy Tarreau 2017-10-24 10:58:20 +02:00
parent 1296382d0b
commit e8f0f1265f
2 changed files with 19 additions and 5 deletions
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4
contrib/trace/trace.awk
View File

@ -72,7 +72,7 @@ function getptr(ptr)
}
getptr($3); caller_loc=loc; caller_name=name
getptr($5); callee_loc=loc; callee_name=name
printf "%s %s %s %s %s [%s:%s] %s [%s:%s]\n",
$1, indents[$4,$2], caller_name, $4, callee_name, caller_loc, $3, $4, callee_loc, $5
printf "%s %s %s %s %s(%s) [%s:%s] %s [%s:%s]\n",
$1, indents[$4,$2], caller_name, $4, callee_name, $6, caller_loc, $3, $4, callee_loc, $5
}
'

20
src/trace.c
View File

@ -171,7 +171,7 @@ static char *emit_hex(unsigned long h, char *out)
return out;
}
static void make_line(void *from, void *to, int level, char dir)
static void make_line(void *from, void *to, int level, char dir, long ret)
{
char *p = line;
@ -221,6 +221,12 @@ static void make_line(void *from, void *to, int level, char dir)
*p++ = ' '; *p++ = '0'; *p++ = 'x';
p = emit_hex((unsigned long)to, p);
if (dir == '<') {
/* " %x", ret */
*p++ = ' '; *p++ = '0'; *p++ = 'x';
p = emit_hex(ret, p);
}
*p++ = '\n';
fwrite(line, p - line, 1, log);
@ -230,13 +236,21 @@ static void make_line(void *from, void *to, int level, char dir)
void __cyg_profile_func_enter(void *to, void *from)
{
if (!disabled)
return make_line(from, to, ++level, '>');
return make_line(from, to, ++level, '>', 0);
}
void __cyg_profile_func_exit(void *to, void *from)
{
long ret = 0;
#if defined(__x86_64__)
/* on x86_64, the return value (eax) is temporarily stored in ebx
* during the call to __cyg_profile_func_exit() so we can snoop it.
*/
asm volatile("mov %%rbx, %0" : "=r"(ret));
#endif
if (!disabled)
return make_line(from, to, level--, '<');
return make_line(from, to, level--, '<', ret);
}
/* the one adds comments in the trace above. The output format is :