CONTRIB: trace: try to display the function's return value on exit
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.
diff --git a/contrib/trace/trace.awk b/contrib/trace/trace.awk
index 6bd5b10..74d953c 100755
--- a/contrib/trace/trace.awk
+++ b/contrib/trace/trace.awk
@@ -72,7 +72,7 @@
}
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
}
'
diff --git a/src/trace.c b/src/trace.c
index 9425be9..ab23a74 100644
--- a/src/trace.c
+++ b/src/trace.c
@@ -171,7 +171,7 @@
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 @@
*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 @@
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 :