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From: <sv...@va...> - 2015-11-18 20:57:02
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Author: philippe
Date: Wed Nov 18 20:56:55 2015
New Revision: 15729
Log:
Fix incorrect (or infinite loop) unwind on RHEL7 x86 32 bits.
On RHEL7 x86 32 bits, Valgrind unwinder cannot properly unwind
the stack just after a thread creation : the unwinder always retrieves
the same pc/sp/bp.
See below for an example.
This has as consequences that some stack traces are bigger than
needed (i.e. they always fill up the ips array). If
--merge-recursive-frames is given, then the unwinder enters in an
infinite loop (as identical frames will be merged, and the ips array
will never be filled in).
Thi patch adds an additional exit condition : after unwinding
a frame, if the previous sp is >= new sp, then unwinding stops.
Patch has been tested on debian 8/x86, RHEL7/x86.
0x0417db67 <+55>: mov 0x18(%esp),%ebx
0x0417db6b <+59>: mov 0x28(%esp),%edi
0x0417db6f <+63>: mov $0x78,%eax
0x0417db74 <+68>: mov %ebx,(%ecx)
0x0417db76 <+70>: int $0x80
=> 0x0417db78 <+72>: pop %edi
0x0417db79 <+73>: pop %esi
0x0417db7a <+74>: pop %ebx
0x0417db7b <+75>: test %eax,%eax
Valgrind stacktrace gives:
==21261== at 0x417DB78: clone (clone.S:110)
==21261== by 0x424702F: ???
==21261== by 0x424702F: ???
==21261== by 0x424702F: ???
==21261== by 0x424702F: ???
==21261== by 0x424702F: ???
==21261== by 0x424702F: ???
==21261== by 0x424702F: ???
...
(till the array of ips is full)
while gdb stacktrace gives:
(gdb) bt
#0 clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:110
#1 0x00000000 in ?? ()
(gdb) p $pc
$2 = (void (*)()) 0x417db78 <clone+72>
(gdb)
With the fix, valgrind gives:
==21261== at 0x417DB78: clone (clone.S:110)
==21261== by 0x424702F: ???
which looks more reasonable.
Modified:
trunk/coregrind/m_stacktrace.c
Modified: trunk/coregrind/m_stacktrace.c
==============================================================================
--- trunk/coregrind/m_stacktrace.c (original)
+++ trunk/coregrind/m_stacktrace.c Wed Nov 18 20:56:55 2015
@@ -350,6 +350,8 @@
uregs.xbp <= fp_max - 1 * sizeof(UWord)/*see comment below*/ &&
VG_IS_4_ALIGNED(uregs.xbp))
{
+ Addr old_xsp;
+
/* fp looks sane, so use it. */
uregs.xip = (((UWord*)uregs.xbp)[1]);
// We stop if we hit a zero (the traditional end-of-stack
@@ -382,6 +384,7 @@
}
}
+ old_xsp = uregs.xsp;
uregs.xsp = uregs.xbp + sizeof(Addr) /*saved %ebp*/
+ sizeof(Addr) /*ra*/;
uregs.xbp = (((UWord*)uregs.xbp)[0]);
@@ -393,6 +396,12 @@
if (debug) VG_(printf)(" cache FPUNWIND >2\n");
if (debug) unwind_case = "FO";
if (do_stats) stats.FO++;
+ if (old_xsp >= uregs.xsp) {
+ if (debug)
+ VG_(printf) (" FO end of stack old_xsp %p >= xsp %p\n",
+ (void*)old_xsp, (void*)uregs.xsp);
+ break;
+ }
} else {
fp_CF_verif_cache [hash] = xip_verified ^ CFUNWIND;
if (debug) VG_(printf)(" cache CFUNWIND >2\n");
@@ -406,6 +415,12 @@
} else {
if (debug) unwind_case = "FF";
if (do_stats) stats.FF++;
+ if (old_xsp >= uregs.xsp) {
+ if (debug)
+ VG_(printf) (" FF end of stack old_xsp %p >= xsp %p\n",
+ (void*)old_xsp, (void*)uregs.xsp);
+ break;
+ }
}
goto unwind_done;
} else {
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