Re: help with bus error/segfault

Xavier Noria Wed, 16 May 2007 12:41:28 -0700

On May 16, 2007, at 6:11 PM, Marvin Humphrey wrote:

On May 16, 2007, at 5:58 AM, Xavier Noria wrote:
Fortunately the tester that reported the problem (David Cantrell)is so kind as to provide a SSH account on his Linux.
He's done that for me, too.  Good bloke.
Indeed, if I run the test under Valgrind in 5.6.2 there's a

==15955== Invalid write of size 4
==15955== at 0x4A0829D: __next_partition_of_size_p (in /home/perluser/FXN/Algorithm-Combinatorics-0.22/blib/arch/auto/Algorithm/Combinatorics/Combinatorics.so)
But in 5.8.8 it completes the test, the only errors come at thebeginning and seem to be unrelated to the module (reported aboutPerl_runops_standard). There were some under 5.6.2 like those aswell, but much less.
Errors? I've seen leaks (including one in DynaLoader), but I don'trecall errors under 5.8.8.

This is the first time I use Valgrind. Using 5.8.8 the test suitepasses but there's a report that reads:


  ERROR SUMMARY: 18 errors from 14 contexts (suppressed: 19 from 1)

and a lot of stuff I don't understand at the beginning. I copy theoutput below. Do you smell in that report that albeit the tests passthere may be some incorrect C code? For instance before the first ok1 there's a suspicious


  Invalid read of size 4

I'll try to figure out whether that happens before or while the firsttest runs.

I have a perl 5.8.8 compiled with -DDEBUGGING that I use forvalgrind testing, and I feed it this suppressions file:
  http://xrl.us/wdve (Link to www.rectangular.com)

The full command is:

  valgrind --leak-check=full --show-reachable=yes \
  --suppressions=../devel/p588_valgrind.supp \
  /usr/local/debugperl/bin/perl5.8.8 -Mblib \
  t/test_file.t

More on these leaks in this thread.

  http://www.nntp.perl.org/group/perl.xs/2007/01/msg2358.html
  http://www.nntp.perl.org/group/perl.xs/2007/01/msg2357.html
Diffing the Combinatorics.c generated by each perl the onlydifferences seem to be calls to PERL_UNUSED_VAR() in 5.6.2
#ifndef PERL_UNUSED_VAR
#  define PERL_UNUSED_VAR(var) if (0) var = var
#endif

that are not generated by 5.8.8. Looks harmless, hmmmmmmm.
Yeah, that's just to avoid compiler warnings about unused variables.
You probably have the tools to track this down now. Throw in somedebug prints until you figure out exactly where in your test codethe error occurs. Keep reducing the test code... yada, yada,standard bug isolation.
With Valgrind, debugging C becomes a lot more like debugging Perl.  :)

Thank you! This stuff is new to me so I appreciate very much yourguidance.


-- fxn

[EMAIL PROTECTED]:~/FXN/Algorithm-Combinatorics-0.22$ ~/FXN/local/bin/valgrind --leak-check=yes perl5.8.8 -Mblib t/10_partitions_of_size_p.t

==29452== Memcheck, a memory error detector.

==29452== Copyright (C) 2004-2007, and GNU GPL'd, by OpenWorks LLP.

==29452== For more details, rerun with: -v
==29452==
==29452== Conditional jump or move depends on uninitialised value(s)
==29452==    at 0x4010C4E: (within /lib/ld-2.3.6.so)
==29452==    by 0x4006704: (within /lib/ld-2.3.6.so)
==29452==    by 0x418C30F: (within /lib/libc-2.3.6.so)
==29452==    by 0x400B44E: (within /lib/ld-2.3.6.so)
==29452==    by 0x418BE9E: _dl_open (in /lib/libc-2.3.6.so)
==29452==    by 0x4025D8D: (within /lib/libdl-2.3.6.so)
==29452==    by 0x400B44E: (within /lib/ld-2.3.6.so)
==29452==    by 0x40261BC: (within /lib/libdl-2.3.6.so)
==29452==    by 0x4025D20: dlopen (in /lib/libdl-2.3.6.so)