in reply to Re: XS Error: Segfault with B::HooksAtRuntime
in thread XS Error: Segfault with B::HooksAtRuntime

I can't solve the problem, but that info turned out to be sufficient for me to guess where to poke. I can reproduce a segfault in just 7 lines of code.

File: mx_segfault.pl 
use lib '.';
use Demo;

[download]
File: Demo.pm 
package Demo;
use MooseX::Extended;
require Stuff;

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File: Stuff.pm 
package Stuff;
use MooseX::Extended;

[download]
With this code, perl -wc mx_segfault.pl segfaults, and valgrind throws a 455-line tantrum. 
==12066== Memcheck, a memory error detector
==12066== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et 
+al.
==12066== Using Valgrind-3.16.1 and LibVEX; rerun with -h for copyrigh
+t info
==12066== Command: perl -wc mx_segfault.pl
==12066== 
==12066== Invalid read of size 2
==12066==    at 0x251CCD: S_pop_eval_context_maybe_croak (in /home/haj
+/perl5/perlbrew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x25FFA0: Perl_pp_leaveeval (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x213312: Perl_runops_standard (in /home/haj/perl5/per
+lbrew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x177DFD: Perl_call_sv (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066==    by 0x17A70D: Perl_call_list (in /home/haj/perl5/perlbrew/
+perls/perl-5.36.0/bin/perl)
==12066==    by 0x15E84A: S_process_special_blocks (in /home/haj/perl5
+/perlbrew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x170805: Perl_newATTRSUB_x (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x1743DA: Perl_utilize (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066==    by 0x1B000E: Perl_yyparse (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066==    by 0x17E836: perl_parse (in /home/haj/perl5/perlbrew/perl
+s/perl-5.36.0/bin/perl)
==12066==    by 0x155295: main (in /home/haj/perl5/perlbrew/perls/perl
+-5.36.0/bin/perl)
==12066==  Address 0x4c2528a is 314 bytes inside a block of size 1,872
+ free'd
==12066==    at 0x483AD7B: realloc (vg_replace_malloc.c:834)
==12066==    by 0x1F385C: Perl_safesysrealloc (in /home/haj/perl5/perl
+brew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x24D3BB: Perl_cxinc (in /home/haj/perl5/perlbrew/perl
+s/perl-5.36.0/bin/perl)
==12066==    by 0x21CED4: Perl_pp_entersub (in /home/haj/perl5/perlbre
+w/perls/perl-5.36.0/bin/perl)
==12066==    by 0x213312: Perl_runops_standard (in /home/haj/perl5/per
+lbrew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x25130B: S_docatch (in /home/haj/perl5/perlbrew/perls
+/perl-5.36.0/bin/perl)
==12066==    by 0x213312: Perl_runops_standard (in /home/haj/perl5/per
+lbrew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x177C5A: Perl_call_sv (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066==    by 0x87D828C: call_after (in /home/haj/perl5/perlbrew/per
+ls/perl-5.36.0/lib/site_perl/5.36.0/x86_64-linux/auto/B/Hooks/AtRunti
+me/AtRuntime.so)
==12066==    by 0x24F7A1: Perl_leave_scope (in /home/haj/perl5/perlbre
+w/perls/perl-5.36.0/bin/perl)
==12066==    by 0x251CCC: S_pop_eval_context_maybe_croak (in /home/haj
+/perl5/perlbrew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x25FFA0: Perl_pp_leaveeval (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066==  Block was alloc'd at
==12066==    at 0x483877F: malloc (vg_replace_malloc.c:307)
==12066==    by 0x1F3502: Perl_safesysmalloc (in /home/haj/perl5/perlb
+rew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x24D316: Perl_new_stackinfo (in /home/haj/perl5/perlb
+rew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x15E9D6: S_process_special_blocks (in /home/haj/perl5
+/perlbrew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x170805: Perl_newATTRSUB_x (in /home/haj/perl5/perlbr
+ew/perls/perl-5.36.0/bin/perl)
==12066==    by 0x1743DA: Perl_utilize (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066==    by 0x1B000E: Perl_yyparse (in /home/haj/perl5/perlbrew/pe
+rls/perl-5.36.0/bin/perl)
==12066==    by 0x17E836: perl_parse (in /home/haj/perl5/perlbrew/perl
+s/perl-5.36.0/bin/perl)
==12066==    by 0x155295: main (in /home/haj/perl5/perlbrew/perls/perl
+-5.36.0/bin/perl)

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Re^3: XS Error: Segfault with B::HooksAtRuntime
by dave_the_m (Monsignor) on Aug 06, 2022 at 18:31 UTC
    In general terms, that valgrind output shows that the calling of a sub while running code via call_after() (which requires a new CXt_SUB context sub to be pushed) grows the context stack (by reallocating it). Sometime later when exiting a use/require, the Cxt_EVAL frame is accessed using the old context stack address (the smaller stack that was freed when a larger one was allocated). So maybe something is holding on to a context stack pointer when it shouldn't - either in core or XS.

    Dave.

[reply]
Re^3: XS Error: Segfault with B::HooksAtRuntime
by Ovid (Cardinal) on Aug 06, 2022 at 16:44 UTC
[reply]

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