Bug#91806: marked as done ($SIG{__DIE__} = \&Carp::confess; and Apache mod_perl SEGV in libperl.so.5.6.0)
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>From karlheg@microsharp.com Mon Mar 26 13:27:29 2001
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Subject: $SIG{__DIE__} = \&Carp::confess; and Apache mod_perl SEGV in libperl.so.5.6.0
X-Face: /Q}=yl}1_v7nP)xXo5XjG8+tl@=uVu7o5u6)f]zN?+<hB!K.m9:[|*p34jVN`O;:XZXVSy>/\R>qDt(t8w!-i{(y0"`jFw^uk8inzO9wXabd'CdjUWfC\GHi:6nO*YC89#-qD>Q4r%9!V"<RYJ=7D#$";q=zML5'!=wvXk^$`6FT=5CMofQX)WUKt0p:OKl.mFOXx/D
From: karlheg@microsharp.com (Karl M. Hegbloom)
Date: 26 Mar 2001 11:26:33 -0800
Message-ID: <87u24gbabk.fsf@microsharp.com>
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Package: libapache-mod-perl
Version: 1.25-3
Severity: normal
I could not get Apache to start; there was a segv occuring. `gdb
apache' caught this backtrace:
(From running "gdb apache")
Program received signal SIGSEGV, Segmentation fault.
0x402d3713 in Perl_newSVsv () from /usr/lib/libperl.so.5.6
(gdb) where
#0 0x402d3713 in Perl_newSVsv () from /usr/lib/libperl.so.5.6
#1 0x402eac89 in Perl_pp_caller () from /usr/lib/libperl.so.5.6
#2 0x402c5731 in Perl_runops_standard () from /usr/lib/libperl.so.5.6
#3 0x4028060c in perl_call_sv () from /usr/lib/libperl.so.5.6
#4 0x40280138 in perl_call_sv () from /usr/lib/libperl.so.5.6
#5 0x402b9eea in Perl_vdie () from /usr/lib/libperl.so.5.6
#6 0x402ba039 in Perl_die () from /usr/lib/libperl.so.5.6
#7 0x402ea31c in Perl_die_where () from /usr/lib/libperl.so.5.6
#8 0x402b9f98 in Perl_vdie () from /usr/lib/libperl.so.5.6
#9 0x402ba039 in Perl_die () from /usr/lib/libperl.so.5.6
#10 0x402f19ac in Perl_pp_die () from /usr/lib/libperl.so.5.6
#11 0x402c5731 in Perl_runops_standard () from /usr/lib/libperl.so.5.6
#12 0x402ed2f9 in Perl_pp_exit () from /usr/lib/libperl.so.5.6
#13 0x402ed385 in Perl_pp_exit () from /usr/lib/libperl.so.5.6
#14 0x402eee4c in Perl_pp_require () from /usr/lib/libperl.so.5.6
#15 0x402c5731 in Perl_runops_standard () from /usr/lib/libperl.so.5.6
#16 0x4028060c in perl_call_sv () from /usr/lib/libperl.so.5.6
#17 0x40280138 in perl_call_sv () from /usr/lib/libperl.so.5.6
#18 0x402ba2b5 in Perl_vcroak () from /usr/lib/libperl.so.5.6
#19 0x402ba439 in Perl_croak () from /usr/lib/libperl.so.5.6
#20 0x402cbfa2 in Perl_pp_method_named () from /usr/lib/libperl.so.5.6
#21 0x402cbe25 in Perl_pp_method_named () from /usr/lib/libperl.so.5.6
#22 0x402c5731 in Perl_runops_standard () from /usr/lib/libperl.so.5.6
---Type <return> to continue, or q <return> to quit---
#23 0x4028060c in perl_call_sv () from /usr/lib/libperl.so.5.6
#24 0x402807ae in perl_eval_sv () from /usr/lib/libperl.so.5.6
#25 0x40241f83 in perl_do_file () from /usr/lib/apache/1.3/mod_perl.so
#26 0x40241fcf in perl_load_startup_script ()
from /usr/lib/apache/1.3/mod_perl.so
#27 0x4023d948 in perl_cmd_require () from /usr/lib/apache/1.3/mod_perl.so
#28 0x8054a79 in ap_clear_module_list ()
#29 0x8054dfa in ap_handle_command ()
#30 0x8054e41 in ap_srm_command_loop ()
#31 0x8057c45 in ap_exists_config_define ()
#32 0x80545ed in ap_clear_module_list ()
#33 0x8054dfa in ap_handle_command ()
#34 0x8054e41 in ap_srm_command_loop ()
#35 0x8055372 in ap_process_resource_config ()
#36 0x8055a6c in ap_read_config ()
#37 0x805d818 in main ()
#38 0x400ce13b in __libc_start_main () from /lib/libc.so.6
I discovered that a combination of two factors is what triggers this
segv. In the handler, I had done:
$SIG{__WARN__} = \&Carp::cluck;
$SIG{__DIE__} = \&Carp::confess;
... and then in a block at toplevel of the handler, inside a set of
braces that confine a "package" declaration (for libhtml-mason-perl
"HTML::Mason::Commands"), I had made a mistake; trying to call a
method on an "undefined object"; one I'd not "new"ed yet. That
triggered the "die", which leads to the segv.
I grepped via Google for "libperl segv mod_perl", and found, in a
mail archive, the idea of declaring a SEGV signal handler...
$SIG{SEGV} = \&Carp::cluck;
... and added that to the handler. Here's what it printed then:
# /etc/init.d/apache start
Starting web server: apache.
Deep recursion on subroutine "Carp::longmess_heavy" at /usr/share/perl/5.6.0/Carp.pm line 98.
Deep recursion on subroutine "Carp::cluck" at /usr/share/perl/5.6.0/Carp/Heavy.pm line 39.
That led me to experimentally commenting off each of the $SIG lines
in turn. The apache daemon started after I commented off the __DIE__
line... and I then found the error:
# /etc/init.d/apache start
Starting web server: apache.
[Mon Mar 26 11:20:40 2001] [error] Can't call method "remote" on an undefined value at /usr/local/src/www/_Handlers.mod_perl line 85.
Compilation failed in require at (eval 7) line 1.
Syntax error on line 1251 of /etc/apache/httpd.conf:
Can't call method "remote" on an undefined value at /usr/local/src/www/_Handlers.mod_perl line 85.
Compilation failed in require at (eval 7) line 1.
/usr/sbin/apachectl start: httpd could not be started
After fixing my mistake, the server starts fine, even with the
__DIE__ signal handler in place, though I suspect that if something
died, it would segv then in the same manner.
The mod_perl_traps page tells of using Carp::confess as a __DIE__
handler, so it is supposed to work. I hope this leads someone who
can do it to a bugfix... I certainly cannot fix it yet. They are
giants.
--
mailto: (Karl M. Hegbloom) karlheg@microsharp.com
http://www.microsharp.com
phone://USA/WA/360-260-2066
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Date: Sun, 9 Nov 2003 11:12:58 +0100 (CET)
From: Fabio Massimo Di Nitto <fabbione@fabbione.net>
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We are not able to reproduce this bug anymore with the recent versions of
apache and mod_perl so we believe that it has been fixed upstream.
Fabio
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