From ef7a02def4468ac7301c120ece586caea7351c4d Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Mon, 1 Feb 2021 05:34:12 +0000
Subject: [PATCH 2/2] carp: set G_ERR in environ before accessing @DB::args

In case accessing @DB::args causes a segfault and core dump;
one can open the core dump with gdb(1) run "p environ[$IDX]"
to figure out what message and sub_name is tickling Perl5's
stack-not-refcounted behavior and causing a segfault.

($IDX is typically the last environment variable index in the
 environ(7) array, but it could be another number)
---
 dist/Carp/lib/Carp.pm | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/dist/Carp/lib/Carp.pm b/dist/Carp/lib/Carp.pm
index 109b7fe..c87e373 100644
--- a/dist/Carp/lib/Carp.pm
+++ b/dist/Carp/lib/Carp.pm
@@ -302,6 +302,8 @@ BEGIN {
     }
 }
 
+our $g_err;
+
 sub caller_info {
     my $i = shift(@_) + 1;
     my %call_info;
@@ -327,6 +329,7 @@ sub caller_info {
 
     my $sub_name = Carp::get_subname( \%call_info );
     if ( $call_info{has_args} ) {
+$ENV{G_ERR} = "$sub_name $g_err";
         # Guard our serialization of the stack from stack refcounting bugs
         # NOTE this is NOT a complete solution, we cannot 100% guard against
         # these bugs.  However in many cases Perl *is* capable of detecting
@@ -594,6 +597,7 @@ sub ret_backtrace {
         $tid_msg = " thread $tid" if $tid;
     }
 
+$g_err = $err;
     my %i = caller_info($i);
     $mess = "$err at $i{file} line $i{line}$tid_msg";
     if( $. ) {
@@ -635,6 +639,7 @@ sub ret_summary {
         my $tid = threads->tid;
         $tid_msg = " thread $tid" if $tid;
     }
+$g_err = $err;
 
     my %i = caller_info($i);
     return "$err at $i{file} line $i{line}$tid_msg\.\n";