From 1aa032b25ab39eebe4a452ff935a39107a322a5b Mon Sep 17 00:00:00 2001
From: Father Chrysostomos <sprout@cpan.org>
Date: Thu, 13 Oct 2011 20:25:39 -0700
Subject: [PATCH] Stop uninit sort warnings from crashing
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Commit d4c6760a made the warning in cases like this mention the
sort operator:

$ ./miniperl -we '()=sort { undef } 1,2'
Use of uninitialized value [in sort] at -e line 1.

It did so by setting PL_op during the SvIV(retval of sort block).  But
sv.c:S_find_uninit_var, called by report_uninit, tries to access the
targets of some ops, which are in PL_curpad on threaded builds.  In
the case of a sort sub (rather than an inlined block), PL_curpad con-
tained whatever was left over from the sort block (I presume, but
have not confirmed; in any case what is in PL_curpad is bad), causing
find_uninit_var to crash.

This commit sets PL_curpad to null and puts a check for it in
report_uninit.

It did not crash in debugging threaded builds, but that was probably
luck (even though I don’t believe in it).
---
 pp_sort.c | 6 ++++++
 sv.c      | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/pp_sort.c b/pp_sort.c
index 0ee42dc..2257d2f 100644
--- a/pp_sort.c
+++ b/pp_sort.c
@@ -1765,6 +1765,7 @@ S_sortcv(pTHX_ SV *const a, SV *const b)
     I32 result;
     PMOP * const pm = PL_curpm;
     OP * const sortop = PL_op;
+    SV **pad;
  
     PERL_ARGS_ASSERT_SORTCV;
 
@@ -1776,7 +1777,9 @@ S_sortcv(pTHX_ SV *const a, SV *const b)
     if (PL_stack_sp != PL_stack_base + 1)
 	Perl_croak(aTHX_ "Sort subroutine didn't return single value");
     PL_op = sortop;
+    pad = PL_curpad; PL_curpad = 0;
     result = SvIV(*PL_stack_sp);
+    PL_curpad = pad;
     while (PL_scopestack_ix > oldscopeix) {
 	LEAVE;
     }
@@ -1795,6 +1798,7 @@ S_sortcv_stacked(pTHX_ SV *const a, SV *const b)
     AV * const av = GvAV(PL_defgv);
     PMOP * const pm = PL_curpm;
     OP * const sortop = PL_op;
+    SV **pad;
 
     PERL_ARGS_ASSERT_SORTCV_STACKED;
 
@@ -1826,7 +1830,9 @@ S_sortcv_stacked(pTHX_ SV *const a, SV *const b)
     if (PL_stack_sp != PL_stack_base + 1)
 	Perl_croak(aTHX_ "Sort subroutine didn't return single value");
     PL_op = sortop;
+    pad = PL_curpad; PL_curpad = 0;
     result = SvIV(*PL_stack_sp);
+    PL_curpad = pad;
     while (PL_scopestack_ix > oldscopeix) {
 	LEAVE;
     }
diff --git a/sv.c b/sv.c
index e0bcfdf..5ee4817 100644
--- a/sv.c
+++ b/sv.c
@@ -14314,7 +14314,7 @@ Perl_report_uninit(pTHX_ const SV *uninit_sv)
     dVAR;
     if (PL_op) {
 	SV* varname = NULL;
-	if (uninit_sv) {
+	if (uninit_sv && PL_curpad) {
 	    varname = find_uninit_var(PL_op, uninit_sv,0);
 	    if (varname)
 		sv_insert(varname, 0, 0, " ", 1);
-- 
2.7.4