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Postings from November 2008
I found an XXX in the perl5 source code:
I32
Perl_cxinc(pTHX)
{
dVAR;
const IV old_max = cxstack_max;
cxstack_max = GROW(cxstack_max);
Renew(cxstack, cxstack_max + 1, PERL_CONTEXT); /* XXX should fix CXINC macro */
/* Without any kind of initialising deep enough recursion
* will end up reading uninitialised PERL_CONTEXTs. */
PoisonNew(cxstack + old_max + 1, cxstack_max - old_max, PERL_CONTEXT);
return cxstack_ix + 1;
}
I wondered what the bug was, and why we can't fix it.
With a bit of digging it turns out that it's a patch from Larry, applied by
Andy, in early 1996:
http://perl5.git.perl.org/?p=perl.git;a=commitdiff;h=a38d6535f8637d53561bc3663eb96f6c054d0bbb;hp=c0c09dfd3cf50dacd0bf01dff34b4904c5ed1cc6
The interesting parts are:
index 360f9a0..738c95c 100644 (file)
--- a/perl.c
+++ b/perl.c
@@ -1722,7 +1745,7 @@ init_stacks()
retstack_ix = 0;
retstack_max = 16;
- New(50,cxstack,128,CONTEXT);
+ New(50,cxstack,129,CONTEXT); /* XXX should fix CXINC macro */
cxstack_ix = -1;
cxstack_max = 128;
diff --git a/scope.c b/scope.c
Index 79740dc..3f48609 100644 (file)
--- a/scope.c
+++ b/scope.c
@@ -30,7 +30,7 @@ I32
cxinc()
{
cxstack_max = cxstack_max * 3 / 2;
- Renew(cxstack, cxstack_max, CONTEXT);
+ Renew(cxstack, cxstack_max + 1, CONTEXT); /* XXX should fix CXINC macro */
return cxstack_ix + 1;
}
What was the problem with CXINC, and what's the correct fix?
Nicholas Clark
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