[perl #103260] Fix s/// with long strings

This is also the subject of perl #123071.

The iteration count was stored in an I32 and was overflowing.  If the
maximum number of iterations possible overflowed, then it would become
negative, and the substitution would fail immediately with ‘Substitu-
tion loop’.

I tried fixing this without increasing the size of the context
stack entries on 64-bit builds (by skipping the loop check for long
strings), but was unable to, because we have to return the number of
iterations, which was also stored as I32.  If we change just that one
to SSize_t, we get an I32-sized alignment hole, so we might as well
make maxiters a SSize_t as well, fixing the bug that way (the more
straightforward way).

1 files changed, 2 insertions, 2 deletions

diff --git a/cop.h b/cop.h
index 9c25555d95..ec3e32f8d4 100644
--- a/cop.h
+++ b/cop.h
@@ -882,9 +882,9 @@ struct subst {
     U8		sbu_type;	/* what kind of context this is */
     U8		sbu_rflags;
     U16		sbu_rxtainted;	/* matches struct block */
-    I32		sbu_iters;
-    I32		sbu_maxiters;
     I32		sbu_oldsave;
+    SSize_t	sbu_iters;
+    SSize_t	sbu_maxiters;
     char *	sbu_orig;
     SV *	sbu_dstr;
     SV *	sbu_targ;