bad things happened with for $x (...) { *x = *y }

fix for [perl #21469]:
since the GP may be pulled from under us and freed, coredumps and strange
things can happen.

Fix this by storing a pointer to the GV in the loop block, rather than a
pointer to the GvSV slot. The ITHREADS variant already stores GV rather
than than &GvSV; extend this to non-threaded builds too.

Also, for both threaded and non-threaded, it used to push &GvSV on the
save stack. Fix this by introducing a new save type, SAVEt_GVSV.
This behaves similarly to SAVEt_SV, but without magic get/set.

This means that

    for $package_var (...)

is now close in behaviour to

    local $package_var = ...

(except for the magic bit).

1 files changed, 9 insertions, 5 deletions

diff --git a/cop.h b/cop.h
index c91e9a4a09..86a67d001e 100644
--- a/cop.h
+++ b/cop.h
@@ -469,15 +469,19 @@ struct block_loop {
 };
 
 #ifdef USE_ITHREADS
-#  define CxITERVAR(c)							\
+#  define CxITERVAR_PADSV(c) \
+	&CX_CURPAD_SV( (c)->blk_loop.itervar_u, (c)->blk_loop.my_op->op_targ)
+#else
+#  define CxITERVAR_PADSV(c) ((c)->blk_loop.itervar_u.svp)
+#endif
+
+#define CxITERVAR(c)							\
 	((c)->blk_loop.itervar_u.oldcomppad				\
 	 ? (CxPADLOOP(c) 						\
-	    ? &CX_CURPAD_SV( (c)->blk_loop.itervar_u, (c)->blk_loop.my_op->op_targ) \
+	    ? CxITERVAR_PADSV(c)					\
 	    : &GvSV((c)->blk_loop.itervar_u.gv))			\
 	 : (SV**)NULL)
-#else
-#  define CxITERVAR(c)		((c)->blk_loop.itervar_u.svp)
-#endif
+
 #define CxLABEL(c)	(0 + CopLABEL((c)->blk_oldcop))
 #define CxHASARGS(c)	(((c)->cx_type & CXp_HASARGS) == CXp_HASARGS)
 #define CxLVAL(c)	(0 + (c)->blk_u16)