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, 6 insertions, 0 deletions

diff --git a/scope.c b/scope.c
index 93ef4b3fc9..046b3387d5 100644
--- a/scope.c
+++ b/scope.c
@@ -778,9 +778,15 @@ Perl_leave_scope(pTHX_ I32 base)
 		*(char**)ptr = str;
 	    }
 	    break;
+	case SAVEt_GVSV:			/* scalar slot in GV */
+	    value = MUTABLE_SV(SSPOPPTR);
+	    gv = MUTABLE_GV(SSPOPPTR);
+	    ptr = &GvSV(gv);
+	    goto restore_svp;
 	case SAVEt_GENERIC_SVREF:		/* generic sv */
 	    value = MUTABLE_SV(SSPOPPTR);
 	    ptr = SSPOPPTR;
+	restore_svp:
 	    sv = *(SV**)ptr;
 	    *(SV**)ptr = value;
 	    SvREFCNT_dec(sv);