Better fix for perl #107440

> > Actually, the simplest solution seem to be to put the av or hv on
> > the mortals stack in pp_aassign and pp_undef, rather than in
> > [ah]v_undef/clear.
>
> This makes me nervous. The tmps stack is typically cleared only on
> statement boundaries, so we run the risks of
>
>     * user-visible delaying of freeing elements;
>     * large tmps stack growth might be possible with
>       certain types of loop that repeatedly assign to an array without
>       freeing tmps (eg map? I think I fixed most map/grep tmps leakage
> a
>       while back, but there may still be some edge cases).
>
> Surely an ENTER/SAVEFREESV/LEAVE inside pp_aassign is just as
> efficient,
> without any attendant risks?
>
> Also, although pp_aassign and pp_undef are now fixed, the
> [ah]v_undef/clear functions aren't, and they're part of the public API
> that can be called independently of pp_aassign etc. Ideally they
> should
> be fixed (so they don't crash in mid-loop), and their documentation
> updated to point out that on return, their AV/HV arg may have been
> freed.

This commit takes care of the first part; it changes pp_aassign to use
ENTER/SAVEFREESV/LEAVE and adds the same to h_freeentries (called both
by hv_undef and hv_clear), av_undef and av_clear.

It effectively reverts the C code part of 9f71cfe6ef2.

4 files changed, 29 insertions, 7 deletions

diff --git a/av.c b/av.c
index 1671f16e40..472600b6f0 100644
--- a/av.c
+++ b/av.c
@@ -437,6 +437,7 @@ Perl_av_clear(pTHX_ register AV *av)
 {
     dVAR;
     I32 extra;
+    bool real;
 
     PERL_ARGS_ASSERT_AV_CLEAR;
     assert(SvTYPE(av) == SVt_PVAV);
@@ -462,9 +463,11 @@ Perl_av_clear(pTHX_ register AV *av)
     if (AvMAX(av) < 0)
 	return;
 
-    if (AvREAL(av)) {
+    if ((real = !!AvREAL(av))) {
 	SV** const ary = AvARRAY(av);
 	I32 index = AvFILLp(av) + 1;
+	ENTER;
+	SAVEFREESV(SvREFCNT_inc_simple_NN(av));
 	while (index) {
 	    SV * const sv = ary[--index];
 	    /* undef the slot before freeing the value, because a
@@ -479,7 +482,7 @@ Perl_av_clear(pTHX_ register AV *av)
 	AvARRAY(av) = AvALLOC(av);
     }
     AvFILLp(av) = -1;
-
+    if (real) LEAVE;
 }
 
 /*
@@ -493,6 +496,8 @@ Undefines the array.  Frees the memory used by the array itself.
 void
 Perl_av_undef(pTHX_ register AV *av)
 {
+    bool real;
+
     PERL_ARGS_ASSERT_AV_UNDEF;
     assert(SvTYPE(av) == SVt_PVAV);
 
@@ -500,8 +505,10 @@ Perl_av_undef(pTHX_ register AV *av)
     if (SvTIED_mg((const SV *)av, PERL_MAGIC_tied)) 
 	av_fill(av, -1);
 
-    if (AvREAL(av)) {
+    if ((real = !!AvREAL(av))) {
 	register I32 key = AvFILLp(av) + 1;
+	ENTER;
+	SAVEFREESV(SvREFCNT_inc_simple_NN(av));
 	while (key)
 	    SvREFCNT_dec(AvARRAY(av)[--key]);
     }
@@ -512,6 +519,7 @@ Perl_av_undef(pTHX_ register AV *av)
     AvMAX(av) = AvFILLp(av) = -1;
 
     if(SvRMAGICAL(av)) mg_clear(MUTABLE_SV(av));
+    if(real) LEAVE;
 }
 
 /*
diff --git a/hv.c b/hv.c
index af41de8691..2cfe25bb4d 100644
--- a/hv.c
+++ b/hv.c
@@ -1681,12 +1681,20 @@ S_hfreeentries(pTHX_ HV *hv)
     STRLEN index = 0;
     XPVHV * const xhv = (XPVHV*)SvANY(hv);
     SV *sv;
+    const bool save = !!SvREFCNT(hv);
 
     PERL_ARGS_ASSERT_HFREEENTRIES;
 
+    if (save) {
+	ENTER;
+	SAVEFREESV(SvREFCNT_inc_simple_NN(hv));
+    }
+
     while ((sv = Perl_hfree_next_entry(aTHX_ hv, &index))||xhv->xhv_keys) {
 	SvREFCNT_dec(sv);
     }
+
+    if (save) LEAVE;
 }
 
 
diff --git a/pp.c b/pp.c
index 5910e8691d..eaf6a85277 100644
--- a/pp.c
+++ b/pp.c
@@ -970,10 +970,10 @@ PP(pp_undef)
     case SVt_NULL:
 	break;
     case SVt_PVAV:
-	av_undef(MUTABLE_AV(sv_2mortal(SvREFCNT_inc_simple_NN(sv))));
+	av_undef(MUTABLE_AV(sv));
 	break;
     case SVt_PVHV:
-	hv_undef(MUTABLE_HV(sv_2mortal(SvREFCNT_inc_simple_NN(sv))));
+	hv_undef(MUTABLE_HV(sv));
 	break;
     case SVt_PVCV:
 	if (cv_const_sv((const CV *)sv))
diff --git a/pp_hot.c b/pp_hot.c
index add940049b..ff834a924e 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -993,8 +993,10 @@ PP(pp_aassign)
 	sv = *lelem++;
 	switch (SvTYPE(sv)) {
 	case SVt_PVAV:
-	    ary = MUTABLE_AV(sv_2mortal(SvREFCNT_inc_simple_NN(sv)));
+	    ary = MUTABLE_AV(sv);
 	    magic = SvMAGICAL(ary) != 0;
+	    ENTER;
+	    SAVEFREESV(SvREFCNT_inc_simple_NN(sv));
 	    av_clear(ary);
 	    av_extend(ary, lastrelem - relem);
 	    i = 0;
@@ -1015,13 +1017,16 @@ PP(pp_aassign)
 	    }
 	    if (PL_delaymagic & DM_ARRAY_ISA)
 		SvSETMAGIC(MUTABLE_SV(ary));
+	    LEAVE;
 	    break;
 	case SVt_PVHV: {				/* normal hash */
 		SV *tmpstr;
 		SV** topelem = relem;
 
-		hash = MUTABLE_HV(sv_2mortal(SvREFCNT_inc_simple_NN(sv)));
+		hash = MUTABLE_HV(sv);
 		magic = SvMAGICAL(hash) != 0;
+		ENTER;
+		SAVEFREESV(SvREFCNT_inc_simple_NN(sv));
 		hv_clear(hash);
 		firsthashrelem = relem;
 
@@ -1058,6 +1063,7 @@ PP(pp_aassign)
 		    do_oddball(hash, relem, firstrelem);
 		    relem++;
 		}
+		LEAVE;
 	    }
 	    break;
 	default: