In sv_chop(), write sentinals over the part of the buffer that is

thrown away, and verify that they are present in sv_backoff().
assert that we are being asked to chop off positive amounts of buffer.

p4raw-id: //depot/perl@32778

diff --git a/sv.c b/sv.c
index bb64eb9..bf8d503 100644 (file)
--- a/sv.c
+++ b/sv.c
@@ -1403,6 +1403,16 @@ Perl_sv_backoff(pTHX_ register SV *sv)
     assert(SvTYPE(sv) != SVt_PVAV);
     if (SvIVX(sv)) {
        const char * const s = SvPVX_const(sv);
+#ifdef DEBUGGING
+       /* Validate the preceding buffer's sentinals to verify that no-one is
+          using it.  */
+       const U8 *p = (const U8*) s;
+       const U8 *const real_start = p - SvIVX(sv);
+       while (p > real_start) {
+           --p;
+           assert (*p == (U8)PTR2UV(p));
+       }
+#endif
        SvLEN_set(sv, SvLEN(sv) + SvIVX(sv));
        SvPV_set(sv, SvPVX(sv) - SvIVX(sv));
        SvIV_set(sv, 0);
@@ -4215,6 +4225,7 @@ Perl_sv_chop(pTHX_ register SV *sv, register const char *ptr)
        /* Nothing to do.  */
        return;
     }
+    assert(ptr > SvPVX_const(sv));
     SV_CHECK_THINKFIRST(sv);
     if (SvTYPE(sv) < SVt_PVIV)
        sv_upgrade(sv,SVt_PVIV);
@@ -4238,6 +4249,18 @@ Perl_sv_chop(pTHX_ register SV *sv, register const char *ptr)
     SvCUR_set(sv, SvCUR(sv) - delta);
     SvPV_set(sv, SvPVX(sv) + delta);
     SvIV_set(sv, SvIVX(sv) + delta);
+#ifdef DEBUGGING
+    {
+       /* Fill the preceding buffer with sentinals to verify that no-one is
+          using it.  */
+       U8 *p = (U8*) SvPVX(sv);
+       const U8 *const real_start = p - SvIVX(sv);
+       while (p > real_start) {
+           --p;
+           *p = (U8)PTR2UV(p);
+       }
+    }
+#endif
 }
 
 /*