Integrate:

[ 23076]
Perl_mode_from_discipline must update len. (else SEGV)
Diagnosis and patch from clkao

[ 23083]
Perl_is_utf8_string(pTHX_ U8 *s, STRLEN len)
Can now handle the case
     is_utf8_string(NULL,0)
again.
Why do we have code dup for Perl_is_utf8_string_loc() ?

[ 23084]
NI-S: IMHO utf8_upgrade is just changing representation not the value
so it has no business calling SvSETMAGIC.

[ 23085]
Bodge to make Tk work - like the UTF8 flag, the READONLY flag has too
many meanings. const const vs mutable in this case.
p4raw-link: @23085 on //depot/perl: d52b7888e9c3eb0ccb038b7c44075ba28e8fefa6
p4raw-link: @23084 on //depot/perl: 7a5fa8a2cb05d06ee722842024d6960f349f483b
p4raw-link: @23083 on //depot/perl: 61468b033262a3098f06f5437d4f3f1f301cacb3
p4raw-link: @23076 on //depot/perl: 18a33fb59fd6afeb2aae93e4a139e231623b401f

p4raw-id: //depot/maint-5.8/perl@23087
p4raw-edited: from //depot/perl@23086 'edit in' sv.c (@23084..)
p4raw-integrated: from //depot/perl@23086 'copy in' utf8.c (@22764..)
	'merge in' doio.c (@22741..)

3 files changed, 10 insertions, 5 deletions

diff --git a/doio.c b/doio.c
index e452bc3a4e..97a6603869 100644
--- a/doio.c
+++ b/doio.c
@@ -1172,6 +1172,7 @@ fail_discipline:
 #ifndef PERLIO_LAYERS
 		Perl_croak(aTHX_ "IO layers (like '%.*s') unavailable", end-s, s);
 #else
+		len -= end-s;
 		s = end;
 #endif
 	    }
diff --git a/sv.c b/sv.c
index 806a838329..5ce1e59e9d 100644
--- a/sv.c
+++ b/sv.c
@@ -3451,11 +3451,16 @@ Perl_sv_utf8_upgrade_flags(pTHX_ register SV *sv, I32 flags)
 	return 0;
     if (!SvPOK(sv)) {
 	STRLEN len = 0;
-	(void) SvPV_force(sv,len);
+	if (SvREADONLY(sv) && (SvPOKp(sv) || SvIOKp(sv) || SvNOKp(sv))) {
+	    (void) sv_2pv_flags(sv,&len, flags);
+	    if (SvUTF8(sv))
+		return len;
+	} else {
+	    (void) SvPV_force(sv,len);
+	}
     }
 
     if (SvUTF8(sv)) {
-	SvSETMAGIC(sv);
 	return SvCUR(sv);
     }
 
@@ -3492,7 +3497,6 @@ Perl_sv_utf8_upgrade_flags(pTHX_ register SV *sv, I32 flags)
 	 /* Mark as UTF-8 even if no hibit - saves scanning loop */
 	 SvUTF8_on(sv);
     }
-    SvSETMAGIC(sv);
     return SvCUR(sv);
 }
 
diff --git a/utf8.c b/utf8.c
index 6f201a23f1..6155fabe3c 100644
--- a/utf8.c
+++ b/utf8.c
@@ -232,7 +232,7 @@ Perl_is_utf8_string(pTHX_ U8 *s, STRLEN len)
     U8* send;
     STRLEN c;
 
-    if (!len)
+    if (!len && s)
 	len = strlen((char *)s);
     send = s + len;
 
@@ -272,7 +272,7 @@ Perl_is_utf8_string_loc(pTHX_ U8 *s, STRLEN len, U8 **p)
     U8* send;
     STRLEN c;
 
-    if (!len)
+    if (!len && s)
 	len = strlen((char *)s);
     send = s + len;