Add a readonly check to Perl_sv_utf8_upgrade_flags, a regresion test

in utf8.t, and fix 3 bugs it exposed in utfhash.t

p4raw-id: //depot/perl@22463

1 files changed, 6 insertions, 2 deletions

diff --git a/sv.c b/sv.c
index f8bd40898d..e49ac5ec00 100644
--- a/sv.c
+++ b/sv.c
@@ -3470,12 +3470,16 @@ Perl_sv_utf8_upgrade_flags(pTHX_ register SV *sv, I32 flags)
 	     return len;
     }
 
+    if (SvUTF8(sv))
+	return SvCUR(sv);
+
     if (SvIsCOW(sv)) {
         sv_force_normal_flags(sv, 0);
     }
 
-    if (SvUTF8(sv))
-	return SvCUR(sv);
+    if (SvREADONLY(sv)) {
+	Perl_croak(aTHX_ PL_no_modify);
+    }
 
     if (PL_encoding && !(flags & SV_UTF8_NO_ENCODING))
         sv_recode_to_utf8(sv, PL_encoding);