Perl_magic_setdbline() should clear and set read-only OP slabs.

The debugger implements breakpoints by setting/clearing OPf_SPECIAL on
OP_DBSTATE ops. This means that it is writing to the optree at runtime,
and it falls foul of the enforced read-only OP slabs when debugging with
-DPERL_DEBUG_READONLY_OPS

Avoid this by removing static from Slab_to_rw(), and using it and Slab_to_ro()
in Perl_magic_setdbline() to temporarily make the slab re-write whilst
changing the breakpoint flag.

With this all tests pass with -DPERL_DEBUG_READONLY_OPS (on this system)

5 files changed, 15 insertions, 17 deletions

diff --git a/embed.fnc b/embed.fnc
index cb26c72f9c..ab2cdec4b3 100644
--- a/embed.fnc
+++ b/embed.fnc
@@ -1797,14 +1797,12 @@ Xp	|void	|Slab_Free	|NN void *op
 #if defined(PERL_DEBUG_READONLY_OPS)
 #    if defined(PERL_CORE)
 px	|void	|Slab_to_ro	|NN OPSLAB *slab
+px	|void	|Slab_to_rw	|NN OPSLAB *const slab
 #    endif
 : Used in OpREFCNT_inc() in sv.c
 poxM	|OP *	|op_refcnt_inc	|NULLOK OP *o
 : FIXME - can be static.
 poxM	|PADOFFSET	|op_refcnt_dec	|NN OP *o
-#    if defined(PERL_IN_OP_C)
-s	|void	|Slab_to_rw	|NN OPSLAB *const slab
-#    endif
 #endif
 
 #if defined(PERL_IN_PERL_C)
diff --git a/embed.h b/embed.h
index ecce32125e..45291f0983 100644
--- a/embed.h
+++ b/embed.h
@@ -1319,6 +1319,7 @@
 #define opslab_free_nopad(a)	Perl_opslab_free_nopad(aTHX_ a)
 #    if defined(PERL_DEBUG_READONLY_OPS)
 #define Slab_to_ro(a)		Perl_Slab_to_ro(aTHX_ a)
+#define Slab_to_rw(a)		Perl_Slab_to_rw(aTHX_ a)
 #    endif
 #  endif
 #  if defined(PERL_CR_FILTER)
@@ -1327,11 +1328,6 @@
 #define strip_return(a)		S_strip_return(aTHX_ a)
 #    endif
 #  endif
-#  if defined(PERL_DEBUG_READONLY_OPS)
-#    if defined(PERL_IN_OP_C)
-#define Slab_to_rw(a)		S_Slab_to_rw(aTHX_ a)
-#    endif
-#  endif
 #  if defined(PERL_IN_AV_C)
 #define get_aux_mg(a)		S_get_aux_mg(aTHX_ a)
 #  endif
diff --git a/mg.c b/mg.c
index 3dea5c2ba4..1f6d0626a8 100644
--- a/mg.c
+++ b/mg.c
@@ -2020,11 +2020,17 @@ Perl_magic_setdbline(pTHX_ SV *sv, MAGIC *mg)
     if (svp && SvIOKp(*svp)) {
 	OP * const o = INT2PTR(OP*,SvIVX(*svp));
 	if (o) {
+#ifdef PERL_DEBUG_READONLY_OPS
+	    Slab_to_rw(OpSLAB(o));
+#endif
 	    /* set or clear breakpoint in the relevant control op */
 	    if (i)
 		o->op_flags |= OPf_SPECIAL;
 	    else
 		o->op_flags &= ~OPf_SPECIAL;
+#ifdef PERL_DEBUG_READONLY_OPS
+	    Slab_to_ro(OpSLAB(o));
+#endif
 	}
     }
     return 0;
diff --git a/op.c b/op.c
index 8beb0fe086..9ad4499e59 100644
--- a/op.c
+++ b/op.c
@@ -261,8 +261,8 @@ Perl_Slab_to_ro(pTHX_ OPSLAB *slab)
     }
 }
 
-STATIC void
-S_Slab_to_rw(pTHX_ OPSLAB *const slab)
+void
+Perl_Slab_to_rw(pTHX_ OPSLAB *const slab)
 {
     OPSLAB *slab2;
 
diff --git a/proto.h b/proto.h
index 07cfd9a3c7..f97fe1fbae 100644
--- a/proto.h
+++ b/proto.h
@@ -5304,6 +5304,11 @@ PERL_CALLCONV void	Perl_Slab_to_ro(pTHX_ OPSLAB *slab)
 #define PERL_ARGS_ASSERT_SLAB_TO_RO	\
 	assert(slab)
 
+PERL_CALLCONV void	Perl_Slab_to_rw(pTHX_ OPSLAB *const slab)
+			__attribute__nonnull__(pTHX_1);
+#define PERL_ARGS_ASSERT_SLAB_TO_RW	\
+	assert(slab)
+
 #  endif
 #endif
 #if defined(PERL_CR_FILTER)
@@ -5323,13 +5328,6 @@ PERL_CALLCONV PADOFFSET	Perl_op_refcnt_dec(pTHX_ OP *o)
 	assert(o)
 
 PERL_CALLCONV OP *	Perl_op_refcnt_inc(pTHX_ OP *o);
-#  if defined(PERL_IN_OP_C)
-STATIC void	S_Slab_to_rw(pTHX_ OPSLAB *const slab)
-			__attribute__nonnull__(pTHX_1);
-#define PERL_ARGS_ASSERT_SLAB_TO_RW	\
-	assert(slab)
-
-#  endif
 #endif
 #if defined(PERL_DEFAULT_DO_EXEC3_IMPLEMENTATION)
 /* PERL_CALLCONV bool	Perl_do_exec(pTHX_ const char* cmd)