RT #76248: double-freed SV with nested sig-handler

There was some buggy code in Perl_sighandler() related to getting an SV
with the signal name to pass to the perl-level handler function.
`
Basically:

on threaded builds, a sig handler that died leaked PL_psig_name[sig];
on unthreaded builds, in a recursive handler that died, PL_sig_sv was
prematurely freed.

PL_sig_sv was originally just a file static var that was not
recursion-save anyway, and got promoted to perlvars.h when it should
instead have been done away with. So I've got rid of it now, and
rationalised the code, which fixed the two issues listed above.

Also added an assert which makes the dodgy manual popping of the save
stack slightly less dodgy.

1 files changed, 1 insertions, 5 deletions

diff --git a/proto.h b/proto.h
index dc25fd2025..c17071b235 100644
--- a/proto.h
+++ b/proto.h
@@ -5644,11 +5644,7 @@ STATIC void	S_save_magic(pTHX_ I32 mgs_ix, SV *sv)
 #define PERL_ARGS_ASSERT_SAVE_MAGIC	\
 	assert(sv)
 
-STATIC void	S_unwind_handler_stack(pTHX_ const void *p)
-			__attribute__nonnull__(pTHX_1);
-#define PERL_ARGS_ASSERT_UNWIND_HANDLER_STACK	\
-	assert(p)
-
+STATIC void	S_unwind_handler_stack(pTHX_ const void *p);
 #endif
 #if defined(PERL_IN_MRO_C)
 STATIC AV*	S_mro_get_linear_isa_dfs(pTHX_ HV* stash, U32 level)