Re: [patch] Fix gdb.cp/gdb2495.exp regression with gcc-4.7 #2

Mark Kettenis
2011-12-28T20:10:07Z

> Date: Wed, 28 Dec 2011 19:01:48 +0100
> From: Jan Kratochvil <jan.kratochvil@redhat.com>
>
> --- a/gdb/infcall.c
> +++ b/gdb/infcall.c
> @@ -627,26 +628,16 @@ call_function_by_hand (struct value *function, int nargs, struct value **args)
> switch (gdbarch_call_dummy_location (gdbarch))
> {
> case ON_STACK:
> + /* ON_STACK has problems on some targets featuring security policies
> + disabling target stack executability. */

Hmm, did you actually try using ON_STACK? We specifically treat
SIGSEGV as a potential breakpoint to deal with non-executable stacks.
And the diff below works just fine on OpenBSD/amd64 where stacks are
non-executable.

Index: i386-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-tdep.c,v
retrieving revision 1.340
diff -u -p -r1.340 i386-tdep.c
--- i386-tdep.c 14 Nov 2011 20:07:20 -0000 1.340
+++ i386-tdep.c 28 Dec 2011 20:06:23 -0000
@@ -2321,6 +2321,19 @@ i386_16_byte_align_p (struct type *type)
}

static CORE_ADDR
+i386_push_dummy_code (struct gdbarch *gdbarch, CORE_ADDR sp,
+ CORE_ADDR funcaddr,
+ struct value **args, int nargs,
+ struct type *value_type,
+ CORE_ADDR *real_pc, CORE_ADDR *bp_addr,
+ struct regcache *regcache)
+{
+ *bp_addr = sp - 1;
+ *real_pc = funcaddr;
+ return sp - 1;
+}
+
+static CORE_ADDR
i386_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
struct regcache *regcache, CORE_ADDR bp_addr, int nargs,
struct value **args, CORE_ADDR sp, int struct_return,
@@ -7366,6 +7379,8 @@ i386_gdbarch_init (struct gdbarch_info i
set_gdbarch_get_longjmp_target (gdbarch, i386_get_longjmp_target);

/* Call dummy code. */
+ set_gdbarch_call_dummy_location (gdbarch, ON_STACK);
+ set_gdbarch_push_dummy_code(gdbarch, i386_push_dummy_code);
set_gdbarch_push_dummy_call (gdbarch, i386_push_dummy_call);
set_gdbarch_frame_align (gdbarch, i386_frame_align);