RE: [PATCH v2 3/3] btrace, frame: fix crash in get_frame_type

["Metzger, Markus T" <markus.t.metzger@intel.com>]

> -----Original Message-----
> From: Pedro Alves [mailto:palves@redhat.com]
> Sent: Wednesday, February 10, 2016 4:34 PM
> To: Metzger, Markus T <markus.t.metzger@intel.com>
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH v2 3/3] btrace, frame: fix crash in get_frame_type
> 
> On 02/10/2016 03:02 PM, Metzger, Markus T wrote:
> 
> > No new fails there, as well (64-bit IA).
> >
> > I added a comment based on your statement that
> frame_unwind_caller_xxx
> > callers should check frame_unwind_caller_id and assert that
> > skip_artificial_frames does not return NULL.
> >
> > Info frame doesn't crash.
> >
> > 	(gdb) info frame
> > 	Stack level 0, frame at 0x0:
> > 	 rip = 0x4005b0 in bar (tailcall-only.c:29); saved rip = 0x4005c2
> > 	 called by frame at 0x0
>          ^^^^^^^^^^^^^^^
> 
> > 	 source 	language c.
> > 	 Arglist at unknown address.
> > 	 Locals at unknown address,Registers are not available in btrace
> > record history
> >
> > This is from a tailcall-only frame stack in replay mode using the tailcall-only
> test.
> > The real caller has not been recorded.
> 
> Not sure how you got that, since "called by frame" seems to indicates that
> the frame was not TAILCALL_FRAME:

That's the sentinel frame.  I forgot to "up".  Now it crashes;-)

There are other cases where frame_unwind_caller_xxx callers don't check
frame_unwind_caller_id:

	gdb/mips-linux-tdep.c
	gdb/glibc-tdep.c
	gdb/obsd-tdep.c
	gdb/tic6x-linux-tdep.c
	gdb/sol2-tdep.c
	gdb/nios2-linux-tdep.c

They're used for skipping syscalls and ld.so.

The latter should be called via gdbarch_skip_solib_resolver (gdbarch, stop_pc)
from infrun.c.

Who is supposed to do the check in those cases?  Maybe they are already OK?

Regards,
Markus.
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