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RE: [PATCH] stack: fix gdb.dwarf2/dw2-undefined-ret-addr.exp regression
- From: "Metzger, Markus T" <markus dot t dot metzger at intel dot com>
- To: Yao Qi <qiyaoltc at gmail dot com>
- Cc: "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>, "palves at redhat dot com" <palves at redhat dot com>
- Date: Thu, 6 Oct 2016 11:03:22 +0000
- Subject: RE: [PATCH] stack: fix gdb.dwarf2/dw2-undefined-ret-addr.exp regression
- Authentication-results: sourceware.org; auth=none
- References: <email@example.com> <firstname.lastname@example.org>
> -----Original Message-----
> From: Yao Qi [mailto:email@example.com]
> Sent: Thursday, October 6, 2016 11:32 AM
> To: Metzger, Markus T <firstname.lastname@example.org>
> Cc: email@example.com; firstname.lastname@example.org; email@example.com
> Subject: Re: [PATCH] stack: fix gdb.dwarf2/dw2-undefined-ret-addr.exp
Thanks for your review.
> It is good to me. I read this patch several times since July, because
> of something else in a038fa3e14a4. Do we need to move
> frame_unwind_caller_id into try block? like this,
> if (!frame_id_p (frame_unwind_caller_id (fi)))
> val_print_unavailable (gdb_stdout);
> caller_pc = frame_unwind_caller_pc (fi);
> caller_pc_p = 1;
> CATCH (ex, ....)
> frame_unwind_caller_id calls get_prev_frame_always which only catches
> MEMORY_ERROR. IIUC, get_prev_frame_always and it callees may throw
I didn't say that get_prev_frame_always may throw NOT_AVAILABLE_ERROR.
I said that I would treat the case where the trace ends with tailcall frames without
an actual caller frame like NOT_AVAILABLE_ERROR (and this patch is changing this
now to OPTIMIZED_OUT_ERROR).
The problem was that get_prev_frame_always may return NULL, which
skip_artificial_frames did not handle, causing GDB to crash. We didn't really have
such a case before, but with record-btrace, you could end up with a bunch of
tailcall frames where the actual caller is not contained in the trace.
Pedro suggested that: "
All the frame_unwind_caller_XXX methods should retrieve information
about the same frame that frame_unwind_caller_id returns. They should
all really be guarded by a frame_unwind_caller_id check, like:
if (frame_id_p (frame_unwind_caller_id (frame)))
As to whether the callers of frame_unwind_caller_id need to expect an exception,
I can't say for sure but I don't think it likely. There are a few such checks in GDB
already and none of them seems to expect an exception.
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