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Date: Wed, 18 Sep 2013 16:30:00 -0000
From: Eli Zaretskii <eliz@gnu.org>
Subject: Re: [PATCH+DOC] Print registers not saved in the frame as "<not saved>", instead of "<optimized out>".
In-reply-to: <5239CCB3.605@redhat.com>
To: Pedro Alves <palves@redhat.com>
Cc: aburgess@broadcom.com, gdb-patches@sourceware.org, mark.kettenis@xs4all.nl
Reply-to: Eli Zaretskii <eliz@gnu.org>
Message-id: <83zjram6sw.fsf@gnu.org>
References: <5200F55E.2050308@broadcom.com> <201308061318.r76DIMdd016369@glazunov.sibelius.xs4all.nl> <5200FECF.7030304@broadcom.com> <201308061541.r76FfYQN022875@glazunov.sibelius.xs4all.nl> <520142D9.4030304@redhat.com> <5208E3C8.7060107@broadcom.com> <5208E938.3080305@redhat.com> <201308122001.r7CK1862007934@glazunov.sibelius.xs4all.nl> <520E7255.7080206@redhat.com> <5211F25A.5070907@broadcom.com> <5228B15F.7060108@redhat.com> <5228B2D8.7060604@broadcom.com> <5237567C.8050406@redhat.com> <5239B2D8.4030403@broadcom.com> <5239CCB3.605@redhat.com>
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> Date: Wed, 18 Sep 2013 16:54:27 +0100
> From: Pedro Alves <palves@redhat.com>
> CC: gdb-patches@sourceware.org, Mark Kettenis <mark.kettenis@xs4all.nl>
> 
> Eli, I've added NEWS and documentation changes to this patch.
> Are those OK?

Almost.

> +* GDB now shows "<not saved>" when printing values of registers that
> +  have not been saved in the frame:
> +
> +    (gdb) p $rax $1 = <not saved>
> +    (gdb) info registers rax rax <not saved>

Wrong formatting of what GDB prints.

> +In some ABIs, some registers may not be preserved, or saved, across
> +function calls.  It may therefore not be possible for @value{GDBN} to
> +know the value a register had before the call (in other words, in a
                                                                     ^
"the"

> +outer frame).  Values of registers that @value{GDBN} can tell were not
> +saved in their stack frames are shown as @w{@samp{<not saved>}}.
> +
> +However, if debug or unwind information is missing, @value{GDBN} must
> +deduce where registers are saved, from the machine code generated by
> +your compiler.  If some registers are not saved, or if @value{GDBN} is
> +unable to locate the saved registers, the selected stack frame makes
> +no difference.

I don't understand the significance of the last paragraph.

Also, shouldn't we mention optimizations as (the main) reason for
registers being unavailable?

Thanks.