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Date: Tue, 13 Nov 2012 15:12:00 -0000
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From: Mark Kettenis <mark.kettenis@xs4all.nl>
To: yao@codesourcery.com
CC: gdb-patches@sourceware.org
In-reply-to: <50A25CB7.6060205@codesourcery.com> (message from Yao Qi on Tue,	13 Nov 2012 22:44:07 +0800)
Subject: Re: [PATCH/arm] Backtrace through exception frames on arm/cortex-m target
References: <1352816140-3221-1-git-send-email-yao@codesourcery.com> <201211131427.qADERVUl015787@glazunov.sibelius.xs4all.nl> <50A25CB7.6060205@codesourcery.com>
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> Date: Tue, 13 Nov 2012 22:44:07 +0800
> From: Yao Qi <yao@codesourcery.com>
> 
> On 11/13/2012 10:27 PM, Mark Kettenis wrote:
> >> +  unwound_sp = get_frame_register_unsigned (this_frame, ARM_SP_REGNUM);
> > Calling get_frame_register_unsign(this_frame, ...) in the unwinder
> > itself is verboten!.
> 
> Really?  It is a surprise to me.  I see get_frame_register_unsigned is 
> called in many other unwinders, for example,
> 
> *** alpha-mdebug-tdep.c:
> alpha_mdebug_frame_unwind_cache[217] vfp = get_frame_register_unsigned 
> (this_frame, PROC_FRAME_REG (proc_desc));
> 
> *** amd64obsd-tdep.c:
> amd64obsd_trapframe_cache[373] sp = get_frame_register_unsigned 
> (this_frame, AMD64_RSP_REGNUM);
> 
> *** arm-linux-tdep.c:
> arm_linux_sigtramp_cache[258]  CORE_ADDR sp = 
> get_frame_register_unsigned (this_frame, ARM_SP_REGNUM);
> 
> *** avr-tdep.c:
> avr_frame_unwind_cache[987]    this_base = get_frame_register_unsigned 
> (this_frame, AVR_FP_REGNUM);
> 
> Am I missing something?

Ugh, no, you're right.  It's unwinding THIS_FRAME in the unwinder that
is verboten.  Objection withdrawn.