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To: Vladimir Prus <ghost@cs.msu.su>
Cc: gdb@sources.redhat.com
Subject: Re: frame_id question
References: <dkt7no$aan$1@sea.gmane.org>
From: Jim Blandy <jimb@redhat.com>
Date: Fri, 11 Nov 2005 10:23:00 -0000
In-Reply-To: <dkt7no$aan$1@sea.gmane.org> (Vladimir Prus's message of "Wed, 09 Nov 2005 19:22:16 +0300")
Message-ID: <vt28xvv5vqj.fsf@theseus.home.>
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Vladimir Prus <ghost@cs.msu.su> writes:
> The question is: why frame id has to include program address at all? It it
> ever possible for two frames to have the same stack address? If so, when?

Some functions don't need any stack space at all.  Such a function can
even call other functions if it moves the return address to a
callee-saved register while doing so.  Unwinding through such a call,
the caller's frame will have the same CFA as the callee, but a
different function address.  Since the two frame ID's have different
function addresses, frame_id_eq will declare them distinct, and GDB
won't complain that it has gotten stuck trying to unwind the stack.