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From: Florian Weimer <fweimer@redhat.com>
To: Michael Matz <matz@suse.de>
Cc: "H.J. Lu" <hjl.tools@gmail.com>, gnu-gabi@sourceware.org
Subject: Re: [PATCH] Make _Unwind_GetIPInfo part of the ABI
Date: Fri, 01 Jan 2016 00:00:00 -0000	[thread overview]
Message-ID: <fd505b01-3f78-b0ea-6afa-3e3e713b7e54@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.20.1610211448060.5714@wotan.suse.de>

On 10/21/2016 02:58 PM, Michael Matz wrote:
> +This function returns the same value as \code{\_Unwind\_GetIP}.  In
> +addition, the argument \code{ip\_before\_insn} must not be not null, and
> +\code{*ip\_before\_insn} is updated with a flag which indicates whether
> +the returned pointer is at or after the first not yet fully executed
> +instruction.

I think this is rather misleading.  On x86_64, the location of the IP 
value is the same for calls and asynchronous signals: it always points 
to the next instruction to be executed.  There are no partially executed 
instructions.

The difference that if we unwind through a call which has not yet 
returned, the caller is assumed to be still within the exception 
handling region in which the call instruction is located.  This is the 
consequence of the desired exception handling semantics of a 
non-returned function call.  It is not directly related to the 
instruction pointer value returned by _Unwind_GetIPInfo.

This is different for the signal case.  There, the instruction pointer 
directly determines the active exception handling region.

Florian

  reply	other threads:[~2016-10-21 13:08 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-01  0:00 Florian Weimer
2016-01-01  0:00 ` Michael Matz
2016-01-01  0:00   ` Florian Weimer [this message]
2016-01-01  0:00     ` Michael Matz
2016-01-01  0:00       ` Florian Weimer
2016-01-01  0:00         ` H.J. Lu
2016-01-01  0:00           ` Florian Weimer
2016-01-01  0:00       ` Michael Matz
2016-01-01  0:00         ` Carlos O'Donell

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