linux-kernel - Re: [PATCH v2 06/19] OpenRISC: PTrace

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Message-Id: <201107051842.11666.arnd@arndb.de>
Date:	Tue, 5 Jul 2011 18:42:11 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jonas Bonn <jonas@...thpole.se>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 06/19] OpenRISC: PTrace

On Tuesday 05 July 2011, Jonas Bonn wrote:
> I've been looking a bit at the ptrace stuff the last couple of days.
> One question that occurred to me was:  is it mandatory to export the
> "struct pt_regs" info in ptrace.h to userspace?

I don't know, it certainly has been the case traditionally, but as
far as I can tell, this was mainly used by ancient gdb ports,
while newer versions just hardcode the offsets for PTRACE_PEEKUSR.

> I'm not sure I like the layout of our struct pt_regs.  It would be
> better to lay out the registers in a way that mirrors the order that
> they are saved during exception/syscall entry in order to make better
> use of the cache.
> 
> Since the registers can be exported via a regset to userspace anyway
> (which doesn't necessarily need to look like pt_regs), I don't see that
> userspace really needs how we lay out the registers on the stack.  By
> not exporting pt_regs, I am free to change the layout... if it's
> exported, it becomes ABI.

Yes. I think you can just change your ptrace code to not export
pt_regs through PEEKUSR but only through elf_gregset_t, which
you can define independently.

	Arnd
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