linux-kernel - Re: [PATCH 1/23] Make register values available to panic notifiers

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Message-Id: <20100414.165851.144419620.davem@davemloft.net>
Date:	Wed, 14 Apr 2010 16:58:51 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dhowells@...hat.com
Cc:	dvomlehn@...co.com, to@...mlehn-lnx2.corp.sa.net,
	linux-arch@...r.kernel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, maint_arch@...mlehn-lnx2.corp.sa.net
Subject: Re: [PATCH 1/23] Make register values available to panic notifiers

From: David Howells <dhowells@...hat.com>
Date: Thu, 15 Apr 2010 00:52:14 +0100

> David VomLehn <dvomlehn@...co.com> wrote:
> 
>> > Can the use of va_start() clobber lots of registers, thereby rendering the
>> > exercise pointless on some arches?
>> >   
>>
>> The implementations I'm familiar with only need one or two registers. What
>> it *does* do is to force the contents of registers being used to pass
>> argument values onto the stack. This is roughly what gcc does for asm()
>> statements when you tell it registers are clobbered.
> 
> How about something like Sparc, where you can pass up to 8 arguments (if I
> remember correctly) in registers.  I'm not sure how Sparc handles varargs
> functions, though.

6 arguments, and all arguments get popped onto the stack into the
argument save area when doing varargs so you can access them as an
array.

Stack looks like:

	struct register_window	window;
	unsigned long args[...];
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