linux-kernel - Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need it

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Message-ID: <49932BF4.2040008@zytor.com>
Date:	Wed, 11 Feb 2009 11:50:12 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Brian Gerst <brgerst@...il.com>
CC:	"H. Peter Anvin" <hpa@...nel.org>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need
 	it

Brian Gerst wrote:
> 
> I guess I could go back to extracting the args from the pt_regs struct
> given just the pointer.  How do you intend to handle system calls in
> your changes (normal ones, not needing pt_regs)?
> 

My plan was to by default load up the three first arguments in (%eax, 
%edx, %ecx) followed by the remaining arguments on the stack... I 
currently have it as a reorganized struct pt_regs, but I'm still trying 
to figure out if it would make more sense from a correctness and 
performance perspective to instead have duplicates of these entries.

For the pt_regs-using registers, they would need a tiny trampoline, 
looking like:

	leal 16(%esp),%eax
	jmp <real function>

	-hpa

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