linux-kernel - Re: [PATCH RFC WIP] x86/paravirt: add register-saving thunks to reduce caller register pressure

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Date:	Tue, 03 Feb 2009 09:23:12 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Pavel Machek <pavel@...e.cz>
CC:	Zachary Amsden <zach@...are.com>, "H. Peter Anvin" <hpa@...or.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC WIP] x86/paravirt: add register-saving thunks to	reduce
 caller register pressure

Pavel Machek wrote:
>> This patch seeks to alleviate this pressure by introducing wrapper
>> thunks that will do the register saving/restoring, so that the
>> callsite doesn't need to worry about it, but the callee function can
>> be conventional compiler-generated code.  In many cases (particularly
>> performance-sensitive cases) the callee will be in assembler anyway,
>> and need not use the compiler's calling convention.
>>
>> Standard calling convention is:
>> 	 arguments	    return	scratch
>> x86-32	 eax edx ecx	    eax		?
>>     
>
> esi edi ebp ?
>   

Those are callee-save, so the caller doesn't need to worry about 
preserving their values.

> actually standard calling convention is all arguments on stack iirc
> but we use regparm=3 for kernel...?
>   

Yes.  "standard" = "standard kernel calling convention"


    J
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