linux-kernel - Re: [PATCH 4 of 7] x86/paravirt: selectively save/restore regs around pvops calls

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Message-ID: <4981773A.1050403@goop.org>
Date:	Thu, 29 Jan 2009 01:30:34 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Xen-devel <xen-devel@...ts.xensource.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Zachary Amsden <zach@...are.com>,
	Ravikiran Thirumalai <kiran@...lemp.com>
Subject: Re: [PATCH 4 of 7] x86/paravirt: selectively save/restore regs around
 pvops calls

Rusty Russell wrote:
> On Thursday 29 January 2009 09:05:04 Jeremy Fitzhardinge wrote:
>   
>> +#define PV_SAVE_REGS(set)			\
>> +	COND_PUSH(set, CLBR_RAX, rax);		\
>> +	COND_PUSH(set, CLBR_RCX, rcx);		\
>> +	COND_PUSH(set, CLBR_RDX, rdx);		\
>> +	COND_PUSH(set, CLBR_RSI, rsi);		\
>> +	COND_PUSH(set, CLBR_RDI, rdi);		\
>> +	COND_PUSH(set, CLBR_R8, r8);		\
>> +	COND_PUSH(set, CLBR_R9, r9);		\
>> +	COND_PUSH(set, CLBR_R10, r10);		\
>> +	COND_PUSH(set, CLBR_R11, r11)
>>     
>
> It's kind of messy.  Can we do something clever here with token pasting?
>   

I tried a few things, but no.  Passing in just RAX, and then pasting 
CLBR_##reg works, and the assembler accepts %RAX - but - the asm code 
also #defines RAX <some stack offset>, so the assembler ends up seeing 
%48.  I considered renaming all the CLBR_ defines to CLBR_rax, but that 
looks unhappy too.  So I stayed with this.

    J
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