linux-kernel - Re: [PATCH v13 8/9] Add 32 bit VDSO time support for 32 bit kernel

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Date:	Sun, 09 Feb 2014 12:11:08 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Stefani Seibold <stefani@...bold.net>,
	Andi Kleen <ak@...ux.intel.com>
CC:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	aarcange@...hat.com, john.stultz@...aro.org, luto@...capital.net,
	xemul@...allels.com, gorcunov@...nvz.org,
	andriy.shevchenko@...ux.intel.com, Martin.Runge@...de-schwarz.com,
	Andreas.Brief@...de-schwarz.com
Subject: Re: [PATCH v13 8/9] Add 32 bit VDSO time support for 32 bit kernel

On 02/09/2014 03:45 AM, Stefani Seibold wrote:
>>
>> Yes the syscall does, but the vsyscall stub does not (for the !0x80 case)
> 
> I cross check all kinds of vsyscall and all do save the ECX registers. 
> 
> So IMHO i see no register modification other than EAX, which is declared
> as the output register in the asm() directive.
> 

That is, indeed, correct, as the 32-bit vsyscall stubs are explicitly
designed to be drop-in replacements for the int $0x80 instruction.

	-hpa


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