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

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Date:	Sun, 9 Feb 2014 02:05:36 -0800
From:	Andi Kleen <ak@...ux.intel.com>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.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

> EBX is a reserved as the base register when compiling with -fPIC.
> Otherwise it get a "error: can't find a register in class 'BREG' while
> reloading 'asm'".

In this case you have to dwarf annotate the push/pop

>  
> > Also I if this calls syscall.S:__kernel_vsyscall it clobbers more registers
> > (ecx at least?) and you need to describe that to gcc with a + 
> 
> Sine ECX is in use as the second parameter it is still marked as
> clobbered. 

No input parameters are not clobbered.

> I think it should word... As i know a system call will preserve all
> register expect the EAX, which is marked as in and out for this asm()
> directive. 

Yes the syscall does, but the vsyscall stub does not (for the !0x80 case)

> This is due the -m32 compilation, i will get a log of 
> "warning: integer constant is too large for 'unsigned long' type",
> because a unsigned long is only 32 bit.

Don't explain it to me, put it into a comment.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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