Date: Sun, 9 Feb 2014 02:05:36 -0800
From: Andi Kleen <ak@linux.intel.com>
To: Stefani Seibold <stefani@seibold.net>
Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, x86@kernel.org,
        tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
        aarcange@redhat.com, john.stultz@linaro.org, luto@amacapital.net,
        xemul@parallels.com, gorcunov@openvz.org,
        andriy.shevchenko@linux.intel.com, Martin.Runge@rohde-schwarz.com,
        Andreas.Brief@rohde-schwarz.com
Subject: Re: [PATCH v13 8/9] Add 32 bit VDSO time support for 32 bit kernel
Message-ID: <20140209100536.GM12219@tassilo.jf.intel.com>
References: <1391894951-6381-1-git-send-email-stefani@seibold.net>
 <1391894951-6381-9-git-send-email-stefani@seibold.net>
 <20140209052230.GL12219@tassilo.jf.intel.com>
 <1391933453.1014.20.camel@wall-e.seibold.net>
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> 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@linux.intel.com -- Speaking for myself only
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