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Re: [Xen-devel] PIC register 'bx' clobbered in 'asm' - xen-unstable buil

To: Jerone Young <jyoung5@xxxxxxxxxx>
Subject: Re: [Xen-devel] PIC register 'bx' clobbered in 'asm' - xen-unstable build error
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Fri, 25 Feb 2005 15:44:20 -0600
Cc: David F Barrera <dfbp@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
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Jerone Young wrote:

The big question is why are you clobbering bx , dx registers on get
cpuid:
CPUID returns information in eax, ebx, ecx, and edx. With -fPIC you have to push ebx onto the stack before calling cpuid and pop it afterward as Bin points out is what the patch to xen-unstable does.

Regards,

        _asm__ __volatile__ ("cpuid"
                         : "=a" (eax), "=c" (ecx)
                         : "0" (1)
                         : "bx", "dx");

You can change this to:
        
                _asm__ __volatile__ ("cpuid"
                         : "=a" (eax), "=c" (ecx)
                         : "0" (1)
                          );

But I am not sure why this is there?


        
On Fri, 2005-02-25 at 15:02 -0600, David F Barrera wrote:
I am trying to build xen-unstable on an x86 box, but it is failing with the following message:

gcc -DPIC -m32 -march=i686 -Wall -Werror -O3 -fno-strict-aliasing -I ../../tools/libxutil -I. -Wp,-MD,.xc_rrobin.opic.d -fPIC -c -o xc_rrobin.opic xc_rrobin.c gcc -DPIC -m32 -march=i686 -Wall -Werror -O3 -fno-strict-aliasing -I ../../tools/libxutil -I. -Wp,-MD,.xc_vmx_build.opic.d -fPIC -c -o xc_vmx_build.opic xc_vmx_build.c
xc_vmx_build.c: In function `vmx_identify':
xc_vmx_build.c:468: error: PIC register `bx' clobbered in `asm'
make[4]: *** [xc_vmx_build.opic] Error 1
make[4]: Leaving directory `/tmp/xen-unstable/tools/libxc'
make[3]: *** [all] Error 2
make[3]: Leaving directory `/tmp/xen-unstable/tools/libxc'
make[2]: *** [install] Error 2
make[2]: Leaving directory `/tmp/xen-unstable/tools'
make[1]: *** [tools] Error 2
make[1]: Leaving directory `/tmp/xen-unstable'
make: *** [world] Error 2
make world failed

I have built xen-unstable on this machine before, so I don't believe it is a setup problem. Has anyone else observed this?

David F Barrera



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