Re: PIC register 'bx' clobbered in 'asm' - xen-unstable build error

[Anthony Liguori <aliguori@us.ibm.com>]

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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