Keir Fraser a écrit :
On 10/7/08 10:21, "Guillaume Rousse" <Guillaume.Rousse@xxxxxxxx> wrote:
I'm trying to port xen-detect.c ASM code into cfengine, which is
currently build as a shared library. However, I'm facing a compilation
error:
misc.c: In function 'Xen_cpuid':
misc.c:1376: error: can't find a register in class 'BREG' while
reloading 'asm'
misc.c:1376: error: 'asm' operand has impossible constraints
From
See tools/libxc/xc_cpuid_x86.c for an example of how to work around this.
Essentially you turn the "=b" constraint into "=r". You then push/pop ebx
(to save/restore it) and you 'mov %%ebx,%1' to save away ebx's value before
restoring its original value.
Thanks, I see the idea, but I feel like a typing monkey here because of
the unknown syntax. Is this supposed to be OK ?
void Xen_cpuid(uint32_t idx, uint32_t *eax, uint32_t *ebx, uint32_t *ecx,
uint32_t *edx)
{
asm volatile (
"test %1,%1 ; jz 1f ; ud2a ; .ascii \"xen\" ;"
#ifdef __i386__
"push %%ebx; cpuid; mov %%ebx,%1; pop %%ebx"
#else
"push %%rbx; cpuid; mov %%ebx,%1; pop %%rbx"
#endif
: "=a" (*eax), "=r" (*ebx), "=c" (*ecx), "=d" (*edx)
: "0" (idx), "1" (0) );
}
Also, the final line was originally:
: "0" (idx), "1" (pv_context) );
I turned it into the current way because I don't need the check in pv
context, but I guess it might be simplified.
--
Guillaume Rousse
Moyens Informatiques - INRIA Futurs
Tel: 01 69 35 69 62
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