svn commit: r253802 - head/contrib/llvm/tools/clang/lib/Headers

[Matthew Fleming]

On Tue, Jul 30, 2013 at 5:33 AM, Dimitry Andric <dim at freebsd.org> wrote:

> Author: dim
> Date: Tue Jul 30 12:33:21 2013
> New Revision: 253802
> URL: http://svnweb.freebsd.org/changeset/base/253802
>
> Log:
>   Pull in r186696 from upstream clang trunk:
>
>     This patch implements __get_cpuid_max() as an inline and __cpuid()
>     and __cpuid_count() as macros to be compatible with GCC's cpuid.h.
>     It also adds bit_<foo> constants for the various feature bits as
>     described in version 039 (May 2011) of Intel's SDM Volume 2 in the
>     description of the CPUID instruction.  The list of bit_<foo>
>     constants is a bit exhaustive (GCC doesn't do near this many).  More
>     bits could be added from a newer version of SDM if desired.
>
>     Patch by John Baldwin!
>
>   This should fix several ports which depend on this functionality being
>   available.
>
>   MFC after:    1 week
>
> Modified:
>   head/contrib/llvm/tools/clang/lib/Headers/cpuid.h
>
> Modified: head/contrib/llvm/tools/clang/lib/Headers/cpuid.h
>
> ==============================================================================
> --- head/contrib/llvm/tools/clang/lib/Headers/cpuid.h   Tue Jul 30
> 12:17:45 2013        (r253801)
> +++ head/contrib/llvm/tools/clang/lib/Headers/cpuid.h   Tue Jul 30
> 12:33:21 2013        (r253802)
> +/* PIC on i386 uses %ebx, so preserve it. */
> +#if __i386__
> +#define __cpuid(__level, __eax, __ebx, __ecx, __edx) \
> +    __asm("  pushl  %%ebx\n" \
> +          "  cpuid\n" \
> +          "  mov    %%ebx,%1\n" \
> +          "  popl   %%ebx" \
> +        : "=a"(__eax), "=r" (__ebx), "=c"(__ecx), "=d"(__edx) \
> +        : "0"(__level))
> +
> +#define __cpuid_count(__level, __count, __eax, __ebx, __ecx, __edx) \
> +    __asm("  pushl  %%ebx\n" \
> +          "  cpuid\n" \
> +          "  mov    %%ebx,%1\n" \
> +          "  popl   %%ebx" \
> +        : "=a"(__eax), "=r" (__ebx), "=c"(__ecx), "=d"(__edx) \
> +        : "0"(__level), "2"(__count))
> +#else
> +#define __cpuid(__level, __eax, __ebx, __ecx, __edx) \
> +    __asm("cpuid" : "=a"(__eax), "=b" (__ebx), "=c"(__ecx), "=d"(__edx) \
> +                  : "0"(__level))
> +
> +#define __cpuid_count(__level, __count, __eax, __ebx, __ecx, __edx) \
> +    __asm("cpuid" : "=a"(__eax), "=b" (__ebx), "=c"(__ecx), "=d"(__edx) \
> +                  : "0"(__level), "2"(__count))
> +#endif
>

PIC mode on amd64 also uses %ebx.  The difference is that FreeBSD makefiles
set -fPIC for i386 kernel compile but not amd64.  Locally we use -fPIC for
amd64 (it was added 6 years ago to our environment because it gave better
kernel debugging).

Anyways, is there some way to detect PIC mode and use that to decide
whether to use %ebx for the cpuid instruction, rather than using i386?

Thanks,
matthew