Re: [PATCH 5/6] include: Add __rdtsc and __rdtscp intrinsics.

[Rémi Bernon]

On 3/10/21 4:40 PM, Rémi Bernon wrote:
> On 3/10/21 4:00 PM, Rémi Bernon wrote:
> > On 3/10/21 3:57 PM, Jacek Caban wrote:
> > > Hi Rémi,
> > >
> > > On 10.03.2021 12:22, Rémi Bernon wrote:
> > > > Signed-off-by: Rémi Bernon
> > > >
> > > > include/msvcrt/intrin.h | 30 ++++++++++++++++++++++++++++++
> > > >   1 file changed, 30 insertions(+)
> > > >
> > > > diff --git a/include/msvcrt/intrin.h b/include/msvcrt/intrin.h
> > > > index 781c6fac823..061866fe63b 100644
> > > > --- a/include/msvcrt/intrin.h
> > > > +++ b/include/msvcrt/intrin.h
> > > > @@ -20,6 +20,36 @@ static inline void __cpuid(int info[4], int ax)
> > > >   {
> > > >       return __cpuidex(info, ax, 0);
> > > >   }
> > > > -
> > > >
> > > > +#ifdef __i386
> > > > +static inline unsigned __int64 __rdtsc(void)
> > > > +{
> > > > +    unsigned __int64 a;
> > > > +    __asm__ ("rdtsc" : "=A" (a));
> > > > +    return a;
> > > > +}
> > > > -
> > > >
> > > > +static inline unsigned __int64 __rdtscp(unsigned int *aux)
> > > > +{
> > > > +    unsigned __int64 a;
> > > > +    __asm__ ("rdtscp" : "=A" (a), "=c" (*aux));
> > > > +    return a;
> > > > +}
> > > > +#elif defined __amd64
> > > > +static inline unsigned __int64 __rdtsc(void)
> > > > +{
> > > > +    unsigned __int64 a, d;
> > > > +    __asm__ ("rdtsc" : "=a" (a), "=d" (d));
> > > > +    return (d << 32) | a;
> > > > +}
> > > > -
> > > >
> > > > +static inline unsigned __int64 __rdtscp(unsigned int *aux)
> > > > +{
> > > > +    unsigned __int64 a, d;
> > > > +    __asm__ ("rdtscp" : "=a" (a), "=d" (d), "=c" (*aux));
> > > > +    return (d << 32) | a;
> > > > +}
> > > > +#endif
> > > >   #endif
> > >
> > > I think you meant __i386__ and __x86_64__ for guards. If guards were 
> > > right, you'd get a redefinition because __rdtsc is a compiler 
> > > builtin. It seems to me that all we need for __rdtsc is to provide 
> > > MSVC-style declaration in winnt.h, like it's done in WinSDK.
> > >
> > > Thanks,
> > >
> > > Jacek
> >
> > Yeah I'm not sure where I got these guards from, but I think the test 
> > failed to compile, so I assumed MinGW missed these intrinsics? I'll 
> > double check.
>
> So I can confirm that although the guard aren't the usual ones there's 
> no __rdtsc(p) intrinsics on MinGW and the test fails to compile without 
> these (and I don't get redefinition errors with them).
>
> Then I agree that these are probably MSVC intrinsics and may need to be 
> guarded for that case, but they are still needed for GCC (and possibly 
> clang?).

Apparently clang >= 4.0.0 has __rdtsc (but not __rdtscp). Can we just 
assume clang >= 4.0.0 is used and something like that would be 
acceptable instead?

#ifndef _MSC_VER
     # ifndef __clang__ /* clang >= 4.0.0 has __rdtsc intrinsic */
     #  if defined(__i386__)
     static inline unsigned __int64 __rdtsc(void)
     {
         unsigned __int64 a;
         __asm__ ("rdtsc" : "=A" (a));
         return a;
     }
     #  elif defined(__x86_64__)
     static inline unsigned __int64 __rdtsc(void)
     {
         unsigned __int64 a, d;
         __asm__ ("rdtsc" : "=a" (a), "=d" (d));
         return (d << 32) | a;
     }
     #  endif
     # endif /* __clang__ */

# if defined(__i386__)
     static inline unsigned __int64 __rdtscp(unsigned int *aux)
     {
         unsigned __int64 a;
         __asm__ ("rdtscp" : "=A" (a), "=c" (*aux));
         return a;
     }
     # elif defined(__x86_64__)
     static inline unsigned __int64 __rdtscp(unsigned int *aux)
     {
         unsigned __int64 a, d;
         __asm__ ("rdtscp" : "=a" (a), "=d" (d), "=c" (*aux));
         return (d << 32) | a;
     }
     # endif
     #endif /* _MSC_VER */

Cheers,