Re: [PATCH v4 02/15] x86/msr: Move rdtsc{,_ordered}() to <asm/tsc.h>

[Xin Li <xin@xxxxxxxxx>]

On 5/2/2025 1:02 AM, Ingo Molnar wrote:
> * Xin Li (Intel) <xin@xxxxxxxxx> wrote:
>
> > index 94408a784c8e..13335a130edf 100644
> > --- a/arch/x86/include/asm/tsc.h
> > +++ b/arch/x86/include/asm/tsc.h
> > @@ -7,7 +7,81 @@
> >   
> >   #include <asm/cpufeature.h>
> >   #include <asm/processor.h>
> > -#include <asm/msr.h>
> > +
> > +/*
> > + * both i386 and x86_64 returns 64-bit value in edx:eax, but gcc's "A"
> > + * constraint has different meanings. For i386, "A" means exactly
> > + * edx:eax, while for x86_64 it doesn't mean rdx:rax or edx:eax. Instead,
> > + * it means rax *or* rdx.
> > + */
> > +#ifdef CONFIG_X86_64
> > +/* Using 64-bit values saves one instruction clearing the high half of low */
> > +#define DECLARE_ARGS(val, low, high)   unsigned long low, high
> > +#define EAX_EDX_VAL(val, low, high)    ((low) | (high) << 32)
> > +#define EAX_EDX_RET(val, low, high)    "=a" (low), "=d" (high)
> > +#else
> > +#define DECLARE_ARGS(val, low, high)   u64 val
> > +#define EAX_EDX_VAL(val, low, high)    (val)
> > +#define EAX_EDX_RET(val, low, high)    "=A" (val)
> > +#endif
> Meh, this patch creates a duplicate copy of DECLARE_ARGS() et al in
> <asm/tsc.h> now:
>
>   arch/x86/include/asm/msr.h:#define DECLARE_ARGS(val, low, high) unsigned long 
> low, high
>   arch/x86/include/asm/msr.h:#define DECLARE_ARGS(val, low, high) u64 val
>   arch/x86/include/asm/msr.h:     DECLARE_ARGS(val, low, high);
>   arch/x86/include/asm/msr.h:     DECLARE_ARGS(val, low, high);
>   arch/x86/include/asm/msr.h:     DECLARE_ARGS(val, low, high);
>   arch/x86/include/asm/tsc.h:#define DECLARE_ARGS(val, low, high) unsigned long 
> low, high
>   arch/x86/include/asm/tsc.h:#define DECLARE_ARGS(val, low, high) u64 val
>   arch/x86/include/asm/tsc.h:     DECLARE_ARGS(val, low, high);
>   arch/x86/include/asm/tsc.h:     DECLARE_ARGS(val, low, high);
>   arch/x86/include/asm/tsc.h:#undef DECLARE_ARGS
>
> Which was both an undeclared change, bloats the code, causes various
> problems, and is totally unnecessary to boot.
>
> Please don't do that ...
Learned!

Especially that every change needs to explicitly called out.