Re: [PATCH v6] coresight: etm4x: avoid build failure with unrolled loops

[Arnd Bergmann]

On Sat, Jul 9, 2022 at 1:15 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote:

>         ({                                                                      \
>                 u64 __val;                                                      \
>                                                                                 \
> -               if (__builtin_constant_p((offset)))                             \
> +               if (__is_constexpr((offset)))                                   \
>                         __val = read_etm4x_sysreg_const_offset((offset));       \
>                 else                                                            \
>                         __val = etm4x_sysreg_read((offset), true, (_64bit));    \
>

This is clearly better than the current version using
__builtin_constant_p(), but
I don't think it's safe in all cases, since there are expressions that
are constant
expressions to the compiler but are not valid input to the assembler.

I would prefer to see this fixed differently, but doing this one first is also
fine with me:

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

        Arnd