Re: [PATCH v2 1/5] mips: add __NR_syscalls along with __NR_Linux_syscalls

[Arnd Bergmann]

On Thu, Nov 15, 2018 at 7:14 AM Firoz Khan <firoz.khan@xxxxxxxxxx> wrote:
>
> The 2nd option will be the recommended one. For that, I
> added the __NR_syscalls macro in uapi/asm/unistd.h along
> with __NR_Linux_syscalls. The macro __NR_syscalls also
> added for making the name convention same across all
> architecture. While __NR_syscalls isn't strictly part of
> the uapi, having it as part of the generated header to
> simplifies the implementation. We also need to enclose
> this macro with #ifdef __KERNEL__ to avoid side effects.

I fear this doesn't work the way you hoped:

> --- a/arch/mips/include/uapi/asm/unistd.h
> +++ b/arch/mips/include/uapi/asm/unistd.h
> @@ -391,16 +391,19 @@
>  #define __NR_rseq                      (__NR_Linux + 367)
>  #define __NR_io_pgetevents             (__NR_Linux + 368)
>
> +#ifdef __KERNEL__
> +#define __NR_syscalls                  368
> +#endif

We now have three different definitions of __NR_syscalls,
one for each ABI. User space previously saw the correct
one (now it doesn't see any, but that's ok).

>  /*
>   * Offset of the last Linux o32 flavoured syscall
>   */
> -#define __NR_Linux_syscalls            368
> +#define __NR_Linux_syscalls            __NR_syscalls

so this part part again is ok.

>  #endif /* _MIPS_SIM == _MIPS_SIM_ABI32 */
>
>  #define __NR_O32_Linux                 4000
> -#define __NR_O32_Linux_syscalls                368
> +#define __NR_O32_Linux_syscalls                __NR_syscalls

but this part is not: Now __NR_O32_Linux_syscalls is defined
to __NR_syscalls, which may be one of the three values.
Any usage of __NR_O32_Linux_syscalls in a 64-bit kernel
is then clearly wrong.

>  #endif /* _MIPS_SIM == _MIPS_SIM_NABI32 */
>
>  #define __NR_N32_Linux                 6000
> -#define __NR_N32_Linux_syscalls                332
> +#define __NR_N32_Linux_syscalls                __NR_syscalls

Same for this one.

       Arnd