linux-kernel - Re: [PATCH v2 1/5] mips: add __NR_syscalls along with __NR_Linux

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Message-ID: <CAK8P3a2CuryCoZKaOXz=nH_WTAZ7VneNoUYHkKFDLQNQvrkWUg@mail.gmail.com>
Date:   Mon, 19 Nov 2018 16:51:44 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Firoz Khan <firoz.khan@...aro.org>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        "open list:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        gregkh <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>
Subject: Re: [PATCH v2 1/5] mips: add __NR_syscalls along with __NR_Linux_syscalls

On Thu, Nov 15, 2018 at 7:14 AM Firoz Khan <firoz.khan@...aro.org> 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