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From:   Mathieu Malaterre <malat@debian.org>
Date:   Fri, 15 Feb 2019 09:11:34 +0100
Message-ID: <CA+7wUswJy0z_+aytawQv6+1pOVvH2z8SfOz1sxziHtgjqZ1F9g@mail.gmail.com>
Subject: Re: [PATCH] powerpc/ptrace: Add prototype for function pt_regs_check
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Oleg Nesterov <oleg@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Sat, Dec 8, 2018 at 4:46 PM Mathieu Malaterre <malat@debian.org> wrote:
>
> `pt_regs_check` is a dummy function, its purpose is to break the build
> if struct pt_regs and struct user_pt_regs don't match.
>
> This function has no functionnal purpose, and will get eliminated at
> link time or after init depending on CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
>
> This commit adds a prototype to fix warning at W=1:
>
>   arch/powerpc/kernel/ptrace.c:3339:13: error: no previous prototype for ‘pt_regs_check’ [-Werror=missing-prototypes]
>
> Suggested-by: Christophe Leroy <christophe.leroy@c-s.fr>
> Signed-off-by: Mathieu Malaterre <malat@debian.org>
> ---
>  arch/powerpc/kernel/ptrace.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index a398999d0770..341c0060b4c8 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -3338,6 +3338,10 @@ void do_syscall_trace_leave(struct pt_regs *regs)
>         user_enter();
>  }
>
> +void __init pt_regs_check(void);
> +/* dummy function, its purpose is to break the build if struct pt_regs and
> + * struct user_pt_regs don't match.
> + */

Another trick which seems to work with GCC is:

-void __init pt_regs_check(void)
+static inline void __init pt_regs_check(void)

>  void __init pt_regs_check(void)
>  {
>         BUILD_BUG_ON(offsetof(struct pt_regs, gpr) !=
> --
> 2.19.2
>