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Subject: Re: [PATCH] powerpc/ptrace: Add prototype for function pt_regs_check
To:     Mathieu Malaterre <malat@debian.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Paul Mackerras <paulus@samba.org>,
        Oleg Nesterov <oleg@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
References: <20181208154624.6504-1-malat@debian.org>
 <CA+7wUswJy0z_+aytawQv6+1pOVvH2z8SfOz1sxziHtgjqZ1F9g@mail.gmail.com>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <e95cb3ea-019f-28b0-0af0-ad8c80b3106b@c-s.fr>
Date:   Fri, 15 Feb 2019 09:21:27 +0100
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Le 15/02/2019 à 09:11, Mathieu Malaterre a écrit :
> 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)

Does this really work ? Did you test to ensure that the BUILD_BUG_ON 
still detect mismatch between struct pt_regs and struct user_pt_regs ?

Christophe

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