linux-kernel - Re: [PATCH] x86/kernel: Fix more -Wmissing-prototypes warnings

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Date:   Fri, 7 Dec 2018 20:48:47 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Banman <andrew.banman@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Mike Travis <mike.travis@....com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yi Wang <wang.yi59@....com.cn>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH] x86/kernel: Fix more -Wmissing-prototypes warnings

On Fri, Dec 07, 2018 at 11:42:10PM +0900, Masami Hiramatsu wrote:
> Hmm, I just thought that the symbol only referred from inline asm should
> be visible. But if it is OK for any version of supported gcc and clang,
> I'm good to remove it. :-) (IOW, I just concerned about older gcc)

I just tried two gcc versions: 8.2 and 4.8.5. Both asms looks good:

ffffffff81044690 <kretprobe_trampoline>:
...


ffffffff810446ab:       41 57                   push   %r15
ffffffff810446ad:       48 89 e7                mov    %rsp,%rdi
ffffffff810446b0:       e8 db 01 00 00          callq  ffffffff81044890 <trampoline_handler>

there's the CALL...

ffffffff810446b5:       48 89 84 24 98 00 00    mov    %rax,0x98(%rsp)
ffffffff810446bc:       00

... and the handler is at the expected address.

ffffffff81044890 <trampoline_handler>:
ffffffff81044890:       e8 ab c9 7b 00          callq  ffffffff81801240 <__fentry__>
ffffffff81044895:       41 57                   push   %r15
ffffffff81044897:       41 56                   push   %r14
ffffffff81044899:       41 55                   push   %r13
ffffffff8104489b:       49 89 fd                mov    %rdi,%r13

Dunno, if you feel like there might be some trouble with some compilers,
I can keep the hunk below as a separate patch and revert it when it
explodes somewhere...?

> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
> 
> Thank you,
> 
> > 
> > ---
> > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> > index 6480056d370f..308bf103cc73 100644
> > --- a/arch/x86/kernel/kprobes/core.c
> > +++ b/arch/x86/kernel/kprobes/core.c
> > @@ -66,8 +66,6 @@
> >  
> >  #include "common.h"
> >  
> > -void *trampoline_handler(struct pt_regs *regs);
> > -
> >  DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
> >  DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> >  
> > @@ -753,7 +751,7 @@ STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
> >  /*
> >   * Called from kretprobe_trampoline
> >   */
> > -__visible __used void *trampoline_handler(struct pt_regs *regs)
> > +static __used void *trampoline_handler(struct pt_regs *regs)
> >  {
> >  	struct kretprobe_instance *ri = NULL;
> >  	struct hlist_head *head, empty_rp;
> > 
> > -- 
> > Regards/Gruss,
> >     Boris.
> > 
> > Good mailing practices for 400: avoid top-posting and trim the reply.
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@...nel.org>

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.