linux-kernel - Re: [RFC][PATCH] Add EXPORT_MACRO

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Date:   Sat, 22 Oct 2016 10:44:41 +1100
From:   Nicholas Piggin <npiggin@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...IV.linux.org.uk>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Gabriel C <nix.or.die@...il.com>
Subject: Re: [RFC][PATCH] Add EXPORT_MACRO_SYMBOL() for asm

On Fri, 21 Oct 2016 12:17:59 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> Commit 784d5699eddc5 ("x86: move exports to actual definitions") removed the
> EXPORT_SYMBOL(__fentry__) and EXPORT_SYMBOL(mcount) from x8664_ksyms_64.c,
> and added EXPORT_SYMBOL(function_hook) in mcount_64.S instead. The problem
> is that function_hook isn't a function at all, but a macro that is defined
> as eithe mcount or __fentry__ depending on the support from gcc. But instead
> of adding more #ifdefs like x8684_ksyms_64.c had, I suggest having another
> export that can handle this similar to the way __string() works with
> converting macros to strings. By having:
> 
>  EXPORT_MACRO_SYMBOL(function_hook)
> 
> Where we have:
> 
>  #define EXPORT_MACRO_SYMBOL(x) EXPORT_SYMBOL(x)
> 
> It will convert the macro into what it is defined as before calling
> EXPORT_SYMBOL(), and this will just work properly again.
> 
> Cc: stable@...r.kernel.org
> Fixes: Commit 784d5699eddc5 ("x86: move exports to actual definitions")
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  arch/x86/kernel/mcount_64.S  | 2 +-
>  include/asm-generic/export.h | 5 +++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
> index efe73aacf966..ccd9d912af27 100644
> --- a/arch/x86/kernel/mcount_64.S
> +++ b/arch/x86/kernel/mcount_64.S
> @@ -295,7 +295,7 @@ trace:
>  	jmp fgraph_trace
>  END(function_hook)
>  #endif /* CONFIG_DYNAMIC_FTRACE */
> -EXPORT_SYMBOL(function_hook)
> +EXPORT_MACRO_SYMBOL(function_hook)
>  #endif /* CONFIG_FUNCTION_TRACER */
>  
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
> index 43199a049da5..cb86e746865e 100644
> --- a/include/asm-generic/export.h
> +++ b/include/asm-generic/export.h
> @@ -90,5 +90,10 @@
>  	__EXPORT_SYMBOL(name, KSYM(name),)
>  #define EXPORT_DATA_SYMBOL_GPL(name)				\
>  	__EXPORT_SYMBOL(name, KSYM(name),_gpl)
> +/*
> + * If "name" is a macro of a function and not a function itself,
> + * it needs a second pass.
> + */
> +#define EXPORT_MACRO_SYMBOL(x) EXPORT_SYMBOL(x)

Seems okay, but what about just calling it EXPORT_SYMBOL?

Thanks,
Nick