linux-kernel - Re: [PATCH] lockdep: Quiet gcc about dangerous __builtin_return

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Date:   Thu, 8 Sep 2016 20:33:13 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] lockdep: Quiet gcc about dangerous
 __builtin_return_address() operations

On Thu, Sep 08, 2016 at 12:34:33PM -0400, Steven Rostedt wrote:
> [
>   Boris, does this quiet gcc for you?
>   I haven't fully tested this yet, as I still don't have a compiler
>   that does the warning.

gcc 6.x should be available in your distro...

> Gcc's new warnings about __builtin_return_address(n) operations with
> n > 0 is popping up around the kernel. The operation is dangerous, and
> the warning is "good to know". But there's instances that we use
> __builtin_return_address(n) with n > 0 and are aware of the issues,
> and work around them. And its used mostly for tracing and debugging. In
> these cases, the warning becomes a distraction and is not helpful.
> 
> To get better lock issue traces, a function like get_lock_parent_ip()
> uses __builtin_return_address() to find the caller of the lock, and
> skip over the internal callers of the lock itself. Currently it is only
> used in the kernel/ directory and only if certain configs are enabled.
> 
> Create a new config called CONFIG_USING_GET_LOCK_PARENT_IP that gets
> selected when another config relies on get_lock_parent_ip(), and this
> will now enable the function get_lock_parent_ip(), otherwise it wont be
> defined. It will also disable the frame-address warnings from gcc in
> the kernel directory.
> 
> Reported-by: Borislav Petkov <bp@...en8.de>

	  -and-tested-by: me

> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Thanks Steve!

-- 
Regards/Gruss,
    Boris.

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