linux-kernel - Re: [PATCH] objtool: prefer memory clobber & %= to volatile & __COUNTER_

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Message-ID: <YedOLva0zos3A1JE@zn.tnic>
Date:   Wed, 19 Jan 2022 00:33:02 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        x86@...nel.org, llvm@...ts.linux.dev, linux-sparse@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH] objtool: prefer memory clobber & %= to volatile &
 __COUNTER__

On Tue, Jan 18, 2022 at 03:01:20PM -0800, Josh Poimboeuf wrote:
> With the two WARN_ONs in media_request_object_complete(), GCC apparently
> considers the two reachable() asm statements as duplicates, and it
> removes the second one.

Could that be the same thing:

net/xfrm/xfrm_output.o: warning: objtool: xfrm_output_resume()+0x2e0: unreachable instruction

I see two WARN_ONs in asm output there too...

-- 
Regards/Gruss,
    Boris.

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