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

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Message-ID: <YfBGVfk5jnHgC4UE@zn.tnic>
Date:   Tue, 25 Jan 2022 19:49:57 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.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>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH] objtool: prefer memory clobber & %= to volatile &
 __COUNTER__

On Mon, Jan 24, 2022 at 03:38:38PM -0800, Nick Desaulniers wrote:
> $ wget https://download.01.org/0day-ci/archive/20220119/202201190702.XNSXrMTK-lkp@intel.com/config
> -O .config
> $ make -j72 -s olddefconfig drivers/net/wireless/mac80211_hwsim.o
> drivers/net/wireless/mac80211_hwsim.o: warning: objtool:
> mac80211_hwsim_tx()+0x9aa: unreachable instruction
> $ gcc --version
> gcc (Debian 11.2.0-12) 11.2.0

Yap, I got mine with:

gcc (Debian 10.2.1-6) 10.2.1 20210110

but since you hit it with gcc11, I don't see why I won't hit it with
gcc10.

> :(

You said it.
 
> Let me see if I can come up with a reduced test case that I will
> report upstream to https://gcc.gnu.org/bugzilla/.

Sounds good.

Please send the bug # once you have that so that I can add myself to Cc.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette