linux-kernel - Re: [PATCH v2] objtool: ignore unreachable trap after call to noreturn functions

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Date:   Mon, 21 Sep 2020 10:19:13 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Ilie Halip <ilie.halip@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Rong Chen <rong.a.chen@...el.com>,
        Marco Elver <elver@...gle.com>,
        Philip Li <philip.li@...el.com>,
        Borislav Petkov <bp@...en8.de>, kasan-dev@...glegroups.com,
        x86@...nel.org, clang-built-linux@...glegroups.com,
        kbuild test robot <lkp@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH v2] objtool: ignore unreachable trap after call to
 noreturn functions

On Sat, Sep 19, 2020 at 09:41:18AM +0300, Ilie Halip wrote:
> With CONFIG_UBSAN_TRAP enabled, the compiler may insert a trap instruction
> after a call to a noreturn function. In this case, objtool warns that the
> ud2 instruction is unreachable.
> 
> This is a behavior seen with clang, from the oldest version capable of
> building the mainline x64_64 kernel (9.0), to the latest experimental
> version (12.0).
> 
> objtool silences similar warnings (trap after dead end instructions), so
> so expand that check to include dead end functions.
> 
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Rong Chen <rong.a.chen@...el.com>
> Cc: Marco Elver <elver@...gle.com>
> Cc: Philip Li <philip.li@...el.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: kasan-dev@...glegroups.com
> Cc: x86@...nel.org
> Cc: clang-built-linux@...glegroups.com
> BugLink: https://github.com/ClangBuiltLinux/linux/issues/1148
> Link: https://lore.kernel.org/lkml/CAKwvOdmptEpi8fiOyWUo=AiZJiX+Z+VHJOM2buLPrWsMTwLnyw@mail.gmail.com
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reported-by: kbuild test robot <lkp@...el.com>
> Signed-off-by: Ilie Halip <ilie.halip@...il.com>
> ---
> 
> Changed in v2:
>  - added a mention that this is a clang issue across all versions
>  - added Nick's Reviewed-by, Tested-by
>  - added Reported-by

Thanks.  Queued.

-- 
Josh