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

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Date:   Thu, 17 Sep 2020 17:16:20 -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,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH] objtool: ignore unreachable trap after call to noreturn
 functions

On Thu, Sep 17, 2020 at 11:49:04AM +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.
> 
> objtool silences similar warnings (trap after dead end instructions), 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>
> Signed-off-by: Ilie Halip <ilie.halip@...il.com>

The patch looks good to me.  Which versions of Clang do the trap after
noreturn call?  It would be good to have that in the commit message.

-- 
Josh