linux-kernel - Re: [PATCH] powerpc: Avoid clang warnings around setjmp and longjmp

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Message-ID: <20190903193128.GC9749@gate.crashing.org>
Date:   Tue, 3 Sep 2019 14:31:28 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "# 3.4.x" <stable@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] powerpc: Avoid clang warnings around setjmp and longjmp

On Mon, Sep 02, 2019 at 10:55:53PM -0700, Nathan Chancellor wrote:
> On Thu, Aug 29, 2019 at 09:59:48AM +0000, David Laight wrote:
> > From: Nathan Chancellor
> > > Sent: 28 August 2019 19:45
> > ...
> > > However, I think that -fno-builtin-* would be appropriate here because
> > > we are providing our own setjmp implementation, meaning clang should not
> > > be trying to do anything with the builtin implementation like building a
> > > declaration for it.
> > 
> > Isn't implementing setjmp impossible unless you tell the compiler that
> > you function is 'setjmp-like' ?
> 
> No idea, PowerPC is the only architecture that does such a thing.

Since setjmp can return more than once, yes, exciting things can happen
if you do not tell the compiler about this.


Segher