linux-kernel - Re: [PATCH 3/3] powerpc: use __builtin

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Message-ID: <20190819132313.GH31406@gate.crashing.org>
Date:   Mon, 19 Aug 2019 08:23:13 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 3/3] powerpc: use __builtin_trap() in BUG/WARN macros.

On Mon, Aug 19, 2019 at 01:06:31PM +0000, Christophe Leroy wrote:
> Note that we keep using an assembly text using "twi 31, 0, 0" for
> inconditional traps because GCC drops all code after
> __builtin_trap() when the condition is always true at build time.

As I said, it can also do this for conditional traps, if it can prove
the condition is always true.

Can you put the bug table asm *before* the __builtin_trap maybe?  That
should make it all work fine...  If you somehow can tell what machine
instruction is that trap, anyway.


Segher