linux-kernel - Re: [PATCH] powerpc/bug: Remove specific powerpc BUG

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Date:   Fri, 12 Feb 2021 08:47:55 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] powerpc/bug: Remove specific powerpc BUG_ON()

Excerpts from Segher Boessenkool's message of February 11, 2021 9:50 pm:
> On Thu, Feb 11, 2021 at 08:04:55PM +1000, Nicholas Piggin wrote:
>> It would be nice if we could have a __builtin_trap_if that gcc would use 
>> conditional traps with, (and which never assumes following code is 
>> unreachable even for constant true, so we can use it with WARN and put 
>> explicit unreachable for BUG).
> 
> It automatically does that with just __builtin_trap, see my other mail :-)

If that is generated without branches (or at least with no more
branches than existing asm implementation), then it could be usable 
without trashing CFAR.

Unfortunately I don't think we will be parsing the dwarf information
to get line numbers from it any time soon, so not a drop in replacement 
but maybe one day someone would find a solution.

Thanks,
Nick