linux-kernel - Re: [PATCH 4/5] Generic BUG for powerpc

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Message-Id: <1159923244.31312.21.camel@localhost.localdomain>
Date:	Wed, 04 Oct 2006 10:54:03 +1000
From:	Michael Ellerman <michael@...erman.id.au>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@....de>, Hugh Dickens <hugh@...itas.com>,
	Paul Mackerras <paulus@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 4/5] Generic BUG for powerpc

On Tue, 2006-10-03 at 13:16 -0700, Jeremy Fitzhardinge wrote:
> plain text document attachment (mm)
> This makes powerpc use the generic BUG machinery.  The biggest
> difference from the previous powerpc bug code is that it no longer
> reports the function name, since it is redundant with kallsyms, and
> not needed in general.
> 
> There is an overall reduction of code, since module_32/64 duplicated several
> functions.
> 
> Unfortunately there's no way to tell gcc that BUG won't return, so the
> BUG macro includes a goto loop.  This will generate a real jmp
> instruction, which is never used.

I posted a patch a few weeks back to use __builtin_trap(), which gives
GCC the hint that it's not going to return.
(http://patchwork.ozlabs.org/linuxppc/patch?id=7047)

Unfortunately this generated some negative feedback from some of our
crackhead ... er wonderful colleagues who want to be able to step over
BUGs in some circumstances.
(http://ozlabs.org/pipermail/linuxppc-dev/2006-September/026161.html)

I think they conceeded that it could be configurable, but I wasn't sure
it was worth the trouble.

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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