linux-kernel - Re: [PATCH v2] powerpc: Fix irq_soft_mask_set() and irq_soft_mask

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Date:   Thu, 1 Sep 2022 12:48:58 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Gabriel Paubert <paubert@...m.es>,
        Michael Ellerman <mpe@...erman.id.au>,
        Zhouyi Zhou <zhouzhouyi@...il.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH v2] powerpc: Fix irq_soft_mask_set() and irq_soft_mask_return() with sanitizer

On Thu, Sep 01, 2022 at 07:47:10AM +0000, Christophe Leroy wrote:
> Le 01/09/2022 à 09:37, Gabriel Paubert a écrit :
> > Agree, but there is one thing which escapes me: why is r3 listed in the
> > outputs section (actually as a read write operand with the "+"
> > constraint modifier) but is not used after the asm which is the last
> > statement of function returning void?
> > 
> > Do I miss something?
> 
> As far as I remember, that's to tell GCC that r3 register is modified by 
> the callee. As it is an input, it couldn't be listed in the clobber list.

Inputs can be clobbered just fine, in general.  But here the operand
is tied to a register variable, and that causes the error ("'asm'
specifier for variable 'r3' conflicts with 'asm' clobber list").

Marking it in/out here is more appropriate anyway :-)


Segher