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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: sxwjean@me.com, linuxppc-dev@lists.ozlabs.org,
	ravi.bangoria@linux.ibm.com, Xiongwei Song <sxwjean@gmail.com>,
	oleg@redhat.com, npiggin@gmail.com, linux-kernel@vger.kernel.org,
	efremov@linux.com, paulus@samba.org, aneesh.kumar@linux.ibm.com,
	peterx@redhat.com, akpm@linux-foundation.org,
	sandipan@linux.ibm.com
Subject: Re: [RFC PATCH 1/4] powerpc: Optimize register usage for esr register
Date: Fri, 6 Aug 2021 09:26:43 -0500	[thread overview]
Message-ID: <20210806142643.GU1583@gate.crashing.org> (raw)
In-Reply-To: <874kc3njxh.fsf@mpe.ellerman.id.au>

On Fri, Aug 06, 2021 at 04:53:14PM +1000, Michael Ellerman wrote:
> But I'm not sure about the use of anonymous unions in UAPI headers. Old
> compilers don't support them, so there's a risk of breakage.

More precisely, it exists only since C11, so even with all not-so-ancient
compilers it will not work if the user uses (say) -std=c99, which still
is popular.

> I'd rather we didn't touch the uapi version.

Yeah.

> > -	err = ___do_page_fault(regs, regs->dar, regs->dsisr);
> > +	if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> > +		err = ___do_page_fault(regs, regs->dar, regs->esr);
> > +	else
> > +		err = ___do_page_fault(regs, regs->dar, regs->dsisr);
> 
> As Christophe said, I don't thinks this is an improvement.
> 
> It makes the code less readable. If anyone is confused about what is
> passed to ___do_page_fault() they can either read the comment above it,
> or look at the definition of pt_regs to see that esr and dsisr share
> storage.

Esp. since the affected platforms are legacy, yup.


Segher

      parent reply	other threads:[~2021-08-06 14:34 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 14:30 sxwjean
2021-07-26 14:30 ` [RFC PATCH 2/4] powerpc/64e: Get esr offset with _ESR macro sxwjean
2021-07-26 14:30 ` [RFC PATCH 3/4] powerpc: Optimize register usage for dear register sxwjean
2021-08-05 10:09   ` Christophe Leroy
2021-08-06  3:16     ` Xiongwei Song
2021-07-26 14:30 ` [RFC PATCH 4/4] powerpc/64e: Get dear offset with _DEAR macro sxwjean
2021-08-05 10:06 ` [RFC PATCH 1/4] powerpc: Optimize register usage for esr register Christophe Leroy
2021-08-06  3:16   ` Xiongwei Song
2021-08-06  7:32     ` Christophe Leroy
2021-08-06 13:22       ` Xiongwei Song
2021-08-06  6:53 ` Michael Ellerman
2021-08-06 13:14   ` Xiongwei Song
2021-08-06 14:26   ` Segher Boessenkool [this message]

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