From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] powerpc: Fix pre-update addressing in inline assembly
Date: Mon, 19 Oct 2020 15:24:41 -0500 [thread overview]
Message-ID: <20201019202441.GU2672@gate.crashing.org> (raw)
In-Reply-To: <fbcdb173cc42da62f00285dfef8c2f7d4960b5c7.1603109522.git.christophe.leroy@csgroup.eu>
On Mon, Oct 19, 2020 at 12:12:48PM +0000, Christophe Leroy wrote:
> In several places, inline assembly uses the "%Un" modifier
> to enable the use of instruction with pre-update addressing,
Calling this "pre-update" is misleading: the register is not updated
before the address is generated (or the memory access done!), and the
addressing is exactly the same as the "non-u" insn would use. It is
called an "update form" instruction, because (at the same time as doing
the memory access, logically anyway) it writes back the address used to
the base register.
> but the associated "<>" constraint is missing.
But that is just fine. Pointless, sure, but not a bug.
> Use UPD_CONSTR macro everywhere %Un modifier is used.
Eww. My poor stomach.
Have you verified that update form is *correct* in all these, and that
we even *want* this there?
Segher
next prev parent reply other threads:[~2020-10-19 20:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-19 12:12 [PATCH 1/3] powerpc/uaccess: Don't use "m<>" constraint with GCC 4.9 Christophe Leroy
2020-10-19 12:12 ` [PATCH 2/3] powerpc: Fix incorrect stw{, ux, u, x} instructions in __set_pte_at Christophe Leroy
2020-10-19 20:14 ` Segher Boessenkool
2020-10-19 12:12 ` [PATCH 3/3] powerpc: Fix pre-update addressing in inline assembly Christophe Leroy
2020-10-19 15:35 ` kernel test robot
2020-10-19 18:23 ` Christophe Leroy
2020-10-19 20:24 ` Segher Boessenkool [this message]
2020-10-20 7:44 ` Christophe Leroy
2020-10-20 11:51 ` Segher Boessenkool
2020-10-19 20:10 ` [PATCH 1/3] powerpc/uaccess: Don't use "m<>" constraint with GCC 4.9 Segher Boessenkool
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