From: Andreas Schwab <schwab@suse.de>
To: Jisheng Zhang <jszhang@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] riscv: uaccess: use input constraints for ptr of __put_user
Date: Wed, 26 Jun 2024 15:12:50 +0200 [thread overview]
Message-ID: <mvmikxvonjh.fsf@suse.de> (raw)
In-Reply-To: <20240625040500.1788-3-jszhang@kernel.org> (Jisheng Zhang's message of "Tue, 25 Jun 2024 12:04:58 +0800")
On Jun 25 2024, Jisheng Zhang wrote:
> I believe the output constraints "=m" is not necessary, because
> the instruction itself is "write", we don't need the compiler
> to "write" for us.
No, this is backwards. Being an output operand means that the *asm* is
writing to it, and the compiler can read the value from there afterwards
(and the previous value is dead before the asm).
--
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."
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WARNING: multiple messages have this Message-ID (diff)
From: Andreas Schwab <schwab@suse.de>
To: Jisheng Zhang <jszhang@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] riscv: uaccess: use input constraints for ptr of __put_user
Date: Wed, 26 Jun 2024 15:12:50 +0200 [thread overview]
Message-ID: <mvmikxvonjh.fsf@suse.de> (raw)
In-Reply-To: <20240625040500.1788-3-jszhang@kernel.org> (Jisheng Zhang's message of "Tue, 25 Jun 2024 12:04:58 +0800")
On Jun 25 2024, Jisheng Zhang wrote:
> I believe the output constraints "=m" is not necessary, because
> the instruction itself is "write", we don't need the compiler
> to "write" for us.
No, this is backwards. Being an output operand means that the *asm* is
writing to it, and the compiler can read the value from there afterwards
(and the previous value is dead before the asm).
--
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."
next prev parent reply other threads:[~2024-06-26 13:13 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-25 4:04 [PATCH 0/4] riscv: uaccess: optimizations Jisheng Zhang
2024-06-25 4:04 ` Jisheng Zhang
2024-06-25 4:04 ` [PATCH 1/4] riscv: implement user_access_begin and families Jisheng Zhang
2024-06-25 4:04 ` Jisheng Zhang
2024-06-26 23:38 ` Cyril Bur
2024-06-26 23:38 ` Cyril Bur
2024-06-25 4:04 ` [PATCH 2/4] riscv: uaccess: use input constraints for ptr of __put_user Jisheng Zhang
2024-06-25 4:04 ` Jisheng Zhang
2024-06-25 5:54 ` Arnd Bergmann
2024-06-25 5:54 ` Arnd Bergmann
2024-06-26 12:32 ` Jisheng Zhang
2024-06-26 12:32 ` Jisheng Zhang
2024-06-26 12:49 ` Jisheng Zhang
2024-06-26 12:49 ` Jisheng Zhang
2024-06-26 13:18 ` Jisheng Zhang
2024-06-26 13:18 ` Jisheng Zhang
2024-06-26 13:35 ` Andreas Schwab
2024-06-26 13:35 ` Andreas Schwab
2024-06-26 13:54 ` Jisheng Zhang
2024-06-26 13:54 ` Jisheng Zhang
2024-06-26 13:12 ` Andreas Schwab [this message]
2024-06-26 13:12 ` Andreas Schwab
2024-06-26 13:12 ` Jisheng Zhang
2024-06-26 13:12 ` Jisheng Zhang
2024-06-26 14:25 ` Arnd Bergmann
2024-06-26 14:25 ` Arnd Bergmann
2024-06-26 16:02 ` Jisheng Zhang
2024-06-26 16:02 ` Jisheng Zhang
2024-06-27 6:46 ` Arnd Bergmann
2024-06-27 6:46 ` Arnd Bergmann
2024-06-28 15:36 ` David Laight
2024-06-28 15:36 ` David Laight
2024-06-25 4:04 ` [PATCH 3/4] riscv: uaccess: use 'asm goto' for put_user() Jisheng Zhang
2024-06-25 4:04 ` Jisheng Zhang
2024-07-05 2:22 ` kernel test robot
2024-07-05 2:22 ` kernel test robot
2024-07-06 0:02 ` kernel test robot
2024-07-06 0:02 ` kernel test robot
2024-06-25 4:05 ` [PATCH 4/4] riscv: uaccess: use 'asm goto output' for get_user Jisheng Zhang
2024-06-25 4:05 ` Jisheng Zhang
2024-07-05 4:13 ` kernel test robot
2024-07-05 4:13 ` kernel test robot
2024-06-25 7:21 ` [PATCH 0/4] riscv: uaccess: optimizations Arnd Bergmann
2024-06-25 7:21 ` Arnd Bergmann
2024-06-25 18:12 ` Linus Torvalds
2024-06-25 18:12 ` Linus Torvalds
2024-06-26 13:04 ` Jisheng Zhang
2024-06-26 13:04 ` Jisheng Zhang
2024-06-30 16:59 ` Linus Torvalds
2024-06-30 16:59 ` Linus Torvalds
2024-07-05 11:25 ` Will Deacon
2024-07-05 11:25 ` Will Deacon
2024-07-05 17:58 ` Linus Torvalds
2024-07-05 17:58 ` Linus Torvalds
2024-07-08 13:52 ` Will Deacon
2024-07-08 13:52 ` Will Deacon
2024-07-08 15:30 ` Mark Rutland
2024-07-08 15:30 ` Mark Rutland
2024-07-23 14:16 ` Will Deacon
2024-07-23 14:16 ` Will Deacon
2024-07-08 15:21 ` Mark Rutland
2024-07-08 15:21 ` Mark Rutland
2024-07-24 22:57 ` Palmer Dabbelt
2024-07-24 22:57 ` Palmer Dabbelt
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