From: Jisheng Zhang <jszhang@kernel.org>
To: Andreas Schwab <schwab@suse.de>
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 21:12:34 +0800 [thread overview]
Message-ID: <ZnwTwnSsnZ8Td9GZ@xhacker> (raw)
In-Reply-To: <mvmikxvonjh.fsf@suse.de>
On Wed, Jun 26, 2024 at 03:12:50PM +0200, Andreas Schwab wrote:
> 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).
Hi Andreas,
I compared tens of __put_user() caller's generated code between orig
version and patched version, they are the same. Sure maybe this is
not enough.
But your explanation can be applied to x86 and arm64 __put_user()
implementations, asm is also writing, then why there's no output
constraints there?(see the other two emails)? Could you please help
me to understand the tricky points?
Thanks in advance
next prev parent reply other threads:[~2024-06-26 13:26 UTC|newest]
Thread overview: 32+ 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 ` [PATCH 1/4] riscv: implement user_access_begin and families Jisheng Zhang
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 5:54 ` Arnd Bergmann
2024-06-26 12:32 ` Jisheng Zhang
2024-06-26 12:49 ` Jisheng Zhang
2024-06-26 13:18 ` Jisheng Zhang
2024-06-26 13:35 ` Andreas Schwab
2024-06-26 13:54 ` Jisheng Zhang
2024-06-26 13:12 ` Andreas Schwab
2024-06-26 13:12 ` Jisheng Zhang [this message]
2024-06-26 14:25 ` Arnd Bergmann
2024-06-26 16:02 ` Jisheng Zhang
2024-06-27 6:46 ` Arnd Bergmann
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
2024-07-05 2:22 ` 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
2024-07-05 4:13 ` kernel test robot
2024-06-25 7:21 ` [PATCH 0/4] riscv: uaccess: optimizations Arnd Bergmann
2024-06-25 18:12 ` Linus Torvalds
2024-06-26 13:04 ` Jisheng Zhang
2024-06-30 16:59 ` Linus Torvalds
2024-07-05 11:25 ` Will Deacon
2024-07-05 17:58 ` Linus Torvalds
2024-07-08 13:52 ` Will Deacon
2024-07-08 15:30 ` Mark Rutland
2024-07-23 14:16 ` Will Deacon
2024-07-08 15:21 ` Mark Rutland
2024-07-24 22:57 ` Palmer Dabbelt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ZnwTwnSsnZ8Td9GZ@xhacker \
--to=jszhang@kernel.org \
--cc=aou@eecs.berkeley.edu \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=palmer@dabbelt.com \
--cc=paul.walmsley@sifive.com \
--cc=schwab@suse.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox