public inbox for linux-mtd@lists.infradead.org
 help / color / mirror / Atom feed
From: Zhihao Cheng <chengzhihao1@huawei.com>
To: Arnd Bergmann <arnd@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Richard Weinberger <richard@nod.at>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Daniel Golle <daniel@makrotopia.org>
Cc: <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mtd: ubi: avoid expensive do_div() on 32-bit machines
Date: Wed, 13 Mar 2024 21:29:38 +0800	[thread overview]
Message-ID: <610231c3-c3ee-e543-1a8a-8e1098ee6a7c@huawei.com> (raw)
In-Reply-To: <b08aaae4-8c69-47eb-9658-5f3f5c8e4056@app.fastmail.com>

在 2024/3/13 20:21, Arnd Bergmann 写道:
> On Wed, Mar 13, 2024, at 13:10, Zhihao Cheng wrote:
>> 在 2024/3/13 19:53, Arnd Bergmann 写道:
>>> On Wed, Mar 13, 2024, at 12:29, Zhihao Cheng wrote:
>>>
>>> The way it usually goes is that someone adds an open-coded
>>> 64-bit division that causes a link failure, which prompts
>> I'm a little confused, what kind of link failure? Could you show an example?
> 
> The open-coded 64-bit division without using do_div() shows up as
> 
> x86_64-linux-ld: drivers/mtd/ubi/nvmem.o: in function `ubi_nvmem_reg_read':
> nvmem.c:(.text+0x10a): undefined reference to `__umoddi3'
> x86_64-linux-ld: nvmem.c:(.text+0x11f): undefined reference to `__udivdi3'
> x86_64-linux-ld: drivers/mtd/ubi/nvmem.o: in function `ubi_nvmem_reg_read.cold':
> nvmem.c:(.text.unlikely+0x2d): undefined reference to `__umoddi3'
>  > The idea is that gcc expects __umoddi3 to be provided by libgcc,
> but Linux intentionally leaves it out in order to catch accidental
> 64-bit divisions.
> 

Thanks for explaination, which means that do_div is used for 64-bit 
division to solve the link failure caused by missed libgcc. Since 
parameter 'from' is u32, there is no need to invoke do_div on a 32-bit 
platform, you just want to stop the wasting behavior on a 32-bit 
platform. Do I understand right?

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

  reply	other threads:[~2024-03-13 13:30 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-13  8:46 [PATCH] mtd: ubi: avoid expensive do_div() on 32-bit machines Arnd Bergmann
2024-03-13 11:29 ` Zhihao Cheng
2024-03-13 11:53   ` Arnd Bergmann
2024-03-13 12:10     ` Zhihao Cheng
2024-03-13 12:21       ` Arnd Bergmann
2024-03-13 13:29         ` Zhihao Cheng [this message]
2024-03-13 13:39           ` Arnd Bergmann
2024-03-13 13:43             ` Zhihao Cheng
2024-03-13 13:51               ` Arnd Bergmann
2024-03-13 13:41 ` Zhihao Cheng

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=610231c3-c3ee-e543-1a8a-8e1098ee6a7c@huawei.com \
    --to=chengzhihao1@huawei.com \
    --cc=arnd@arndb.de \
    --cc=arnd@kernel.org \
    --cc=daniel@makrotopia.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mtd@lists.infradead.org \
    --cc=miquel.raynal@bootlin.com \
    --cc=richard@nod.at \
    --cc=vigneshr@ti.com \
    /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