Messages in this thread | | | Subject | Re: [PATCH] mtd: ubi: avoid expensive do_div() on 32-bit machines | From | Zhihao Cheng <> | Date | Wed, 13 Mar 2024 21:29:38 +0800 |
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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?
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