Re: [PATCH] mtd: ubi: avoid expensive do_div() on 32-bit machines

[Arnd Bergmann]

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.

     Arnd