Re: [PATCH v3] LoongArch: add addr_global attribute

[Lulu Cheng <chenglulu@loongson.cn>]

在 2022/7/30 上午1:17, Xi Ruoyao 写道:
> Change v2 to v3:
> - Disable section anchor for addr_global symbols.
> - Use -O2 in test to make sure section anchor is disabled.
>
> --
>
> Background:
> https://lore.kernel.org/loongarch/d7670b60-2782-4642-995b-7baa01779a66@loongson.cn/T/#e1d47e2fe185f2e2be8fdc0784f0db2f644119379
>
> Question:  Do you have a better name than "addr_global"?

I think the name can be changed to "get_through_got".What do you think of it?

>
> Alternatives:
>
> 1. Just use "-mno-explicit-relocs -mla-local-with-abs" for kernel
> modules.  It's stupid IMO.
> 2. Implement a "-maddress-local-with-got" option for GCC and use it for
> kernel modules.  It seems too overkill: we might create many unnecessary
> GOT entries.
> 3. For all variables with a section attribute, consider it global.  It
> may make sense, but I just checked x86_64 and riscv and they don't do
> this.
> 4. Implement -mcmodel=extreme and use it for kernel modules.  To me
> "extreme" seems really too extreme.
> 5. More hacks in kernel. (Convert relocations against .data..percpu with
> objtool?  But objtool is not even implemented for LoongArch yet.)
>
> Note: I'll be mostly AFK in the following week.  My attempt to finish
> the kernel support for new relocs before going AFK now failed miserably
> :(.
>
> -- >8 --
>
> A linker script and/or a section attribute may locate a local object in
> some way unexpected by the code model, leading to a link failure.  This
> happens when the Linux kernel loads a module with "local" per-CPU
> variables.
>
> Add an attribute to explicitly mark an variable with the address
> unlimited by the code model so we would be able to work around such
> problems.
>

Others I think are ok.