Re: global pointer gets overwritten with dlopen(3) on RISC-V

[Florian Weimer <fweimer@redhat.com>]

* Fangrui Song:

>>1. Make -mno-relax the default for ld(1) (on Linux?). We have no
>>benchmarks whatsoever, but global variables aren't very popular in
>>application code these days and the gp register allows access to a
>>single memory page (4kB) only. No big deal really.
>
> I do agree that --no-relax-gp is a sensible default choice for GNU ld.
> https://maskray.me/blog/2021-03-14-the-dark-side-of-riscv-linker-relaxation#global-pointer-relaxation
>
> Perhaps you can start a separate topic on binutils? :)
>
> According to a doc from SiFive about -static -mcpu=sifive-u74 builds,
> https://docs.google.com/spreadsheets/d/14V7cPbyc80AcGHzsMaw9hYb232dzRbGCmTApnxj-SpU/edit#gid=0
> global pointer relaxation saves at best 0.5% size (I guess that refers
> to .text. If we count all allocable sections, the percentage is likely
> even smaller.)

For a mature toolchain, 0.5% in code size reduction would be *a lot*,
so I wouldn't dismiss that.

Do we have a reproducer?  Is the issue actually about gp relaxation for
the main executable?

Thanks,
Florian