Re: [musl] Draft riscv64 TLSDESC implementation

[Fangrui Song <i@maskray.me>]

On Sun, Jan 21, 2024 at 2:28 PM Rich Felker <dalias@libc.org> wrote:
>
> On Tue, Aug 22, 2023 at 01:38:21PM -0400, Rich Felker wrote:
> > The psABI work is not finalized, but based on the current status of
> > https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/373, I think
> > the attached is a valid (but untested) implementation of TLSDESC for
> > riscv64. Actually activating it requires also adding the relocation
> > type macro to riscv64/reloc.h.
> >
> > If any rv folks could look it over and make sure I haven't made any
> > stupid asm errors or missed any obvious optimizations, that would help
> > to quickly get this merged when the psABI is finalized.
> >
> > Rich
>
> > .text
> > .global __tlsdesc_static
> > .hidden __tlsdesc_static
> > .type __tlsdesc_static,%function
> > __tlsdesc_static:
> >       ld a0,8(a0)
> >       jr t0
> >
> > .global __tlsdesc_dynamic
> > .hidden __tlsdesc_dynamic
> > .type __tlsdesc_dynamic,%function
> > __tlsdesc_dynamic:
> >       add sp,sp,-8
> >       sd t1,(sp)
> >       sd t2,8(sp)
> >
> >       ld t2,-8(tp) # t2=dtv
> >
> >       ld a0,8(a0)  # a0=&{modidx,off}
> >       ld t1,8(a0)  # t1=off
> >       ld a0,(a0)   # a0=modidx
> >       sll a0,a0,3  # a0=8*modidx
> >
> >       add a0,a0,t2 # a0=dtv+8*modidx
> >       ld a0,(a0)   # a0=dtv[modidx]
> >       add a0,a0,t1 # a0=dtv[modidx]+off
> >       sub a0,a0,tp # a0=dtv[modidx]+off-tp
> >
> >       ld t1,(sp)
> >       ld t2,8(sp)
> >       add sp,sp,8
> >       jr t0
>
> Any feedback on this? Offhand, it looks like adjusting sp by 8 is
> wrong and that should be 16. Anything else? Does anyone have recent
> enough tooling to test this?

Tatsuyuki, do you have links to the latest version of
gcc/binutils/glibc patches?
Downloading patches from these mailing lists is probably a large
hurdle for many users, so having the relevant repositories online may
help.

mold has implemented RISC-V TLSDESC.

On the LLVM side, I have reviewed
https://github.com/llvm/llvm-project/pull/66915 and am waiting for it
to land, before I can check the lld status.