Stream: git-wasmtime

Topic: wasmtime / issue #4546 cranelift: Add COFF TLS Support

Wasmtime GitHub notifications bot (Jul 28 2022 at 14:16):

bjorn3 commented on issue #4546:

Do we need to mark the gs register as used?

The gs register is not allocatable by regalloc, so it doesn't need to be marked as usable.

Wasmtime GitHub notifications bot (Jul 28 2022 at 14:31):

bjorn3 commented on issue #4546:

Thanks a lot for working on this!

Wasmtime GitHub notifications bot (Jul 28 2022 at 14:34):

bjorn3 commented on issue #4546:

#![feature(thread_local)]                                                                                                                          1 ↵ bjorn@laptopbjorn-lenovo

use std::cell::Cell;

#[thread_local]
pub static FOO: Cell<u8> = Cell::new(42);
pub static mut BAR: u8 = 43;
pub fn get_foo() -> u8 {
    FOO.get()
}

pub fn set_foo(foo: u8) {
    FOO.set(foo)
}' | rustc +nightly --target x86_64-pc-windows-msvc --emit obj - --crate-type lib -O

produces an object file for which objdump -dr gives:

rust_out.o:     file format pe-x86-64


Disassembly of section .text:

0000000000000000 <_ZN8rust_out7get_foo17h9e4ed845564f4123E>:
   0:   8b 05 00 00 00 00       mov    0x0(%rip),%eax        # 6 <_ZN8rust_out7get_foo17h9e4ed845564f4123E+0x6>
                        2: R_X86_64_PC32        _tls_index
   6:   65 48 8b 0c 25 58 00    mov    %gs:0x58,%rcx
   d:   00 00
   f:   48 8b 04 c1             mov    (%rcx,%rax,8),%rax
  13:   8a 80 00 00 00 00       mov    0x0(%rax),%al
                        15: secrel32    _ZN8rust_out3FOO17he424d0489633cb80E
  19:   c3                      retq

Disassembly of section .text:

0000000000000000 <_ZN8rust_out7set_foo17hb5fb9735547d2b58E>:
   0:   8b 05 00 00 00 00       mov    0x0(%rip),%eax        # 6 <_ZN8rust_out7set_foo17hb5fb9735547d2b58E+0x6>
                        2: R_X86_64_PC32        _tls_index
   6:   65 48 8b 14 25 58 00    mov    %gs:0x58,%rdx
   d:   00 00
   f:   48 8b 04 c2             mov    (%rdx,%rax,8),%rax
  13:   88 88 00 00 00 00       mov    %cl,0x0(%rax)
                        15: secrel32    _ZN8rust_out3FOO17he424d0489633cb80E
  19:   c3                      retq

and objdump --syms:

rust_out.o:     file format pe-x86-64

SYMBOL TABLE:
[  0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .text
AUX scnlen 0x0 nreloc 0 nlnno 0 checksum 0x0 assoc 1 comdat 0
[  2](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .data
AUX scnlen 0x0 nreloc 0 nlnno 0 checksum 0x0 assoc 2 comdat 0
[  4](sec  3)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .bss
AUX scnlen 0x0 nreloc 0 nlnno 0 checksum 0x0 assoc 3 comdat 0
[  6](sec  4)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .text
AUX scnlen 0x1a nreloc 2 nlnno 0 checksum 0xa84d5eee assoc 4 comdat 1
[  8](sec  4)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 _ZN8rust_out7get_foo17h9e4ed845564f4123E
[  9](sec  5)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .text
AUX scnlen 0x1a nreloc 2 nlnno 0 checksum 0xac4f1caa assoc 5 comdat 1
[ 11](sec  5)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 _ZN8rust_out7set_foo17hb5fb9735547d2b58E
[ 12](sec  6)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .tls$
AUX scnlen 0x1 nreloc 0 nlnno 0 checksum 0xdbbbc9d6 assoc 6 comdat 1
[ 14](sec  6)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000000000000 _ZN8rust_out3FOO17he424d0489633cb80E
[ 15](sec  7)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .data
AUX scnlen 0x1 nreloc 0 nlnno 0 checksum 0xacbcf940 assoc 7 comdat 1
[ 17](sec  7)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000000000000 _ZN8rust_out3BAR17hab28e85eef212a9aE
[ 18](sec  8)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .data
AUX scnlen 0x8 nreloc 1 nlnno 0 checksum 0x0 assoc 8 comdat 1
[ 20](sec  8)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000000000000 __imp__ZN8rust_out3FOO17he424d0489633cb80E
[ 21](sec  9)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x0000000000000000 .data
AUX scnlen 0x8 nreloc 1 nlnno 0 checksum 0x0 assoc 9 comdat 1
[ 23](sec  9)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000000000000 __imp__ZN8rust_out3BAR17hab28e85eef212a9aE
[ 24](sec -1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x0000000000000000 @feat.00
[ 25](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000000000000 _tls_index
[ 26](sec -2)(fl 0x00)(ty   0)(scl 103) (nx 2) 0x0000000000000000 rust_out.cb515bd7-
File
File

Wasmtime GitHub notifications bot (Jul 28 2022 at 17:34):

bjorn3 commented on issue #4546:

I managed to run a small tls example on windows! :tada:

#![feature(thread_local)]
use std::cell::Cell;
#[thread_local]
static FOO: Cell<u8> = Cell::new(42);
fn main() {
    assert_eq!(FOO.get(), 42);
    std::thread::spawn(|| {
        FOO.set(43);
        assert_eq!(FOO.get(), 43);
    }).join();
    assert_eq!(FOO.get(), 42);
}

Wasmtime GitHub notifications bot (Jul 28 2022 at 17:39):

afonso360 commented on issue #4546:

I managed to run a small tls example on windows! :tada:

That's really cool! I'm going to try an compile cg_clif with this, to see where it breaks next. I suspect we don't have a very complete TLS implementation.

Wasmtime GitHub notifications bot (Jul 28 2022 at 17:53):

afonso360 edited a comment on issue #4546:

I managed to run a small tls example on windows! :tada:

That's really cool! I'm going to try and compile cg_clif with this, to see where it breaks next. I suspect we don't have a very complete TLS implementation.

Wasmtime GitHub notifications bot (Aug 10 2022 at 20:26):

afonso360 commented on issue #4546:

Rebased this on top of main. I've also renamed the TlsIndex symbol to CoffTlsIndex.

With this rebase we've also lost the lookup function. But we can add it later if we need it in the JIT, is this okay @bjorn3 ?

Wasmtime GitHub notifications bot (Aug 10 2022 at 20:28):

afonso360 edited a comment on issue #4546:

Rebased this on top of main. I've also renamed the TlsIndex symbol to CoffTlsIndex.

With this rebase we've also lost the lookup function. But we can add it later when we need it in the JIT, is this okay @bjorn3 ?

Wasmtime GitHub notifications bot (Aug 10 2022 at 20:29):

bjorn3 commented on issue #4546:

Fine with me.

Wasmtime GitHub notifications bot (Aug 11 2022 at 00:46):

jameysharp commented on issue #4546:

Do you both feel this is ready for merge, then? I've glanced over it and it looks reasonable to me, but I'm not at all familiar with how thread-local storage works on any platform.

Wasmtime GitHub notifications bot (Aug 11 2022 at 05:56):

afonso360 commented on issue #4546:

Yes, this should be ready to merge!

Last updated: Dec 06 2025 at 06:05 UTC