[RISCV] Use lld as the default linker; Enable C extension; Add riscv32imc-unknown-none-elf target by dvc94ch · Pull Request #53822 · rust-lang/rust (original) (raw)

Ah yes, loads and stores up to pointer width should be atomic.

LLVM says otherwise:

#![no_std]

use core::sync::atomic::{Ordering, AtomicUsize};

#[no_mangle] pub fn foo(x: &AtomicUsize) -> usize { x.load(Ordering::SeqCst) }

IMAC

$ $(rustc +nightly --print sysroot)/bin/llvm-objdump -d target/riscv32imac-unknown-none-elf/release/libfoo.rlib

target/riscv32imac-unknown-none-elf/release/libfoo.rlib(foo-5c3d4a3cd43899d6.foo.axz7xdhy-cgu.0.rcgu.o): file format ELF32-riscv

Disassembly of section .text.foo: foo: 0: 0f 00 30 03 fence rw, rw 4: 08 41 lw a0, 0(a0) 6: 0f 00 30 02 fence r, rw a: 82 80 ret

$ $(rustc +nightly --print sysroot)/bin/llvm-nm target/riscv32imac-unknown-none-elf/release/libfoo.rlib

foo-5c3d4a3cd43899d6.foo.axz7xdhy-cgu.0.rcgu.o: 00000000 T foo

IMC

$ $(rustc +nightly --print sysroot)/bin/llvm-objdump -d target/riscv32imc-unknown-none-elf/release/libfoo.rlib target/riscv32imc-unknown-none-elf/release/libfoo.rlib(foo-5c3d4a3cd43899d6.foo.axz7xdhy-cgu.0.rcgu.o): file format ELF32-riscv

Disassembly of section .text.foo: foo: 0: 41 11 addi sp, sp, -16 2: 06 c6 sw ra, 12(sp) 4: 95 45 addi a1, zero, 5 6: 97 00 00 00 auipc ra, 0 a: e7 80 00 00 jalr ra e: b2 40 lw ra, 12(sp) 10: 41 01 addi sp, sp, 16 12: 82 80 ret

$(rustc +nightly --print sysroot)/bin/llvm-nm target/riscv32imc-unknown-none-elf/release/libfoo.rlib

foo-5c3d4a3cd43899d6.foo.axz7xdhy-cgu.0.rcgu.o: U __atomic_load_4 00000000 T foo

So the IMC target should have max_atomic_width: None.

P.S. Could you push new commits rather than rewriting the existing ones? New commits are easier to review.