riscv32i: `__atomic_load_4` is referenced in libcompiler_builtins

[xobs]

The atomic function __atomic_load_4 is getting referenced somehow in libcompiler_builtins. I'm not sure how to trigger the linker issue, however we've started running into it on CI:

https://ci.betrusted.io/job/betrusted-ec-fw/117/console

22:12:25   = note: "rust-lld" "-flavor" "gnu" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/deps/sw-d670ba951948c61d.sw.eb99c8ab-cgu.0.rcgu.o" "--as-needed" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/deps" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/release/deps" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/build/sw-5aeb8f44ae52ec32/out" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/build/riscv-3af36cb162907fdc/out" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/build/riscv-rt-10c1a68888f3c71a/out" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/build/riscv-rt-10c1a68888f3c71a/out" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/build/wfx_sys-435e2ecbf8d2b6bf/out" "-L" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/build/vexriscv-ef796b3ba7eaa702/out" "-L" "/var/lib/jenkins/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/riscv32i-unknown-none-elf/lib" "-Bstatic" "/tmp/rustct4qDCB/libriscv_rt-23b03c226d1df842.rlib" "/tmp/rustct4qDCB/libvexriscv-abccfdbcb773d5aa.rlib" "/tmp/rustct4qDCB/libwfx_sys-b5ebfbb5dde2c0d0.rlib" "/tmp/rustct4qDCB/libriscv-5c53201af539b932.rlib" "/var/lib/jenkins/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/riscv32i-unknown-none-elf/lib/libcompiler_builtins-6af234694b8e479b.rlib" "-Bdynamic" "-znoexecstack" "-L" "/var/lib/jenkins/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/riscv32i-unknown-none-elf/lib" "-o" "/var/lib/jenkins/workspace/betrusted-ec/target/riscv32i-unknown-none-elf/release/deps/sw-d670ba951948c61d" "--gc-sections" "-Tmemory.x" "-Tlink.x" "-Map=betrusted-ec.map"
22:12:25   = note: rust-lld: error: undefined symbol: __atomic_load_4
22:12:25           >>> referenced by uint_macros.rs:1222 (/rustc/02072b482a8b5357f7fb5e5637444ae30e423c40/library/core/src/num/uint_macros.rs:1222)
22:12:25           >>>               compiler_builtins-6af234694b8e479b.compiler_builtins.3786cd3d-cgu.96.rcgu.o:(memcpy) in archive /var/lib/jenkins/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/riscv32i-unknown-none-elf/lib/libcompiler_builtins-6af234694b8e479b.rlib

Version it worked on

It used to work on Rust 1.57.1, however it has broken on Rust 1.58.0.

[xobs]

More information: This symbol is clearly present in the object files. Inside libcompiler_builtins-6af234694b8e479b.rlib there is an object file compiler_builtins-6af234694b8e479b.compiler_builtins.3786cd3d-cgu.96.rcgu.o. This contains references to this function, even though it doesn't appear to actually be used:

riscv64-unknown-elf-readelf.exe -a .\compiler_builtins-6af234694b8e479b.compiler_builtins.3786cd3d-cgu.96.rcgu.o | rg __atomic
0000009c  00017913 R_RISCV_CALL_PLT  00000000   __atomic_load_4 + 0
000000b4  00017913 R_RISCV_CALL_PLT  00000000   __atomic_load_4 + 0
00000158  00017913 R_RISCV_CALL_PLT  00000000   __atomic_load_4 + 0
   377: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __atomic_load_4

Note that I previously opened #85736, however this seems to be different because it doesn't involve LTO and I can tell that libcompiler_builtins is actually getting shipped with these references in place.

[xobs]

A workaround we've done to get it to at least compile on 1.58.0 is to add this code somewhere in the project:

#[no_mangle]
pub fn __atomic_load_4(arg: *const usize, _ordering: usize) -> usize {
    unsafe { *arg }
}

[Amanieu]

This is fixed by rust-lang/compiler-builtins@e0187f1 which is included in compiler-builtins version 0.1.54. However Rust 1.58.0 uses compiler_builtins 0.1.53.

[apiraino]

Nominating for stable backport as per Zulip discussion

@rustbot label +stable-nominated

[apiraino]

Stable backport of rust-lang/compiler-builtins@e0187f1 approved as per compiler team on Zulip

@rustbot label +stable-accepted