undefined reference to __atomic_load_4 on Rust versions newer than nightly-2022-08-12

[Lymia]

Hi. I'm a previous developer on the abandoned gba crate, and I've been wanting to port some of the modules I wrote for that (e.g. the flash save code) to the agb crate. I have a problem that I don't personally know where to begin debugging.

When I try to run just build-roms, I get the following error:

+ cargo build --release --target thumbv4t-none-eabi
   Compiling the-purple-night v0.1.0 (/home/aino/data/projects/crates/agb/examples/the-purple-night)
error: linking with `arm-none-eabi-ld` failed: exit status: 1
  |
  = note: "arm-none-eabi-ld" "/tmp/rustconD6i5/symbols.o" "/home/aino/data/projects/crates/agb/target/thumbv4t-none-eabi/release/deps/the_purple_night-b8ba75b4faeb98b5.the_purple_night.62ef94b1-cgu.0.rcgu.o" "--as-needed" "-L" "/home/aino/data/projects/crates/agb/target/thumbv4t-none-eabi/release/deps" "-L" "/home/aino/data/projects/crates/agb/target/release/deps" "-L" "/home/aino/data/projects/crates/agb/target/thumbv4t-none-eabi/release/build/agb-5ac9222d9e5ae2ce/out" "-L" "/home/aino/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/thumbv4t-none-eabi/lib" "--start-group" "--end-group" "-Bstatic" "/home/aino/data/projects/crates/agb/target/thumbv4t-none-eabi/release/deps/libcompiler_builtins-3b5407e0191965f8.rlib" "-Bdynamic" "--eh-frame-hdr" "-znoexecstack" "-L" "/home/aino/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/thumbv4t-none-eabi/lib" "-o" "/home/aino/data/projects/crates/agb/target/thumbv4t-none-eabi/release/deps/the_purple_night-b8ba75b4faeb98b5" "--gc-sections" "-O1" "-Tgba.ld"
  = note: arm-none-eabi-ld: /home/aino/data/projects/crates/agb/target/thumbv4t-none-eabi/release/deps/libcompiler_builtins-3b5407e0191965f8.rlib(compiler_builtins-3b5407e0191965f8.compiler_builtins.01837706-cgu.0.rcgu.o): in function `compiler_builtins::mem::memmove':
          compiler_builtins.01837706-cgu.0:(.text._ZN17compiler_builtins3mem7memmove17h382c238f4a6131d3E+0x66): undefined reference to `__atomic_load_4'
          arm-none-eabi-ld: compiler_builtins.01837706-cgu.0:(.text._ZN17compiler_builtins3mem7memmove17h382c238f4a6131d3E+0xe8): undefined reference to `__atomic_load_4'
          
  = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

error: could not compile `the-purple-night` due to previous error
error: Recipe `_build-rom` failed with exit code 101
error: Recipe `build-roms` failed on line 51 with exit code 101

I can work around the error for now by providing a definition for this function in the agb crate, but that is far from an ideal solution. I would very much appreciate help with this problem.

I am running latest rust nightly, and have a updated system.

[Lymia]

Best I can tell, this may be a regression in newer nightly versions? It compiles just fine on nightly-2022-08-02. Use the RUSTUP_TOOLCHAIN="nightly-2022-08-12" environment variable, I guess.

rustc issue: rust-lang/rust#100619
agb issue: #297