fmodf symbol missing on i686-unknown-uefi since nightly-2024-07-30

[YtvwlD]

I'm using (a library that uses) floating point math on UEFI targets. For quite some time, fmodf was missing on i686-unknown-uefi (but available on x86_64-unknown-uefi). Since rust-lang/compiler-builtins#490, rust-lang/compiler-builtins#553, #119019, this was available, but it's gone missing a few days ago. I suspect it's due to this update to compiler-builtins, but I have not confirmed it.

Code

This is a minimal (but nonsensical) example code that compiles:

#![no_std]
#![no_main]

extern "C" { fn fmodf(); }

use core::panic::PanicInfo;

#[panic_handler]
fn panic(_: &PanicInfo) -> ! {
        loop {}
}

#[no_mangle]
pub fn efi_main() {
        unsafe { fmodf(); }
}

I expected to see this happen: The code should should compile.

Instead, this happened:

$ cargo build --target i686-unknown-uefi
   Compiling foo v0.1.0 (/tmp/tmp.4CIirv1HGb/foo)
error: linking with `rust-lld` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/niklas/.local/bin:/home/niklas/.cargo/bin:/home/niklas/.gopath/bin:/home/niklas/bin:/snap/bin:/home/niklas/.local/bin:/home/niklas/.cargo/bin:/home/niklas/.gopath/bin:/home/niklas/bin:/snap/bin" VSLANG="1033" "rust-lld" "-flavor" "link" "/NOLOGO" "/entry:efi_main" "/subsystem:efi_application" "/tmp/rustckZUbYQ/symbols.o" "/tmp/tmp.4CIirv1HGb/foo/target/i686-unknown-uefi/debug/deps/foo-b50eac0687aac12d.21wnwtpp1uzembi52ejbydrsb.rcgu.o" "/LIBPATH:/tmp/tmp.4CIirv1HGb/foo/target/i686-unknown-uefi/debug/deps" "/LIBPATH:/tmp/tmp.4CIirv1HGb/foo/target/debug/deps" "/LIBPATH:/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib" "/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/librustc_std_workspace_core-26a6383b0ec19675.rlib" "/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/libcore-70427371e67f0ba1.rlib" "/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/libcompiler_builtins-f2416250465866e5.rlib" "/NXCOMPAT" "/LIBPATH:/home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib" "/OUT:/tmp/tmp.4CIirv1HGb/foo/target/i686-unknown-uefi/debug/deps/foo-b50eac0687aac12d.efi" "/OPT:REF,NOICF" "/DEBUG" "/PDBALTPATH:%_PDB%" "/NODEFAULTLIB"
  = note: rust-lld: error: undefined symbol: _fmodf
          >>> referenced by /tmp/tmp.4CIirv1HGb/foo/src/main.rs:15
          >>>               /tmp/tmp.4CIirv1HGb/foo/target/i686-unknown-uefi/debug/deps/foo-b50eac0687aac12d.21wnwtpp1uzembi52ejbydrsb.rcgu.o:(_efi_main)
          

error: could not compile `foo` (bin "foo") due to 1 previous error

Version it worked on

It most recently worked on:

$ rustc --version --verbose
rustc 1.82.0-nightly (2cbbe8b8b 2024-07-28)
binary: rustc
commit-hash: 2cbbe8b8bb2be672b14cf741a2f0ec24a49f3f0b
commit-date: 2024-07-28
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 18.1.7

Version with regression

$ rustc --version --verbose
rustc 1.82.0-nightly (612a33f20 2024-07-29)
binary: rustc
commit-hash: 612a33f20b9b2c27380edbc4b26a01433ed114bc
commit-date: 2024-07-29
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 18.1.7

Backtrace

There's no crash.

[tgross35]

Could you run nm -Cg /home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/libcompiler_builtins-f2416250465866e5.rlib | grep fmodf and post the output? The symbols should still be available, just as weak, so this should help confirm.

[YtvwlD]

$ LANG=C nm -Cg /home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/libcompiler_builtins-f2416250465866e5.rlib | grep fmodf
nm: compiler_builtins-f2416250465866e5.compiler_builtins.326ac9b642684df2-cgu.000.rcgu.o: no symbols
nm: compiler_builtins-f2416250465866e5.compiler_builtins.326ac9b642684df2-cgu.001.rcgu.o: no symbols
...

[tgross35]

Does it show up on the working version?

[YtvwlD]

No, I guess.

$ LANG=C nm -Cg /home/niklas/.rustup/toolchains/nightly-2024-07-29-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/libcompiler_builtins-b5d296eafb84defb.rlib | grep fmodf
nm: compiler_builtins-b5d296eafb84defb.compiler_builtins.b7ee1e4ea5a8642f-cgu.000.rcgu.o: no symbols
nm: compiler_builtins-b5d296eafb84defb.compiler_builtins.b7ee1e4ea5a8642f-cgu.001.rcgu.o: no symbols
...

[YtvwlD]

But it seems to be there, somehow:

$ LANG=C grep -r fmodf /home/niklas/.rustup/toolchains/nightly-2024-07-29-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/
grep: /home/niklas/.rustup/toolchains/nightly-2024-07-29-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/libcompiler_builtins-b5d296eafb84defb.rlib: binary file matches
$ LANG=C grep -r fmodf /home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/i686-unknown-uefi/lib/
$

[tgross35]

(edited the above comments to remove output noise)

[tgross35]

Thanks for looking into it. compiler_builtins recently had an update that should have made math symbols available on platforms that support it (Linux), but maybe in doing so it disabled the symbols completely on platforms that don't support it.

[YtvwlD]

It's still available on x86_64-unknown-uefi though:

$ LANG=C grep -r fmodf /home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-uefi/lib/
grep: /home/niklas/.rustup/toolchains/nightly-2024-07-30-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-uefi/lib/libcompiler_builtins-b761541e09399289.rlib: binary file matches
$ LANG=C grep -r fmodf /home/niklas/.rustup/toolchains/nightly-2024-07-29-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-uefi/lib/
grep: /home/niklas/.rustup/toolchains/nightly-2024-07-29-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-uefi/lib/libcompiler_builtins-3c95a63685c02bd4.rlib: binary file matches

[apiraino]

@YtvwlD I'm visiting this issue again. On current stable I cannot reproduce (unless I'm doing it wrong)

$ cargo build --target i686-unknown-uefi
   Compiling issue-128533 v0.1.0 (/home/me/tmp/issue-128533)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.67s

$ rustc --version --verbose
rustc 1.81.0 (eeb90cda1 2024-09-04)
binary: rustc
commit-hash: eeb90cda1969383f56a2637cbd3037bdf598841c
commit-date: 2024-09-04
host: x86_64-unknown-linux-gnu
release: 1.81.0
LLVM version: 18.1.7

can you confirm if it's fixed for you or you can still reproduce?

thanks