hexagon-unknown-none-elf cannot build core, "symbol 'fma' is already defined"

[saethlin]

In an empty #![no_std] Cargo project, run cargo +nightly build -Zbuild-std=core --target=hexagon-unknown-none-elf:

   Compiling compiler_builtins v0.1.123
   Compiling core v0.0.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling rustc-std-workspace-core v1.99.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling byteorder v1.5.0
   Compiling zerocopy v0.7.34
error: symbol 'fma' is already defined

error: could not compile `compiler_builtins` (lib) due to 1 previous error

Pinging target maintainer @androm3da (Nobody is expecting you to fix this, just a heads-up)

[androm3da]

Thanks for the heads up. I'll fix it.

[androm3da]

Oh, err ... if I can reproduce it. I tried using rustc 1.82.0-nightly (0d634185d 2024-08-29) and didn't see the issue, but maybe I didn't make the test case quite right? In my case I didn't end up seeing byteorder, zerocopy dependencies being built.

But I looked around a bit, could this have shown up in 7240da0? If so, it seems plenty old enough to have been in scope for this nightly, so now I'm puzzled why I wouldn't encounter the issue.

$ cat src/lib.rs 
#![no_std]

pub fn add(left: usize, right: usize) -> usize {
    left + right
}
brian@yueh:~/src/testit$ cargo +nightly build -Zbuild-std=core --target=hexagon-unknown-none-elf
   Compiling compiler_builtins v0.1.123
   Compiling core v0.0.0 (/home/brian/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling rustc-std-workspace-core v1.99.0 (/home/brian/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling testit v0.1.0 (/home/brian/src/testit)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 4.31s

[saethlin]

The zerocopy and byteorder were me looking at something else. Sorry about that.

But even if I remove them, I still get this error:

╭ ➜ ben@archlinux:/tmp/scratch
╰ ➤ cargo +nightly build -Zbuild-std=core --target=hexagon-unknown-none-elf
   Compiling compiler_builtins v0.1.123
   Compiling core v0.0.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling rustc-std-workspace-core v1.99.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling scratch v0.1.0 (/tmp/scratch)
error: symbol 'fma' is already defined

error: could not compile `compiler_builtins` (lib) due to 1 previous error
╭ ➜ ben@archlinux:/tmp/scratch
╰ ➤ rustc +nightly -vV
rustc 1.82.0-nightly (0d634185d 2024-08-29)
binary: rustc
commit-hash: 0d634185dfddefe09047881175f35c65d68dcff1
commit-date: 2024-08-29
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 19.1.0
╭ ➜ ben@archlinux:/tmp/scratch
╰ ➤ cat src/lib.rs 
#![no_std]
pub fn add(left: usize, right: usize) -> usize {
    left + right
}

[androm3da]

I'm not quite sure why I can't reproduce the problem. But maybe that's moot because it's clear that my contribution to compiler-builtins is wrong.

But even if I remove them, I still get this error:

You're right - I think this should fix it - rust-lang/compiler-builtins#682

[saethlin]

Like all things related to linkage, it looks like a codegen-units issue. Behold:

╭ ➜ ben@archlinux:/tmp/scratch
╰ ➤ cargo +nightly build -Zbuild-std=core --target=hexagon-unknown-none-elf
   Compiling compiler_builtins v0.1.123
   Compiling scratch v0.1.0 (/tmp/scratch)
error: symbol 'fma' is already defined

error: could not compile `compiler_builtins` (lib) due to 1 previous error
╭ ➜ ben@archlinux:/tmp/scratch
╰ ➤ RUSTFLAGS=-Ccodegen-units=1 cargo +nightly build -Zbuild-std=core --target=hexagon-unknown-none-elf
   Compiling core v0.0.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling compiler_builtins v0.1.123
   Compiling rustc-std-workspace-core v1.99.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling scratch v0.1.0 (/tmp/scratch)
error: symbol 'fma' is already defined

error: symbol 'fmin' is already defined

error: symbol 'fmax' is already defined

error: could not compile `compiler_builtins` (lib) due to 3 previous errors
warning: build failed, waiting for other jobs to finish...
╭ ➜ ben@archlinux:/tmp/scratch
╰ ➤ RUSTFLAGS=-Ccodegen-units=4096 cargo +nightly build -Zbuild-std=core --target=hexagon-unknown-none-elf
   Compiling core v0.0.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling compiler_builtins v0.1.123
   Compiling rustc-std-workspace-core v1.99.0 (/home/ben/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling scratch v0.1.0 (/tmp/scratch)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 4.80s

The standard library has a profile override for compiler_builtins which clearly isn't being applied here (the code says profile.release but you can get the same diagnostics as above if you add --release):

rust/library/Cargo.toml

Lines 14 to 25 in a7399ba

	[profile.release.package.compiler_builtins]
	# For compiler-builtins we always use a high number of codegen units.
	# The goal here is to place every single intrinsic into its own object
	# file to avoid symbol clashes with the system libgcc if possible. Note
	# that this number doesn't actually produce this many object files, we
	# just don't create more than this number of object files.
	#
	# It's a bit of a bummer that we have to pass this here, unfortunately.
	# Ideally this would be specified through an env var to Cargo so Cargo
	# knows how many CGUs are for this specific crate, but for now
	# per-crate configuration isn't specifiable in the environment.
	codegen-units = 10000

Is this error we're looking at the sort of thing this override is supposed to prevent? It mentions "the system libgcc" and I definitely do not have a hexagon libgcc, if such a thing even exists. I'm trying to figure out if I should be filing a bug about -Zbuild-std ignoring library/Cargo.toml. Probably?

[androm3da]

The compiler-builtins PR should fix it. I am not yet familiar with the override but I don't think it's related/necessary.