1
linux/rust/compiler_builtins.rs
Miguel Ojeda 02dfd63afe rust: add intrinsics to fix -Os builds
Alice reported [1] that an arm64 build failed with:

    ld.lld: error: undefined symbol: __extendsfdf2
    >>> referenced by core.a6f5fc5794e7b7b3-cgu.0
    >>>               rust/core.o:(<f32>::midpoint) in archive vmlinux.a
    >>> referenced by core.a6f5fc5794e7b7b3-cgu.0
    >>>               rust/core.o:(<f32>::midpoint) in archive vmlinux.a

    ld.lld: error: undefined symbol: __truncdfsf2
    >>> referenced by core.a6f5fc5794e7b7b3-cgu.0
    >>>               rust/core.o:(<f32>::midpoint) in archive vmlinux.a

Rust 1.80.0 or later together with `CONFIG_CC_OPTIMIZE_FOR_SIZE=y`
is what triggers it.

In addition, x86_64 builds also fail the same way.

Similarly, compiling with Rust 1.82.0 (currently in nightly) makes
another one appear, possibly due to the LLVM 19 upgrade there:

    ld.lld: error: undefined symbol: __eqdf2
    >>> referenced by core.20495ea57a9f069d-cgu.0
    >>>               rust/core.o:(<f64>::next_up) in archive vmlinux.a
    >>> referenced by core.20495ea57a9f069d-cgu.0
    >>>               rust/core.o:(<f64>::next_down) in archive vmlinux.a

Gary adds [1]:

> Usually the fix on rustc side is to mark those functions as `#[inline]`
>
> All of {midpoint,next_up,next_down} are indeed unstable functions not
> marked as inline...

Fix all those by adding those intrinsics to our usual workaround.

[ Trevor quickly submitted a fix to upstream Rust [2] that has already
  been merged, to be released in Rust 1.82.0 (2024-10-17). - Miguel ]

Cc: Gary Guo <gary@garyguo.net>
Reported-by: Alice Ryhl <aliceryhl@google.com>
Closes: https://rust-for-linux.zulipchat.com/#narrow/stream/x/topic/x/near/455637364 [1]
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://github.com/rust-lang/rust/pull/128749 [2]
Link: https://lore.kernel.org/r/20240806150619.192882-1-ojeda@kernel.org
[ Shortened Zulip link. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2024-08-10 00:05:10 +02:00

78 lines
2.0 KiB
Rust

// SPDX-License-Identifier: GPL-2.0
//! Our own `compiler_builtins`.
//!
//! Rust provides [`compiler_builtins`] as a port of LLVM's [`compiler-rt`].
//! Since we do not need the vast majority of them, we avoid the dependency
//! by providing this file.
//!
//! At the moment, some builtins are required that should not be. For instance,
//! [`core`] has 128-bit integers functionality which we should not be compiling
//! in. We will work with upstream [`core`] to provide feature flags to disable
//! the parts we do not need. For the moment, we define them to [`panic!`] at
//! runtime for simplicity to catch mistakes, instead of performing surgery
//! on `core.o`.
//!
//! In any case, all these symbols are weakened to ensure we do not override
//! those that may be provided by the rest of the kernel.
//!
//! [`compiler_builtins`]: https://github.com/rust-lang/compiler-builtins
//! [`compiler-rt`]: https://compiler-rt.llvm.org/
#![allow(internal_features)]
#![feature(compiler_builtins)]
#![compiler_builtins]
#![no_builtins]
#![no_std]
macro_rules! define_panicking_intrinsics(
($reason: tt, { $($ident: ident, )* }) => {
$(
#[doc(hidden)]
#[export_name = concat!("__rust", stringify!($ident))]
pub extern "C" fn $ident() {
panic!($reason);
}
)*
}
);
define_panicking_intrinsics!("`f32` should not be used", {
__addsf3,
__eqsf2,
__extendsfdf2,
__gesf2,
__lesf2,
__ltsf2,
__mulsf3,
__nesf2,
__truncdfsf2,
__unordsf2,
});
define_panicking_intrinsics!("`f64` should not be used", {
__adddf3,
__eqdf2,
__ledf2,
__ltdf2,
__muldf3,
__unorddf2,
});
define_panicking_intrinsics!("`i128` should not be used", {
__ashrti3,
__muloti4,
__multi3,
});
define_panicking_intrinsics!("`u128` should not be used", {
__ashlti3,
__lshrti3,
__udivmodti4,
__udivti3,
__umodti3,
});
// NOTE: if you are adding a new intrinsic here, you should also add it to
// `redirect-intrinsics` in `rust/Makefile`.