Re: [PATCH] rust: add intrinsics to fix `-Os` builds

From: Boqun Feng
Date: Tue Aug 06 2024 - 13:28:35 EST


On Tue, Aug 06, 2024 at 05:06:19PM +0200, Miguel Ojeda wrote:
> 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.
>
> Cc: Gary Guo <gary@xxxxxxxxxxx>
> Reported-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> Closes: https://rust-for-linux.zulipchat.com/#narrow/stream/288089-General/topic/v6.2E11-rc1.20doesn't.20build.20for.20arm64/near/455637364
> Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>

Put this one into rust-dev and confirm this could fix the issue with
Rust 1.80. I also add a test with CONFIG_CC_OPTIMIZE_FOR_SIZE=y in my
rust-dev script, so we can catch the similar issues earlier.

Tested-by: Boqun Feng <boqun.feng@xxxxxxxxx>

Regards,
Boqun

> ---
> rust/Makefile | 4 ++--
> rust/compiler_builtins.rs | 3 +++
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/rust/Makefile b/rust/Makefile
> index 1f10f92737f2..77836388377d 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -354,8 +354,8 @@ rust-analyzer:
> $(if $(KBUILD_EXTMOD),$(extmod_prefix),$(objtree))/rust-project.json
>
> redirect-intrinsics = \
> - __addsf3 __eqsf2 __gesf2 __lesf2 __ltsf2 __mulsf3 __nesf2 __unordsf2 \
> - __adddf3 __ledf2 __ltdf2 __muldf3 __unorddf2 \
> + __addsf3 __eqsf2 __extendsfdf2 __gesf2 __lesf2 __ltsf2 __mulsf3 __nesf2 __truncdfsf2 __unordsf2 \
> + __adddf3 __eqdf2 __ledf2 __ltdf2 __muldf3 __unorddf2 \
> __muloti4 __multi3 \
> __udivmodti4 __udivti3 __umodti3
>
> diff --git a/rust/compiler_builtins.rs b/rust/compiler_builtins.rs
> index bba2922c6ef7..f14b8d7caf89 100644
> --- a/rust/compiler_builtins.rs
> +++ b/rust/compiler_builtins.rs
> @@ -40,16 +40,19 @@ pub extern "C" fn $ident() {
> 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,
>
> base-commit: de9c2c66ad8e787abec7c9d7eff4f8c3cdd28aed
> --
> 2.46.0
>
>