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

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Message-ID: <ZrJc9UE3xAV1ezdG@boqun-archlinux>
Date: Tue, 6 Aug 2024 10:27:17 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Nathan Chancellor <nathan@...nel.org>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>, llvm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH] rust: add intrinsics to fix `-Os` builds

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@...yguo.net>
> Reported-by: Alice Ryhl <aliceryhl@...gle.com>
> 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@...nel.org>

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@...il.com>

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
> 
>