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

[Gary Guo <gary@garyguo.net>]

On Tue,  6 Aug 2024 17:06:19 +0200
Miguel Ojeda <ojeda@kernel.org> 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@garyguo.net>
> Reported-by: Alice Ryhl <aliceryhl@google.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@kernel.org>

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
>  rust/Makefile             | 4 ++--
>  rust/compiler_builtins.rs | 3 +++
>  2 files changed, 5 insertions(+), 2 deletions(-)