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

From: Miguel Ojeda
Date: Tue Aug 06 2024 - 11:06:44 EST


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>
---
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