The Rust compiler added support for `-Zfunction-return=thunk-extern` [1]
in 1.76.0 [2], i.e. the equivalent of `-mfunction-return=thunk-extern`.
Thus add support for `MITIGATION_RETHUNK`.
Without this, `objtool` would warn if enabled for Rust and already warns
under IBT builds, e.g.:
samples/rust/rust_print.o: warning: objtool:
_R...init+0xa5c: 'naked' return found in RETHUNK build
Link: https://github.com/rust-lang/rust/issues/116853 [1]
Link: https://github.com/rust-lang/rust/pull/116892 [2]
Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
arch/x86/Makefile | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index e8214bff1aeb..a1883a30a5d8 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -24,11 +24,15 @@ RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch-cs-prefix)
ifdef CONFIG_MITIGATION_RETHUNK
RETHUNK_CFLAGS := -mfunction-return=thunk-extern
+RETHUNK_RUSTFLAGS := -Zfunction-return=thunk-extern
RETPOLINE_CFLAGS += $(RETHUNK_CFLAGS)
+RETPOLINE_RUSTFLAGS += $(RETHUNK_RUSTFLAGS)
endif
export RETHUNK_CFLAGS
+export RETHUNK_RUSTFLAGS
export RETPOLINE_CFLAGS
+export RETPOLINE_RUSTFLAGS
export RETPOLINE_VDSO_CFLAGS
# For gcc stack alignment is specified with -mpreferred-stack-boundary,
@@ -218,6 +222,7 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
# Avoid indirect branches in kernel to deal with Spectre
ifdef CONFIG_MITIGATION_RETPOLINE
KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
+ KBUILD_RUSTFLAGS += $(RETPOLINE_RUSTFLAGS)
# Additionally, avoid generating expensive indirect jumps which
# are subject to retpolines for small number of switch cases.
# LLVM turns off jump table generation by default when under
--
2.45.2