[RFC,4/4] x86/rust: support RETHUNK
Commit Message
When support for `-Zfunction-return` lands in Rust [1], this patch may
be used to enable RETHUNK support on top of the previous patch.
Link: https://github.com/rust-lang/rust/pull/116892 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
Note that this patch is not meant to be applied now, it is only here to
show what will be needed to drop the depends on from the previous patch.
arch/x86/Makefile | 5 +++++
init/Kconfig | 1 -
2 files changed, 5 insertions(+), 1 deletion(-)
--
2.42.0
@@ -24,11 +24,15 @@ RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch-cs-prefix)
ifdef CONFIG_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,
@@ -193,6 +197,7 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
# Avoid indirect branches in kernel to deal with Spectre
ifdef CONFIG_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
@@ -1889,7 +1889,6 @@ config RUST
depends on !GCC_PLUGINS
depends on !RANDSTRUCT
depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
- depends on !RETHUNK
select CONSTRUCTORS
help
Enables Rust support in the kernel.