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rust: compiler_builtins: make stubs non-global 

Currently we define a number of stubs for compiler-builtin intrinsics
that compiled libcore generates. The defined stubs are weak so they will
not conflict with genuine implementation of these intrinsics, but their
effect is global and will cause non-libcore code that accidently
generate these intrinsics calls compile and bug on runtime.

Instead of defining a stub that can affect all code, this patch uses
objcopy's `--redefine-sym` flag to redirect these calls (from libcore
only) to a prefixed version (e.g. redirect `__multi3` to `__rust_multi3`),
so we can define panciking stubs that are only visible to libcore.

This patch was previously discussed on GitHub [1]. This approach was also
independently proposed by Nick Desaulniers in [2].

Link: https://github.com/Rust-for-Linux/linux/pull/779 [1]
Link: https://lore.kernel.org/lkml/CAKwvOdkc0Qhwu=gfe1+H23TnAa6jnO6A3ZCO687dH6mSrATmDA@mail.gmail.com/
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Gary Guo 2022-12-05 21:50:00 +00:00 committed by Miguel Ojeda
parent 8909a80e3f
commit cb7d9defda
2 changed files with 18 additions and 1 deletions
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14
rust/Makefile
View File

@ -360,8 +360,22 @@ rust-analyzer:
$(Q)$(srctree)/scripts/generate_rust_analyzer.py $(srctree) $(objtree) \
$(RUST_LIB_SRC) > $(objtree)/rust-project.json
redirect-intrinsics = \
__eqsf2 __gesf2 __lesf2 __nesf2 __unordsf2 \
__unorddf2 \
__muloti4 __multi3 \
__udivmodti4 __udivti3 __umodti3
ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
# These intrinsics are defined for ARM64 and RISCV64
redirect-intrinsics += \
__ashrti3 \
__ashlti3 __lshrti3
endif
$(obj)/core.o: private skip_clippy = 1
$(obj)/core.o: private skip_flags = -Dunreachable_pub
$(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
$(obj)/core.o: private rustc_target_flags = $(core-cfgs)
$(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs $(obj)/target.json FORCE
$(call if_changed_dep,rustc_library)

5
rust/compiler_builtins.rs
View File

@ -28,7 +28,7 @@ macro_rules! define_panicking_intrinsics(
($reason: tt, { $($ident: ident, )* }) => {
$(
#[doc(hidden)]
#[no_mangle]
#[export_name = concat!("__rust", stringify!($ident))]
pub extern "C" fn $ident() {
panic!($reason);
}
@ -61,3 +61,6 @@ define_panicking_intrinsics!("`u128` should not be used", {
__udivti3,
__umodti3,
});
// NOTE: if you are adding a new intrinsic here, you should also add it to
// `redirect-intrinsics` in `rust/Makefile`.