From: Gary Guo A new experimental Kconfig option, `RUST_INLINE_HELPERS` is added to allow C helpers (which were created to allow Rust to call into inline/macro C functions without having to re-implement the logic in Rust) to be inlined into Rust crates without performing global LTO. If the option is enabled, the following is performed: * For helpers, instead of compiling them to an object file to be linked into vmlinux, they're compiled to LLVM IR. * The LLVM IR is compiled to bitcode (This is step is not necessary, but is a performance optimisation to prevent LLVM from always have to reparse the same IR). * When a Rust crate is compiled, instead of generating an object file, we ask LLVM bitcode to be generated. * llvm-link is invoked with --internalize to combine the helper bitcode with the crate bitcode. This step is similar to LTO, but this is much faster since it only needs to inline the helpers. * clang is invoked to turn the combined bitcode into a final object file. The --internalize flag tells llvm-link to treat all symbols in helpers.bc using `internal` linkage. This matches the behavior of `clang` on `static inline` functions, and avoids exporting the symbol from the object file. To ensure that RUST_INLINE_HELPERS is not incompatible with BTF, we pass the -g0 flag when building helpers. See commit 5daa0c35a1f0 ("rust: Disallow BTF generation with Rust + LTO") for details. We have an intended triple mismatch of `aarch64-unknown-none` vs `aarch64-unknown-linux-gnu`, so we suppress the warning. Co-developed-by: Boqun Feng Signed-off-by: Boqun Feng Co-developed-by: Matthew Maurer Signed-off-by: Matthew Maurer Signed-off-by: Gary Guo Co-developed-by: Alice Ryhl Signed-off-by: Alice Ryhl --- Makefile | 4 +++- lib/Kconfig.debug | 15 +++++++++++++++ rust/Makefile | 26 ++++++++++++++++++++++---- rust/exports.c | 5 ++++- scripts/Makefile.build | 5 ++++- 5 files changed, 48 insertions(+), 7 deletions(-) diff --git a/Makefile b/Makefile index 96ddbaae7e12de71bcfabef4639de3a13a6e4815..5834bfd568548d1bee34b328dccce5d60f85526f 100644 --- a/Makefile +++ b/Makefile @@ -517,6 +517,8 @@ OBJCOPY = $(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX) OBJDUMP = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX) READELF = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX) STRIP = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX) +LLVM_LINK = $(LLVM_PREFIX)llvm-link$(LLVM_SUFFIX) +LLVM_AS = $(LLVM_PREFIX)llvm-as$(LLVM_SUFFIX) else CC = $(CROSS_COMPILE)gcc LD = $(CROSS_COMPILE)ld @@ -625,7 +627,7 @@ export RUSTC_BOOTSTRAP := 1 export CLIPPY_CONF_DIR := $(srctree) export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC HOSTPKG_CONFIG -export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN +export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN LLVM_LINK LLVM_AS export HOSTRUSTC KBUILD_HOSTRUSTFLAGS export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 3034e294d50df55c4003c5fa5df442f59e711bd8..e63c5eb57b049aff988419ccd12dfd99d59f5080 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -3427,6 +3427,21 @@ config RUST_KERNEL_DOCTESTS If unsure, say N. +config RUST_INLINE_HELPERS + bool "Inline C helpers into Rust crates (EXPERIMENTAL)" + depends on RUST && RUSTC_CLANG_LLVM_COMPATIBLE + depends on EXPERT + help + Links C helpers into Rust crates through LLVM IR. + + If this option is enabled, instead of generating object files directly, + rustc is asked to produce LLVM IR, which is then linked together with + the LLVM IR of C helpers, before object file is generated. + + This requires a matching LLVM version for Clang and rustc. + + If unsure, say N. + endmenu # "Rust" endmenu # Kernel hacking diff --git a/rust/Makefile b/rust/Makefile index d7d19c21b671dea10242b1772a8bcf0bf5dcc1cd..2344e2662ce29280582215954132c09f63cd8c9d 100644 --- a/rust/Makefile +++ b/rust/Makefile @@ -6,15 +6,19 @@ rustdoc_output := $(objtree)/Documentation/output/rust/rustdoc obj-$(CONFIG_RUST) += core.o compiler_builtins.o ffi.o always-$(CONFIG_RUST) += exports_core_generated.h +ifdef CONFIG_RUST_INLINE_HELPERS +always-$(CONFIG_RUST) += helpers/helpers.bc +else +obj-$(CONFIG_RUST) += helpers/helpers.o +always-$(CONFIG_RUST) += exports_helpers_generated.h +endif # Missing prototypes are expected in the helpers since these are exported # for Rust only, thus there is no header nor prototypes. -obj-$(CONFIG_RUST) += helpers/helpers.o CFLAGS_REMOVE_helpers/helpers.o = -Wmissing-prototypes -Wmissing-declarations always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs obj-$(CONFIG_RUST) += bindings.o pin_init.o kernel.o -always-$(CONFIG_RUST) += exports_helpers_generated.h \ - exports_bindings_generated.h exports_kernel_generated.h +always-$(CONFIG_RUST) += exports_bindings_generated.h exports_kernel_generated.h always-$(CONFIG_RUST) += uapi/uapi_generated.rs obj-$(CONFIG_RUST) += uapi.o @@ -468,6 +472,13 @@ $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ; $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FORCE $(call if_changed_dep,bindgen) +quiet_cmd_rust_helper = HELPER $@ + cmd_rust_helper = \ + $(CC) $(filter-out $(CFLAGS_REMOVE_helpers/helpers.o), $(c_flags)) -c -g0 $< -emit-llvm -o $@ + +$(obj)/helpers/helpers.bc: $(obj)/helpers/helpers.c FORCE + +$(call if_changed_dep,rust_helper) + rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3!~/__(pfx|cfi|odr_asan)/ { printf $(2),$$3 }' quiet_cmd_exports = EXPORTS $@ @@ -547,11 +558,13 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L OBJTREE=$(abspath $(objtree)) \ $(if $(skip_clippy),$(RUSTC),$(RUSTC_OR_CLIPPY)) \ $(filter-out $(skip_flags),$(rust_flags)) $(rustc_target_flags) \ - --emit=dep-info=$(depfile) --emit=obj=$@ \ + --emit=dep-info=$(depfile) --emit=$(if $(link_helper),llvm-bc=$(patsubst %.o,%.bc,$@),obj=$@) \ --emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \ --crate-type rlib -L$(objtree)/$(obj) \ --crate-name $(patsubst %.o,%,$(notdir $@)) $< \ --sysroot=/dev/null \ + $(if $(link_helper),;$(LLVM_LINK) --internalize --suppress-warnings $(patsubst %.o,%.bc,$@) $(obj)/helpers/helpers.bc -o $(patsubst %.o,%.m.bc,$@); \ + $(CC) $(CLANG_FLAGS) $(KBUILD_CFLAGS) -Wno-override-module -c $(patsubst %.o,%.m.bc,$@) -o $@) \ $(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@) \ $(cmd_objtool) @@ -678,4 +691,9 @@ $(obj)/kernel.o: $(obj)/kernel/generated_arch_warn_asm.rs $(obj)/kernel/generate endif endif +ifdef CONFIG_RUST_INLINE_HELPERS +$(obj)/kernel.o: private link_helper = 1 +$(obj)/kernel.o: $(obj)/helpers/helpers.bc +endif + endif # CONFIG_RUST diff --git a/rust/exports.c b/rust/exports.c index 587f0e776aba52854080f15aa91094b55996c072..1b52460b0f4eeef6df9081abb9b7e054a28c3c21 100644 --- a/rust/exports.c +++ b/rust/exports.c @@ -16,10 +16,13 @@ #define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym) #include "exports_core_generated.h" -#include "exports_helpers_generated.h" #include "exports_bindings_generated.h" #include "exports_kernel_generated.h" +#ifndef CONFIG_RUST_INLINE_HELPERS +#include "exports_helpers_generated.h" +#endif + // For modules using `rust/build_error.rs`. #ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW EXPORT_SYMBOL_RUST_GPL(rust_build_error); diff --git a/scripts/Makefile.build b/scripts/Makefile.build index d0ee33a487be95f8ba9a5c964ebecfbebc6c4bf8..04eaf2b4fbca2245f904a6dc7875cb3275aa7df6 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -343,7 +343,10 @@ rust_common_cmd = \ # would not match each other. quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@ - cmd_rustc_o_rs = $(rust_common_cmd) --emit=obj=$@ $< $(cmd_objtool) + cmd_rustc_o_rs = $(rust_common_cmd) --emit=$(if $(CONFIG_RUST_INLINE_HELPERS),llvm-bc=$(patsubst %.o,%.bc,$@),obj=$@) $< \ + $(if $(CONFIG_RUST_INLINE_HELPERS),;$(LLVM_LINK) --internalize --suppress-warnings $(patsubst %.o,%.bc,$@) $(objtree)/rust/helpers/helpers.bc -o $(patsubst %.o,%.m.bc,$@); \ + $(CC) $(CLANG_FLAGS) $(KBUILD_CFLAGS) -Wno-override-module -c $(patsubst %.o,%.m.bc,$@) -o $@) \ + $(cmd_objtool) define rule_rustc_o_rs $(call cmd_and_fixdep,rustc_o_rs) -- 2.52.0.158.g65b55ccf14-goog