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l=9996; i=aliceryhl@google.com; h=from:subject:message-id; bh=ccYqFunpYUJ3E9tFyGaM8o4GOz90mNx5YokAm40heqc=; b=owEBbQKS/ZANAwAKAQRYvu5YxjlGAcsmYgBpgd09hi110q+7UOnBQB1eL+5EOe+WuCfuQr49U unbqQxlHpmJAjMEAAEKAB0WIQSDkqKUTWQHCvFIvbIEWL7uWMY5RgUCaYHdPQAKCRAEWL7uWMY5 RmdyEAC8Gb4J7AKABnGI1ESN5mKs8wfRAVbeEptQbCRE5TG56C8/CwBu3BxngSIJaR/jsj4cg+v 7E0sKl/e97o+ZFQ1e9+FgXjFE7mVT12T4WUYBVqLBjTCamAok2TTrixp+zYddUq+ccwGolxU2MY wBGy5AIj3hlrdI1XTXv0NYJa4I4Glhfer2cK5LuX/6pkbjv7AQywMBrJtEapUtDvygG+cs0Uz4n zHRznz9Xh6RSnlT17RKc8EABqA3R7Z/Y1TfSPuiYNT+i1vFhkHNGluu0cxtkBL/PEZd15dIpN9B CXvT+lZRPcrEVVL2fuqYe+gQgP56/sgeJvjD7jcfyJI3zXMfQpMyFC8pB+rbFKJIVG7GNB7L0Rt 4WqgYZBp0kM9WfQ+cmN7CaAFLaSsq6PDDnQFm61oEIBCoup6Q5tW2ceX6RNTUETpSUxy80qbzu8 Rhm7tuiSWxxpbMg+aRVGw5nFrxnliAzu/PFfSdq7Ro9SOo045XuS6+UKMlWE9o9WbFN/DB0TD9L w8uffrD51wqql0njRGx4d6VDYm6dS3Zi9JOQVznM/Z2AIqWquCTTwpocObwK8qDoX6PwKhb9ix/ H5C5Hb9A4mUHv16LwURptoWOxXnWZP3I9pTQEulcrf6CnuKSZ9eQszFn5hXt60Q4x6yPGd9DXBd EsK/t8LslrkpMww== X-Mailer: b4 0.14.2 Message-ID: <20260203-inline-helpers-v2-3-beb8547a03c9@google.com> Subject: [PATCH v2 3/3] build: rust: provide an option to inline C helpers into Rust From: Alice Ryhl To: Miguel Ojeda Cc: Boqun Feng , Gary Guo , "=?utf-8?q?Bj=C3=B6rn_Roy_Baron?=" , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , Alexandre Courbot , Will Deacon , Peter Zijlstra , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Nicolas Schier , Andrew Morton , Uladzislau Rezki , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, Alice Ryhl , Matthew Maurer Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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 bitcode. Two versions are generated: one for built-in code (`helpers.bc`) and one for modules (`helpers_module.bc`, with -DMODULE defined). This ensures that C macros/inlines that behave differently for modules (e.g. static calls) function correctly when inlined. * When a Rust crate or object is compiled, instead of generating an object file, LLVM bitcode is 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. * Since clang may produce LLVM bitcode when LTO is enabled, and objtool requires ELF input, $(cmd_ld_single) is invoked to ensure the object is converted to ELF before objtool runs. The --internalize flag tells llvm-link to treat all symbols in helpers.bc using `internal` linkage [1]. 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 pass --suppress-warnings to llvm-link to suppress it. We add $(cmd_ld_single) before $(cmd_objtool). Otherwise objtool fails to parse the resulting files as Elf when CONFIG_LTO is enabled. I considered adding some sort of check that KBUILD_MODNAME is not present in helpers_module.bc, but this is actually not so easy to carry out because .bc files store strings in a weird binary format, so you cannot just grep it for a string to check whether it ended up using KBUILD_MODNAME anywhere. Link: https://github.com/llvm/llvm-project/pull/170397 [1] 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 | 3 ++- lib/Kconfig.debug | 15 +++++++++++++++ rust/Makefile | 29 +++++++++++++++++++++++++---- rust/exports.c | 5 ++++- scripts/Makefile.build | 7 ++++++- 5 files changed, 52 insertions(+), 7 deletions(-) diff --git a/Makefile b/Makefile index c97f06ee0dda1c922aa23bd5249052591d528eb6..155db03cf489d931eefdb4bd7e3= b93e5aa3ea2d6 100644 --- a/Makefile +++ b/Makefile @@ -519,6 +519,7 @@ OBJCOPY =3D $(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX) OBJDUMP =3D $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX) READELF =3D $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX) STRIP =3D $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX) +LLVM_LINK =3D $(LLVM_PREFIX)llvm-link$(LLVM_SUFFIX) else CC =3D $(CROSS_COMPILE)gcc LD =3D $(CROSS_COMPILE)ld @@ -627,7 +628,7 @@ export RUSTC_BOOTSTRAP :=3D 1 export CLIPPY_CONF_DIR :=3D $(srctree) =20 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPI= LE 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 export HOSTRUSTC KBUILD_HOSTRUSTFLAGS export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX Y= ACC AWK INSTALLKERNEL export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 7570a694d54e6170ae6738634218b37e38a4b76a..c44c08b49f3a3c2e06fca42adeb= 9e04304e7a869 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -3551,6 +3551,21 @@ config RUST_KERNEL_DOCTESTS =20 If unsure, say N. =20 +config RUST_INLINE_HELPERS + bool "Inline C helpers into Rust code" + depends on RUST && RUSTC_CLANG_LLVM_COMPATIBLE + depends on EXPERT + help + Inlines C helpers into Rust code using Link Time Optimization. + + If this option is enabled, C helper functions declared in + rust/helpers/ are inlined into Rust code, which is helpful for + performance of Rust code. This requires a matching LLVM version for + Clang and rustc. + + If you are sure that you're using Clang and rustc with matching LLVM + versions, say Y. Otherwise say N. + endmenu # "Rust" =20 endmenu # Kernel hacking diff --git a/rust/Makefile b/rust/Makefile index 63464bd2c1e9734cd6e659f7ee3db58bf995d6dd..a6839f2d39feefcfea497384ae2= 02a7c6b475942 100644 --- a/rust/Makefile +++ b/rust/Makefile @@ -6,15 +6,19 @@ rustdoc_output :=3D $(objtree)/Documentation/output/rust/= rustdoc obj-$(CONFIG_RUST) +=3D core.o compiler_builtins.o ffi.o always-$(CONFIG_RUST) +=3D exports_core_generated.h =20 +ifdef CONFIG_RUST_INLINE_HELPERS +always-$(CONFIG_RUST) +=3D helpers/helpers.bc helpers/helpers_module.bc +else +obj-$(CONFIG_RUST) +=3D helpers/helpers.o +always-$(CONFIG_RUST) +=3D 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-$(CONFIG_RUST) +=3D helpers/helpers.o CFLAGS_REMOVE_helpers/helpers.o =3D -Wmissing-prototypes -Wmissing-declara= tions =20 always-$(CONFIG_RUST) +=3D bindings/bindings_generated.rs bindings/binding= s_helpers_generated.rs obj-$(CONFIG_RUST) +=3D bindings.o pin_init.o kernel.o -always-$(CONFIG_RUST) +=3D exports_helpers_generated.h \ - exports_bindings_generated.h exports_kernel_generated.h +always-$(CONFIG_RUST) +=3D exports_bindings_generated.h exports_kernel_gen= erated.h =20 always-$(CONFIG_RUST) +=3D uapi/uapi_generated.rs obj-$(CONFIG_RUST) +=3D uapi.o @@ -480,6 +484,14 @@ $(obj)/bindings/bindings_helpers_generated.rs: private= bindgen_target_extra =3D ; $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FO= RCE $(call if_changed_dep,bindgen) =20 +quiet_cmd_rust_helper =3D HELPER $@ + cmd_rust_helper =3D \ + $(CC) $(filter-out $(CFLAGS_REMOVE_helpers/helpers.o), $(c_flags)) \ + -c -g0 $< $(if $(filter %_module.bc,$@),-DMODULE) -emit-llvm -o $@ + +$(obj)/helpers/helpers.bc $(obj)/helpers/helpers_module.bc: $(src)/helpers= /helpers.c FORCE + +$(call if_changed_dep,rust_helper) + rust_exports =3D $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$= 3!~/__(pfx|cfi|odr_asan)/ { printf $(2),$$3 }' =20 quiet_cmd_exports =3D EXPORTS $@ @@ -561,12 +573,16 @@ quiet_cmd_rustc_library =3D $(if $(skip_clippy),RUSTC= ,$(RUSTC_OR_CLIPPY_QUIET)) L OBJTREE=3D$(abspath $(objtree)) \ $(if $(skip_clippy),$(RUSTC),$(RUSTC_OR_CLIPPY)) \ $(filter-out $(skip_flags),$(rust_flags)) $(rustc_target_flags) \ - --emit=3Ddep-info=3D$(depfile) --emit=3Dobj=3D$@ \ + --emit=3Ddep-info=3D$(depfile) --emit=3D$(if $(link_helper),llvm-bc=3D$(= patsubst %.o,%.bc,$@),obj=3D$@) \ --emit=3Dmetadata=3D$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \ --crate-type rlib -L$(objtree)/$(obj) \ --crate-name $(patsubst %.o,%,$(notdir $@)) $< \ --sysroot=3D/dev/null \ + $(if $(link_helper),;$(LLVM_LINK) --internalize --suppress-warnings $(pat= subst %.o,%.bc,$@) \ + $(obj)/helpers/helpers$(if $(part-of-module),_module).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_ld_single) \ $(cmd_objtool) =20 rust-analyzer: @@ -696,4 +712,9 @@ $(obj)/kernel.o: $(obj)/kernel/generated_arch_warn_asm.= rs $(obj)/kernel/generate endif endif =20 +ifdef CONFIG_RUST_INLINE_HELPERS +$(obj)/kernel.o: private link_helper =3D 1 +$(obj)/kernel.o: $(obj)/helpers/helpers.bc +endif + endif # CONFIG_RUST diff --git a/rust/exports.c b/rust/exports.c index 587f0e776aba52854080f15aa91094b55996c072..1b52460b0f4eeef6df9081abb9b= 7e054a28c3c21 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) =20 #include "exports_core_generated.h" -#include "exports_helpers_generated.h" #include "exports_bindings_generated.h" #include "exports_kernel_generated.h" =20 +#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 0c838c467c764e14a51ad132444544373e90a84c..7176d997ecab7c3ffd1e00400a8= a79a8309485e1 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -343,7 +343,12 @@ rust_common_cmd =3D \ # would not match each other. =20 quiet_cmd_rustc_o_rs =3D $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@ - cmd_rustc_o_rs =3D $(rust_common_cmd) --emit=3Dobj=3D$@ $< $(cmd_obj= tool) + cmd_rustc_o_rs =3D $(rust_common_cmd) --emit=3D$(if $(CONFIG_RUST_IN= LINE_HELPERS),llvm-bc=3D$(patsubst %.o,%.bc,$@),obj=3D$@) $< \ + $(if $(CONFIG_RUST_INLINE_HELPERS),;$(LLVM_LINK) --internalize --suppress= -warnings $(patsubst %.o,%.bc,$@) \ + $(objtree)/rust/helpers/helpers$(if $(part-of-module),_module).bc -o $(p= atsubst %.o,%.m.bc,$@); \ + $(CC) $(CLANG_FLAGS) $(KBUILD_CFLAGS) -Wno-override-module -c $(patsubst= %.o,%.m.bc,$@) -o $@) \ + $(cmd_ld_single) \ + $(cmd_objtool) =20 define rule_rustc_o_rs $(call cmd_and_fixdep,rustc_o_rs) --=20 2.53.0.rc1.225.gd81095ad13-goog