rust/Makefile

   1 # SPDX-License-Identifier: GPL-2.0
   2
   3 # Where to place rustdoc generated documentation
   4 rustdoc_output := $(objtree)/Documentation/output/rust/rustdoc
   5
   6 obj-$(CONFIG_RUST) += core.o compiler_builtins.o
   7 always-$(CONFIG_RUST) += exports_core_generated.h
   8
   9 # Missing prototypes are expected in the helpers since these are exported
  10 # for Rust only, thus there is no header nor prototypes.
  11 obj-$(CONFIG_RUST) += helpers.o
  12 CFLAGS_REMOVE_helpers.o = -Wmissing-prototypes -Wmissing-declarations
  13
  14 always-$(CONFIG_RUST) += libmacros.so
  15 no-clean-files += libmacros.so
  16
  17 always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs
  18 obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
  19 always-$(CONFIG_RUST) += exports_alloc_generated.h exports_bindings_generated.h \
  20     exports_kernel_generated.h
  21
  22 always-$(CONFIG_RUST) += uapi/uapi_generated.rs
  23 obj-$(CONFIG_RUST) += uapi.o
  24
  25 ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW
  26 obj-$(CONFIG_RUST) += build_error.o
  27 else
  28 always-$(CONFIG_RUST) += build_error.o
  29 endif
  30
  31 obj-$(CONFIG_RUST) += exports.o
  32
  33 always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.rs
  34 always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.c
  35
  36 obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.o
  37 obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.o
  38
  39 # Avoids running `$(RUSTC)` for the sysroot when it may not be available.
  40 ifdef CONFIG_RUST
  41
  42 # `$(rust_flags)` is passed in case the user added `--sysroot`.
  43 rustc_sysroot := $(shell MAKEFLAGS= $(RUSTC) $(rust_flags) --print sysroot)
  44 rustc_host_target := $(shell $(RUSTC) --version --verbose | grep -F 'host: ' | cut -d' ' -f2)
  45 RUST_LIB_SRC ?= $(rustc_sysroot)/lib/rustlib/src/rust/library
  46
  47 ifneq ($(quiet),)
  48 rust_test_quiet=-q
  49 rustdoc_test_quiet=--test-args -q
  50 rustdoc_test_kernel_quiet=>/dev/null
  51 endif
  52
  53 core-cfgs = \
  54     --cfg no_fp_fmt_parse
  55
  56 alloc-cfgs = \
  57     --cfg no_global_oom_handling \
  58     --cfg no_rc \
  59     --cfg no_sync
  60
  61 quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
  62       cmd_rustdoc = \
  63         OBJTREE=$(abspath $(objtree)) \
  64         $(RUSTDOC) $(if $(rustdoc_host),$(rust_common_flags),$(rust_flags)) \
  65                 $(rustc_target_flags) -L$(objtree)/$(obj) \
  66                 --output $(rustdoc_output) \
  67                 --crate-name $(subst rustdoc-,,$@) \
  68                 $(if $(rustdoc_host),,--sysroot=/dev/null) \
  69                 @$(objtree)/include/generated/rustc_cfg $<
  70
  71 # The `html_logo_url` and `html_favicon_url` forms of the `doc` attribute
  72 # can be used to specify a custom logo. However:
  73 #   - The given value is used as-is, thus it cannot be relative or a local file
  74 #     (unlike the non-custom case) since the generated docs have subfolders.
  75 #   - It requires adding it to every crate.
  76 #   - It requires changing `core` which comes from the sysroot.
  77 #
  78 # Using `-Zcrate-attr` would solve the last two points, but not the first.
  79 # The https://github.com/rust-lang/rfcs/pull/3226 RFC suggests two new
  80 # command-like flags to solve the issue. Meanwhile, we use the non-custom case
  81 # and then retouch the generated files.
  82 rustdoc: rustdoc-core rustdoc-macros rustdoc-compiler_builtins \
  83     rustdoc-alloc rustdoc-kernel
  84         $(Q)cp $(srctree)/Documentation/images/logo.svg $(rustdoc_output)/static.files/
  85         $(Q)cp $(srctree)/Documentation/images/COPYING-logo $(rustdoc_output)/static.files/
  86         $(Q)find $(rustdoc_output) -name '*.html' -type f -print0 | xargs -0 sed -Ei \
  87                 -e 's:rust-logo-[0-9a-f]+\.svg:logo.svg:g' \
  88                 -e 's:favicon-[0-9a-f]+\.svg:logo.svg:g' \
  89                 -e 's:<link rel="alternate icon" type="image/png" href="[/.]+/static\.files/favicon-(16x16|32x32)-[0-9a-f]+\.png">::g' \
  90                 -e 's:<a href="srctree/([^"]+)">:<a href="$(realpath $(srctree))/\1">:g'
  91         $(Q)for f in $(rustdoc_output)/static.files/rustdoc-*.css; do \
  92                 echo ".logo-container > img { object-fit: contain; }" >> $$f; done
  93
  94 rustdoc-macros: private rustdoc_host = yes
  95 rustdoc-macros: private rustc_target_flags = --crate-type proc-macro \
  96     --extern proc_macro
  97 rustdoc-macros: $(src)/macros/lib.rs FORCE
  98         +$(call if_changed,rustdoc)
  99
 100 rustdoc-core: private rustc_target_flags = $(core-cfgs)
 101 rustdoc-core: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
 102         +$(call if_changed,rustdoc)
 103
 104 rustdoc-compiler_builtins: $(src)/compiler_builtins.rs rustdoc-core FORCE
 105         +$(call if_changed,rustdoc)
 106
 107 # We need to allow `rustdoc::broken_intra_doc_links` because some
 108 # `no_global_oom_handling` functions refer to non-`no_global_oom_handling`
 109 # functions. Ideally `rustdoc` would have a way to distinguish broken links
 110 # due to things that are "configured out" vs. entirely non-existing ones.
 111 rustdoc-alloc: private rustc_target_flags = $(alloc-cfgs) \
 112     -Arustdoc::broken_intra_doc_links
 113 rustdoc-alloc: $(RUST_LIB_SRC)/alloc/src/lib.rs rustdoc-core rustdoc-compiler_builtins FORCE
 114         +$(call if_changed,rustdoc)
 115
 116 rustdoc-kernel: private rustc_target_flags = --extern alloc \
 117     --extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so \
 118     --extern bindings --extern uapi
 119 rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-macros \
 120     rustdoc-compiler_builtins rustdoc-alloc $(obj)/libmacros.so \
 121     $(obj)/bindings.o FORCE
 122         +$(call if_changed,rustdoc)
 123
 124 quiet_cmd_rustc_test_library = RUSTC TL $<
 125       cmd_rustc_test_library = \
 126         OBJTREE=$(abspath $(objtree)) \
 127         $(RUSTC) $(rust_common_flags) \
 128                 @$(objtree)/include/generated/rustc_cfg $(rustc_target_flags) \
 129                 --crate-type $(if $(rustc_test_library_proc),proc-macro,rlib) \
 130                 --out-dir $(objtree)/$(obj)/test --cfg testlib \
 131                 -L$(objtree)/$(obj)/test \
 132                 --crate-name $(subst rusttest-,,$(subst rusttestlib-,,$@)) $<
 133
 134 rusttestlib-build_error: $(src)/build_error.rs FORCE
 135         +$(call if_changed,rustc_test_library)
 136
 137 rusttestlib-macros: private rustc_target_flags = --extern proc_macro
 138 rusttestlib-macros: private rustc_test_library_proc = yes
 139 rusttestlib-macros: $(src)/macros/lib.rs FORCE
 140         +$(call if_changed,rustc_test_library)
 141
 142 rusttestlib-bindings: $(src)/bindings/lib.rs FORCE
 143         +$(call if_changed,rustc_test_library)
 144
 145 rusttestlib-uapi: $(src)/uapi/lib.rs FORCE
 146         +$(call if_changed,rustc_test_library)
 147
 148 quiet_cmd_rustdoc_test = RUSTDOC T $<
 149       cmd_rustdoc_test = \
 150         OBJTREE=$(abspath $(objtree)) \
 151         $(RUSTDOC) --test $(rust_common_flags) \
 152                 @$(objtree)/include/generated/rustc_cfg \
 153                 $(rustc_target_flags) $(rustdoc_test_target_flags) \
 154                 $(rustdoc_test_quiet) \
 155                 -L$(objtree)/$(obj)/test --output $(rustdoc_output) \
 156                 --crate-name $(subst rusttest-,,$@) $<
 157
 158 quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 159       cmd_rustdoc_test_kernel = \
 160         rm -rf $(objtree)/$(obj)/test/doctests/kernel; \
 161         mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
 162         OBJTREE=$(abspath $(objtree)) \
 163         $(RUSTDOC) --test $(rust_flags) \
 164                 -L$(objtree)/$(obj) --extern alloc --extern kernel \
 165                 --extern build_error --extern macros \
 166                 --extern bindings --extern uapi \
 167                 --no-run --crate-name kernel -Zunstable-options \
 168                 --sysroot=/dev/null \
 169                 --test-builder $(objtree)/scripts/rustdoc_test_builder \
 170                 $< $(rustdoc_test_kernel_quiet); \
 171         $(objtree)/scripts/rustdoc_test_gen
 172
 173 %/doctests_kernel_generated.rs %/doctests_kernel_generated_kunit.c: \
 174     $(src)/kernel/lib.rs $(obj)/kernel.o \
 175     $(objtree)/scripts/rustdoc_test_builder \
 176     $(objtree)/scripts/rustdoc_test_gen FORCE
 177         +$(call if_changed,rustdoc_test_kernel)
 178
 179 # We cannot use `-Zpanic-abort-tests` because some tests are dynamic,
 180 # so for the moment we skip `-Cpanic=abort`.
 181 quiet_cmd_rustc_test = RUSTC T  $<
 182       cmd_rustc_test = \
 183         OBJTREE=$(abspath $(objtree)) \
 184         $(RUSTC) --test $(rust_common_flags) \
 185                 @$(objtree)/include/generated/rustc_cfg \
 186                 $(rustc_target_flags) --out-dir $(objtree)/$(obj)/test \
 187                 -L$(objtree)/$(obj)/test \
 188                 --crate-name $(subst rusttest-,,$@) $<; \
 189         $(objtree)/$(obj)/test/$(subst rusttest-,,$@) $(rust_test_quiet) \
 190                 $(rustc_test_run_flags)
 191
 192 rusttest: rusttest-macros rusttest-kernel
 193
 194 rusttest-macros: private rustc_target_flags = --extern proc_macro
 195 rusttest-macros: private rustdoc_test_target_flags = --crate-type proc-macro
 196 rusttest-macros: $(src)/macros/lib.rs FORCE
 197         +$(call if_changed,rustc_test)
 198         +$(call if_changed,rustdoc_test)
 199
 200 rusttest-kernel: private rustc_target_flags = --extern alloc \
 201     --extern build_error --extern macros --extern bindings --extern uapi
 202 rusttest-kernel: $(src)/kernel/lib.rs \
 203     rusttestlib-build_error rusttestlib-macros rusttestlib-bindings \
 204     rusttestlib-uapi FORCE
 205         +$(call if_changed,rustc_test)
 206         +$(call if_changed,rustc_test_library)
 207
 208 ifdef CONFIG_CC_IS_CLANG
 209 bindgen_c_flags = $(c_flags)
 210 else
 211 # bindgen relies on libclang to parse C. Ideally, bindgen would support a GCC
 212 # plugin backend and/or the Clang driver would be perfectly compatible with GCC.
 213 #
 214 # For the moment, here we are tweaking the flags on the fly. This is a hack,
 215 # and some kernel configurations may not work (e.g. `GCC_PLUGIN_RANDSTRUCT`
 216 # if we end up using one of those structs).
 217 bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
 218         -mskip-rax-setup -mgeneral-regs-only -msign-return-address=% \
 219         -mindirect-branch=thunk-extern -mindirect-branch-register \
 220         -mfunction-return=thunk-extern -mrecord-mcount -mabi=lp64 \
 221         -mindirect-branch-cs-prefix -mstack-protector-guard% -mtraceback=no \
 222         -mno-pointers-to-nested-functions -mno-string \
 223         -mno-strict-align -mstrict-align \
 224         -fconserve-stack -falign-jumps=% -falign-loops=% \
 225         -femit-struct-debug-baseonly -fno-ipa-cp-clone -fno-ipa-sra \
 226         -fno-partial-inlining -fplugin-arg-arm_ssp_per_task_plugin-% \
 227         -fno-reorder-blocks -fno-allow-store-data-races -fasan-shadow-offset=% \
 228         -fzero-call-used-regs=% -fno-stack-clash-protection \
 229         -fno-inline-functions-called-once -fsanitize=bounds-strict \
 230         -fstrict-flex-arrays=% -fmin-function-alignment=% \
 231         --param=% --param asan-%
 232
 233 # Derived from `scripts/Makefile.clang`.
 234 BINDGEN_TARGET_x86      := x86_64-linux-gnu
 235 BINDGEN_TARGET_arm64    := aarch64-linux-gnu
 236 BINDGEN_TARGET          := $(BINDGEN_TARGET_$(SRCARCH))
 237
 238 # All warnings are inhibited since GCC builds are very experimental,
 239 # many GCC warnings are not supported by Clang, they may only appear in
 240 # some configurations, with new GCC versions, etc.
 241 bindgen_extra_c_flags = -w --target=$(BINDGEN_TARGET)
 242
 243 # Auto variable zero-initialization requires an additional special option with
 244 # clang that is going to be removed sometime in the future (likely in
 245 # clang-18), so make sure to pass this option only if clang supports it
 246 # (libclang major version < 16).
 247 #
 248 # https://github.com/llvm/llvm-project/issues/44842
 249 # https://github.com/llvm/llvm-project/blob/llvmorg-16.0.0-rc2/clang/docs/ReleaseNotes.rst#deprecated-compiler-flags
 250 ifdef CONFIG_INIT_STACK_ALL_ZERO
 251 libclang_maj_ver=$(shell $(BINDGEN) $(srctree)/scripts/rust_is_available_bindgen_libclang.h 2>&1 | sed -ne 's/.*clang version \([0-9]*\).*/\1/p')
 252 ifeq ($(shell expr $(libclang_maj_ver) \< 16), 1)
 253 bindgen_extra_c_flags += -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
 254 endif
 255 endif
 256
 257 bindgen_c_flags = $(filter-out $(bindgen_skip_c_flags), $(c_flags)) \
 258         $(bindgen_extra_c_flags)
 259 endif
 260
 261 ifdef CONFIG_LTO
 262 bindgen_c_flags_lto = $(filter-out $(CC_FLAGS_LTO), $(bindgen_c_flags))
 263 else
 264 bindgen_c_flags_lto = $(bindgen_c_flags)
 265 endif
 266
 267 bindgen_c_flags_final = $(bindgen_c_flags_lto) -D__BINDGEN__
 268
 269 quiet_cmd_bindgen = BINDGEN $@
 270       cmd_bindgen = \
 271         $(BINDGEN) $< $(bindgen_target_flags) \
 272                 --use-core --with-derive-default --ctypes-prefix core::ffi --no-layout-tests \
 273                 --no-debug '.*' \
 274                 -o $@ -- $(bindgen_c_flags_final) -DMODULE \
 275                 $(bindgen_target_cflags) $(bindgen_target_extra)
 276
 277 $(obj)/bindings/bindings_generated.rs: private bindgen_target_flags = \
 278     $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters)
 279 $(obj)/bindings/bindings_generated.rs: private bindgen_target_extra = ; \
 280     sed -Ei 's/pub const RUST_CONST_HELPER_([a-zA-Z0-9_]*)/pub const \1/g' $@
 281 $(obj)/bindings/bindings_generated.rs: $(src)/bindings/bindings_helper.h \
 282     $(src)/bindgen_parameters FORCE
 283         $(call if_changed_dep,bindgen)
 284
 285 $(obj)/uapi/uapi_generated.rs: private bindgen_target_flags = \
 286     $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters)
 287 $(obj)/uapi/uapi_generated.rs: $(src)/uapi/uapi_helper.h \
 288     $(src)/bindgen_parameters FORCE
 289         $(call if_changed_dep,bindgen)
 290
 291 # See `CFLAGS_REMOVE_helpers.o` above. In addition, Clang on C does not warn
 292 # with `-Wmissing-declarations` (unlike GCC), so it is not strictly needed here
 293 # given it is `libclang`; but for consistency, future Clang changes and/or
 294 # a potential future GCC backend for `bindgen`, we disable it too.
 295 $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_flags = \
 296     --blocklist-type '.*' --allowlist-var '' \
 297     --allowlist-function 'rust_helper_.*'
 298 $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_cflags = \
 299     -I$(objtree)/$(obj) -Wno-missing-prototypes -Wno-missing-declarations
 300 $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ; \
 301     sed -Ei 's/pub fn rust_helper_([a-zA-Z0-9_]*)/#[link_name="rust_helper_\1"]\n    pub fn \1/g' $@
 302 $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers.c FORCE
 303         $(call if_changed_dep,bindgen)
 304
 305 quiet_cmd_exports = EXPORTS $@
 306       cmd_exports = \
 307         $(NM) -p --defined-only $< \
 308                 | awk '/ (T|R|D|B) / {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
 309
 310 $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
 311         $(call if_changed,exports)
 312
 313 $(obj)/exports_alloc_generated.h: $(obj)/alloc.o FORCE
 314         $(call if_changed,exports)
 315
 316 $(obj)/exports_bindings_generated.h: $(obj)/bindings.o FORCE
 317         $(call if_changed,exports)
 318
 319 $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
 320         $(call if_changed,exports)
 321
 322 quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
 323       cmd_rustc_procmacro = \
 324         $(RUSTC_OR_CLIPPY) $(rust_common_flags) \
 325                 -Clinker-flavor=gcc -Clinker=$(HOSTCC) \
 326                 -Clink-args='$(call escsq,$(KBUILD_HOSTLDFLAGS))' \
 327                 --emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
 328                 --crate-type proc-macro \
 329                 --crate-name $(patsubst lib%.so,%,$(notdir $@)) $<
 330
 331 # Procedural macros can only be used with the `rustc` that compiled it.
 332 # Therefore, to get `libmacros.so` automatically recompiled when the compiler
 333 # version changes, we add `core.o` as a dependency (even if it is not needed).
 334 $(obj)/libmacros.so: $(src)/macros/lib.rs $(obj)/core.o FORCE
 335         +$(call if_changed_dep,rustc_procmacro)
 336
 337 quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L $@
 338       cmd_rustc_library = \
 339         OBJTREE=$(abspath $(objtree)) \
 340         $(if $(skip_clippy),$(RUSTC),$(RUSTC_OR_CLIPPY)) \
 341                 $(filter-out $(skip_flags),$(rust_flags) $(rustc_target_flags)) \
 342                 --emit=dep-info=$(depfile) --emit=obj=$@ \
 343                 --emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \
 344                 --crate-type rlib -L$(objtree)/$(obj) \
 345                 --crate-name $(patsubst %.o,%,$(notdir $@)) $< \
 346                 --sysroot=/dev/null \
 347         $(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@)
 348
 349 rust-analyzer:
 350         $(Q)$(srctree)/scripts/generate_rust_analyzer.py \
 351                 --cfgs='core=$(core-cfgs)' --cfgs='alloc=$(alloc-cfgs)' \
 352                 $(realpath $(srctree)) $(realpath $(objtree)) \
 353                 $(rustc_sysroot) $(RUST_LIB_SRC) $(KBUILD_EXTMOD) > \
 354                 $(if $(KBUILD_EXTMOD),$(extmod_prefix),$(objtree))/rust-project.json
 355
 356 redirect-intrinsics = \
 357         __addsf3 __eqsf2 __extendsfdf2 __gesf2 __lesf2 __ltsf2 __mulsf3 __nesf2 __truncdfsf2 __unordsf2 \
 358         __adddf3 __eqdf2 __ledf2 __ltdf2 __muldf3 __unorddf2 \
 359         __muloti4 __multi3 \
 360         __udivmodti4 __udivti3 __umodti3
 361
 362 ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
 363         # These intrinsics are defined for ARM64 and RISCV64
 364         redirect-intrinsics += \
 365                 __ashrti3 \
 366                 __ashlti3 __lshrti3
 367 endif
 368
 369 $(obj)/core.o: private skip_clippy = 1
 370 $(obj)/core.o: private skip_flags = -Wunreachable_pub
 371 $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
 372 $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
 373 $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
 374         +$(call if_changed_dep,rustc_library)
 375 ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
 376 $(obj)/core.o: scripts/target.json
 377 endif
 378
 379 $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
 380 $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 381         +$(call if_changed_dep,rustc_library)
 382
 383 $(obj)/alloc.o: private skip_clippy = 1
 384 $(obj)/alloc.o: private skip_flags = -Wunreachable_pub
 385 $(obj)/alloc.o: private rustc_target_flags = $(alloc-cfgs)
 386 $(obj)/alloc.o: $(RUST_LIB_SRC)/alloc/src/lib.rs $(obj)/compiler_builtins.o FORCE
 387         +$(call if_changed_dep,rustc_library)
 388
 389 $(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
 390         +$(call if_changed_dep,rustc_library)
 391
 392 $(obj)/bindings.o: $(src)/bindings/lib.rs \
 393     $(obj)/compiler_builtins.o \
 394     $(obj)/bindings/bindings_generated.rs \
 395     $(obj)/bindings/bindings_helpers_generated.rs FORCE
 396         +$(call if_changed_dep,rustc_library)
 397
 398 $(obj)/uapi.o: $(src)/uapi/lib.rs \
 399     $(obj)/compiler_builtins.o \
 400     $(obj)/uapi/uapi_generated.rs FORCE
 401         +$(call if_changed_dep,rustc_library)
 402
 403 $(obj)/kernel.o: private rustc_target_flags = --extern alloc \
 404     --extern build_error --extern macros --extern bindings --extern uapi
 405 $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
 406     $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE
 407         +$(call if_changed_dep,rustc_library)
 408
 409 endif # CONFIG_RUST