Merge tag 'kbuild-7.1-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux

Pull Kbuild/Kconfig updates from Nicolas Schier:
 "Kbuild:
   - reject unexpected values for LLVM=
   - uapi: remove usage of toolchain headers
   - switch from '-fms-extensions' to '-fms-anonymous-structs' when
     available (currently: clang >= 23.0.0)
   - reduce the number of compiler-generated suffixes for clang thin-lto
     build
   - reduce output spam ("GEN Makefile") when building out of tree
   - improve portability for testing headers
   - also test UAPI headers against C++ compilers
   - drop build ID architecture allow-list in vdso_install
   - only run checksyscalls when necessary
   - update the debug information notes in reproducible-builds.rst
   - expand inlining hints with -fdiagnostics-show-inlining-chain

  Kconfig:
   - forbid multiple entries with the same symbol in a choice
   - error out on duplicated kconfig inclusion"

* tag 'kbuild-7.1-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux: (35 commits)
  kbuild: expand inlining hints with -fdiagnostics-show-inlining-chain
  kconfig: forbid multiple entries with the same symbol in a choice
  Documentation: kbuild: Update the debug information notes in reproducible-builds.rst
  checksyscalls: move instance functionality into generic code
  checksyscalls: only run when necessary
  checksyscalls: fail on all intermediate errors
  checksyscalls: move path to reference table to a variable
  kbuild: vdso_install: drop build ID architecture allow-list
  kbuild: vdso_install: gracefully handle images without build ID
  kbuild: vdso_install: hide readelf warnings
  kbuild: vdso_install: split out the readelf invocation
  kbuild: uapi: also test UAPI headers against C++ compilers
  kbuild: uapi: provide a C++ compatible dummy definition of NULL
  kbuild: uapi: handle UML in architecture-specific exclusion lists
  kbuild: uapi: move all include path flags together
  kbuild: uapi: move some compiler arguments out of the command definition
  check-uapi: use dummy libc includes
  check-uapi: honor ${CROSS_COMPILE} setting
  check-uapi: link into shared objects
  kbuild: reduce output spam when building out of tree
  ...

Documentation/kbuild/llvm.rst

@@ -71,10 +71,6 @@ recommend::
 
 	PATH=/path/to/llvm/:$PATH make LLVM=-14
 
-``LLVM=0`` is not the same as omitting ``LLVM`` altogether, it will behave like
-``LLVM=1``. If you only wish to use certain LLVM utilities, use their
-respective make variables.
-
 The same value used for ``LLVM=`` should be set for each invocation of ``make``
 if configuring and building via distinct commands. ``LLVM=`` should also be set
 as an environment variable when running scripts that will eventually run

Documentation/kbuild/reproducible-builds.rst

@@ -50,8 +50,10 @@ Absolute filenames
 ------------------
 
 When the kernel is built out-of-tree, debug information may include
-absolute filenames for the source files.  This must be overridden by
+absolute filenames for the source files and build directory.  These must
-including the ``-fdebug-prefix-map`` option in the `KCFLAGS`_ variable.
+be overridden by including a ``-fdebug-prefix-map`` option for each in
+the `KCFLAGS`_ and `KAFLAGS`_ variables to cover both ``.c`` and ``.S``
+files.
 
 Depending on the compiler used, the ``__FILE__`` macro may also expand
 to an absolute filename in an out-of-tree build.  Kbuild automatically
@@ -135,6 +137,7 @@ See ``scripts/setlocalversion`` for details.
 .. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp
 .. _KBUILD_BUILD_USER and KBUILD_BUILD_HOST: kbuild.html#kbuild-build-user-kbuild-build-host
 .. _KCFLAGS: kbuild.html#kcflags
+.. _KAFLAGS: kbuild.html#kaflags
 .. _prefix-map options: https://reproducible-builds.org/docs/build-path/
 .. _Reproducible Builds project: https://reproducible-builds.org/
 .. _SOURCE_DATE_EPOCH: https://reproducible-builds.org/docs/source-date-epoch/

Kbuild

@@ -47,12 +47,18 @@ $(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
 
 # Check for missing system calls
 
-quiet_cmd_syscalls = CALL    $<
+missing-syscalls-file := .tmp_missing-syscalls$(missing_syscalls_instance)
-      cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
+
+targets += $(missing-syscalls-file)
+
+quiet_cmd_syscalls = CALL    $< $(addprefix for ,$(missing_syscalls_instance))
+      cmd_syscalls = DEPFILE=$(depfile) $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags); touch $@
+
+$(missing-syscalls-file): scripts/checksyscalls.sh $(rq-offsets-file) FORCE
+	$(call if_changed_dep,syscalls)
 
 PHONY += missing-syscalls
-missing-syscalls: scripts/checksyscalls.sh $(rq-offsets-file)
+missing-syscalls: $(missing-syscalls-file)
-	$(call cmd,syscalls)
 
 # Check the manual modification of atomic headers
 

Makefile

@@ -591,7 +591,6 @@ LINUXINCLUDE    := \
 KBUILD_AFLAGS   := -D__ASSEMBLY__ -fno-PIE
 
 KBUILD_CFLAGS :=
-KBUILD_CFLAGS += -std=gnu11
 KBUILD_CFLAGS += -fshort-wchar
 KBUILD_CFLAGS += -funsigned-char
 KBUILD_CFLAGS += -fno-common
@@ -680,14 +679,19 @@ print_env_for_makefile = \
 	echo "export KBUILD_OUTPUT = $(CURDIR)"
 endif
 
-quiet_cmd_makefile = GEN     Makefile
+filechk_makefile = { \
-      cmd_makefile = { \
 	echo "\# Automatically generated by $(abs_srctree)/Makefile: don't edit"; \
 	$(print_env_for_makefile); \
 	echo "include $(abs_srctree)/Makefile"; \
-	} > Makefile
+	}
 
-outputmakefile:
+$(objtree)/Makefile: FORCE
+	$(call filechk,makefile)
+
+# Prevent $(srcroot)/Makefile from inhibiting the rule to run.
+PHONY += $(objtree)/Makefile
+
+outputmakefile: $(objtree)/Makefile
 ifeq ($(KBUILD_EXTMOD),)
 	@if [ -f $(srctree)/.config -o \
 		 -d $(srctree)/include/config -o \
@@ -708,7 +712,6 @@ else
 	fi
 endif
 	$(Q)ln -fsn $(srcroot) source
-	$(call cmd,makefile)
 	$(Q)test -e .gitignore || \
 	{ echo "# this is build directory, ignore it"; echo "*"; } > .gitignore
 endif
@@ -794,6 +797,18 @@ ifdef need-config
 include $(objtree)/include/config/auto.conf
 endif
 
+CC_FLAGS_DIALECT := -std=gnu11
+# Allow including a tagged struct or union anonymously in another struct/union.
+CC_FLAGS_DIALECT += $(CONFIG_CC_MS_EXTENSIONS)
+# Clang enables warnings about GNU and Microsoft extensions by default, disable
+# them because this is expected with the above options.
+ifdef CONFIG_CC_IS_CLANG
+CC_FLAGS_DIALECT += -Wno-gnu
+CC_FLAGS_DIALECT += -Wno-microsoft-anon-tag
+endif
+export CC_FLAGS_DIALECT
+KBUILD_CFLAGS += $(CC_FLAGS_DIALECT)
+
 ifeq ($(KBUILD_EXTMOD),)
 # Objects we will link into vmlinux / subdirs we need to visit
 core-y		:=
@@ -990,6 +1005,10 @@ KBUILD_CFLAGS	+= $(call cc-option, -fno-stack-clash-protection)
 # Get details on warnings generated due to GCC value tracking.
 KBUILD_CFLAGS	+= $(call cc-option, -fdiagnostics-show-context=2)
 
+# Show inlining notes for __attribute__((warning/error)) call chains.
+# GCC supports this unconditionally while Clang 23+ provides a flag.
+KBUILD_CFLAGS	+= $(call cc-option, -fdiagnostics-show-inlining-chain)
+
 # Clear used registers at func exit (to reduce data lifetime and ROP gadgets).
 ifdef CONFIG_ZERO_CALL_USED_REGS
 KBUILD_CFLAGS	+= -fzero-call-used-regs=used-gpr
@@ -1052,6 +1071,7 @@ endif
 ifdef CONFIG_LTO_CLANG
 ifdef CONFIG_LTO_CLANG_THIN
 CC_FLAGS_LTO	:= -flto=thin -fsplit-lto-unit
+KBUILD_LDFLAGS += $(call ld-option,--lto-whole-program-visibility -mllvm -always-rename-promoted-locals=false)
 else
 CC_FLAGS_LTO	:= -flto
 endif
@@ -1111,9 +1131,6 @@ NOSTDINC_FLAGS += -nostdinc
 # perform bounds checking.
 KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3)
 
-# Allow including a tagged struct or union anonymously in another struct/union.
-KBUILD_CFLAGS += -fms-extensions
-
 # disable invalid "can't wrap" optimizations for signed / pointers
 KBUILD_CFLAGS	+= -fno-strict-overflow
 

arch/arm64/kernel/vdso32/Makefile

@@ -63,7 +63,7 @@ VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
                $(filter -Werror,$(KBUILD_CPPFLAGS)) \
                -Werror-implicit-function-declaration \
                -Wno-format-security \
-               -std=gnu11 -fms-extensions
+               $(CC_FLAGS_DIALECT)
 VDSO_CFLAGS  += -O2
 # Some useful compiler-dependent flags from top-level Makefile
 VDSO_CFLAGS += $(call cc32-option,-Wno-pointer-sign)
@@ -71,7 +71,6 @@ VDSO_CFLAGS += -fno-strict-overflow
 VDSO_CFLAGS += $(call cc32-option,-Werror=strict-prototypes)
 VDSO_CFLAGS += -Werror=date-time
 VDSO_CFLAGS += $(call cc32-option,-Werror=incompatible-pointer-types)
-VDSO_CFLAGS += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag)
 
 # Compile as THUMB2 or ARM. Unwinding via frame-pointers in THUMB2 is
 # unreliable.

arch/hexagon/include/uapi/asm/sigcontext.h

@@ -29,6 +29,6 @@
  */
 struct sigcontext {
 	struct user_regs_struct sc_regs;
-} __aligned(8);
+} __attribute__((aligned(8)));
 
 #endif

arch/loongarch/vdso/Makefile

@@ -24,7 +24,7 @@ endif
 cflags-vdso := $(ccflags-vdso) \
 	-isystem $(shell $(CC) -print-file-name=include) \
 	$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
-	-std=gnu11 -fms-extensions -O2 -g -fno-strict-aliasing -fno-common -fno-builtin \
+	$(CC_FLAGS_DIALECT) -O2 -g -fno-strict-aliasing -fno-common -fno-builtin \
 	-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
 	$(call cc-option, -fasynchronous-unwind-tables) \
 	$(call cc-option, -fno-stack-protector)

arch/mips/Makefile

@@ -421,12 +421,10 @@ CLEAN_FILES += vmlinux.32 vmlinux.64
 
 archprepare:
 ifdef CONFIG_MIPS32_N32
-	@$(kecho) '  Checking missing-syscalls for N32'
+	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_instance="N32" missing_syscalls_flags="-mabi=n32"
-	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_flags="-mabi=n32"
 endif
 ifdef CONFIG_MIPS32_O32
-	@$(kecho) '  Checking missing-syscalls for O32'
+	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_instance="O32" missing_syscalls_flags="-mabi=32"
-	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_flags="-mabi=32"
 endif
 
 install:

arch/parisc/boot/compressed/Makefile

@@ -18,7 +18,7 @@ KBUILD_CFLAGS += -fno-PIE -mno-space-regs -mdisable-fpregs -Os
 ifndef CONFIG_64BIT
 KBUILD_CFLAGS += -mfast-indirect-calls
 endif
-KBUILD_CFLAGS += -std=gnu11 -fms-extensions
+KBUILD_CFLAGS += $(CC_FLAGS_DIALECT)
 
 LDFLAGS_vmlinux := -X -e startup --as-needed -T
 $(obj)/vmlinux: $(obj)/vmlinux.lds $(addprefix $(obj)/, $(OBJECTS)) $(LIBGCC) FORCE

arch/powerpc/boot/Makefile

@@ -70,7 +70,7 @@ BOOTCPPFLAGS	:= -nostdinc $(LINUXINCLUDE)
 BOOTCPPFLAGS	+= -isystem $(shell $(BOOTCC) -print-file-name=include)
 
 BOOTCFLAGS	:= $(BOOTTARGETFLAGS) \
-		   -std=gnu11 -fms-extensions \
+		   $(CC_FLAGS_DIALECT) \
 		   -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
 		   -fno-strict-aliasing -O2 \
 		   -msoft-float -mno-altivec -mno-vsx \
@@ -86,7 +86,6 @@ BOOTARFLAGS	:= -crD
 
 ifdef CONFIG_CC_IS_CLANG
 BOOTCFLAGS += $(CLANG_FLAGS)
-BOOTCFLAGS += -Wno-microsoft-anon-tag
 BOOTAFLAGS += $(CLANG_FLAGS)
 endif
 

arch/s390/Makefile

@@ -22,7 +22,7 @@ KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__
 ifndef CONFIG_AS_IS_LLVM
 KBUILD_AFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),$(aflags_dwarf))
 endif
-KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -mpacked-stack -std=gnu11 -fms-extensions
+KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -mpacked-stack $(CC_FLAGS_DIALECT)
 KBUILD_CFLAGS_DECOMPRESSOR += -DDISABLE_BRANCH_PROFILING -D__NO_FORTIFY
 KBUILD_CFLAGS_DECOMPRESSOR += -D__DECOMPRESSOR
 KBUILD_CFLAGS_DECOMPRESSOR += -Wno-pointer-sign
@@ -35,7 +35,6 @@ KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, address-of-packed-membe
 KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),-g)
 KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO_DWARF4), $(call cc-option, -gdwarf-4,))
 KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_NO_ARRAY_BOUNDS),-Wno-array-bounds)
-KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag)
 
 UTS_MACHINE	:= s390x
 STACK_SIZE	:= $(if $(CONFIG_KASAN),65536,$(if $(CONFIG_KMSAN),65536,16384))

arch/s390/purgatory/Makefile

@@ -13,7 +13,7 @@ CFLAGS_sha256.o := -D__NO_FORTIFY
 $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE
 	$(call if_changed_rule,as_o_S)
 
-KBUILD_CFLAGS := -std=gnu11 -fms-extensions -fno-strict-aliasing -Wall -Wstrict-prototypes
+KBUILD_CFLAGS := $(CC_FLAGS_DIALECT) -fno-strict-aliasing -Wall -Wstrict-prototypes
 KBUILD_CFLAGS += -Wno-pointer-sign -Wno-sign-compare
 KBUILD_CFLAGS += -fno-zero-initialized-in-bss -fno-builtin -ffreestanding
 KBUILD_CFLAGS += -Os -m64 -msoft-float -fno-common
@@ -21,7 +21,6 @@ KBUILD_CFLAGS += -fno-stack-protector
 KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
 KBUILD_CFLAGS += -D__DISABLE_EXPORTS
 KBUILD_CFLAGS += $(CLANG_FLAGS)
-KBUILD_CFLAGS += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag)
 KBUILD_CFLAGS += $(call cc-option,-fno-PIE)
 KBUILD_CFLAGS += $(call cc-option, -Wno-default-const-init-unsafe)
 KBUILD_AFLAGS := $(filter-out -DCC_USING_EXPOLINE,$(KBUILD_AFLAGS))

arch/x86/Makefile

@@ -48,7 +48,7 @@ endif
 
 # How to compile the 16-bit code.  Note we always compile for -march=i386;
 # that way we can complain to the user if the CPU is insufficient.
-REALMODE_CFLAGS	:= -std=gnu11 -fms-extensions -m16 -g -Os \
+REALMODE_CFLAGS	:= $(CC_FLAGS_DIALECT) -m16 -g -Os \
 		   -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \
 		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
 		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
@@ -59,10 +59,6 @@ REALMODE_CFLAGS += -fno-stack-protector
 REALMODE_CFLAGS += -Wno-address-of-packed-member
 REALMODE_CFLAGS += $(cc_stack_align4)
 REALMODE_CFLAGS += $(CLANG_FLAGS)
-ifdef CONFIG_CC_IS_CLANG
-REALMODE_CFLAGS += -Wno-gnu
-REALMODE_CFLAGS += -Wno-microsoft-anon-tag
-endif
 export REALMODE_CFLAGS
 
 # BITS is used as extension for files which are available in a 32 bit

arch/x86/boot/compressed/Makefile

@@ -25,7 +25,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
 # avoid errors with '-march=i386', and future flags may depend on the target to
 # be valid.
 KBUILD_CFLAGS := -m$(BITS) -O2 $(CLANG_FLAGS)
-KBUILD_CFLAGS += -std=gnu11 -fms-extensions
+KBUILD_CFLAGS += $(CC_FLAGS_DIALECT)
 KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
 KBUILD_CFLAGS += -Wundef
 KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
@@ -36,10 +36,6 @@ KBUILD_CFLAGS += -mno-mmx -mno-sse
 KBUILD_CFLAGS += -ffreestanding -fshort-wchar
 KBUILD_CFLAGS += -fno-stack-protector
 KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
-ifdef CONFIG_CC_IS_CLANG
-KBUILD_CFLAGS += -Wno-gnu
-KBUILD_CFLAGS += -Wno-microsoft-anon-tag
-endif
 KBUILD_CFLAGS += -Wno-pointer-sign
 KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 KBUILD_CFLAGS += -D__DISABLE_EXPORTS

drivers/firmware/efi/libstub/Makefile

@@ -11,12 +11,11 @@ cflags-y			:= $(KBUILD_CFLAGS)
 
 cflags-$(CONFIG_X86_32)		:= -march=i386
 cflags-$(CONFIG_X86_64)		:= -mcmodel=small
-cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ -std=gnu11 -fms-extensions \
+cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ $(CC_FLAGS_DIALECT) \
 				   -fPIC -fno-strict-aliasing -mno-red-zone \
 				   -mno-mmx -mno-sse -fshort-wchar \
 				   -Wno-pointer-sign \
 				   $(call cc-disable-warning, address-of-packed-member) \
-				   $(if $(CONFIG_CC_IS_CLANG),-Wno-gnu -Wno-microsoft-anon-tag) \
 				   -fno-asynchronous-unwind-tables \
 				   $(CLANG_FLAGS)
 

init/Kconfig

@@ -969,6 +969,11 @@ config CC_IMPLICIT_FALLTHROUGH
 	default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
 	default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
 
+config CC_MS_EXTENSIONS
+	string
+	default "-fms-anonymous-structs" if $(cc-option,-fms-anonymous-structs)
+	default "-fms-extensions"
+
 # Currently, disable gcc-10+ array-bounds globally.
 # It's still broken in gcc-13, so no upper bound yet.
 config GCC10_NO_ARRAY_BOUNDS

scripts/Makefile.vdsoinst

@@ -19,9 +19,10 @@ __default: $$(dest)
 $$(dest): $(1) FORCE
 	$$(call cmd,install)
 
-# Some architectures create .build-id symlinks
+build-id-file := $$(shell $(READELF) -n $(1) 2>/dev/null | sed -n 's@^.*Build ID: \(..\)\(.*\)@\1/\2@p')
-ifneq ($(filter arm s390 sparc x86, $(SRCARCH)),)
+
-link := $(install-dir)/.build-id/$$(shell $(READELF) -n $(1) | sed -n 's@^.*Build ID: \(..\)\(.*\)@\1/\2@p').debug
+ifneq ($$(build-id-file),)
+link := $(install-dir)/.build-id/$$(build-id-file).debug
 
 __default: $$(link)
 $$(link): $$(dest) FORCE

scripts/Makefile.warn

@@ -28,11 +28,6 @@ endif
 KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
 
 ifdef CONFIG_CC_IS_CLANG
-# The kernel builds with '-std=gnu11' and '-fms-extensions' so use of GNU and
-# Microsoft extensions is acceptable.
-KBUILD_CFLAGS += -Wno-gnu
-KBUILD_CFLAGS += -Wno-microsoft-anon-tag
-
 # Clang checks for overflow/truncation with '%p', while GCC does not:
 # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
 KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow-non-kprintf)

scripts/check-uapi.sh

@@ -33,9 +33,10 @@ Options:
     -v             Verbose operation (print more information about each header being checked).
 
 Environmental args:
-    ABIDIFF  Custom path to abidiff binary
+    ABIDIFF        Custom path to abidiff binary
-    CC       C compiler (default is "gcc")
+    CROSS_COMPILE  Toolchain prefix for compiler
-    ARCH     Target architecture for the UAPI check (default is host arch)
+    CC             C compiler (default is "\${CROSS_COMPILE}gcc")
+    ARCH           Target architecture for the UAPI check (default is host arch)
 
 Exit codes:
     $SUCCESS) Success
@@ -178,8 +179,11 @@ do_compile() {
 	local -r inc_dir="$1"
 	local -r header="$2"
 	local -r out="$3"
-	printf "int main(void) { return 0; }\n" | \
+	printf "int f(void) { return 0; }\n" | \
-		"$CC" -c \
+		"$CC" \
+		  -shared \
+		  -nostdlib \
+		  -fPIC \
 		  -o "$out" \
 		  -x c \
 		  -O0 \
@@ -187,6 +191,7 @@ do_compile() {
 		  -fno-eliminate-unused-debug-types \
 		  -g \
 		  "-I${inc_dir}" \
+		  "-Iusr/dummy-include" \
 		  -include "$header" \
 		  -
 }
@@ -195,7 +200,7 @@ do_compile() {
 run_make_headers_install() {
 	local -r ref="$1"
 	local -r install_dir="$(get_header_tree "$ref")"
-	make -j "$MAX_THREADS" ARCH="$ARCH" INSTALL_HDR_PATH="$install_dir" \
+	make -j "$MAX_THREADS" CROSS_COMPILE="${CROSS_COMPILE}" ARCH="$ARCH" INSTALL_HDR_PATH="$install_dir" \
 		headers_install > /dev/null
 }
 
@@ -404,7 +409,7 @@ min_version_is_satisfied() {
 # Make sure we have the tools we need and the arguments make sense
 check_deps() {
 	ABIDIFF="${ABIDIFF:-abidiff}"
-	CC="${CC:-gcc}"
+	CC="${CC:-${CROSS_COMPILE}gcc}"
 	ARCH="${ARCH:-$(uname -m)}"
 	if [ "$ARCH" = "x86_64" ]; then
 		ARCH="x86"

scripts/checksyscalls.sh

@@ -10,6 +10,10 @@
 # checksyscalls.sh gcc gcc-options
 #
 
+set -e
+
+reference_table="$(dirname $0)/../arch/x86/entry/syscalls/syscall_32.tbl"
+
 ignore_list() {
 cat << EOF
 #include <asm/types.h>
@@ -269,5 +273,10 @@ syscall_list() {
 	done
 }
 
-(ignore_list && syscall_list $(dirname $0)/../arch/x86/entry/syscalls/syscall_32.tbl) | \
+(ignore_list && syscall_list ${reference_table}) | \
 $* -Wno-error -Wno-unused-macros -E -x c - > /dev/null
+
+# For fixdep
+if [ -n "${DEPFILE}" ]; then
+	echo "${0}: ${0} ${reference_table}" >> "${DEPFILE}"
+fi

scripts/kconfig/lexer.l

@@ -402,7 +402,7 @@ void zconf_initscan(const char *name)
 		exit(1);
 	}
 
-	cur_filename = file_lookup(name);
+	cur_filename = file_lookup(name, NULL, 0);
 	yylineno = 1;
 }
 
@@ -443,7 +443,7 @@ void zconf_nextfile(const char *name)
 	}
 
 	yylineno = 1;
-	cur_filename = file_lookup(name);
+	cur_filename = file_lookup(name, cur_filename, cur_lineno);
 }
 
 static void zconf_endfile(void)

scripts/kconfig/lkc.h

@@ -51,7 +51,8 @@ static inline void xfwrite(const void *str, size_t len, size_t count, FILE *out)
 }
 
 /* util.c */
-const char *file_lookup(const char *name);
+const char *file_lookup(const char *name,
+			const char *parent_name, int parent_lineno);
 
 /* lexer.l */
 int yylex(void);

scripts/kconfig/parser.y

@@ -159,14 +159,8 @@ config_stmt: config_entry_start config_option_list
 			yynerrs++;
 		}
 
-		/*
+		list_add_tail(&current_entry->sym->choice_link,
-		 * If the same symbol appears twice in a choice block, the list
+			      &current_choice->choice_members);
-		 * node would be added twice, leading to a broken linked list.
-		 * list_empty() ensures that this symbol has not yet added.
-		 */
-		if (list_empty(&current_entry->sym->choice_link))
-			list_add_tail(&current_entry->sym->choice_link,
-				      &current_choice->choice_members);
 	}
 
 	printd(DEBUG_PARSE, "%s:%d:endconfig\n", cur_filename, cur_lineno);
@@ -546,11 +540,10 @@ static int choice_check_sanity(const struct menu *menu)
 			ret = -1;
 		}
 
-		if (prop->menu != menu && prop->type == P_PROMPT &&
+		if (prop->menu != menu && prop->type == P_PROMPT) {
-		    prop->menu->parent != menu->parent) {
 			fprintf(stderr, "%s:%d: error: %s",
 				prop->filename, prop->lineno,
-				"choice value has a prompt outside its choice group\n");
+				"choice value must not have a prompt in another entry\n");
 			ret = -1;
 		}
 	}

scripts/kconfig/tests/err_repeated_inc/Kconfig

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+source "Kconfig.inc1"

scripts/kconfig/tests/err_repeated_inc/Kconfig.inc1

@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+source "Kconfig.inc2"
+source "Kconfig.inc3"

scripts/kconfig/tests/err_repeated_inc/Kconfig.inc2

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+source "Kconfig.inc3"

scripts/kconfig/tests/err_repeated_inc/Kconfig.inc3

@@ -0,0 +1 @@
+# SPDX-License-Identifier: GPL-2.0-only

scripts/kconfig/tests/err_repeated_inc/__init__.py

@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Detect repeated inclusion error.
+
+If repeated inclusion is detected, it should fail with error message.
+"""
+
+def test(conf):
+    assert conf.oldaskconfig() != 0
+    assert conf.stderr_contains('expected_stderr')

scripts/kconfig/tests/err_repeated_inc/expected_stderr

@@ -0,0 +1,2 @@
+Kconfig.inc1:4: error: Repeated inclusion of Kconfig.inc3
+Kconfig.inc2:3: note: Location of first inclusion of Kconfig.inc3

scripts/kconfig/util.c

@@ -18,25 +18,50 @@ static HASHTABLE_DEFINE(file_hashtable, 1U << 11);
 
 struct file {
 	struct hlist_node node;
+	struct {
+		const char *name;
+		int lineno;
+	} parent;
 	char name[];
 };
 
-/* file already present in list? If not add it */
+static void die_duplicated_include(struct file *file,
-const char *file_lookup(const char *name)
+				   const char *parent, int lineno)
 {
+	fprintf(stderr,
+		"%s:%d: error: repeated inclusion of %s\n"
+		"%s:%d: note: location of first inclusion of %s\n",
+		parent, lineno, file->name,
+		file->parent.name, file->parent.lineno, file->name);
+	exit(1);
+}
+
+/* file already present in list? If not add it */
+const char *file_lookup(const char *name,
+			const char *parent_name, int parent_lineno)
+{
+	const char *parent = NULL;
 	struct file *file;
 	size_t len;
 	int hash = hash_str(name);
 
+	if (parent_name)
+		parent = file_lookup(parent_name, NULL, 0);
+
 	hash_for_each_possible(file_hashtable, file, node, hash)
-		if (!strcmp(name, file->name))
+		if (!strcmp(name, file->name)) {
-			return file->name;
+			if (!parent_name)
+				return file->name;
+			die_duplicated_include(file, parent, parent_lineno);
+		}
 
 	len = strlen(name);
 	file = xmalloc(sizeof(*file) + len + 1);
 	memset(file, 0, sizeof(*file));
 	memcpy(file->name, name, len);
 	file->name[len] = '\0';
+	file->parent.name = parent;
+	file->parent.lineno = parent_lineno;
 
 	hash_add(file_hashtable, &file->node, hash);
 

tools/scripts/Makefile.include

@@ -56,6 +56,8 @@ ifneq ($(filter %/,$(LLVM)),)
 LLVM_PREFIX := $(LLVM)
 else ifneq ($(filter -%,$(LLVM)),)
 LLVM_SUFFIX := $(LLVM)
+else ifneq ($(LLVM),1)
+$(error Invalid value for LLVM, see Documentation/kbuild/llvm.rst)
 endif
 
 $(call allow-override,CC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))

usr/dummy-include/limits.h

@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DUMMY_LIMITS_H
+#define _DUMMY_LIMITS_H
+
+#define INT_MAX ((int)(~0U >> 1))
+#define INT_MIN (-INT_MAX - 1)
+
+#endif /* _DUMMY_LIMITS_H */

usr/dummy-include/stdbool.h

@@ -1,7 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-#ifndef _STDBOOL_H
-#define _STDBOOL_H
-
-#error "Please do not include <stdbool.h> from exported headers"
-
-#endif /* _STDBOOL_H */

usr/dummy-include/stddef.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DUMMY_STDDEF_H
+#define _DUMMY_STDDEF_H
+
+#define offsetof(TYPE, MEMBER)	__builtin_offsetof(TYPE, MEMBER)
+
+#ifdef __cplusplus
+#define NULL 0
+#else
+#define NULL ((void *)0)
+#endif
+
+#endif /* _DUMMY_STDDEF_H */

usr/dummy-include/stdint.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DUMMY_STDINT_H
+#define _DUMMY_STDINT_H
+
+#include <linux/types.h>
+
+typedef	__u64	uint64_t;
+typedef	__u32	uint32_t;
+typedef	__u16	uint16_t;
+typedef	__u8	uint8_t;
+
+typedef	__s64	int64_t;
+typedef	__s32	int32_t;
+typedef	__s16	int16_t;
+typedef	__s8	int8_t;
+
+#endif /* _DUMMY_STDINT_H */

usr/dummy-include/stdlib.h

@@ -1,7 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-#ifndef _STDLIB_H
-#define _STDLIB_H
-
-#error "Please do not include <stdlib.h> from exported headers"
-
-#endif /* _STDLIB_H */

usr/dummy-include/string.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DUMMY_STRING_H
+#define _DUMMY_STRING_H
+
+#include <stddef.h>
+
+#define memset(_s, _c, _n) __builtin_memset(_s, _c, _n)
+#define memcpy(_dest, _src, _n) __builtin_memcpy(_dest, _src, _n)
+
+#define strlen(_s) __builtin_strlen(_s)
+
+#endif /* _DUMMY_STRING_H */

usr/dummy-include/sys/socket.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DUMMY_SYS_SOCKET_H
+#define _DUMMY_SYS_SOCKET_H
+
+#include <linux/socket.h>
+
+struct sockaddr {
+	__kernel_sa_family_t	sa_family;	/* address family, AF_xxx	*/
+	char			sa_data[14];	/* 14 bytes of protocol address	*/
+};
+
+#endif /* _DUMMY_SYS_SOCKET_H */

usr/dummy-include/sys/time.h

@@ -0,0 +1,3 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/time.h>

usr/include/Makefile

@@ -7,8 +7,10 @@
 # -std=c90 (equivalent to -ansi) catches the violation of those.
 # We cannot go as far as adding -Wpedantic since it emits too many warnings.
 UAPI_CFLAGS := -std=c90 -Werror=implicit-function-declaration
+UAPI_ARCH := $(or $(HEADER_ARCH),$(SRCARCH))
 
-override c_flags = $(KBUILD_USERCFLAGS) $(UAPI_CFLAGS) -Wp,-MMD,$(depfile) -I $(obj) -I $(srctree)/usr/dummy-include
+override c_flags = $(KBUILD_USERCFLAGS) $(UAPI_CFLAGS) -Wp,-MMD,$(depfile)
+cxx_flags = $(filter-out -Wmissing-prototypes -Wstrict-prototypes -std=%, $(KBUILD_USERCFLAGS)) -std=c++98
 
 # The following are excluded for now because they fail to build.
 #
@@ -48,30 +50,39 @@ no-header-test += xen/privcmd.h
 
 # More headers are broken in some architectures
 
-ifeq ($(SRCARCH),arc)
+ifneq ($(filter arc openrisc xtensa nios2, $(UAPI_ARCH)),)
 no-header-test += linux/bpf_perf_event.h
 endif
 
-ifeq ($(SRCARCH),openrisc)
+ifeq ($(UAPI_ARCH),sparc)
-no-header-test += linux/bpf_perf_event.h
-endif
-
-ifeq ($(SRCARCH),powerpc)
-no-header-test += linux/bpf_perf_event.h
-endif
-
-ifeq ($(SRCARCH),sparc)
 no-header-test += asm/uctx.h
 no-header-test += asm/fbio.h
 endif
 
-ifeq ($(SRCARCH),xtensa)
-no-header-test += linux/bpf_perf_event.h
-endif
-
 # asm-generic/*.h is used by asm/*.h, and should not be included directly
 no-header-test += asm-generic/%
 
+# The following are not compatible with C++.
+#
+# Do not add a new header to the list without legitimate reason.
+# Please consider to fix the header first.
+#
+# Sorted alphabetically.
+no-header-test-cxx += linux/auto_dev-ioctl.h
+no-header-test-cxx += linux/map_to_14segment.h
+no-header-test-cxx += linux/map_to_7segment.h
+no-header-test-cxx += linux/netfilter/xt_sctp.h
+no-header-test-cxx += linux/target_core_user.h
+no-header-test-cxx += linux/vhost.h
+no-header-test-cxx += linux/vhost_types.h
+no-header-test-cxx += linux/virtio_net.h
+no-header-test-cxx += linux/virtio_ring.h
+no-header-test-cxx += scsi/fc/fc_els.h
+
+ifeq ($(UAPI_ARCH),x86)
+no-header-test-cxx += asm/elf.h
+endif
+
 # The following are using libc header and types.
 #
 # Do not add a new header to the list without legitimate reason.
@@ -134,32 +145,38 @@ uses-libc += linux/wireless.h
 uses-libc += regulator/regulator.h
 uses-libc += scsi/fc/fc_els.h
 
-ifeq ($(SRCARCH),hexagon)
+ifeq ($(UAPI_ARCH),hexagon)
 uses-libc += asm/sigcontext.h
 endif
 
-ifeq ($(SRCARCH),nios2)
+ifeq ($(UAPI_ARCH),nios2)
 uses-libc += asm/ptrace.h
-uses-libc += linux/bpf_perf_event.h
 endif
 
-ifeq ($(SRCARCH),s390)
+ifeq ($(UAPI_ARCH),s390)
 uses-libc += asm/chpid.h
 uses-libc += asm/chsc.h
 endif
 
 always-y := $(patsubst $(obj)/%.h,%.hdrtest, $(shell find $(obj) -name '*.h' 2>/dev/null))
 
-target-no-libc = $(filter-out $(uses-libc), $*.h)
+# $(cc-option) forces '-x c' which breaks '-x c++' detection.
-target-can-compile = $(and $(filter-out $(no-header-test), $*.h), \
+cc-can-compile-cxx := $(call try-run,$(CC) $(CLANG_FLAGS) -c -x c++ /dev/null -o "$$TMP", 1)
-                           $(or $(CONFIG_CC_CAN_LINK), $(target-no-libc)))
+
+target-libc = $(filter $(uses-libc), $*.h)
+target-can-compile = $(filter-out $(no-header-test), $*.h)
+target-can-compile-cxx = $(and $(cc-can-compile-cxx), $(target-can-compile), $(filter-out $(no-header-test-cxx), $*.h))
+
+hdrtest-flags = -fsyntax-only -Werror \
+		-nostdinc -I $(obj) $(if $(target-libc), -I $(srctree)/usr/dummy-include)
 
 # Include the header twice to detect missing include guard.
 quiet_cmd_hdrtest = HDRTEST $<
       cmd_hdrtest = \
-		$(CC) $(c_flags) -fsyntax-only -Werror -x c /dev/null \
+		$(CC) $(c_flags) $(hdrtest-flags) -x c /dev/null \
-			$(if $(target-no-libc), -nostdinc) \
 			$(if $(target-can-compile), -include $< -include $<); \
+		$(if $(target-can-compile-cxx), \
+			$(CC) $(cxx_flags) $(hdrtest-flags) -x c++ /dev/null -include $<;) \
 		$(PERL) $(src)/headers_check.pl $(obj) $<; \
 		touch $@