Kbuild fixes for v5.10 (2nd)

- Move -Wcast-align to W=3, which tends to be false-positive and there
    is no tree-wide solution.
 
  - Pass -fmacro-prefix-map to KBUILD_CPPFLAGS because it is a preprocessor
    option and makes sense for .S files as well.
 
  - Disable -gdwarf-2 for Clang's integrated assembler to avoid warnings.
 
  - Disable --orphan-handling=warn for LLD 10.0.1 to avoid warnings.
 
  - Fix undesirable line breaks in *.mod files.
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Merge tag 'kbuild-fixes-v5.10-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

Pull Kbuild fixes from Masahiro Yamada:

 - Move -Wcast-align to W=3, which tends to be false-positive and there
   is no tree-wide solution.

 - Pass -fmacro-prefix-map to KBUILD_CPPFLAGS because it is a
   preprocessor option and makes sense for .S files as well.

 - Disable -gdwarf-2 for Clang's integrated assembler to avoid warnings.

 - Disable --orphan-handling=warn for LLD 10.0.1 to avoid warnings.

 - Fix undesirable line breaks in *.mod files.

* tag 'kbuild-fixes-v5.10-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  kbuild: avoid split lines in .mod files
  kbuild: Disable CONFIG_LD_ORPHAN_WARN for ld.lld 10.0.1
  kbuild: Hoist '--orphan-handling' into Kconfig
  Kbuild: do not emit debug info for assembly with LLVM_IAS=1
  kbuild: use -fmacro-prefix-map for .S sources
  Makefile.extrawarn: move -Wcast-align to W=3

MAINTAINERS

@@ -4287,6 +4287,7 @@ B:	https://github.com/ClangBuiltLinux/linux/issues
 C:	irc://chat.freenode.net/clangbuiltlinux
 F:	Documentation/kbuild/llvm.rst
 F:	scripts/clang-tools/
+F:	scripts/lld-version.sh
 K:	\b(?i:clang|llvm)\b
 
 CLEANCACHE API

Makefile

@@ -826,7 +826,9 @@ else
 DEBUG_CFLAGS	+= -g
 endif
 
+ifneq ($(LLVM_IAS),1)
 KBUILD_AFLAGS	+= -Wa,-gdwarf-2
+endif
 
 ifdef CONFIG_DEBUG_INFO_DWARF4
 DEBUG_CFLAGS	+= -gdwarf-4
@@ -944,7 +946,7 @@ KBUILD_CFLAGS   += $(call cc-option,-Werror=incompatible-pointer-types)
 KBUILD_CFLAGS   += $(call cc-option,-Werror=designated-init)
 
 # change __FILE__ to the relative path from the srctree
-KBUILD_CFLAGS	+= $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
+KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
 
 # ensure -fcf-protection is disabled when using retpoline as it is
 # incompatible with -mindirect-branch=thunk-extern
@@ -982,6 +984,12 @@ ifeq ($(CONFIG_RELR),y)
 LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr
 endif
 
+# We never want expected sections to be placed heuristically by the
+# linker. All sections should be explicitly named in the linker script.
+ifdef CONFIG_LD_ORPHAN_WARN
+LDFLAGS_vmlinux += --orphan-handling=warn
+endif
+
 # Align the bit size of userspace programs with the kernel
 KBUILD_USERCFLAGS  += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))
 KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))

arch/Kconfig

@@ -1028,6 +1028,15 @@ config HAVE_STATIC_CALL_INLINE
 	bool
 	depends on HAVE_STATIC_CALL
 
+config ARCH_WANT_LD_ORPHAN_WARN
+	bool
+	help
+	  An arch should select this symbol once all linker sections are explicitly
+	  included, size-asserted, or discarded in the linker scripts. This is
+	  important because we never want expected sections to be placed heuristically
+	  by the linker, since the locations of such sections can change between linker
+	  versions.
+
 source "kernel/gcov/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"

arch/arm/Kconfig

@@ -35,6 +35,7 @@ config ARM
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
 	select ARCH_WANT_IPC_PARSE_VERSION
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select BINFMT_FLAT_ARGVP_ENVP_ON_STACK
 	select BUILDTIME_TABLE_SORT if MMU
 	select CLONE_BACKWARDS

arch/arm/Makefile

@@ -16,10 +16,6 @@ LDFLAGS_vmlinux	+= --be8
 KBUILD_LDFLAGS_MODULE	+= --be8
 endif
 
-# We never want expected sections to be placed heuristically by the
-# linker. All sections should be explicitly named in the linker script.
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
-
 GZFLAGS		:=-9
 #KBUILD_CFLAGS	+=-pipe
 

arch/arm/boot/compressed/Makefile

@@ -129,7 +129,9 @@ LDFLAGS_vmlinux += --no-undefined
 # Delete all temporary local symbols
 LDFLAGS_vmlinux += -X
 # Report orphan sections
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
+ifdef CONFIG_LD_ORPHAN_WARN
+LDFLAGS_vmlinux += --orphan-handling=warn
+endif
 # Next argument is a linker script
 LDFLAGS_vmlinux += -T
 

arch/arm64/Kconfig

@@ -81,6 +81,7 @@ config ARM64
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARM_AMBA
 	select ARM_ARCH_TIMER

arch/arm64/Makefile

@@ -28,10 +28,6 @@ LDFLAGS_vmlinux	+= --fix-cortex-a53-843419
   endif
 endif
 
-# We never want expected sections to be placed heuristically by the
-# linker. All sections should be explicitly named in the linker script.
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
-
 ifeq ($(CONFIG_ARM64_USE_LSE_ATOMICS), y)
   ifneq ($(CONFIG_ARM64_LSE_ATOMICS), y)
 $(warning LSE atomics not supported by binutils)

arch/powerpc/Kconfig

@@ -152,6 +152,7 @@ config PPC
 	select ARCH_USE_QUEUED_SPINLOCKS	if PPC_QUEUED_SPINLOCKS
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WEAK_RELEASE_ACQUIRE
 	select BINFMT_ELF
 	select BUILDTIME_TABLE_SORT

arch/powerpc/Makefile

@@ -123,7 +123,6 @@ endif
 LDFLAGS_vmlinux-y := -Bstatic
 LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
 LDFLAGS_vmlinux	:= $(LDFLAGS_vmlinux-y)
-LDFLAGS_vmlinux += $(call ld-option,--orphan-handling=warn)
 
 ifdef CONFIG_PPC64
 ifeq ($(call cc-option-yn,-mcmodel=medium),y)

arch/x86/Kconfig

@@ -100,6 +100,7 @@ config X86
 	select ARCH_WANT_DEFAULT_BPF_JIT	if X86_64
 	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
 	select ARCH_WANT_HUGE_PMD_SHARE
+	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANTS_THP_SWAP		if X86_64
 	select BUILDTIME_TABLE_SORT
 	select CLKEVT_I8253

arch/x86/Makefile

@@ -209,9 +209,6 @@ ifdef CONFIG_X86_64
 LDFLAGS_vmlinux += -z max-page-size=0x200000
 endif
 
-# We never want expected sections to be placed heuristically by the
-# linker. All sections should be explicitly named in the linker script.
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
 
 archscripts: scripts_basic
 	$(Q)$(MAKE) $(build)=arch/x86/tools relocs

arch/x86/boot/compressed/Makefile

@@ -61,7 +61,9 @@ KBUILD_LDFLAGS += $(call ld-option,--no-ld-generated-unwind-info)
 # Compressed kernel should be built as PIE since it may be loaded at any
 # address by the bootloader.
 LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker)
-LDFLAGS_vmlinux += $(call ld-option, --orphan-handling=warn)
+ifdef CONFIG_LD_ORPHAN_WARN
+LDFLAGS_vmlinux += --orphan-handling=warn
+endif
 LDFLAGS_vmlinux += -T
 
 hostprogs	:= mkpiggy

init/Kconfig

@@ -47,6 +47,10 @@ config CLANG_VERSION
 	int
 	default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
 
+config LLD_VERSION
+	int
+	default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
+
 config CC_CAN_LINK
 	bool
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT
@@ -1348,6 +1352,12 @@ config LD_DEAD_CODE_DATA_ELIMINATION
 	  present. This option is not well tested yet, so use at your
 	  own risk.
 
+config LD_ORPHAN_WARN
+	def_bool y
+	depends on ARCH_WANT_LD_ORPHAN_WARN
+	depends on !LD_IS_LLD || LLD_VERSION >= 110000
+	depends on $(ld-option,--orphan-handling=warn)
+
 config SYSCTL
 	bool
 

scripts/Makefile.build

@@ -252,6 +252,9 @@ objtool_dep = $(objtool_obj)					\
 ifdef CONFIG_TRIM_UNUSED_KSYMS
 cmd_gen_ksymdeps = \
 	$(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
+
+# List module undefined symbols
+undefined_syms = $(NM) $< | $(AWK) '$$1 == "U" { printf("%s%s", x++ ? " " : "", $$2) }';
 endif
 
 define rule_cc_o_c
@@ -271,13 +274,6 @@ define rule_as_o_S
 	$(call cmd,modversions_S)
 endef
 
-# List module undefined symbols (or empty line if not enabled)
-ifdef CONFIG_TRIM_UNUSED_KSYMS
-cmd_undef_syms = $(NM) $< | sed -n 's/^  *U //p' | xargs echo
-else
-cmd_undef_syms = echo
-endif
-
 # Built-in and composite module parts
 $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
 	$(call if_changed_rule,cc_o_c)
@@ -285,7 +281,7 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
 
 cmd_mod = { \
 	echo $(if $($*-objs)$($*-y)$($*-m), $(addprefix $(obj)/, $($*-objs) $($*-y) $($*-m)), $(@:.mod=.o)); \
-	$(cmd_undef_syms); \
+	$(undefined_syms) echo; \
 	} > $@
 
 $(obj)/%.mod: $(obj)/%.o FORCE

scripts/Makefile.extrawarn

@@ -60,7 +60,6 @@ endif
 #
 ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
 
-KBUILD_CFLAGS += -Wcast-align
 KBUILD_CFLAGS += -Wdisabled-optimization
 KBUILD_CFLAGS += -Wnested-externs
 KBUILD_CFLAGS += -Wshadow
@@ -80,6 +79,7 @@ endif
 ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),)
 
 KBUILD_CFLAGS += -Wbad-function-cast
+KBUILD_CFLAGS += -Wcast-align
 KBUILD_CFLAGS += -Wcast-qual
 KBUILD_CFLAGS += -Wconversion
 KBUILD_CFLAGS += -Wpacked

scripts/lld-version.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Usage: $ ./scripts/lld-version.sh ld.lld
+#
+# Print the linker version of `ld.lld' in a 5 or 6-digit form
+# such as `100001' for ld.lld 10.0.1 etc.
+
+linker_string="$($* --version)"
+
+if ! ( echo $linker_string | grep -q LLD ); then
+	echo 0
+	exit 1
+fi
+
+VERSION=$(echo $linker_string | cut -d ' ' -f 2)
+MAJOR=$(echo $VERSION | cut -d . -f 1)
+MINOR=$(echo $VERSION | cut -d . -f 2)
+PATCHLEVEL=$(echo $VERSION | cut -d . -f 3)
+printf "%d%02d%02d\\n" $MAJOR $MINOR $PATCHLEVEL