Commit 1a6369ba authored by Andrii Nakryiko's avatar Andrii Nakryiko
Browse files

Merge branch 'tools/bpf: Enable cross-building with clang' 

Jean-Philippe Brucker says:

====================

Since v1 [1], I added Quentin's acks and applied Andrii's suggestions:
* Pass CFLAGS to libbpf link in patch 3
* Substitute CLANG_CROSS_FLAGS whole in HOST_CFLAGS to avoid accidents,
  patch 4

Add support for cross-building BPF tools and selftests with clang, by
passing LLVM=1 or CC=clang to make, as well as CROSS_COMPILE. A single
clang toolchain can generate binaries for multiple architectures, so
instead of having prefixes such as aarch64-linux-gnu-gcc, clang uses the
-target parameter: `clang -target aarch64-linux-gnu'.

Patch 1 adds the parameter in Makefile.include so tools can easily
support this. Patch 2 prepares for the libbpf change from patch 3 (keep
building resolve_btfids's libbpf in the host arch, when cross-building
the kernel with clang). Patches 3-6 enable cross-building BPF tools with
clang.

[1] https://lore.kernel.org/bpf/20211122192019.1277299-1-jean-philippe@linaro.org/


====================

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
parents f9798239 ea79020a

tools/bpf/bpftool/Makefile

+7 −6
Original line number Diff line number Diff line
@@ -57,7 +57,7 @@ $(LIBBPF_INTERNAL_HDRS): $(LIBBPF_HDRS_DIR)/%.h: $(BPF_DIR)/%.h | $(LIBBPF_HDRS_ 
$(LIBBPF_BOOTSTRAP): $(wildcard $(BPF_DIR)/*.[ch] $(BPF_DIR)/Makefile) | $(LIBBPF_BOOTSTRAP_OUTPUT)

	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_BOOTSTRAP_OUTPUT) \

		DESTDIR=$(LIBBPF_BOOTSTRAP_DESTDIR) prefix= \

		ARCH= CC=$(HOSTCC) LD=$(HOSTLD) $@ install_headers

		ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD) $@ install_headers



$(LIBBPF_BOOTSTRAP_INTERNAL_HDRS): $(LIBBPF_BOOTSTRAP_HDRS_DIR)/%.h: $(BPF_DIR)/%.h | $(LIBBPF_BOOTSTRAP_HDRS_DIR)

	$(call QUIET_INSTALL, $@)
@@ -152,6 +152,9 @@ CFLAGS += -DHAVE_LIBBFD_SUPPORT 
SRCS += $(BFD_SRCS)

endif



HOST_CFLAGS = $(subst -I$(LIBBPF_INCLUDE),-I$(LIBBPF_BOOTSTRAP_INCLUDE),\

		$(subst $(CLANG_CROSS_FLAGS),,$(CFLAGS)))



BPFTOOL_BOOTSTRAP := $(BOOTSTRAP_OUTPUT)bpftool



BOOTSTRAP_OBJS = $(addprefix $(BOOTSTRAP_OUTPUT),main.o common.o json_writer.o gen.o btf.o xlated_dumper.o btf_dumper.o disasm.o)
@@ -202,7 +205,7 @@ endif 
CFLAGS += $(if $(BUILD_BPF_SKELS),,-DBPFTOOL_WITHOUT_SKELETONS)



$(BOOTSTRAP_OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c

	$(QUIET_CC)$(HOSTCC) $(CFLAGS) -c -MMD $< -o $@

	$(QUIET_CC)$(HOSTCC) $(HOST_CFLAGS) -c -MMD $< -o $@



$(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c

	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD $< -o $@
@@ -213,15 +216,13 @@ ifneq ($(feature-zlib), 1) 
endif



$(BPFTOOL_BOOTSTRAP): $(BOOTSTRAP_OBJS) $(LIBBPF_BOOTSTRAP)

	$(QUIET_LINK)$(HOSTCC) $(CFLAGS) $(LDFLAGS) $(BOOTSTRAP_OBJS) $(LIBS_BOOTSTRAP) -o $@

	$(QUIET_LINK)$(HOSTCC) $(HOST_CFLAGS) $(LDFLAGS) $(BOOTSTRAP_OBJS) $(LIBS_BOOTSTRAP) -o $@



$(OUTPUT)bpftool: $(OBJS) $(LIBBPF)

	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $(OBJS) $(LIBS) -o $@



$(BOOTSTRAP_OUTPUT)%.o: %.c $(LIBBPF_BOOTSTRAP_INTERNAL_HDRS) | $(BOOTSTRAP_OUTPUT)

	$(QUIET_CC)$(HOSTCC) \

		$(subst -I$(LIBBPF_INCLUDE),-I$(LIBBPF_BOOTSTRAP_INCLUDE),$(CFLAGS)) \

		-c -MMD $< -o $@

	$(QUIET_CC)$(HOSTCC) $(HOST_CFLAGS) -c -MMD $< -o $@



$(OUTPUT)%.o: %.c

	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD $< -o $@

tools/bpf/resolve_btfids/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ CC = $(HOSTCC) 
LD       = $(HOSTLD)

ARCH     = $(HOSTARCH)

RM      ?= rm

CROSS_COMPILE =



OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/

tools/bpf/runqslower/Makefile

+2 −2
Original line number Diff line number Diff line
@@ -12,7 +12,7 @@ BPFOBJ := $(BPFOBJ_OUTPUT)libbpf.a 
BPF_DESTDIR := $(BPFOBJ_OUTPUT)

BPF_INCLUDE := $(BPF_DESTDIR)/include

INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../include/uapi)

CFLAGS := -g -Wall

CFLAGS := -g -Wall $(CLANG_CROSS_FLAGS)



# Try to detect best kernel BTF source

KERNEL_REL := $(shell uname -r)
@@ -88,4 +88,4 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(BPFOBJ_OU 


$(DEFAULT_BPFTOOL): $(BPFOBJ) | $(BPFTOOL_OUTPUT)

	$(Q)$(MAKE) $(submake_extras) -C ../bpftool OUTPUT=$(BPFTOOL_OUTPUT)   \

		    CC=$(HOSTCC) LD=$(HOSTLD)
 
		    ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD)

tools/lib/bpf/Makefile

+2 −1
Original line number Diff line number Diff line
@@ -90,6 +90,7 @@ override CFLAGS += -Werror -Wall 
override CFLAGS += $(INCLUDES)

override CFLAGS += -fvisibility=hidden

override CFLAGS += -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64

override CFLAGS += $(CLANG_CROSS_FLAGS)



# flags specific for shared library

SHLIB_FLAGS := -DSHARED -fPIC
@@ -162,7 +163,7 @@ $(BPF_HELPER_DEFS): $(srctree)/tools/include/uapi/linux/bpf.h 
$(OUTPUT)libbpf.so: $(OUTPUT)libbpf.so.$(LIBBPF_VERSION)



$(OUTPUT)libbpf.so.$(LIBBPF_VERSION): $(BPF_IN_SHARED) $(VERSION_SCRIPT)

	$(QUIET_LINK)$(CC) $(LDFLAGS) \

	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) \

		--shared -Wl,-soname,libbpf.so.$(LIBBPF_MAJOR_VERSION) \

		-Wl,--version-script=$(VERSION_SCRIPT) $< -lelf -lz -o $@

	@ln -sf $(@F) $(OUTPUT)libbpf.so

tools/scripts/Makefile.include

+12 −1
Original line number Diff line number Diff line
@@ -87,7 +87,18 @@ LLVM_STRIP ?= llvm-strip 


ifeq ($(CC_NO_CLANG), 1)

EXTRA_WARNINGS += -Wstrict-aliasing=3

endif



else ifneq ($(CROSS_COMPILE),)

CLANG_CROSS_FLAGS := --target=$(notdir $(CROSS_COMPILE:%-=%))

GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)gcc))

ifneq ($(GCC_TOOLCHAIN_DIR),)

CLANG_CROSS_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))

CLANG_CROSS_FLAGS += --sysroot=$(shell $(CROSS_COMPILE)gcc -print-sysroot)

CLANG_CROSS_FLAGS += --gcc-toolchain=$(realpath $(GCC_TOOLCHAIN_DIR)/..)

endif # GCC_TOOLCHAIN_DIR

CFLAGS += $(CLANG_CROSS_FLAGS)

AFLAGS += $(CLANG_CROSS_FLAGS)

endif # CROSS_COMPILE



# Hack to avoid type-punned warnings on old systems such as RHEL5:

# We should be changing CFLAGS and checking gcc version, but this