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.or...
Jean-Philippe Brucker (6): tools: Help cross-building with clang tools/resolve_btfids: Support cross-building the kernel with clang tools/libbpf: Enable cross-building with clang bpftool: Enable cross-building with clang tools/runqslower: Enable cross-building with clang selftests/bpf: Enable cross-building with clang
tools/bpf/bpftool/Makefile | 13 +++++++------ tools/bpf/resolve_btfids/Makefile | 1 + tools/bpf/runqslower/Makefile | 4 ++-- tools/lib/bpf/Makefile | 3 ++- tools/scripts/Makefile.include | 13 ++++++++++++- tools/testing/selftests/bpf/Makefile | 8 ++++---- 6 files changed, 28 insertions(+), 14 deletions(-)
Cross-compilation with clang uses the -target parameter rather than a toolchain prefix. Just like the kernel Makefile, add that parameter to CFLAGS when CROSS_COMPILE is set.
Unlike the kernel Makefile, we use the --sysroot and --gcc-toolchain options because unlike the kernel, tools require standard libraries. Commit c91d4e47e10e ("Makefile: Remove '--gcc-toolchain' flag") provides some background about --gcc-toolchain. Normally clang finds on its own the additional utilities and libraries that it needs (for example GNU ld or glibc). On some systems however, this autodetection doesn't work. There, our only recourse is asking GCC directly, and pass the result to --sysroot and --gcc-toolchain. Of course that only works when a cross GCC is available.
Autodetection worked fine on Debian, but to use the aarch64-linux-gnu toolchain from Archlinux I needed both --sysroot (for crt1.o) and --gcc-toolchain (for crtbegin.o, -lgcc). The --prefix parameter wasn't needed there, but it might be useful on other distributions.
Use the CLANG_CROSS_FLAGS variable instead of CLANG_FLAGS because it allows tools such as bpftool, that need to build both host and target binaries, to easily filter out the cross-build flags from CFLAGS.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- Most tools I looked at needed additional changes to support cross-build with clang. I've only done the work for bpf tools. --- tools/scripts/Makefile.include | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include index 071312f5eb92..b0be5f40a3f1 100644 --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -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
On Thu, Dec 16, 2021 at 8:50 AM Jean-Philippe Brucker jean-philippe@linaro.org wrote:
Cross-compilation with clang uses the -target parameter rather than a toolchain prefix. Just like the kernel Makefile, add that parameter to CFLAGS when CROSS_COMPILE is set.
Unlike the kernel Makefile, we use the --sysroot and --gcc-toolchain options because unlike the kernel, tools require standard libraries. Commit c91d4e47e10e ("Makefile: Remove '--gcc-toolchain' flag") provides some background about --gcc-toolchain. Normally clang finds on its own the additional utilities and libraries that it needs (for example GNU ld or glibc). On some systems however, this autodetection doesn't work. There, our only recourse is asking GCC directly, and pass the result to --sysroot and --gcc-toolchain. Of course that only works when a cross GCC is available.
Autodetection worked fine on Debian, but to use the aarch64-linux-gnu toolchain from Archlinux I needed both --sysroot (for crt1.o) and --gcc-toolchain (for crtbegin.o, -lgcc). The --prefix parameter wasn't needed there, but it might be useful on other distributions.
Use the CLANG_CROSS_FLAGS variable instead of CLANG_FLAGS because it allows tools such as bpftool, that need to build both host and target binaries, to easily filter out the cross-build flags from CFLAGS.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org
Most tools I looked at needed additional changes to support cross-build with clang. I've only done the work for bpf tools.
tools/scripts/Makefile.include | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include index 071312f5eb92..b0be5f40a3f1 100644 --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -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)
^ this is a neat trick; it does rely on having $(CROSS_COMPILE)gcc installed though. Technically only the header include path is needed and the path to the cross libc shared object. I think we should take this patch&series as a starting point, but there might be future revisions here to support environments that don't have $(CROSS_COMPILE)gcc (such as Android's build env).
Acked-by: Nick Desaulniers ndesaulniers@google.com
Thanks for the series!
+CLANG_CROSS_FLAGS += --gcc-toolchain=$(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
2.34.1
Hi Jean-Philippe,
On Thu, Dec 16, 2021 at 04:38:38PM +0000, Jean-Philippe Brucker wrote:
Cross-compilation with clang uses the -target parameter rather than a toolchain prefix. Just like the kernel Makefile, add that parameter to CFLAGS when CROSS_COMPILE is set.
Unlike the kernel Makefile, we use the --sysroot and --gcc-toolchain options because unlike the kernel, tools require standard libraries. Commit c91d4e47e10e ("Makefile: Remove '--gcc-toolchain' flag") provides some background about --gcc-toolchain. Normally clang finds on its own the additional utilities and libraries that it needs (for example GNU ld or glibc). On some systems however, this autodetection doesn't work. There, our only recourse is asking GCC directly, and pass the result to --sysroot and --gcc-toolchain. Of course that only works when a cross GCC is available.
Autodetection worked fine on Debian, but to use the aarch64-linux-gnu toolchain from Archlinux I needed both --sysroot (for crt1.o) and --gcc-toolchain (for crtbegin.o, -lgcc). The --prefix parameter wasn't needed there, but it might be useful on other distributions.
Use the CLANG_CROSS_FLAGS variable instead of CLANG_FLAGS because it allows tools such as bpftool, that need to build both host and target binaries, to easily filter out the cross-build flags from CFLAGS.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org
Most tools I looked at needed additional changes to support cross-build with clang. I've only done the work for bpf tools.
tools/scripts/Makefile.include | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include index 071312f5eb92..b0be5f40a3f1 100644 --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -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 $(CROSS_COMPILE)gcc))
Apologies for noticing this so late, I only ran into this recently.
This line causes a warning when running 'make clean' when '$(CROSS_COMPILE)gcc' does not exist in PATH. For example:
$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- LLVM=1 LLVM_IAS=0 clean which: no powerpc-linux-gnu-gcc in ($PATH)
I only have powerpc-linux-gnu binutils in my PATH, not GCC, as I am only working with clang.
This happens because of the 'resolve_btfids_clean target', which always runs when running the 'clean' target on an in-tree build (since $(objtree) = $(srctree)).
I tried looking into the best way to fix this but I am not at all familiar with the tools/ build system; would you mind taking a look? I see some machinery at the top of tools/bpf/Makefile for avoiding running some commands under certain commands but I am unsure how to shuffle that around to make everything work.
Cheers, Nathan
+ifneq ($(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 += $(CLANG_CROSS_FLAGS) +endif # CROSS_COMPILE # Hack to avoid type-punned warnings on old systems such as RHEL5:
# We should be changing CFLAGS and checking gcc version, but this
2.34.1
Hi Nathan,
On Fri, Jan 28, 2022 at 06:10:24PM -0700, Nathan Chancellor wrote:
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include index 071312f5eb92..b0be5f40a3f1 100644 --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -87,7 +87,18 @@ LLVM_STRIP ?= llvm-strip ifeq ($(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 $(CROSS_COMPILE)gcc))
Apologies for noticing this so late, I only ran into this recently.
This line causes a warning when running 'make clean' when '$(CROSS_COMPILE)gcc' does not exist in PATH. For example:
$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- LLVM=1 LLVM_IAS=0 clean which: no powerpc-linux-gnu-gcc in ($PATH)
I only have powerpc-linux-gnu binutils in my PATH, not GCC, as I am only working with clang.
This happens because of the 'resolve_btfids_clean target', which always runs when running the 'clean' target on an in-tree build (since $(objtree) = $(srctree)).
I tried looking into the best way to fix this but I am not at all familiar with the tools/ build system; would you mind taking a look? I see some machinery at the top of tools/bpf/Makefile for avoiding running some commands under certain commands but I am unsure how to shuffle that around to make everything work.
I think it's simpler than that, we should just suppress the errors from 'which'. It's fine that $(CROSS_COMPILE)gcc doesn't exist and $(GCC_TOOLCHAIN_DIR) is empty, but 'which' should keep quiet about it. I did test this patch with cross-build and no gcc, but Debian's 'which' is quiet by default so I missed the error. I'll send a fix shortly.
Thanks, Jean
On Mon, Jan 31, 2022 at 02:10:30PM +0000, Jean-Philippe Brucker wrote:
Hi Nathan,
On Fri, Jan 28, 2022 at 06:10:24PM -0700, Nathan Chancellor wrote:
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include index 071312f5eb92..b0be5f40a3f1 100644 --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -87,7 +87,18 @@ LLVM_STRIP ?= llvm-strip ifeq ($(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 $(CROSS_COMPILE)gcc))
Apologies for noticing this so late, I only ran into this recently.
This line causes a warning when running 'make clean' when '$(CROSS_COMPILE)gcc' does not exist in PATH. For example:
$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- LLVM=1 LLVM_IAS=0 clean which: no powerpc-linux-gnu-gcc in ($PATH)
I only have powerpc-linux-gnu binutils in my PATH, not GCC, as I am only working with clang.
This happens because of the 'resolve_btfids_clean target', which always runs when running the 'clean' target on an in-tree build (since $(objtree) = $(srctree)).
I tried looking into the best way to fix this but I am not at all familiar with the tools/ build system; would you mind taking a look? I see some machinery at the top of tools/bpf/Makefile for avoiding running some commands under certain commands but I am unsure how to shuffle that around to make everything work.
I think it's simpler than that, we should just suppress the errors from 'which'. It's fine that $(CROSS_COMPILE)gcc doesn't exist and $(GCC_TOOLCHAIN_DIR) is empty, but 'which' should keep quiet about it.
Ha, that's what I get for looking into something at the very end of a long work week because that is a great and simple solution I probably would not have seen :)
I did test this patch with cross-build and no gcc, but Debian's 'which' is quiet by default so I missed the error. I'll send a fix shortly.
Ah, that is an interesting observation. TIL that Debian rolls their own which [1], versus most other distros, which use GNU which [2].
I will keep an eye out for your patch so I can review it.
[1]: https://salsa.debian.org/debian/debianutils/-/blob/de14223e5bffe15e374a44130... [2]: https://savannah.gnu.org/projects/which/
Cheers, Nathan
The CROSS_COMPILE variable may be present during resolve_btfids build if the kernel is being cross-built. Since resolve_btfids is always executed on the host, we set CC to HOSTCC in order to use the host toolchain when cross-building with GCC. But instead of a toolchain prefix, cross-build with clang uses a "-target" parameter, which Makefile.include deduces from the CROSS_COMPILE variable. In order to avoid cross-building libbpf, clear CROSS_COMPILE before building resolve_btfids.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- tools/bpf/resolve_btfids/Makefile | 1 + 1 file changed, 1 insertion(+)
diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile index 751643f860b2..9ddeca947635 100644 --- a/tools/bpf/resolve_btfids/Makefile +++ b/tools/bpf/resolve_btfids/Makefile @@ -19,6 +19,7 @@ CC = $(HOSTCC) LD = $(HOSTLD) ARCH = $(HOSTARCH) RM ?= rm +CROSS_COMPILE =
OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
Cross-building using clang requires passing the "-target" flag rather than using the CROSS_COMPILE prefix. Makefile.include transforms CROSS_COMPILE into CLANG_CROSS_FLAGS. Add them to the CFLAGS.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- tools/lib/bpf/Makefile | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile index 5f7086fae31c..f947b61b2107 100644 --- a/tools/lib/bpf/Makefile +++ b/tools/lib/bpf/Makefile @@ -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
Cross-building using clang requires passing the "-target" flag rather than using the CROSS_COMPILE prefix. Makefile.include transforms CROSS_COMPILE into CLANG_CROSS_FLAGS, and adds that to CFLAGS. Remove the cross flags for the bootstrap bpftool, and erase the CROSS_COMPILE flag for the bootstrap libbpf.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- tools/bpf/bpftool/Makefile | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile index 42eb8eee3d89..83369f55df61 100644 --- a/tools/bpf/bpftool/Makefile +++ b/tools/bpf/bpftool/Makefile @@ -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 $@
Cross-building using clang requires passing the "-target" flag rather than using the CROSS_COMPILE prefix. Makefile.include transforms CROSS_COMPILE into CLANG_CROSS_FLAGS. Add them to CFLAGS, and erase CROSS_COMPILE for the bpftool build, since it needs to be executed on the host.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- tools/bpf/runqslower/Makefile | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile index 8791d0e2762b..da6de16a3dfb 100644 --- a/tools/bpf/runqslower/Makefile +++ b/tools/bpf/runqslower/Makefile @@ -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)
Cross building using clang requires passing the "-target" flag rather than using the CROSS_COMPILE prefix. Makefile.include transforms CROSS_COMPILE into CLANG_CROSS_FLAGS. Clear CROSS_COMPILE for bpftool and the host libbpf, and use the clang flags for urandom_read and bench.
Acked-by: Quentin Monnet quentin@isovalent.com Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org --- tools/testing/selftests/bpf/Makefile | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 43f6f3159431..42ffc24e9e71 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -170,7 +170,7 @@ $(OUTPUT)/%:%.c
$(OUTPUT)/urandom_read: urandom_read.c $(call msg,BINARY,,$@) - $(Q)$(CC) $(LDFLAGS) $< $(LDLIBS) -Wl,--build-id=sha1 -o $@ + $(Q)$(CC) $(CFLAGS) $(LDFLAGS) $< $(LDLIBS) -Wl,--build-id=sha1 -o $@
$(OUTPUT)/bpf_testmod.ko: $(VMLINUX_BTF) $(wildcard bpf_testmod/Makefile bpf_testmod/*.[ch]) $(call msg,MOD,,$@) @@ -217,7 +217,7 @@ BPFTOOL ?= $(DEFAULT_BPFTOOL) $(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) \ $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool $(Q)$(MAKE) $(submake_extras) -C $(BPFTOOLDIR) \ - CC=$(HOSTCC) LD=$(HOSTLD) \ + ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD) \ EXTRA_CFLAGS='-g -O0' \ OUTPUT=$(HOST_BUILD_DIR)/bpftool/ \ LIBBPF_OUTPUT=$(HOST_BUILD_DIR)/libbpf/ \ @@ -248,7 +248,7 @@ $(HOST_BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile) \ $(APIDIR)/linux/bpf.h \ | $(HOST_BUILD_DIR)/libbpf $(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) \ - EXTRA_CFLAGS='-g -O0' \ + EXTRA_CFLAGS='-g -O0' ARCH= CROSS_COMPILE= \ OUTPUT=$(HOST_BUILD_DIR)/libbpf/ CC=$(HOSTCC) LD=$(HOSTLD) \ DESTDIR=$(HOST_SCRATCH_DIR)/ prefix= all install_headers endif @@ -551,7 +551,7 @@ $(OUTPUT)/bench: $(OUTPUT)/bench.o \ $(OUTPUT)/bench_bpf_loop.o \ $(OUTPUT)/bench_strncmp.o $(call msg,BINARY,,$@) - $(Q)$(CC) $(LDFLAGS) $(filter %.a %.o,$^) $(LDLIBS) -o $@ + $(Q)$(CC) $(CFLAGS) $(LDFLAGS) $(filter %.a %.o,$^) $(LDLIBS) -o $@
EXTRA_CLEAN := $(TEST_CUSTOM_PROGS) $(SCRATCH_DIR) $(HOST_SCRATCH_DIR) \ prog_tests/tests.h map_tests/tests.h verifier/tests.h \
Hello:
This series was applied to bpf/bpf-next.git (master) by Andrii Nakryiko andrii@kernel.org:
On Thu, 16 Dec 2021 16:38:37 +0000 you wrote:
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'.
[...]
Here is the summary with links: - [bpf-next,v2,1/6] tools: Help cross-building with clang https://git.kernel.org/bpf/bpf-next/c/cebdb7374577 - [bpf-next,v2,2/6] tools/resolve_btfids: Support cross-building the kernel with clang https://git.kernel.org/bpf/bpf-next/c/bf1be903461a - [bpf-next,v2,3/6] tools/libbpf: Enable cross-building with clang https://git.kernel.org/bpf/bpf-next/c/4980beb4cda2 - [bpf-next,v2,4/6] bpftool: Enable cross-building with clang https://git.kernel.org/bpf/bpf-next/c/bdadbb44c90a - [bpf-next,v2,5/6] tools/runqslower: Enable cross-building with clang https://git.kernel.org/bpf/bpf-next/c/bb7b75e860ee - [bpf-next,v2,6/6] selftests/bpf: Enable cross-building with clang https://git.kernel.org/bpf/bpf-next/c/ea79020a2d9e
You are awesome, thank you!
linux-kselftest-mirror@lists.linaro.org
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Jean-Philippe Brucker -
Nathan Chancellor -
Nick Desaulniers -
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