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Subject[PATCH bpf v3] libbpf: Fix build on read-only filesystems
Date
I got the following error when I tried to build perf on a read-only
filesystem with O=dir option.

$ cd /some/where/ro/linux/tools/perf
$ make O=$HOME/build/perf
...
CC /home/namhyung/build/perf/lib.o
/bin/sh: bpf_helper_defs.h: Read-only file system
make[3]: *** [Makefile:184: bpf_helper_defs.h] Error 1
make[2]: *** [Makefile.perf:778: /home/namhyung/build/perf/libbpf.a] Error 2
make[2]: *** Waiting for unfinished jobs....
LD /home/namhyung/build/perf/libperf-in.o
AR /home/namhyung/build/perf/libperf.a
PERF_VERSION = 5.4.0
make[1]: *** [Makefile.perf:225: sub-make] Error 2
make: *** [Makefile:70: all] Error 2

It was becaused bpf_helper_defs.h was generated in current directory.
Move it to OUTPUT directory.

Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/lib/bpf/Makefile | 15 ++++++++-------
tools/testing/selftests/bpf/.gitignore | 1 +
tools/testing/selftests/bpf/Makefile | 6 +++---
3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index defae23a0169..97830e46d1a0 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -138,6 +138,7 @@ STATIC_OBJDIR := $(OUTPUT)staticobjs/
BPF_IN_SHARED := $(SHARED_OBJDIR)libbpf-in.o
BPF_IN_STATIC := $(STATIC_OBJDIR)libbpf-in.o
VERSION_SCRIPT := libbpf.map
+BPF_HELPER_DEFS := $(OUTPUT)bpf_helper_defs.h

LIB_TARGET := $(addprefix $(OUTPUT),$(LIB_TARGET))
LIB_FILE := $(addprefix $(OUTPUT),$(LIB_FILE))
@@ -159,7 +160,7 @@ all: fixdep

all_cmd: $(CMD_TARGETS) check

-$(BPF_IN_SHARED): force elfdep bpfdep bpf_helper_defs.h
+$(BPF_IN_SHARED): force elfdep bpfdep $(BPF_HELPER_DEFS)
@(test -f ../../include/uapi/linux/bpf.h -a -f ../../../include/uapi/linux/bpf.h && ( \
(diff -B ../../include/uapi/linux/bpf.h ../../../include/uapi/linux/bpf.h >/dev/null) || \
echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'" >&2 )) || true
@@ -177,12 +178,12 @@ $(BPF_IN_SHARED): force elfdep bpfdep bpf_helper_defs.h
echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'" >&2 )) || true
$(Q)$(MAKE) $(build)=libbpf OUTPUT=$(SHARED_OBJDIR) CFLAGS="$(CFLAGS) $(SHLIB_FLAGS)"

-$(BPF_IN_STATIC): force elfdep bpfdep bpf_helper_defs.h
+$(BPF_IN_STATIC): force elfdep bpfdep $(BPF_HELPER_DEFS)
$(Q)$(MAKE) $(build)=libbpf OUTPUT=$(STATIC_OBJDIR)

-bpf_helper_defs.h: $(srctree)/tools/include/uapi/linux/bpf.h
+$(BPF_HELPER_DEFS): $(srctree)/tools/include/uapi/linux/bpf.h
$(Q)$(srctree)/scripts/bpf_helpers_doc.py --header \
- --file $(srctree)/tools/include/uapi/linux/bpf.h > bpf_helper_defs.h
+ --file $(srctree)/tools/include/uapi/linux/bpf.h > $(BPF_HELPER_DEFS)

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

@@ -243,7 +244,7 @@ install_lib: all_cmd
$(call do_install_mkdir,$(libdir_SQ)); \
cp -fpR $(LIB_FILE) $(DESTDIR)$(libdir_SQ)

-install_headers: bpf_helper_defs.h
+install_headers: $(BPF_HELPER_DEFS)
$(call QUIET_INSTALL, headers) \
$(call do_install,bpf.h,$(prefix)/include/bpf,644); \
$(call do_install,libbpf.h,$(prefix)/include/bpf,644); \
@@ -251,7 +252,7 @@ install_headers: bpf_helper_defs.h
$(call do_install,libbpf_util.h,$(prefix)/include/bpf,644); \
$(call do_install,xsk.h,$(prefix)/include/bpf,644); \
$(call do_install,bpf_helpers.h,$(prefix)/include/bpf,644); \
- $(call do_install,bpf_helper_defs.h,$(prefix)/include/bpf,644); \
+ $(call do_install,$(BPF_HELPER_DEFS),$(prefix)/include/bpf,644); \
$(call do_install,bpf_tracing.h,$(prefix)/include/bpf,644); \
$(call do_install,bpf_endian.h,$(prefix)/include/bpf,644); \
$(call do_install,bpf_core_read.h,$(prefix)/include/bpf,644);
@@ -271,7 +272,7 @@ install: install_lib install_pkgconfig
clean:
$(call QUIET_CLEAN, libbpf) $(RM) -rf $(CMD_TARGETS) \
*.o *~ *.a *.so *.so.$(LIBBPF_MAJOR_VERSION) .*.d .*.cmd \
- *.pc LIBBPF-CFLAGS bpf_helper_defs.h \
+ *.pc LIBBPF-CFLAGS $(BPF_HELPER_DEFS) \
$(SHARED_OBJDIR) $(STATIC_OBJDIR)
$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index 419652458da4..1ff0a9f49c01 100644
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -40,3 +40,4 @@ xdping
test_cpp
/no_alu32
/bpf_gcc
+bpf_helper_defs.h
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index e0fe01d9ec33..e2fd6f8d579c 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -120,9 +120,9 @@ $(OUTPUT)/test_cgroup_attach: cgroup_helpers.c
$(BPFOBJ): force
$(MAKE) -C $(BPFDIR) OUTPUT=$(OUTPUT)/

-BPF_HELPERS := $(BPFDIR)/bpf_helper_defs.h $(wildcard $(BPFDIR)/bpf_*.h)
-$(BPFDIR)/bpf_helper_defs.h:
- $(MAKE) -C $(BPFDIR) OUTPUT=$(OUTPUT)/ bpf_helper_defs.h
+BPF_HELPERS := $(OUTPUT)/bpf_helper_defs.h $(wildcard $(BPFDIR)/bpf_*.h)
+$(OUTPUT)/bpf_helper_defs.h:
+ $(MAKE) -C $(BPFDIR) OUTPUT=$(OUTPUT)/ $(OUTPUT)/bpf_helper_defs.h

# Get Clang's default includes on this system, as opposed to those seen by
# '-target bpf'. This fixes "missing" files on some architectures/distros,
--
2.24.1.735.g03f4e72817-goog
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