Bpftool's Makefile uses $(HOST_CFLAGS) to build the bootstrap version of bpftool, in order to pick the flags for the host (where we run the bootstrap version) and not for the target system (where we plan to run the full bpftool binary). But we pass too much information through this variable. In particular, we set HOST_CFLAGS by copying most of the $(CFLAGS); but we do this after the feature detection for bpftool, which means that $(CFLAGS), hence $(HOST_CFLAGS), contain all macro definitions for using the different optional features. For example, -DHAVE_LLVM_SUPPORT may be passed to the $(HOST_CFLAGS), even though the LLVM disassembler is not used in the bootstrap version, and the related library may even be missing for the host architecture. A similar thing happens with the $(LDFLAGS), that we use unchanged for linking the bootstrap version even though they may contains flags to link against additional libraries. To address the $(HOST_CFLAGS) issue, we move the definition of $(HOST_CFLAGS) earlier in the Makefile, before the $(CFLAGS) update resulting from the feature probing - none of which being relevant to the bootstrap version. To clean up the $(LDFLAGS) for the bootstrap version, we introduce a dedicated $(HOST_LDFLAGS) variable that we base on $(LDFLAGS), before the feature probing as well. On my setup, the following macro and libraries are removed from the compiler invocation to build bpftool after this patch: -DUSE_LIBCAP -DHAVE_LLVM_SUPPORT -I/usr/lib/llvm-17/include -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -lLLVM-17 -L/usr/lib/llvm-17/lib Another advantage of cleaning up these flags is that displaying available features with "bpftool version" becomes more accurate for the bootstrap bpftool, and no longer reflects the features detected (and available only) for the final binary. Cc: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> Signed-off-by: Quentin Monnet <qmo@xxxxxxxxxx> --- tools/bpf/bpftool/Makefile | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile index e9154ace80ff..972f8d727130 100644 --- a/tools/bpf/bpftool/Makefile +++ b/tools/bpf/bpftool/Makefile @@ -89,6 +89,10 @@ ifneq ($(EXTRA_LDFLAGS),) LDFLAGS += $(EXTRA_LDFLAGS) endif +HOST_CFLAGS := $(subst -I$(LIBBPF_INCLUDE),-I$(LIBBPF_BOOTSTRAP_INCLUDE),\ + $(subst $(CLANG_CROSS_FLAGS),,$(CFLAGS))) +HOST_LDFLAGS := $(LDFLAGS) + INSTALL ?= install RM ?= rm -f @@ -178,9 +182,6 @@ ifeq ($(filter -DHAVE_LLVM_SUPPORT -DHAVE_LIBBFD_SUPPORT,$(CFLAGS)),) SRCS := $(filter-out jit_disasm.c,$(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) @@ -238,7 +239,7 @@ $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c $(QUIET_CC)$(CC) $(CFLAGS) -c -MMD $< -o $@ $(BPFTOOL_BOOTSTRAP): $(BOOTSTRAP_OBJS) $(LIBBPF_BOOTSTRAP) - $(QUIET_LINK)$(HOSTCC) $(HOST_CFLAGS) $(LDFLAGS) $(BOOTSTRAP_OBJS) $(LIBS_BOOTSTRAP) -o $@ + $(QUIET_LINK)$(HOSTCC) $(HOST_CFLAGS) $(HOST_LDFLAGS) $(BOOTSTRAP_OBJS) $(LIBS_BOOTSTRAP) -o $@ $(OUTPUT)bpftool: $(OBJS) $(LIBBPF) $(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $(OBJS) $(LIBS) -o $@ -- 2.34.1
