From: Quentin Monnet Date: Sat, 9 Oct 2021 21:03:40 +0000 (+0100) Subject: bpftool: Do not FORCE-build libbpf X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=ced846c65e8ffdaac7138936cdbbc9337a939fb9;p=linux.git bpftool: Do not FORCE-build libbpf In bpftool's Makefile, libbpf has a FORCE dependency, to make sure we rebuild it in case its source files changed. Let's instead make the rebuild depend on the source files directly, through a call to the "$(wildcard ...)" function. This avoids descending into libbpf's directory if there is nothing to update. Do the same for the bootstrap libbpf version. This results in a slightly faster operation and less verbose output when running make a second time in bpftool's directory. Before: Auto-detecting system features: ... libbfd: [ on ] ... disassembler-four-args: [ on ] ... zlib: [ on ] ... libcap: [ on ] ... clang-bpf-co-re: [ on ] make[1]: Entering directory '/root/dev/linux/tools/lib/bpf' make[1]: Entering directory '/root/dev/linux/tools/lib/bpf' make[1]: Nothing to be done for 'install_headers'. make[1]: Leaving directory '/root/dev/linux/tools/lib/bpf' make[1]: Leaving directory '/root/dev/linux/tools/lib/bpf' After: Auto-detecting system features: ... libbfd: [ on ] ... disassembler-four-args: [ on ] ... zlib: [ on ] ... libcap: [ on ] ... clang-bpf-co-re: [ on ] Other ways to clean up the output could be to pass the "-s" option, or to redirect the output to >/dev/null, when calling make recursively to descend into libbpf's directory. However, this would suppress some useful output if something goes wrong during the build. A better alternative would be to pass "--no-print-directory" to the recursive make, but that would still leave us with some noise for "install_headers". Skipping the descent into libbpf's directory if no source file has changed works best, and seems the most logical option overall. Reported-by: Andrii Nakryiko Signed-off-by: Quentin Monnet Signed-off-by: Andrii Nakryiko Acked-by: John Fastabend Link: https://lore.kernel.org/bpf/20211009210341.6291-3-quentin@isovalent.com --- diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile index 646fd40b32533..331019f6d5b16 100644 --- a/tools/bpf/bpftool/Makefile +++ b/tools/bpf/bpftool/Makefile @@ -42,7 +42,7 @@ endif $(LIBBPF_OUTPUT) $(BOOTSTRAP_OUTPUT) $(LIBBPF_BOOTSTRAP_OUTPUT): $(QUIET_MKDIR)mkdir -p $@ -$(LIBBPF): FORCE | $(LIBBPF_OUTPUT) +$(LIBBPF): $(wildcard $(BPF_DIR)/*.[ch] $(BPF_DIR)/Makefile) | $(LIBBPF_OUTPUT) $(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_OUTPUT) \ DESTDIR=$(LIBBPF_DESTDIR) prefix= $(LIBBPF) install_headers @@ -50,7 +50,7 @@ $(LIBBPF_INTERNAL_HDRS): $(LIBBPF_HDRS_DIR)/%.h: $(BPF_DIR)/%.h $(LIBBPF) $(call QUIET_INSTALL, $@) $(Q)install -m 644 -t $(LIBBPF_HDRS_DIR) $< -$(LIBBPF_BOOTSTRAP): FORCE | $(LIBBPF_BOOTSTRAP_OUTPUT) +$(LIBBPF_BOOTSTRAP): $(wildcard $(BPF_DIR)/*.[ch] $(BPF_DIR)/Makefile) | $(LIBBPF_BOOTSTRAP_OUTPUT) $(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_BOOTSTRAP_OUTPUT) \ ARCH= CC=$(HOSTCC) LD=$(HOSTLD) $@