Hi Andrii, thanks for a review. On Monday, August 26th, 2024 at 2:59 PM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: [...] > I'm not sure what md5sum buys us here, tbh... To compute checksum you > need to read entire contents anyways, so you are not really saving > anything performance-wise. > > I was originally thinking that we'll extend existing rule for > $(INCLUDE_DIR)/vmlinux.h to do bpftool dump into temporary file, then > do `cmp --silent` over it and existing vmlinux.h (if it does exist, of > course), and if they are identical just exit and not modify anything. > If not, we just mv temp file over destination vmlinux.h. > > In my head this would prevent make from triggering dependent targets > because vmlinux.h's modification time won't change. > > Does the above not work? I tried your suggestion and it works too. I like it better, as it's a smaller change (see below). A checksum was just the first idea I had about saving the previous state of vmlinux.h, and I went with it. Copying an entire file seemed excessive to me, but it's not necessary as it turns out. Please let me know if the cmp version is ok, and I'll send v2 of the patch. diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index c120617b64ad..25412b9194bd 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -402,7 +402,8 @@ endif $(INCLUDE_DIR)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) | $(INCLUDE_DIR) ifeq ($(VMLINUX_H),) $(call msg,GEN,,$@) - $(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@ + $(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $(INCLUDE_DIR)/.vmlinux.h.tmp + $(Q)cmp -s $(INCLUDE_DIR)/.vmlinux.h.tmp $@ || mv $(INCLUDE_DIR)/.vmlinux.h.tmp $@ else $(call msg,CP,,$@) $(Q)cp "$(VMLINUX_H)" $@ @@ -516,6 +517,12 @@ xdp_features.skel.h-deps := xdp_features.bpf.o LINKED_BPF_OBJS := $(foreach skel,$(LINKED_SKELS),$($(skel)-deps)) LINKED_BPF_SRCS := $(patsubst %.bpf.o,%.c,$(LINKED_BPF_OBJS)) +HEADERS_FOR_BPF_OBJS := $(wildcard $(BPFDIR)/*.bpf.h) \ + $(addprefix $(BPFDIR)/, bpf_core_read.h \ + bpf_endian.h \ + bpf_helpers.h \ + bpf_tracing.h) + # Set up extra TRUNNER_XXX "temporary" variables in the environment (relies on # $eval()) and pass control to DEFINE_TEST_RUNNER_RULES. # Parameters: @@ -566,8 +573,7 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.bpf.o: \ $(TRUNNER_BPF_PROGS_DIR)/%.c \ $(TRUNNER_BPF_PROGS_DIR)/*.h \ $$(INCLUDE_DIR)/vmlinux.h \ - $(wildcard $(BPFDIR)/bpf_*.h) \ - $(wildcard $(BPFDIR)/*.bpf.h) \ + $(HEADERS_FOR_BPF_OBJS) \ | $(TRUNNER_OUTPUT) $$(BPFOBJ) $$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@, \ $(TRUNNER_BPF_CFLAGS) \ -- 2.34.1
