[PATCH bpf-next v4] selftests/bpf: use auto-dependencies for test objects

Ihor Solodrai
2024-07-18T22:57:54Z

Make use of -M compiler options when building .test.o objects to
generate .d files and avoid re-building all tests every time.

Previously, if a single test bpf program under selftests/bpf/progs/*.c
has changed, make would rebuild all the *.bpf.o, *.skel.h and *.test.o
objects, which is a lot of unnecessary work.

A typical dependency chain is:
progs/x.c -> x.bpf.o -> x.skel.h -> x.test.o -> trunner_binary

However for many tests it's not a 1:1 mapping by name, and so far
%.test.o have been simply dependent on all %.skel.h files, and
%.skel.h files on all %.bpf.o objects.

Avoid full rebuilds by instructing the compiler (via -MMD) to
produce *.d files with real dependencies, and appropriately including
them. Exploit make feature that rebuilds included makefiles if they
were changed by setting %.test.d as prerequisite for %.test.o files.

A couple of examples of compilation time speedup (after the first
clean build):

$ touch progs/verifier_and.c && time make -j8
Before: real 0m16.651s
After: real 0m2.245s
$ touch progs/read_vsyscall.c && time make -j8
Before: real 0m15.743s
After: real 0m1.575s

A drawback of this change is that now there is an overhead due to make
processing lots of .d files, which potentially may slow down unrelated
targets. However a time to make all from scratch hasn't changed
significantly:

$ make clean && time make -j8
Before: real 1m31.148s
After: real 1m30.309s

Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@pm.me>

---
v3 -> v4: Make $(TRUNNER_BPF_OBJS) order only prereq of trunner binary
v2 -> v3: Restore dependency on $(TRUNNER_BPF_OBJS)
v1 -> v2: Make %.test.d prerequisite order only
---
tools/testing/selftests/bpf/.gitignore | 1 +
tools/testing/selftests/bpf/Makefile | 44 +++++++++++++++++++-------
2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index 5025401323af..4e4aae8aa7ec 100644
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -31,6 +31,7 @@ test_tcp_check_syncookie_user
test_sysctl
xdping
test_cpp
+*.d
*.subskel.h
*.skel.h
*.lskel.h
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index dd49c1d23a60..66478446af9d 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -477,7 +477,8 @@ xsk_xdp_progs.skel.h-deps := xsk_xdp_progs.bpf.o
xdp_hw_metadata.skel.h-deps := xdp_hw_metadata.bpf.o
xdp_features.skel.h-deps := xdp_features.bpf.o

-LINKED_BPF_SRCS := $(patsubst %.bpf.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
+LINKED_BPF_OBJS := $(foreach skel,$(LINKED_SKELS),$($(skel)-deps))
+LINKED_BPF_SRCS := $(patsubst %.bpf.o,%.c,$(LINKED_BPF_OBJS))

# Set up extra TRUNNER_XXX "temporary" variables in the environment (relies on
# $eval()) and pass control to DEFINE_TEST_RUNNER_RULES.
@@ -556,7 +557,11 @@ $(TRUNNER_BPF_LSKELS): %.lskel.h: %.bpf.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
$(Q)$$(BPFTOOL) gen skeleton -L $$(<:.o=.llinked3.o) name $$(notdir $$(<:.bpf.o=_lskel)) > $$@
$(Q)rm -f $$(<:.o=.llinked1.o) $$(<:.o=.llinked2.o) $$(<:.o=.llinked3.o)

-$(TRUNNER_BPF_SKELS_LINKED): $(TRUNNER_BPF_OBJS) $(BPFTOOL) | $(TRUNNER_OUTPUT)
+$(LINKED_BPF_OBJS): %: $(TRUNNER_OUTPUT)/%
+
+# .SECONDEXPANSION here allows to correctly expand %-deps variables as prerequisites
+.SECONDEXPANSION:
+$(TRUNNER_BPF_SKELS_LINKED): $(TRUNNER_OUTPUT)/%: $$$$(%-deps) $(BPFTOOL) | $(TRUNNER_OUTPUT)
$$(call msg,LINK-BPF,$(TRUNNER_BINARY),$$(@:.skel.h=.bpf.o))
$(Q)$$(BPFTOOL) gen object $$(@:.skel.h=.linked1.o) $$(addprefix $(TRUNNER_OUTPUT)/,$$($$(@F)-deps))
$(Q)$$(BPFTOOL) gen object $$(@:.skel.h=.linked2.o) $$(@:.skel.h=.linked1.o)
@@ -566,6 +571,14 @@ $(TRUNNER_BPF_SKELS_LINKED): $(TRUNNER_BPF_OBJS) $(BPFTOOL) | $(TRUNNER_OUTPUT)
$(Q)$$(BPFTOOL) gen skeleton $$(@:.skel.h=.linked3.o) name $$(notdir $$(@:.skel.h=)) > $$@
$(Q)$$(BPFTOOL) gen subskeleton $$(@:.skel.h=.linked3.o) name $$(notdir $$(@:.skel.h=)) > $$(@:.skel.h=.subskel.h)
$(Q)rm -f $$(@:.skel.h=.linked1.o) $$(@:.skel.h=.linked2.o) $$(@:.skel.h=.linked3.o)
+
+# When the compiler generates a %.d file, only skel basenames (not
+# full paths) are specified as prerequisites for corresponding %.o
+# file. This target makes %.skel.h basename dependent on full paths,
+# linking generated %.d dependency with actual %.skel.h files.
+$(notdir %.skel.h): $(TRUNNER_OUTPUT)/%.skel.h
+ @true
+
endif

# ensure we set up tests.h header generation rule just once
@@ -583,14 +596,20 @@ endif
# Note: we cd into output directory to ensure embedded BPF object is found
$(TRUNNER_TEST_OBJS): $(TRUNNER_OUTPUT)/%.test.o: \
$(TRUNNER_TESTS_DIR)/%.c \
- $(TRUNNER_EXTRA_HDRS) \
- $(TRUNNER_BPF_OBJS) \
- $(TRUNNER_BPF_SKELS) \
- $(TRUNNER_BPF_LSKELS) \
- $(TRUNNER_BPF_SKELS_LINKED) \
- $$(BPFOBJ) | $(TRUNNER_OUTPUT)
+ $(TRUNNER_OUTPUT)/%.test.d
$$(call msg,TEST-OBJ,$(TRUNNER_BINARY),$$@)
- $(Q)cd $$(@D) && $$(CC) -I. $$(CFLAGS) -c $(CURDIR)/$$< $$(LDLIBS) -o $$(@F)
+ $(Q)cd $$(@D) && $$(CC) -I. $$(CFLAGS) -MMD -MT $$@ -c $(CURDIR)/$$< $$(LDLIBS) -o $$(@F)
+
+$(TRUNNER_TEST_OBJS:.o=.d): $(TRUNNER_OUTPUT)/%.test.d: \
+ $(TRUNNER_TESTS_DIR)/%.c \
+ $(TRUNNER_EXTRA_HDRS) \
+ $(TRUNNER_BPF_SKELS) \
+ $(TRUNNER_BPF_LSKELS) \
+ $(TRUNNER_BPF_SKELS_LINKED) \
+ $$(BPFOBJ) | $(TRUNNER_OUTPUT)
+
+include $(wildcard $(TRUNNER_TEST_OBJS:.o=.d))
+

$(TRUNNER_EXTRA_OBJS): $(TRUNNER_OUTPUT)/%.o: \
%.c \
@@ -608,6 +627,9 @@ ifneq ($2:$(OUTPUT),:$(shell pwd))
$(Q)rsync -aq $$^ $(TRUNNER_OUTPUT)/
endif

+# some X.test.o files have runtime dependencies on Y.bpf.o files
+$(OUTPUT)/$(TRUNNER_BINARY): | $(TRUNNER_BPF_OBJS)
+
$(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS) \
$(TRUNNER_EXTRA_OBJS) $$(BPFOBJ) \
$(RESOLVE_BTFIDS) \
@@ -768,8 +790,8 @@ $(OUTPUT)/uprobe_multi: uprobe_multi.c

EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR) \
prog_tests/tests.h map_tests/tests.h verifier/tests.h \
- feature bpftool \
- $(addprefix $(OUTPUT)/,*.o *.skel.h *.lskel.h *.subskel.h \
+ feature bpftool \
+ $(addprefix $(OUTPUT)/,*.o *.d *.skel.h *.lskel.h *.subskel.h \
no_alu32 cpuv4 bpf_gcc bpf_testmod.ko \
bpf_test_no_cfi.ko \
liburandom_read.so)
--
2.34.1