selftests/bpf: Use auto-dependencies for test objects

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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/VJihUTnvtwEgv_mOnpfy7EgD9D2MPNoHO-MlANeLIzLJPGhDeyOuGKIYyKgk0O6KPjfM-MuhtvPwZcngN8WFqbTnTRyCSMc2aMZ1ODm1T_g=@pm.me

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index 5025401323afb53e3d1a26c05074ef5cbf39f3f9..4e4aae8aa7ec711dd546a1f259a668d52ad60307 100644 (file)
--- 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 dd49c1d23a604cc86953139576a57bf681ef7912..05b234248b3807e8901329789507695fa5c49525 100644 (file)
--- 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 +596,19 @@ 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 +626,9 @@ 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 +789,8 @@ $(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)