[PATCH v2 3/4] selftests/hid: build the BPF program via the shared lib.bpf.mk

[Ziyang Men <ziyang.meme@gmail.com>]

hid carries its own ~150 lines of libbpf + bpftool + vmlinux.h +
BPF-object + skeleton build machinery, copied from selftests/bpf.
Replace it with an include of the shared
tools/testing/selftests/lib.bpf.mk, so that the previous ~150 lines of
BPF build configuration can now be achieved in only ~10 lines.

hid keeps the legacy progs/<name>.c layout, so it sets BPF_PROG_EXT := .c
and passes its shared BPF headers through BPF_EXTRA_HDRS.  It also gains
the fragment's -Wall on the BPF compile, which its old Makefile did not
set; hid.c has a few pre-existing unused locals, so
BPF_EXTRA_CFLAGS := -Wno-unused-variable keeps the previous behaviour
without touching the program source.

The conversion drops two pieces of dead machinery hid had copied from
selftests/bpf: a resolve_btfids build that was never a prerequisite of
any target, and a CLANG_CFLAGS variable that was never passed to any
compile.

No functional change: the generated hid.skel.h public API is
byte-identical before and after, hid_bpf and hidraw are built and linked
the same way, and the folder builds cleanly under both plain make and
LLVM=1.

Suggested-by: Shakeel Butt <shakeel.butt@linux.dev>
Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Suggested-by: Mykola Lysenko <mykolal@meta.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Ziyang Men <ziyang.meme@gmail.com>
---
 tools/testing/selftests/hid/Makefile | 182 +++------------------------
 1 file changed, 20 insertions(+), 162 deletions(-)

diff --git a/tools/testing/selftests/hid/Makefile b/tools/testing/selftests/hid/Makefile
index 2f423de83147..48def484703c 100644
--- a/tools/testing/selftests/hid/Makefile
+++ b/tools/testing/selftests/hid/Makefile
@@ -58,172 +58,31 @@ override define CLEAN
 	$(Q)$(RM) -r $(EXTRA_CLEAN)
 endef
 
-include ../lib.mk
+# The BPF program (progs/hid.c) is compiled into a skeleton by the shared
+# tools/testing/selftests/lib.bpf.mk fragment.  hid keeps the legacy
+# progs/<name>.c layout, so point BPF_PROG_EXT at .c and hand the fragment
+# hid's shared BPF headers as extra prerequisites.  BPF_EXTRA_HDRS is deferred
+# because it references $(BPFDIR), which lib.bpf.mk defines.
+BPF_SRCS       := progs/hid.c
+BPF_PROG_EXT   := .c
+BPF_EXTRA_HDRS  = $(wildcard progs/*.h) $(wildcard $(BPFDIR)/hid_bpf_*.h) \
+		  $(wildcard $(BPFDIR)/*.bpf.h)
+# hid.c predates the shared -Wall (hid's old Makefile didn't set it) and has a
+# few unused locals; tolerate that pre-existing warning without touching the
+# program source.
+BPF_EXTRA_CFLAGS := -Wno-unused-variable
 
-TOOLSDIR := $(top_srcdir)/tools
-LIBDIR := $(TOOLSDIR)/lib
-BPFDIR := $(LIBDIR)/bpf
-TOOLSINCDIR := $(TOOLSDIR)/include
-BPFTOOLDIR := $(TOOLSDIR)/bpf/bpftool
-SCRATCH_DIR := $(OUTPUT)/tools
-BUILD_DIR := $(SCRATCH_DIR)/build
-INCLUDE_DIR := $(SCRATCH_DIR)/include
-BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
-ifneq ($(CROSS_COMPILE),)
-HOST_BUILD_DIR		:= $(BUILD_DIR)/host
-HOST_SCRATCH_DIR	:= $(OUTPUT)/host-tools
-HOST_INCLUDE_DIR	:= $(HOST_SCRATCH_DIR)/include
-else
-HOST_BUILD_DIR		:= $(BUILD_DIR)
-HOST_SCRATCH_DIR	:= $(SCRATCH_DIR)
-HOST_INCLUDE_DIR	:= $(INCLUDE_DIR)
-endif
-HOST_BPFOBJ := $(HOST_BUILD_DIR)/libbpf/libbpf.a
-RESOLVE_BTFIDS := $(HOST_BUILD_DIR)/resolve_btfids/resolve_btfids
-
-VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)				\
-		     $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)	\
-		     ../../../../vmlinux				\
-		     /sys/kernel/btf/vmlinux				\
-		     /boot/vmlinux-$(shell uname -r)
-VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
-ifeq ($(VMLINUX_BTF),)
-$(error Cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)")
-endif
+include ../lib.mk
+include ../lib.bpf.mk
 
-# Define simple and short `make test_progs`, `make test_sysctl`, etc targets
-# to build individual tests.
+# Define simple and short `make hid_bpf`, `make hidraw` targets.
 # NOTE: Semicolon at the end is critical to override lib.mk's default static
 # rule for binaries.
 $(notdir $(TEST_GEN_PROGS)): %: $(OUTPUT)/% ;
 
-# sort removes libbpf duplicates when not cross-building
-MAKE_DIRS := $(sort $(BUILD_DIR)/libbpf $(HOST_BUILD_DIR)/libbpf		\
-	       $(HOST_BUILD_DIR)/bpftool $(HOST_BUILD_DIR)/resolve_btfids	\
-	       $(INCLUDE_DIR))
-$(MAKE_DIRS):
-	$(call msg,MKDIR,,$@)
-	$(Q)mkdir -p $@
-
-DEFAULT_BPFTOOL := $(HOST_SCRATCH_DIR)/sbin/bpftool
-
-TEST_GEN_PROGS_EXTENDED += $(DEFAULT_BPFTOOL)
-
-$(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED): $(BPFOBJ)
-
-BPFTOOL ?= $(DEFAULT_BPFTOOL)
-$(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)    \
-		    $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool
-	$(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)			       \
-		    ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD) 	       \
-		    EXTRA_CFLAGS='-g -O0'				       \
-		    OUTPUT=$(HOST_BUILD_DIR)/bpftool/			       \
-		    LIBBPF_OUTPUT=$(HOST_BUILD_DIR)/libbpf/		       \
-		    LIBBPF_DESTDIR=$(HOST_SCRATCH_DIR)/			       \
-		    prefix= DESTDIR=$(HOST_SCRATCH_DIR)/ install-bin
-
-$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
-	   | $(BUILD_DIR)/libbpf
-	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
-		    EXTRA_CFLAGS='-g -O0'				       \
-		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
-
-ifneq ($(BPFOBJ),$(HOST_BPFOBJ))
-$(HOST_BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
-		| $(HOST_BUILD_DIR)/libbpf
-	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR)                             \
-		    EXTRA_CFLAGS='-g -O0' ARCH= CROSS_COMPILE=		       \
-		    OUTPUT=$(HOST_BUILD_DIR)/libbpf/ CC=$(HOSTCC) LD=$(HOSTLD) \
-		    DESTDIR=$(HOST_SCRATCH_DIR)/ prefix= all install_headers
-endif
-
-$(INCLUDE_DIR)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) | $(INCLUDE_DIR)
-ifeq ($(VMLINUX_H),)
-	$(call msg,GEN,,$@)
-	$(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@
-else
-	$(call msg,CP,,$@)
-	$(Q)cp "$(VMLINUX_H)" $@
-endif
-
-$(RESOLVE_BTFIDS): $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/resolve_btfids	\
-		       $(TOOLSDIR)/bpf/resolve_btfids/main.c	\
-		       $(TOOLSDIR)/lib/rbtree.c			\
-		       $(TOOLSDIR)/lib/zalloc.c			\
-		       $(TOOLSDIR)/lib/string.c			\
-		       $(TOOLSDIR)/lib/ctype.c			\
-		       $(TOOLSDIR)/lib/str_error_r.c
-	$(Q)$(MAKE) $(submake_extras) -C $(TOOLSDIR)/bpf/resolve_btfids	\
-		CC=$(HOSTCC) LD=$(HOSTLD) AR=$(HOSTAR) \
-		LIBBPF_INCLUDE=$(HOST_INCLUDE_DIR) \
-		OUTPUT=$(HOST_BUILD_DIR)/resolve_btfids/ BPFOBJ=$(HOST_BPFOBJ)
-
-# Get Clang's default includes on this system, as opposed to those seen by
-# '--target=bpf'. This fixes "missing" files on some architectures/distros,
-# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
-#
-# Use '-idirafter': Don't interfere with include mechanics except where the
-# build would have failed anyways.
-define get_sys_includes
-$(shell $(1) -v -E - </dev/null 2>&1 \
-	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }') \
-$(shell $(1) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}')
-endef
-
-# Determine target endianness.
-IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
-			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
-MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
-
-CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
-BPF_CFLAGS = -g -Werror -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 		\
-	     -Wno-microsoft-anon-tag                                    \
-	     -fms-extensions                                            \
-	     -I$(INCLUDE_DIR)
-
-CLANG_CFLAGS = $(CLANG_SYS_INCLUDES) \
-	       -Wno-compare-distinct-pointer-types
-
-# Build BPF object using Clang
-# $1 - input .c file
-# $2 - output .o file
-# $3 - CFLAGS
-define CLANG_BPF_BUILD_RULE
-	$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
-	$(Q)$(CLANG) $3 -O2 --target=bpf -c $1 -mcpu=v3 -o $2
-endef
-# Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32
-define CLANG_NOALU32_BPF_BUILD_RULE
-	$(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2)
-	$(Q)$(CLANG) $3 -O2 --target=bpf -c $1 -mcpu=v2 -o $2
-endef
-# Build BPF object using GCC
-define GCC_BPF_BUILD_RULE
-	$(call msg,GCC-BPF,$(TRUNNER_BINARY),$2)
-	$(Q)$(BPF_GCC) $3 -O2 -c $1 -o $2
-endef
-
-BPF_PROGS_DIR := progs
-BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
-BPF_SRCS := $(notdir $(wildcard $(BPF_PROGS_DIR)/*.c))
-BPF_OBJS := $(patsubst %.c,$(OUTPUT)/%.bpf.o, $(BPF_SRCS))
-BPF_SKELS := $(patsubst %.c,$(OUTPUT)/%.skel.h, $(BPF_SRCS))
-TEST_GEN_FILES += $(BPF_OBJS)
-
-$(BPF_PROGS_DIR)-bpfobjs := y
-$(BPF_OBJS): $(OUTPUT)/%.bpf.o:				\
-	     $(BPF_PROGS_DIR)/%.c			\
-	     $(wildcard $(BPF_PROGS_DIR)/*.h)		\
-	     $(INCLUDE_DIR)/vmlinux.h				\
-	     $(wildcard $(BPFDIR)/hid_bpf_*.h)			\
-	     $(wildcard $(BPFDIR)/*.bpf.h)			\
-	     | $(OUTPUT) $(BPFOBJ)
-	$(call $(BPF_BUILD_RULE),$<,$@, $(BPF_CFLAGS))
-
-$(BPF_SKELS): %.skel.h: %.bpf.o $(BPFTOOL) | $(OUTPUT)
-	$(call msg,GEN-SKEL,$(BINARY),$@)
-	$(Q)$(BPFTOOL) gen object $(<:.o=.linked1.o) $<
-	$(Q)$(BPFTOOL) gen skeleton $(<:.o=.linked1.o) name $(notdir $(<:.bpf.o=)) > $@
+# Each test binary links against the in-tree static libbpf that lib.bpf.mk
+# built (lib.mk has already prefixed TEST_GEN_PROGS with $(OUTPUT)/).
+$(TEST_GEN_PROGS): $(BPFOBJ)
 
 $(OUTPUT)/%.o: %.c $(BPF_SKELS) hid_common.h
 	$(call msg,CC,,$@)
@@ -233,5 +92,4 @@ $(OUTPUT)/%: $(OUTPUT)/%.o
 	$(call msg,BINARY,,$@)
 	$(Q)$(LINK.c) $^ $(LDLIBS) -o $@
 
-EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR) feature bpftool	\
-	$(addprefix $(OUTPUT)/,*.o *.skel.h no_alu32)
+EXTRA_CLEAN += feature bpftool $(addprefix $(OUTPUT)/,*.o no_alu32)
-- 
2.53.0-Meta