selftests: add default rules for c source file

There are difference rules for compiling c source file in different
testcases. In order to enable KBUILD_OUTPUT support in later patch,
this patch introduce the default rules in
"tools/testing/selftest/lib.mk" and remove the existing rules in each
testcase.

Acked-by: Michael Ellerman <[e-mail]>
Signed-off-by: Bamvor Jian Zhang <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/exec/Makefile

···
 execveat.denatured: execveat
 	cp $< $@
 	chmod -x $@
-%: %.c
-	$(CC) $(CFLAGS) -o $@ $^
 
 TEST_GEN_PROGS := execveat
 TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir

tools/testing/selftests/lib.mk

···
 clean:
 	$(RM) -r $(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED) $(TEST_GEN_FILES)
 
+%: %.c
+	$(CC) $(CFLAGS) $(LDFLAGS) $(LDLIBS) -o $@ $^
+
 .PHONY: run_tests all clean install emit_tests

tools/testing/selftests/mount/Makefile

···
 CFLAGS = -Wall \
          -O2
 
-unprivileged-remount-test: unprivileged-remount-test.c
-	$(CC) $(CFLAGS) unprivileged-remount-test.c -o unprivileged-remount-test
-
 TEST_GEN_PROGS := unprivileged-remount-test
 
 include ../lib.mk

tools/testing/selftests/net/Makefile

···
 CFLAGS += -I../../../../usr/include/
 
 reuseport_bpf_numa: LDFLAGS += -lnuma
-%: %.c
-	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^
 
 TEST_PROGS := run_netsocktests run_afpackettests test_bpf.sh
 TEST_GEN_FILES =  socket

tools/testing/selftests/size/Makefile

···
-
-get_size: get_size.c
-	$(CC) -static -ffreestanding -nostartfiles -s $< -o $@
+CFLAGS := -static -ffreestanding -nostartfiles -s
 
 TEST_GEN_PROGS := get_size
 

tools/testing/selftests/vm/Makefile

···
 # Makefile for vm selftests
 
 CFLAGS = -Wall -I ../../../../usr/include $(EXTRA_CFLAGS)
+LDLIBS = -lrt
 TEST_GEN_FILES = compaction_test
 TEST_GEN_FILES += hugepage-mmap
 TEST_GEN_FILES += hugepage-shm
···
 TEST_GEN_FILES += userfaultfd
 TEST_GEN_FILES += mlock-random-test
 
-%: %.c
-	$(CC) $(CFLAGS) -o $@ $^ -lrt
-userfaultfd: userfaultfd.c ../../../../usr/include/linux/kernel.h
-	$(CC) $(CFLAGS) -O2 -o $@ $< -lpthread
-
-mlock-random-test: mlock-random-test.c
-	$(CC) $(CFLAGS) -o $@ $< -lcap
-
-../../../../usr/include/linux/kernel.h:
-	make -C ../../../.. headers_install
-
 TEST_PROGS := run_vmtests
 
 include ../lib.mk
 
+userfaultfd: LDLIBS += -lpthread ../../../../usr/include/linux/kernel.h
+mlock-random-test: LDLIBS += -lcap
+
+../../../../usr/include/linux/kernel.h:
+	make -C ../../../.. headers_install