bpf/selftests: Allow vmtest.sh to build statically linked test_progs.

Dynamic linking when compiling on the host can cause issues when the
libc version does not match the one in the VM image.
Allow the user to use static compilation when this issue arises:

Before:
  ./vmtest.sh -- ./test_progs -t test_ima
  ./test_progs: /usr/lib/libc.so.6: version `GLIBC_2.33' not found (required by ./test_progs)

After:

  TRUNNER_LDFLAGS=-static ./vmtest.sh -- ./test_progs -t test_ima
  test_ima:OK
  Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED

Not using static as the default as some distros may not have dependent
static libraries.

Reported-by: "Geyslan G. Bem" <[email protected]>
Signed-off-by: KP Singh <[email protected]>

Author: KP Singh

tools/testing/selftests/bpf/Makefile

@@ -162,7 +162,7 @@ $(MAKE_DIRS):
 
 $(OUTPUT)/%.o: %.c
 	$(call msg,CC,,$@)
-	$(Q)$(CC) $(CFLAGS) -c $(filter %.c,$^) $(LDLIBS) -o $@
+	$(Q)$(CC) $(CFLAGS) $(TRUNNER_LDFLAGS) -c $(filter %.c,$^) $(LDLIBS) -o $@
 
 $(OUTPUT)/%:%.c
 	$(call msg,BINARY,,$@)
@@ -468,7 +468,7 @@ $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS)			\
 			     $(RESOLVE_BTFIDS)				\
 			     | $(TRUNNER_BINARY)-extras
 	$$(call msg,BINARY,,$$@)
-	$(Q)$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) -o $$@
+	$(Q)$$(CC) $$(CFLAGS) $(TRUNNER_LDFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) -o $$@
 	$(Q)$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.o $$@
 	$(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/bootstrap/bpftool $(if $2,$2/)bpftool
 

tools/testing/selftests/bpf/vmtest.sh

@@ -37,6 +37,7 @@ NUM_COMPILE_JOBS="$(nproc)"
 LOG_FILE_BASE="$(date +"bpf_selftests.%Y-%m-%d_%H-%M-%S")"
 LOG_FILE="${LOG_FILE_BASE}.log"
 EXIT_STATUS_FILE="${LOG_FILE_BASE}.exit_status"
+TRUNNER_LDFLAGS="${TRUNNER_LDFLAGS:=""}"
 
 usage()
 {
@@ -155,7 +156,7 @@ update_selftests()
 	local selftests_dir="${kernel_checkout}/tools/testing/selftests/bpf"
 
 	cd "${selftests_dir}"
-	${make_command}
+	${make_command} TRUNNER_LDFLAGS="${TRUNNER_LDFLAGS}"
 
 	# Mount the image and copy the selftests to the image.
 	mount_image