[PATCH v2 bpf-next] bpf/selftests: Allow vmtest.sh to build statically linked test_progs.

[KP Singh <kpsingh@kernel.org>]

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" <geyslan@gmail.com>
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 tools/testing/selftests/bpf/Makefile  | 4 ++--
 tools/testing/selftests/bpf/vmtest.sh | 3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index fe12b4f5fe20..2473c9b0cb2e 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/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
 
diff --git a/tools/testing/selftests/bpf/vmtest.sh b/tools/testing/selftests/bpf/vmtest.sh
index e0bb04a97e10..9e4d8eefcd07 100755
--- a/tools/testing/selftests/bpf/vmtest.sh
+++ b/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
-- 
2.35.1.616.g0bdcbb4464-goog