selftests/bpf: Allow selftests to build with older xxd

Currently selftests require xxd with the "-n <name>" option
which allows the user to specify a name not derived from
the input object path.  Instead of relying on this newer
feature, older xxd can be used if we link our desired name
("test_progs_verification_cert") to the input object.

Many distros ship xxd in vim-common package and do not have
the latest xxd with -n support.

Fixes: b720903 ("selftests/bpf: Enable signature verification for some lskel tests")
Signed-off-by: Alan Maguire <[email protected]>

Author: alan-maguire

tools/testing/selftests/bpf/Makefile

@@ -731,7 +731,8 @@ $(VERIFICATION_CERT) $(PRIVATE_KEY): $(VERIFY_SIG_SETUP)
 	$(Q)$(VERIFY_SIG_SETUP) genkey $(BUILD_DIR)
 
 $(VERIFY_SIG_HDR): $(VERIFICATION_CERT)
-	$(Q)xxd -i -n test_progs_verification_cert $< > $@
+	$(Q)ln -fs $< test_progs_verification_cert && \
+	xxd -i test_progs_verification_cert > $@
 
 # Define test_progs test runner.
 TRUNNER_TESTS_DIR := prog_tests