[PATCH v4 13/24] tracing: Check for undefined symbols in simple_ring_buffer

[Vincent Donnefort]

The simple_ring_buffer implementation must remain simple enough to be
used by the pKVM hypervisor. Prevent the object build if unresolved
symbols are found.

Signed-off-by: Vincent Donnefort <vdonnefort at google.com>

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 8f5e194eba71..a2f1489e11af 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -114,4 +114,19 @@ obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o
 obj-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o
 obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o
 
+#
+# simple_ring_buffer is used by the pKVM hypervisor which does not have access
+# to all kernel symbols. Fail the build if forbidden symbols are found.
+#
+UNDEFINED_ALLOWLIST := alt_cb_patch_nops
+UNDEFINED_ALLOWLIST := $(addprefix -e , $(UNDEFINED_ALLOWLIST))
+
+quiet_cmd_check_undefined = NM      $<
+      cmd_check_undefined = test -z "`$(NM) -u $< | grep -v $(UNDEFINED_ALLOWLIST)`"
+
+$(obj)/%.o.checked: $(obj)/%.o FORCE
+	$(call if_changed,check_undefined)
+
+always-$(CONFIG_SIMPLE_RING_BUFFER) +=  simple_ring_buffer.o.checked
+
 libftrace-y := ftrace.o
-- 
2.49.0.967.g6a0df3ecc3-goog