linux-kernel - [PATCH v4 13/24] tracing: Check for undefined symbols in simple_ring

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Message-ID: <20250506164820.515876-14-vdonnefort@google.com>
Date: Tue,  6 May 2025 17:48:09 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com, 
	linux-trace-kernel@...r.kernel.org, maz@...nel.org, oliver.upton@...ux.dev, 
	joey.gouly@....com, suzuki.poulose@....com, yuzenghui@...wei.com
Cc: kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	jstultz@...gle.com, qperret@...gle.com, will@...nel.org, 
	kernel-team@...roid.com, linux-kernel@...r.kernel.org, 
	Vincent Donnefort <vdonnefort@...gle.com>
Subject: [PATCH v4 13/24] tracing: Check for undefined symbols in simple_ring_buffer

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@...gle.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