tracing: Adjust cmd_check_undefined to show unexpected undefined symbols

When the check_undefined command in kernel/trace/Makefile fails, there
is no output, making it hard to understand why the build failed. Capture
the output of the $(NM) + grep command and print it when failing to make
it clearer what the problem is.

Fixes: a717943d8ecc ("tracing: Check for undefined symbols in simple_ring_buffer")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260320-cmd_check_undefined-verbose-v1-1-54fc5b061f94@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index c5e14ffd36ee2263c915aa66150c8a41ccc33288..d662c1a64cd556f51d3357748ff4bd94a141abd3 100644 (file)
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -174,7 +174,13 @@ UNDEFINED_ALLOWLIST = __asan __gcov __kasan __kcsan __hwasan __sancov __sanitize
                      $(shell $(NM) -u $(obj)/undefsyms_base.o 2>/dev/null | awk '{print $$2}')
 
 quiet_cmd_check_undefined = NM      $<
-      cmd_check_undefined = test -z "`$(NM) -u $< | grep -v $(addprefix -e , $(UNDEFINED_ALLOWLIST))`"
+      cmd_check_undefined = \
+          undefsyms=$$($(NM) -u $< | grep -v $(addprefix -e , $(UNDEFINED_ALLOWLIST)) || true); \
+          if [ -n "$$undefsyms" ]; then \
+              echo "Unexpected symbols in $<:" >&2; \
+              echo "$$undefsyms" >&2; \
+              false; \
+          fi
 
 $(obj)/%.o.checked: $(obj)/%.o $(obj)/undefsyms_base.o FORCE
        $(call if_changed,check_undefined)