kbuild: Check for functions with ambiguous -ffunction-sections section names

Commit 9c7dc1d ("objtool: Warn on functions with ambiguous
-ffunction-sections section names") only works for drivers which are
compiled on architectures supported by objtool.

Make a script to perform the same check for all architectures.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/a6a49644a34964f7e02f3a8ce43af03e72817180.1763669451.git.jpoimboe@kernel.org

Author: jpoimboe

include/asm-generic/vmlinux.lds.h

@@ -110,7 +110,7 @@
  * .text.startup could be __attribute__((constructor)) code in a *non*
  * ffunction-sections object, which should be placed in .init.text; or it could
  * be an actual function named startup() in an ffunction-sections object, which
- * should be placed in .text.  Objtool will detect and complain about any such
+ * should be placed in .text.  The build will detect and complain about any such
  * ambiguously named functions.
  */
 #define TEXT_MAIN							\

scripts/Makefile.vmlinux_o

@@ -63,11 +63,15 @@ quiet_cmd_ld_vmlinux.o = LD      $@
 	--start-group $(KBUILD_VMLINUX_LIBS) --end-group \
 	$(cmd_objtool)
 
+cmd_check_function_names = $(srctree)/scripts/check-function-names.sh $@
+
 define rule_ld_vmlinux.o
 	$(call cmd_and_savecmd,ld_vmlinux.o)
 	$(call cmd,gen_objtooldep)
+	$(call cmd,check_function_names)
 endef
 
+
 vmlinux.o: $(initcalls-lds) vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
 	$(call if_changed_rule,ld_vmlinux.o)
 

scripts/check-function-names.sh

@@ -0,0 +1,25 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Certain function names are disallowed due to section name ambiguities
+# introduced by -ffunction-sections.
+#
+# See the comment above TEXT_MAIN in include/asm-generic/vmlinux.lds.h.
+
+objfile="$1"
+
+if [ ! -f "$objfile" ]; then
+	echo "usage: $0 <file.o>" >&2
+	exit 1
+fi
+
+bad_symbols=$(nm "$objfile" | awk '$2 ~ /^[TtWw]$/ {print $3}' | grep -E '^(startup|exit|split|unlikely|hot|unknown)(\.|$)')
+
+if [ -n "$bad_symbols" ]; then
+	echo "$bad_symbols" | while read -r sym; do
+		echo "$objfile: error: $sym() function name creates ambiguity with -ffunction-sections" >&2
+	done
+	exit 1
+fi
+
+exit 0