1 files changed, 70 insertions, 0 deletions
diff --git a/scripts/check-local-export b/scripts/check-local-export
new file mode 100755
index 000000000000..f90b5a9c67b3
--- /dev/null
+++ b/scripts/check-local-export
@@ -0,0 +1,70 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Copyright (C) 2022 Masahiro Yamada <masahiroy@kernel.org>
+# Copyright (C) 2022 Owen Rafferty <owen@owenrafferty.com>
+#
+# Exit with error if a local exported symbol is found.
+# EXPORT_SYMBOL should be used for global symbols.
+
+set -e
+pid=$$
+
+# If there is no symbol in the object, ${NM} (both GNU nm and llvm-nm) shows
+# 'no symbols' diagnostic (but exits with 0). It is harmless and hidden by
+# '2>/dev/null'. However, it suppresses real error messages as well. Add a
+# hand-crafted error message here.
+#
+# TODO:
+# Use --quiet instead of 2>/dev/null when we upgrade the minimum version of
+# binutils to 2.37, llvm to 13.0.0.
+# Then, the following line will be simpler:
+#   { ${NM} --quiet ${1} || kill 0; } |
+
+{ ${NM} ${1} 2>/dev/null || { echo "${0}: ${NM} failed" >&2; kill $pid; } } |
+${AWK} -v "file=${1}" '
+BEGIN {
+	i = 0
+}
+
+# Skip the line if the number of fields is less than 3.
+#
+# case 1)
+#   For undefined symbols, the first field (value) is empty.
+#   The outout looks like this:
+#     "                 U _printk"
+#   It is unneeded to record undefined symbols.
+#
+# case 2)
+#   For Clang LTO, llvm-nm outputs a line with type t but empty name:
+#     "---------------- t"
+!length($3) {
+	next
+}
+
+# save (name, type) in the associative array
+{ symbol_types[$3]=$2 }
+
+# append the exported symbol to the array
+($3 ~ /^__ksymtab_/) {
+	export_symbols[i] = $3
+	sub(/^__ksymtab_/, "", export_symbols[i])
+	i++
+}
+
+END {
+	exit_code = 0
+	for (j = 0; j < i; ++j) {
+		name = export_symbols[j]
+		# nm(3) says "If lowercase, the symbol is usually local"
+		if (symbol_types[name] ~ /[a-z]/) {
+			printf "%s: error: local symbol %s was exported\n",
+				file, name | "cat 1>&2"
+			exit_code = 1
+		}
+	}
+
+	exit exit_code
+}'
+
+exit $?