check-local-export

#!/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 ~ /^__export_symbol_.*/) {
	export_symbols[i] = $3
	sub(/^__export_symbol_/, "", 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 $?