modpost: check static EXPORT_SYMBOL* by modpost again

Commit 31cb50b5 ("kbuild: check static EXPORT_SYMBOL* by script
instead of modpost") moved the static EXPORT_SYMBOL* check from the
mostpost to a shell script because I thought it must be checked per
compilation unit to avoid false negatives.

I came up with an idea to do this in modpost, against combined ELF
files. The relocation entries in ELF will find the correct exported
symbol even if there exist symbols with the same name in different
compilation units.

Again, the same sample code.

  Makefile:

    obj-y += foo1.o foo2.o

  foo1.c:

    #include <linux/export.h>
    static void foo(void) {}
    EXPORT_SYMBOL(foo);

  foo2.c:

    void foo(void) {}

Then, modpost can catch it correctly.

    MODPOST Module.symvers
  ERROR: modpost: vmlinux: local symbol 'foo' was exported
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

scripts/Makefile.build

@@ -222,8 +222,6 @@ cmd_gen_ksymdeps = \
 	$(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
 endif
 
-cmd_check_local_export = $(srctree)/scripts/check-local-export $@
-
 ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
 cmd_warn_shared_object = $(if $(word 2, $(modname-multi)),$(warning $(kbuild-file): $*.o is added to multiple modules: $(modname-multi)))
 endif
@@ -231,7 +229,6 @@ endif
 define rule_cc_o_c
 	$(call cmd_and_fixdep,cc_o_c)
 	$(call cmd,gen_ksymdeps)
-	$(call cmd,check_local_export)
 	$(call cmd,checksrc)
 	$(call cmd,checkdoc)
 	$(call cmd,gen_objtooldep)
@@ -243,7 +240,6 @@ endef
 define rule_as_o_S
 	$(call cmd_and_fixdep,as_o_S)
 	$(call cmd,gen_ksymdeps)
-	$(call cmd,check_local_export)
 	$(call cmd,gen_objtooldep)
 	$(call cmd,gen_symversions_S)
 	$(call cmd,warn_shared_object)

scripts/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 $?

scripts/mod/modpost.c

@@ -1210,6 +1210,13 @@ static void check_export_symbol(struct module *mod, struct elf_info *elf,
 		return;
 	}
 
+	if (ELF_ST_BIND(sym->st_info) != STB_GLOBAL &&
+	    ELF_ST_BIND(sym->st_info) != STB_WEAK) {
+		error("%s: local symbol '%s' was exported\n", mod->name,
+		      label_name + strlen(prefix));
+		return;
+	}
+
 	name = sym_name(elf, sym);
 	if (strcmp(label_name + strlen(prefix), name)) {
 		error("%s: .export_symbol section references '%s', but it does not seem to be an export symbol\n",