linux/export.h: make <linux/export.h> independent of CONFIG_MODULES

Currently, all files with EXPORT_SYMBOL() are rebuilt when CONFIG_MODULES
is flipped due to <linux/export.h> depending on CONFIG_MODULES.

Now that modpost can make a final decision about export symbols,
<linux/export.h> does not need to make EXPORT_SYMBOL() no-op.
Instead, modpost can skip emitting KSYMTAB when CONFIG_MODULES is unset.

This commit will reduce the number of recompilation when CONFIG_MODULES
is toggled.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

include/linux/export.h

@@ -50,7 +50,7 @@ extern struct module __this_module;
 		__EXPORT_SYMBOL_REF(sym)	ASM_NL	\
 	.previous
 
-#if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)
+#if defined(__DISABLE_EXPORTS)
 
 /*
  * Allow symbol exports to be disabled completely so that C code may
@@ -75,7 +75,7 @@ extern struct module __this_module;
 	__ADDRESSABLE(sym)					\
 	asm(__stringify(___EXPORT_SYMBOL(sym, license, ns)))
 
-#endif /* CONFIG_MODULES */
+#endif
 
 #ifdef DEFAULT_SYMBOL_NAMESPACE
 #define _EXPORT_SYMBOL(sym, license)	__EXPORT_SYMBOL(sym, license, __stringify(DEFAULT_SYMBOL_NAMESPACE))

scripts/Makefile.modpost

@@ -41,6 +41,7 @@ include $(srctree)/scripts/Kbuild.include
 MODPOST = scripts/mod/modpost
 
 modpost-args =										\
+	$(if $(CONFIG_MODULES),-M)							\
 	$(if $(CONFIG_MODVERSIONS),-m)							\
 	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
 	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\

scripts/mod/modpost.c

@@ -24,6 +24,7 @@
 #include "../../include/linux/license.h"
 #include "../../include/linux/module_symbol.h"
 
+static bool module_enabled;
 /* Are we using CONFIG_MODVERSIONS? */
 static bool modversions;
 /* Is CONFIG_MODULE_SRCVERSION_ALL set? */
@@ -1242,7 +1243,7 @@ static void check_section_mismatch(struct module *mod, struct elf_info *elf,
 	const char *tosec = sec_name(elf, get_secindex(elf, sym));
 	const struct sectioncheck *mismatch;
 
-	if (elf->export_symbol_secndx == fsecndx) {
+	if (module_enabled && elf->export_symbol_secndx == fsecndx) {
 		check_export_symbol(mod, elf, faddr, tosec, sym);
 		return;
 	}
@@ -2272,7 +2273,7 @@ int main(int argc, char **argv)
 	LIST_HEAD(dump_lists);
 	struct dump_list *dl, *dl2;
 
-	while ((opt = getopt(argc, argv, "ei:mnT:to:au:WwENd:")) != -1) {
+	while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:")) != -1) {
 		switch (opt) {
 		case 'e':
 			external_module = true;
@@ -2282,6 +2283,9 @@ int main(int argc, char **argv)
 			dl->file = optarg;
 			list_add_tail(&dl->list, &dump_lists);
 			break;
+		case 'M':
+			module_enabled = true;
+			break;
 		case 'm':
 			modversions = true;
 			break;