kbuild: Bogus "has no CRC" in external module builds

From: Pavel Roskin <proski@gnu.org>
The recent fixes for the external module build have fixed the major
breakage, but they left one annoyance unfixed.  If CONFIG_MODVERSIONS is
disabled, a warning is printed for every exported symbol that is has no
CRC.  For instance, I see this when compiling the standalone Orinoco
driver on Linux 2.6.6-rc3:

*** Warning: "__orinoco_down" [/usr/local/src/orinoco/spectrum_cs.ko] has
no CRC!
*** Warning: "hermes_struct_init" [/usr/local/src/orinoco/spectrum_cs.ko]
has no CRC!
*** Warning: "free_orinocodev" [/usr/local/src/orinoco/spectrum_cs.ko] has
no CRC!
[further warnings skipped]

I have found that the "-i" option for modpost is used for external builds,
whereas the internal modules use "-o".  The "-i" option causes read_dump()
in modpost.c to be called.  This function sets "modversions" variable
under some conditions that I don't understand.  The comment before the
modversions declarations says: "Are we using CONFIG_MODVERSIONS?"

Apparently modpost fails to answer this question.  I think it's better to
use an explicit option rather than a kludge.

The attached patch adds a new option "-m" that is specified if and only if
CONFIG_MODVERSIONS is enabled.  The patch has been successfully tested
both with and without CONFIG_MODVERSIONS.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/Makefile.modpost

@@ -50,7 +50,8 @@ _modpost: $(modules)
 # Step 2), invoke modpost
 #  Includes step 3,4
 quiet_cmd_modpost = MODPOST
-      cmd_modpost = scripts/mod/modpost \
+      cmd_modpost = scripts/mod/modpost            \
+        $(if $(CONFIG_MODVERSIONS),-m)             \
 	$(if $(KBUILD_EXTMOD),-i,-o) $(symverfile) \
 	$(filter-out FORCE,$^)
 

scripts/mod/modpost.c

@@ -343,7 +343,6 @@ handle_modversions(struct module *mod, struct elf_info *info,
 			crc = (unsigned int) sym->st_value;
 			add_exported_symbol(symname + strlen(CRC_PFX),
 					    mod, &crc);
-			modversions = 1;
 		}
 		break;
 	case SHN_UNDEF:
@@ -649,7 +648,6 @@ read_dump(const char *fname)
 
 		if (!(mod = find_module(modname))) {
 			if (is_vmlinux(modname)) {
-				modversions = 1;
 				have_vmlinux = 1;
 			}
 			mod = new_module(NOFAIL(strdup(modname)));
@@ -696,11 +694,14 @@ main(int argc, char **argv)
 	char *dump_read = NULL, *dump_write = NULL;
 	int opt;
 
-	while ((opt = getopt(argc, argv, "i:o:")) != -1) {
+	while ((opt = getopt(argc, argv, "i:mo:")) != -1) {
 		switch(opt) {
 			case 'i':
 				dump_read = optarg;
 				break;
+			case 'm':
+				modversions = 1;
+				break;
 			case 'o':
 				dump_write = optarg;
 				break;