kbuild: improved modversioning support for external modules

With following patch a second option is enabled to obtain
symbol information from a second external module when a
external module is build.
The recommended approach is to use a common kbuild file but
that may be impractical in certain cases.
With this patch one can copy over a Module.symvers from one
external module to make symbols (and symbol versions) available
for another external module.

Updated documentation in Documentation/kbuild/modules.txt

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

2 files changed, 78 insertions, 52 deletions

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index bf96a61d4b86..563e3c5bd8dd 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -39,7 +39,8 @@ include .config
 include scripts/Kbuild.include
 include scripts/Makefile.lib
 
-symverfile := $(objtree)/Module.symvers
+kernelsymfile := $(objtree)/Module.symvers
+modulesymfile := $(KBUILD_EXTMOD)/Modules.symvers
 
 # Step 1), find all modules listed in $(MODVERDIR)/
 __modules := $(sort $(shell grep -h '\.ko' /dev/null $(wildcard $(MODVERDIR)/*.mod)))
@@ -54,7 +55,9 @@ quiet_cmd_modpost = MODPOST
       cmd_modpost = scripts/mod/modpost            \
         $(if $(CONFIG_MODVERSIONS),-m)             \
         $(if $(CONFIG_MODULE_SRCVERSION_ALL),-a,)  \
-        $(if $(KBUILD_EXTMOD),-i,-o) $(symverfile) \
+        $(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile) \
+        $(if $(KBUILD_EXTMOD),-I $(modulesymfile)) \
+        $(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
         $(filter-out FORCE,$^)
 
 .PHONY: __modpost
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 4a2f2e38d27f..976adf152db3 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -20,6 +20,8 @@ int modversions = 0;
 int have_vmlinux = 0;
 /* Is CONFIG_MODULE_SRCVERSION_ALL set? */
 static int all_versions = 0;
+/* If we are modposting external module set to 1 */
+static int external_module = 0;
 
 void fatal(const char *fmt, ...)
 {
@@ -45,6 +47,18 @@ void warn(const char *fmt, ...)
         va_end(arglist);
 }
 
+static int is_vmlinux(const char *modname)
+{
+        const char *myname;
+
+        if ((myname = strrchr(modname, '/')))
+                myname++;
+        else
+                myname = modname;
+
+        return strcmp(myname, "vmlinux") == 0;
+}
+
 void *do_nofail(void *ptr, const char *expr)
 {
         if (!ptr) {
@@ -100,6 +114,9 @@ struct symbol {
         unsigned int crc;
         int crc_valid;
         unsigned int weak:1;
+        unsigned int vmlinux:1;    /* 1 if symbol is defined in vmlinux */
+        unsigned int kernel:1;     /* 1 if symbol is from kernel
+                                    *  (only for external modules) **/
         char name[0];
 };
 
@@ -135,8 +152,7 @@ static struct symbol *alloc_symbol(const char *name, unsigned int weak,
 }
 
 /* For the hash of exported symbols */
-static void new_symbol(const char *name, struct module *module,
-                       unsigned int *crc)
+static struct symbol *new_symbol(const char *name, struct module *module)
 {
         unsigned int hash;
         struct symbol *new;
@@ -144,10 +160,7 @@ static void new_symbol(const char *name, struct module *module,
         hash = tdb_hash(name) % SYMBOL_HASH_SIZE;
         new = symbolhash[hash] = alloc_symbol(name, 0, symbolhash[hash]);
         new->module = module;
-        if (crc) {
-                new->crc = *crc;
-                new->crc_valid = 1;
-        }
+        return new;
 }
 
 static struct symbol *find_symbol(const char *name)
@@ -169,19 +182,27 @@ static struct symbol *find_symbol(const char *name)
  * Add an exported symbol - it may have already been added without a
  * CRC, in this case just update the CRC
  **/
-static void add_exported_symbol(const char *name, struct module *module,
-                                unsigned int *crc)
+static struct symbol *sym_add_exported(const char *name, struct module *mod)
 {
         struct symbol *s = find_symbol(name);
 
-        if (!s) {
-                new_symbol(name, module, crc);
-                return;
-        }
-        if (crc) {
-                s->crc = *crc;
-                s->crc_valid = 1;
-        }
+        if (!s)
+                s = new_symbol(name, mod);
+
+        s->vmlinux   = is_vmlinux(mod->name);
+        s->kernel    = 0;
+        return s;
+}
+
+static void sym_update_crc(const char *name, struct module *mod,
+                           unsigned int crc)
+{
+        struct symbol *s = find_symbol(name);
+
+        if (!s)
+                s = new_symbol(name, mod);
+        s->crc = crc;
+        s->crc_valid = 1;
 }
 
 void *grab_file(const char *filename, unsigned long *size)
@@ -332,8 +353,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
                 /* CRC'd symbol */
                 if (memcmp(symname, CRC_PFX, strlen(CRC_PFX)) == 0) {
                         crc = (unsigned int) sym->st_value;
-                        add_exported_symbol(symname + strlen(CRC_PFX),
-                                            mod, &crc);
+                        sym_update_crc(symname + strlen(CRC_PFX), mod, crc);
                 }
                 break;
         case SHN_UNDEF:
@@ -377,8 +397,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
         default:
                 /* All exported symbols */
                 if (memcmp(symname, KSYMTAB_PFX, strlen(KSYMTAB_PFX)) == 0) {
-                        add_exported_symbol(symname + strlen(KSYMTAB_PFX),
-                                            mod, NULL);
+                        sym_add_exported(symname + strlen(KSYMTAB_PFX), mod);
                 }
                 if (strcmp(symname, MODULE_SYMBOL_PREFIX "init_module") == 0)
                         mod->has_init = 1;
@@ -388,18 +407,6 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
         }
 }
 
-static int is_vmlinux(const char *modname)
-{
-        const char *myname;
-
-        if ((myname = strrchr(modname, '/')))
-                myname++;
-        else
-                myname = modname;
-
-        return strcmp(myname, "vmlinux") == 0;
-}
-
 /**
  * Parse tag=value strings from .modinfo section
  **/
@@ -450,9 +457,7 @@ static void read_symbols(char *modname)
         /* When there's no vmlinux, don't print warnings about
          * unresolved symbols (since there'll be too many ;) */
         if (is_vmlinux(modname)) {
-                unsigned int fake_crc = 0;
                 have_vmlinux = 1;
-                add_exported_symbol("struct_module", mod, &fake_crc);