modpost: add support for symbol namespaces

Add support for symbols that are exported into namespaces. For that,
extract any namespace suffix from the symbol name. In addition, emit a
warning whenever a module refers to an exported symbol without
explicitly importing the namespace that it is defined in. This patch
consistently adds the namespace suffix to symbol names exported into
Module.symvers.

Example warning emitted by modpost in case of the above violation:

WARNING: module ums-usbat uses symbol usb_stor_resume from namespace
USB_STORAGE, but does not import it.

Co-developed-by: Martijn Coenen <[e-mail]>
Signed-off-by: Martijn Coenen <[e-mail]>
Reviewed-by: Joel Fernandes (Google) <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Matthias Maennich <[e-mail]>
Signed-off-by: Jessica Yu <[e-mail]>

Documentation/kbuild/modules.rst

···
 
 	The syntax of the Module.symvers file is::
 
-		<CRC>	    <Symbol>	       <module>
+	<CRC>       <Symbol>          <Namespace>  <Module>                         <Export Type>
 
-		0x2d036834  scsi_remove_host   drivers/scsi/scsi_mod
+	0xe1cc2a05  usb_stor_suspend  USB_STORAGE  drivers/usb/storage/usb-storage  EXPORT_SYMBOL_GPL
+
+	The fields are separated by tabs and values may be empty (e.g.
+	if no namespace is defined for an exported symbol).
 
 	For a kernel build without CONFIG_MODVERSIONS enabled, the CRC
 	would read 0x00000000.

scripts/export_report.pl

···
 #
 while ( <$module_symvers> ) {
 	chomp;
-	my (undef, $symbol, $module, $gpl) = split;
+	my (undef, $symbol, $namespace, $module, $gpl) = split('\t');
 	$SYMBOL { $symbol } =  [ $module , "0" , $symbol, $gpl];
 }
 close($module_symvers);

scripts/mod/modpost.c

···
 	struct module *module;
 	unsigned int crc;
 	int crc_valid;
+	const char *namespace;
 	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
···
 			return s;
 	}
 	return NULL;
+}
+
+static bool contains_namespace(struct namespace_list *list,
+			       const char *namespace)
+{
+	struct namespace_list *ns_entry;
+
+	for (ns_entry = list; ns_entry != NULL; ns_entry = ns_entry->next)
+		if (strcmp(ns_entry->namespace, namespace) == 0)
+			return true;
+
+	return false;
+}
+
+static void add_namespace(struct namespace_list **list, const char *namespace)
+{
+	struct namespace_list *ns_entry;
+
+	if (!contains_namespace(*list, namespace)) {
+		ns_entry = NOFAIL(malloc(sizeof(struct namespace_list) +
+					 strlen(namespace) + 1));
+		strcpy(ns_entry->namespace, namespace);
+		ns_entry->next = *list;
+		*list = ns_entry;
+	}
+}
+
+static bool module_imports_namespace(struct module *module,
+				     const char *namespace)
+{
+	return contains_namespace(module->imported_namespaces, namespace);
 }
 
 static const struct {
···
 		return export_unknown;
 }
 
+static const char *sym_extract_namespace(const char **symname)
+{
+	size_t n;
+	char *dupsymname;
+
+	n = strcspn(*symname, ".");
+	if (n < strlen(*symname) - 1) {
+		dupsymname = NOFAIL(strdup(*symname));
+		dupsymname[n] = '\0';
+		*symname = dupsymname;
+		return dupsymname + n + 1;
+	}
+
+	return NULL;
+}
+
 /**
  * Add an exported symbol - it may have already been added without a
  * CRC, in this case just update the CRC
  **/
-static struct symbol *sym_add_exported(const char *name, struct module *mod,
-				       enum export export)
+static struct symbol *sym_add_exported(const char *name, const char *namespace,
+				       struct module *mod, enum export export)
 {
 	struct symbol *s = find_symbol(name);
 
 	if (!s) {
 		s = new_symbol(name, mod, export);
+		s->namespace = namespace;
 	} else {
 		if (!s->preloaded) {
-			warn("%s: '%s' exported twice. Previous export "
-			     "was in %s%s\n", mod->name, name,
-			     s->module->name,
-			     is_vmlinux(s->module->name) ?"":".ko");
+			warn("%s: '%s' exported twice. Previous export was in %s%s\n",
+			     mod->name, name, s->module->name,
+			     is_vmlinux(s->module->name) ? "" : ".ko");
 		} else {
 			/* In case Module.symvers was out of date */
 			s->module = mod;
···
 	unsigned int crc;
 	enum export export;
 	bool is_crc = false;
+	const char *name, *namespace;
 
 	if ((!is_vmlinux(mod->name) || mod->is_dot_o) &&
 	    strstarts(symname, "__ksymtab"))
···
 	default:
 		/* All exported symbols */
 		if (strstarts(symname, "__ksymtab_")) {
-			sym_add_exported(symname + strlen("__ksymtab_"), mod,
-					export);
+			name = symname + strlen("__ksymtab_");
+			namespace = sym_extract_namespace(&name);
+			sym_add_exported(name, namespace, mod, export);
 		}
 		if (strcmp(symname, "init_module") == 0)
 			mod->has_init = 1;
···
 	const char *symname;
 	char *version;
 	char *license;
+	char *namespace;
 	struct module *mod;
 	struct elf_info info = { };
 	Elf_Sym *sym;
···
 			break;
 		}
 		license = get_next_modinfo(&info, "license", license);
+	}
+
+	namespace = get_modinfo(&info, "import_ns");
+	while (namespace) {
+		add_namespace(&mod->imported_namespaces, namespace);
+		namespace = get_next_modinfo(&info, "import_ns", namespace);
 	}
 
 	for (sym = info.symtab_start; sym < info.symtab_stop; sym++) {
···
 			basename++;
 		else
 			basename = mod->name;
+
+		if (exp->namespace &&
+		    !module_imports_namespace(mod, exp->namespace)) {
+			warn("module %s uses symbol %s from namespace %s, but does not import it.\n",
+			     basename, exp->name, exp->namespace);
+		}
+
 		if (!mod->gpl_compatible)
 			check_for_gpl_usage(exp->export, basename, exp->name);
 		check_for_unused(exp->export, basename, exp->name);
···
 		return;
 
 	while ((line = get_next_line(&pos, file, size))) {
-		char *symname, *modname, *d, *export, *end;
+		char *symname, *namespace, *modname, *d, *export, *end;
 		unsigned int crc;
 		struct module *mod;
 		struct symbol *s;
···
 		if (!(symname = strchr(line, '\t')))
 			goto fail;
 		*symname++ = '\0';
-		if (!(modname = strchr(symname, '\t')))
+		if (!(namespace = strchr(symname, '\t')))
+			goto fail;
+		*namespace++ = '\0';
+		if (!(modname = strchr(namespace, '\t')))
 			goto fail;
 		*modname++ = '\0';
 		if ((export = strchr(modname, '\t')) != NULL)
···
 			mod = new_module(modname);
 			mod->skip = 1;
 		}
-		s = sym_add_exported(symname, mod, export_no(export));
+		s = sym_add_exported(symname, namespace, mod,
+				     export_no(export));
 		s->kernel    = kernel;
 		s->preloaded = 1;
 		sym_update_crc(symname, mod, crc, export_no(export));
···
 {
 	struct buffer buf = { };
 	struct symbol *symbol;
+	const char *namespace;
 	int n;
 
 	for (n = 0; n < SYMBOL_HASH_SIZE ; n++) {
 		symbol = symbolhash[n];
 		while (symbol) {
-			if (dump_sym(symbol))
-				buf_printf(&buf, "0x%08x\t%s\t%s\t%s\n",
-					symbol->crc, symbol->name,
-					symbol->module->name,
-					export_str(symbol->export));
+			if (dump_sym(symbol)) {
+				namespace = symbol->namespace;
+				buf_printf(&buf, "0x%08x\t%s\t%s\t%s\t%s\n",
+					   symbol->crc, symbol->name,
+					   namespace ? namespace : "",
+					   symbol->module->name,
+					   export_str(symbol->export));
+			}
 			symbol = symbol->next;
 		}
 	}

scripts/mod/modpost.h

···
 void
 buf_write(struct buffer *buf, const char *s, int len);
 
+struct namespace_list {
+	struct namespace_list *next;
+	char namespace[0];
+};
+
 struct module {
 	struct module *next;
 	const char *name;
···
 	struct buffer dev_table_buf;
 	char	     srcversion[25];
 	int is_dot_o;
+	// Actual imported namespaces
+	struct namespace_list *imported_namespaces;
 };
 
 struct elf_info {