module: swap the order of symbol.namespace

Currently, EXPORT_SYMBOL_NS(_GPL) constructs the kernel symbol as
follows:

  __ksymtab_SYMBOL.NAMESPACE

The sym_extract_namespace() in modpost allocates memory for the part
SYMBOL.NAMESPACE when '.' is contained. One problem is that the pointer
returned by strdup() is lost because the symbol name will be copied to
malloc'ed memory by alloc_symbol(). No one will keep track of the
pointer of strdup'ed memory.

sym->namespace still points to the NAMESPACE part. So, you can free it
with complicated code like this:

   free(sym->namespace - strlen(sym->name) - 1);

It complicates memory free.

To fix it elegantly, I swapped the order of the symbol and the
namespace as follows:

  __ksymtab_NAMESPACE.SYMBOL

then, simplified sym_extract_namespace() so that it allocates memory
only for the NAMESPACE part.

I prefer this order because it is intuitive and also matches to major
languages. For example, NAMESPACE::NAME in C++, MODULE.NAME in Python.
Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>

include/linux/export.h

@@ -52,7 +52,7 @@ extern struct module __this_module;
 	__ADDRESSABLE(sym)						\
 	asm("	.section \"___ksymtab" sec "+" #sym "\", \"a\"	\n"	\
 	    "	.balign	4					\n"	\
-	    "__ksymtab_" #sym NS_SEPARATOR #ns ":		\n"	\
+	    "__ksymtab_" #ns NS_SEPARATOR #sym ":		\n"	\
 	    "	.long	" #sym "- .				\n"	\
 	    "	.long	__kstrtab_" #sym "- .			\n"	\
 	    "	.long	__kstrtab_ns_" #sym "- .		\n"	\
@@ -76,7 +76,7 @@ struct kernel_symbol {
 #else
 #define __KSYMTAB_ENTRY_NS(sym, sec, ns)				\
 	static const struct kernel_symbol __ksymtab_##sym##__##ns	\
-	asm("__ksymtab_" #sym NS_SEPARATOR #ns)				\
+	asm("__ksymtab_" #ns NS_SEPARATOR #sym)				\
 	__attribute__((section("___ksymtab" sec "+" #sym), used))	\
 	__aligned(sizeof(void *))					\
 	= { (unsigned long)&sym, __kstrtab_##sym, __kstrtab_ns_##sym }

scripts/mod/modpost.c

@@ -350,18 +350,16 @@ static enum export export_from_sec(struct elf_info *elf, unsigned int sec)
 
 static const char *sym_extract_namespace(const char **symname)
 {
-	size_t n;
-	char *dupsymname;
+	char *namespace = NULL;
+	char *ns_separator;
 
-	n = strcspn(*symname, ".");
-	if (n < strlen(*symname) - 1) {
-		dupsymname = NOFAIL(strdup(*symname));
-		dupsymname[n] = '\0';
-		*symname = dupsymname;
-		return dupsymname + n + 1;
+	ns_separator = strchr(*symname, '.');
+	if (ns_separator) {
+		namespace = NOFAIL(strndup(*symname, ns_separator - *symname));
+		*symname = ns_separator + 1;
 	}
 
-	return NULL;
+	return namespace;
 }
 
 /**