modules: add default loader hook implementations

The module loader code allows architectures to hook into the code by
providing a small number of entry points that each arch must implement.
This patch provides __weakly linked generic implementations of these
entry points for architectures that don't need to do anything special.

Signed-off-by: Jonas Bonn <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>

include/linux/moduleloader.h

···
 #include <linux/module.h>
 #include <linux/elf.h>
 
-/* These must be implemented by the specific architecture */
+/* These may be implemented by architectures that need to hook into the
+ * module loader code.  Architectures that don't need to do anything special
+ * can just rely on the 'weak' default hooks defined in kernel/module.c.
+ * Note, however, that at least one of apply_relocate or apply_relocate_add
+ * must be implemented by each architecture.
+ */
 
 /* Adjust arch-specific sections.  Return 0 on success.  */
 int module_frob_arch_sections(Elf_Ehdr *hdr,

kernel/module.c

···
 static void unset_module_init_ro_nx(struct module *mod) { }
 #endif
 
+void __weak module_free(struct module *mod, void *module_region)
+{
+	vfree(module_region);
+}
+
+void __weak module_arch_cleanup(struct module *mod)
+{
+}
+
 /* Free a module, remove from lists, etc. */
 static void free_module(struct module *mod)
 {
···
 	}
 
 	return ret;
+}
+
+int __weak apply_relocate(Elf_Shdr *sechdrs,
+			  const char *strtab,
+			  unsigned int symindex,
+			  unsigned int relsec,
+			  struct module *me)
+{
+	pr_err("module %s: REL relocation unsupported\n", me->name);
+	return -ENOEXEC;
+}
+
+int __weak apply_relocate_add(Elf_Shdr *sechdrs,
+			      const char *strtab,
+			      unsigned int symindex,
+			      unsigned int relsec,
+			      struct module *me)
+{
+	pr_err("module %s: RELA relocation unsupported\n", me->name);
+	return -ENOEXEC;
 }
 
 static int apply_relocations(struct module *mod, const struct load_info *info)
···
 {
 	if (debug)
 		ddebug_remove_module(debug->modname);
+}
+
+void * __weak module_alloc(unsigned long size)
+{
+	return size == 0 ? NULL : vmalloc_exec(size);
 }
 
 static void *module_alloc_update_bounds(unsigned long size)
···
 	set_fs(old_fs);
 }
 
+int __weak module_frob_arch_sections(Elf_Ehdr *hdr,
+				     Elf_Shdr *sechdrs,
+				     char *secstrings,
+				     struct module *mod)
+{
+	return 0;
+}
+
 static struct module *layout_and_allocate(struct load_info *info)
 {
 	/* Module within temporary copy. */
···
 	percpu_modfree(mod);
 	module_free(mod, mod->module_init);
 	module_free(mod, mod->module_core);
+}
+
+int __weak module_finalize(const Elf_Ehdr *hdr,
+			   const Elf_Shdr *sechdrs,
+			   struct module *me)
+{
+	return 0;
 }
 
 static int post_relocation(struct module *mod, const struct load_info *info)