[RFC PATCH 3/7] static_call: use helper to access non-exported key

@@ -38,10 +38,4 @@
 	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")
 
 
-#define ARCH_ADD_TRAMP_KEY(name)					\
-	asm(".pushsection .static_call_tramp_key, \"a\"		\n"	\
-	    ".long " STATIC_CALL_TRAMP_STR(name) " - .		\n"	\
-	    ".long " STATIC_CALL_KEY_STR(name) " - .		\n"	\
-	    ".popsection					\n")
-
 #endif /* _ASM_STATIC_CALL_H */

@@ -408,10 +408,7 @@
 	. = ALIGN(8);							\
 	__start_static_call_sites = .;					\
 	KEEP(*(.static_call_sites))					\
-	__stop_static_call_sites = .;					\
-	__start_static_call_tramp_key = .;				\
-	KEEP(*(.static_call_tramp_key))					\
-	__stop_static_call_tramp_key = .;
+	__stop_static_call_sites = .;
 
 /*
  * Allow architectures to handle ro_after_init data on their

@@ -161,12 +161,6 @@ struct static_call_mod {
 	struct static_call_site *sites;
 };
 
-/* For finding the key associated with a trampoline */
-struct static_call_tramp_key {
-	s32 tramp;
-	s32 key;
-};
-
 extern void __static_call_update(struct static_call_key *key, void *tramp, void *func);
 extern int static_call_mod_init(struct module *mod);
 extern int static_call_text_reserved(void *start, void *end);

@@ -196,13 +190,21 @@ extern long __static_call_return0(void);
 	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name));			\
 	EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
 
+#define EXPORT_STATIC_CALL_GETKEY_HELPER(name)				\
+	struct static_call_key *STATIC_CALL_GETKEY(name)(void) {	\
+		BUG_ON(!core_kernel_text(				\
+			(unsigned long)__builtin_return_address(0)));	\
+		return &STATIC_CALL_KEY(name);				\
+	}								\
+	EXPORT_SYMBOL_GPL(STATIC_CALL_GETKEY(name))
+
 /* Leave the key unexported, so modules can't change static call targets: */
 #define EXPORT_STATIC_CALL_TRAMP(name)					\
 	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name));				\
-	ARCH_ADD_TRAMP_KEY(name)
+	EXPORT_STATIC_CALL_GETKEY_HELPER(name)
 #define EXPORT_STATIC_CALL_TRAMP_GPL(name)				\
 	EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name));			\
-	ARCH_ADD_TRAMP_KEY(name)
+	EXPORT_STATIC_CALL_GETKEY_HELPER(name)
 
 #elif defined(CONFIG_HAVE_STATIC_CALL)
 

@@ -18,6 +18,11 @@
 #define STATIC_CALL_TRAMP(name)		__PASTE(STATIC_CALL_TRAMP_PREFIX, name)
 #define STATIC_CALL_TRAMP_STR(name)	__stringify(STATIC_CALL_TRAMP(name))
 
+#define STATIC_CALL_GETKEY_PREFIX	__SCG__
+#define STATIC_CALL_GETKEY_PREFIX_STR	__stringify(STATIC_CALL_GETKEY_PREFIX)
+#define STATIC_CALL_GETKEY_PREFIX_LEN	(sizeof(STATIC_CALL_GETKEY_PREFIX_STR) - 1)
+#define STATIC_CALL_GETKEY(name)	__PASTE(STATIC_CALL_GETKEY_PREFIX, name)
+
 /*
  * Flags in the low bits of static_call_site::key.
  */

@@ -32,11 +37,12 @@
 struct static_call_site {
 	s32 addr;
 	s32 key;
-	s32 tramp;
+	s32 helper;
 };
 
 #define DECLARE_STATIC_CALL(name, func)					\
 	extern __weak struct static_call_key STATIC_CALL_KEY(name);	\
+	extern __weak struct static_call_key *STATIC_CALL_GETKEY(name)(void);\
 	extern typeof(func) STATIC_CALL_TRAMP(name);
 
 #ifdef CONFIG_HAVE_STATIC_CALL

@@ -55,6 +61,7 @@ struct static_call_site {
  * .static_call_sites section.
  */
 #define __STATIC_CALL_ADDRESSABLE(name) \
+	__ADDRESSABLE(STATIC_CALL_GETKEY(name)) \
 	__ADDRESSABLE(STATIC_CALL_KEY(name))
 
 struct static_call_key {

@@ -81,6 +81,7 @@ int notrace core_kernel_text(unsigned long addr)
 		return 1;
 	return 0;
 }
+EXPORT_SYMBOL_GPL(core_kernel_text);
 
 /**
  * core_kernel_data - tell if addr points to kernel data

@@ -12,8 +12,6 @@
 
 extern struct static_call_site __start_static_call_sites[],
 			       __stop_static_call_sites[];
-extern struct static_call_tramp_key __start_static_call_tramp_key[],
-				    __stop_static_call_tramp_key[];
 
 static bool static_call_initialized;
 

@@ -333,23 +331,6 @@ static int __static_call_mod_text_reserved(void *start, void *end)
 	return ret;
 }
 
-static unsigned long tramp_key_lookup(unsigned long addr)
-{
-	struct static_call_tramp_key *start = __start_static_call_tramp_key;
-	struct static_call_tramp_key *stop = __stop_static_call_tramp_key;
-	struct static_call_tramp_key *tramp_key;
-
-	for (tramp_key = start; tramp_key != stop; tramp_key++) {
-		unsigned long tramp;
-
-		tramp = (long)tramp_key->tramp + (long)&tramp_key->tramp;
-		if (tramp == addr)
-			return (long)tramp_key->key + (long)&tramp_key->key;
-	}
-
-	return 0;
-}
-
 static int static_call_add_module(struct module *mod)
 {
 	struct static_call_site *start = mod->static_call_sites;

@@ -359,6 +340,7 @@ static int static_call_add_module(struct module *mod)
 	for (site = start; site != stop; site++) {
 		unsigned long s_key = __static_call_key(site);
 		unsigned long addr = s_key & ~STATIC_CALL_SITE_FLAGS;
+		unsigned long (*key_helper)(void);
 		unsigned long key;
 
 		/*

@@ -375,7 +357,8 @@ static int static_call_add_module(struct module *mod)
 		if (addr)
 			continue;
 
-		key = tramp_key_lookup((unsigned long)offset_to_ptr(&site->tramp));
+		key_helper = offset_to_ptr(&site->helper);
+		key = key_helper();
 		if (!key) {
 			pr_warn("Failed to fixup static_call() usage at: %ps\n",
 				static_call_addr(site));

@@ -18,6 +18,11 @@
 #define STATIC_CALL_TRAMP(name)		__PASTE(STATIC_CALL_TRAMP_PREFIX, name)
 #define STATIC_CALL_TRAMP_STR(name)	__stringify(STATIC_CALL_TRAMP(name))
 
+#define STATIC_CALL_GETKEY_PREFIX	__SCG__
+#define STATIC_CALL_GETKEY_PREFIX_STR	__stringify(STATIC_CALL_GETKEY_PREFIX)
+#define STATIC_CALL_GETKEY_PREFIX_LEN	(sizeof(STATIC_CALL_GETKEY_PREFIX_STR) - 1)
+#define STATIC_CALL_GETKEY(name)	__PASTE(STATIC_CALL_GETKEY_PREFIX, name)
+
 /*
  * Flags in the low bits of static_call_site::key.
  */

@@ -32,11 +37,12 @@
 struct static_call_site {
 	s32 addr;
 	s32 key;
-	s32 tramp;
+	s32 helper;
 };
 
 #define DECLARE_STATIC_CALL(name, func)					\
 	extern __weak struct static_call_key STATIC_CALL_KEY(name);	\
+	extern __weak struct static_call_key *STATIC_CALL_GETKEY(name)(void);\
 	extern typeof(func) STATIC_CALL_TRAMP(name);
 
 #ifdef CONFIG_HAVE_STATIC_CALL

@@ -55,6 +61,7 @@ struct static_call_site {
  * .static_call_sites section.
  */
 #define __STATIC_CALL_ADDRESSABLE(name) \
+	__ADDRESSABLE(STATIC_CALL_GETKEY(name)) \
 	__ADDRESSABLE(STATIC_CALL_KEY(name))
 
 struct static_call_key {

@@ -600,7 +600,7 @@ static int create_static_call_sections(struct objtool_file *file)
 	struct section *sec;
 	struct static_call_site *site;
 	struct instruction *insn;
-	struct symbol *key_sym;
+	struct symbol *key_sym, *helper_sym;
 	char *key_name, *tmp;
 	int idx;
 

@@ -655,7 +655,6 @@ static int create_static_call_sections(struct objtool_file *file)
 			WARN("static_call: can't find static_call_key symbol: %s", tmp);
 			return -1;
 		}
-		free(key_name);
 
 		/* populate reloc for 'key' */
 		if (elf_add_reloc(file->elf, sec,

@@ -664,18 +663,27 @@ static int create_static_call_sections(struct objtool_file *file)
 				  is_sibling_call(insn) * STATIC_CALL_SITE_TAIL))
 			return -1;
 
+		memcpy(tmp, STATIC_CALL_GETKEY_PREFIX_STR, STATIC_CALL_GETKEY_PREFIX_LEN);
+
+		helper_sym = find_symbol_by_name(file->elf, tmp);
+		if (!helper_sym) {
+			WARN("static_call: can't find static_call_key symbol: %s", tmp);
+			return -1;
+		}
+		free(key_name);
+
 		/*
 		 * For modules(), the key might not be exported, which means
 		 * the module can make static calls but isn't allowed to change
 		 * them.
 		 *
-		 * For this case, we pass the trampoline in .static_call_sites
-		 * as well. This is used to lookup the key in
-		 * static_call_add_module().
+		 * For this case, we pass the special key helper routine in
+		 * .static_call_sites as well. This is used to lookup the key
+		 * in static_call_add_module().
 		 */
 		if (elf_add_reloc(file->elf, sec,
 				  idx * sizeof(struct static_call_site) + 8,
-				  R_X86_64_PC32, insn->call_dest, 0))
+				  R_X86_64_PC32, helper_sym, 0))
 			return -1;
 
 		idx++;