[PATCH V3 06/13] ftrace: Add symbols for ftrace trampolines

[Adrian Hunter <adrian.hunter@intel.com>]

Symbols are needed for tools to describe instruction addresses. Pages
allocated for ftrace's purposes need symbols to be created for them.
Add such symbols to be visible via /proc/kallsyms.

Example on x86 with CONFIG_DYNAMIC_FTRACE=y

	# echo function > /sys/kernel/debug/tracing/current_tracer
	# cat /proc/kallsyms | grep '\[ftrace\]'
	ffffffffc02f8000 t ftrace_trampoline    [ftrace]

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 arch/x86/kernel/ftrace.c | 26 +++++++++++---------
 include/linux/ftrace.h   | 15 +++++++++---
 kernel/trace/ftrace.c    | 53 +++++++++++++++++++++++++++++++++++++++-
 3 files changed, 77 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 108ee96f8b66..76920ce85b9c 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -307,9 +307,9 @@ union ftrace_op_code_union {
 
 #define RET_SIZE		1
 
-static unsigned long
-create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
+static void create_trampoline(struct ftrace_ops *ops)
 {
+	unsigned int tramp_size;
 	unsigned long start_offset;
 	unsigned long end_offset;
 	unsigned long op_offset;
@@ -347,10 +347,10 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	 */
 	trampoline = alloc_tramp(size + RET_SIZE + sizeof(void *));
 	if (!trampoline)
-		return 0;
+		return;
 
-	*tramp_size = size + RET_SIZE + sizeof(void *);
-	npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
+	tramp_size = size + RET_SIZE + sizeof(void *);
+	npages = DIV_ROUND_UP(tramp_size, PAGE_SIZE);
 
 	/* Copy ftrace_caller onto the trampoline memory */
 	ret = probe_kernel_read(trampoline, (void *)start_offset, size);
@@ -403,15 +403,18 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 
 	/* ALLOC_TRAMP flags lets us know we created it */
 	ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
+	ops->trampoline = (unsigned long)trampoline;
+	ops->trampoline_size = tramp_size;
+
+	ftrace_add_trampoline_to_kallsyms(ops);
 
 	set_vm_flush_reset_perms(trampoline);
 
 	set_memory_ro((unsigned long)trampoline, npages);
 	set_memory_x((unsigned long)trampoline, npages);
-	return (unsigned long)trampoline;
+	return;
 fail:
 	tramp_free(trampoline);
-	return 0;
 }
 
 static unsigned long calc_trampoline_call_offset(bool save_regs)
@@ -435,14 +438,10 @@ void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
 	ftrace_func_t func;
 	unsigned long offset;
 	unsigned long ip;
-	unsigned int size;
 	const char *new;
 
 	if (!ops->trampoline) {
-		ops->trampoline = create_trampoline(ops, &size);
-		if (!ops->trampoline)
-			return;
-		ops->trampoline_size = size;
+		create_trampoline(ops);
 		return;
 	}
 
@@ -535,6 +534,9 @@ void arch_ftrace_trampoline_free(struct ftrace_ops *ops)
 	if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
 		return;
 
+	ftrace_remove_trampoline_from_kallsyms(ops);
+	synchronize_rcu();
+
 	tramp_free((void *)ops->trampoline);
 	ops->trampoline = 0;
 }
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index db95244a62d4..70dea4785443 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -58,9 +58,6 @@ struct ftrace_direct_func;
 const char *
 ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
 		   unsigned long *off, char **modname, char *sym);
-int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
-			   char *type, char *name,
-			   char *module_name, int *exported);
 #else
 static inline const char *
 ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
@@ -68,6 +65,13 @@ ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
 {
 	return NULL;
 }
+#endif
+
+#if defined(CONFIG_FUNCTION_TRACER) && defined(CONFIG_DYNAMIC_FTRACE)
+int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
+			   char *type, char *name,
+			   char *module_name, int *exported);
+#else
 static inline int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
 					 char *type, char *name,
 					 char *module_name, int *exported)
@@ -76,7 +80,6 @@ static inline int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *val
 }
 #endif
 
-
 #ifdef CONFIG_FUNCTION_TRACER
 
 extern int ftrace_enabled;
@@ -179,6 +182,9 @@ struct ftrace_ops_hash {
 
 void ftrace_free_init_mem(void);
 void ftrace_free_mem(struct module *mod, void *start, void *end);
+#define FTRACE_TRAMPOLINE_SYM "ftrace_trampoline"
+void ftrace_add_trampoline_to_kallsyms(struct ftrace_ops *ops);
+void ftrace_remove_trampoline_from_kallsyms(struct ftrace_ops *ops);
 #else
 static inline void ftrace_free_init_mem(void) { }
 static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { }
@@ -207,6 +213,7 @@ struct ftrace_ops {
 	struct ftrace_ops_hash		old_hash;
 	unsigned long			trampoline;
 	unsigned long			trampoline_size;
+	struct list_head		list;
 #endif
 };
 
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9bf1f2cd515e..1911fa832a79 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6174,6 +6174,42 @@ struct ftrace_mod_map {
 	unsigned int		num_funcs;
 };
 
+/* List of trace_ops that have allocated trampolines */
+static LIST_HEAD(ftrace_ops_trampoline_list);
+
+void ftrace_add_trampoline_to_kallsyms(struct ftrace_ops *ops)
+{
+	lockdep_assert_held(&ftrace_lock);
+	list_add_rcu(&ops->list, &ftrace_ops_trampoline_list);
+}
+
+void ftrace_remove_trampoline_from_kallsyms(struct ftrace_ops *ops)
+{
+	lockdep_assert_held(&ftrace_lock);
+	list_del_rcu(&ops->list);
+}
+
+static int ftrace_get_trampoline_kallsym(unsigned int symnum,
+					 unsigned long *value, char *type,
+					 char *name, char *module_name,
+					 int *exported)
+{
+	struct ftrace_ops *op;
+
+	list_for_each_entry_rcu(op, &ftrace_ops_trampoline_list, list) {
+		if (!op->trampoline || symnum--)
+			continue;
+		*value = op->trampoline;
+		*type = 't';
+		strlcpy(name, FTRACE_TRAMPOLINE_SYM, KSYM_NAME_LEN);
+		strlcpy(module_name, "ftrace", MODULE_NAME_LEN);
+		*exported = 0;
+		return 0;
+	}
+
+	return -ERANGE;
+}
+
 #ifdef CONFIG_MODULES
 
 #define next_to_ftrace_page(p) container_of(p, struct ftrace_page, next)
@@ -6510,6 +6546,7 @@ int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
 {
 	struct ftrace_mod_map *mod_map;
 	struct ftrace_mod_func *mod_func;
+	int ret;
 
 	preempt_disable();
 	list_for_each_entry_rcu(mod_map, &ftrace_mod_maps, list) {
@@ -6536,8 +6573,10 @@ int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
 		WARN_ON(1);
 		break;
 	}
+	ret = ftrace_get_trampoline_kallsym(symnum, value, type, name,
+					    module_name, exported);
 	preempt_enable();
-	return -ERANGE;
+	return ret;
 }
 
 #else
@@ -6549,6 +6588,18 @@ allocate_ftrace_mod_map(struct module *mod,
 {
 	return NULL;
 }
+int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
+			   char *type, char *name, char *module_name,
+			   int *exported)
+{
+	int ret;
+
+	preempt_disable();
+	ret = ftrace_get_trampoline_kallsym(symnum, value, type, name,
+					    module_name, exported);
+	preempt_enable();
+	return ret;
+}
 #endif /* CONFIG_MODULES */
 
 struct ftrace_init_func {
-- 
2.17.1