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ftrace: Add symbols for ftrace trampolines

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 '\[__builtin__ftrace\]' ffffffffc0238000 t ftrace_trampoline [__builtin__ftrace] Note: This patch adds "__builtin__ftrace" as a module name in /proc/kallsyms for symbols for pages allocated for ftrace's purposes, even though "__builtin__ftrace" is not a module.

Adrian Hunter committed 6 years ago

Commit fc0ea791 parent 3e46bb43 files · +88 −6Browse files

Unified · Split

3 files
  1. include/linux/ftrace.h +8 −4
  2. kernel/kallsyms.c +5 −0
  3. kernel/trace/ftrace.c +75 −2
include/linux/ftrace.h+8−4
@@ -58,9 +58,6 @@ struct ftrace_direct_func; · 57 unmodified lines
5858 const char *
5959 ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
6060 unsigned long *off, char **modname, char *sym);
61−int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
62− char *type, char *name,
63− char *module_name, int *exported);
6461 #else
6562 static inline const char *
6663 ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
@@ -68,6 +65,13 @@ ftrace_mod_address_lookup(unsigned long addr, unsigned long *size, · 1 unmodified line
6865 {
6966 return NULL;
7067 }
68+#endif
69+
70+#if defined(CONFIG_FUNCTION_TRACER) && defined(CONFIG_DYNAMIC_FTRACE)
71+int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
72+ char *type, char *name,
73+ char *module_name, int *exported);
74+#else
7175 static inline int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
7276 char *type, char *name,
7377 char *module_name, int *exported)
@@ -76,7 +80,6 @@ static inline int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *val · 2 unmodified lines
7680 }
7781 #endif
7882
79−
8083 #ifdef CONFIG_FUNCTION_TRACER
8184
8285 extern int ftrace_enabled;
@@ -207,6 +210,7 @@ struct ftrace_ops { · 124 unmodified lines
207210 struct ftrace_ops_hash old_hash;
208211 unsigned long trampoline;
209212 unsigned long trampoline_size;
213+ struct list_head list;
210214 #endif
211215 };
212216
kernel/kallsyms.c+5−0
@@ -482,6 +482,11 @@ static int get_ksymbol_mod(struct kallsym_iter *iter) · 481 unmodified lines
482482 return 1;
483483 }
484484
485+/*
486+ * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
487+ * purposes. In that case "__builtin__ftrace" is used as a module name, even
488+ * though "__builtin__ftrace" is not a module.
489+ */
485490 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
486491 {
487492 int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
kernel/trace/ftrace.c+75−2
@@ -2764,6 +2764,38 @@ void __weak arch_ftrace_trampoline_free(struct ftrace_ops *ops) · 2763 unmodified lines
27642764 {
27652765 }
27662766
2767+/* List of trace_ops that have allocated trampolines */
2768+static LIST_HEAD(ftrace_ops_trampoline_list);
2769+
2770+static void ftrace_add_trampoline_to_kallsyms(struct ftrace_ops *ops)
2771+{
2772+ lockdep_assert_held(&ftrace_lock);
2773+ list_add_rcu(&ops->list, &ftrace_ops_trampoline_list);
2774+}
2775+
2776+static void ftrace_remove_trampoline_from_kallsyms(struct ftrace_ops *ops)
2777+{
2778+ lockdep_assert_held(&ftrace_lock);
2779+ list_del_rcu(&ops->list);
2780+}
2781+
2782+/*
2783+ * "__builtin__ftrace" is used as a module name in /proc/kallsyms for symbols
2784+ * for pages allocated for ftrace purposes, even though "__builtin__ftrace" is
2785+ * not a module.
2786+ */
2787+#define FTRACE_TRAMPOLINE_MOD "__builtin__ftrace"
2788+#define FTRACE_TRAMPOLINE_SYM "ftrace_trampoline"
2789+
2790+static void ftrace_trampoline_free(struct ftrace_ops *ops)
2791+{
2792+ if (ops && (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP) &&
2793+ ops->trampoline)
2794+ ftrace_remove_trampoline_from_kallsyms(ops);
2795+
2796+ arch_ftrace_trampoline_free(ops);
2797+}
2798+
27672799 static void ftrace_startup_enable(int command)
27682800 {
27692801 if (saved_ftrace_func != ftrace_trace_function) {
@@ -2934,7 +2966,7 @@ int ftrace_shutdown(struct ftrace_ops *ops, int command) · 164 unmodified lines
29342966 synchronize_rcu_tasks();
29352967
29362968 free_ops:
2937− arch_ftrace_trampoline_free(ops);
2969+ ftrace_trampoline_free(ops);
29382970 }
29392971
29402972 return 0;
@@ -6178,6 +6210,27 @@ struct ftrace_mod_map { · 3237 unmodified lines
61786210 unsigned int num_funcs;
61796211 };
61806212
6213+static int ftrace_get_trampoline_kallsym(unsigned int symnum,
6214+ unsigned long *value, char *type,
6215+ char *name, char *module_name,
6216+ int *exported)
6217+{
6218+ struct ftrace_ops *op;
6219+
6220+ list_for_each_entry_rcu(op, &ftrace_ops_trampoline_list, list) {
6221+ if (!op->trampoline || symnum--)
6222+ continue;
6223+ *value = op->trampoline;
6224+ *type = 't';
6225+ strlcpy(name, FTRACE_TRAMPOLINE_SYM, KSYM_NAME_LEN);
6226+ strlcpy(module_name, FTRACE_TRAMPOLINE_MOD, MODULE_NAME_LEN);
6227+ *exported = 0;
6228+ return 0;
6229+ }
6230+
6231+ return -ERANGE;
6232+}
6233+
61816234 #ifdef CONFIG_MODULES
61826235
61836236 #define next_to_ftrace_page(p) container_of(p, struct ftrace_page, next)
@@ -6514,6 +6567,7 @@ int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value, · 330 unmodified lines
65146567 {
65156568 struct ftrace_mod_map *mod_map;
65166569 struct ftrace_mod_func *mod_func;
6570+ int ret;
65176571
65186572 preempt_disable();
65196573 list_for_each_entry_rcu(mod_map, &ftrace_mod_maps, list) {
@@ -6540,8 +6594,10 @@ int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value, · 20 unmodified lines
65406594 WARN_ON(1);
65416595 break;
65426596 }
6597+ ret = ftrace_get_trampoline_kallsym(symnum, value, type, name,
6598+ module_name, exported);
65436599 preempt_enable();
6544− return -ERANGE;
6600+ return ret;
65456601 }
65466602
65476603 #else
@@ -6553,6 +6609,18 @@ allocate_ftrace_mod_map(struct module *mod, · 5 unmodified lines
65536609 {
65546610 return NULL;
65556611 }
6612+int ftrace_mod_get_kallsym(unsigned int symnum, unsigned long *value,
6613+ char *type, char *name, char *module_name,
6614+ int *exported)
6615+{
6616+ int ret;
6617+
6618+ preempt_disable();
6619+ ret = ftrace_get_trampoline_kallsym(symnum, value, type, name,
6620+ module_name, exported);
6621+ preempt_enable();
6622+ return ret;
6623+}
65566624 #endif /* CONFIG_MODULES */
65576625
65586626 struct ftrace_init_func {
@@ -6733,7 +6801,12 @@ void __weak arch_ftrace_update_trampoline(struct ftrace_ops *ops) · 174 unmodified lines
67336801
67346802 static void ftrace_update_trampoline(struct ftrace_ops *ops)
67356803 {
6804+ unsigned long trampoline = ops->trampoline;
6805+
67366806 arch_ftrace_update_trampoline(ops);
6807+ if (ops->trampoline && ops->trampoline != trampoline &&
6808+ (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
6809+ ftrace_add_trampoline_to_kallsyms(ops);
67376810 }
67386811
67396812 void ftrace_init_trace_array(struct trace_array *tr)