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ftrace: Add symbols for ftrace trampolines

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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.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200512121922.8997-7-adrian.hunter@intel.com
This commit is contained in:
Adrian Hunter 2020-05-12 15:19:13 +03:00 committed by Peter Zijlstra
parent 3e46bb40af
commit fc0ea795f5
3 changed files with 88 additions and 6 deletions
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12
include/linux/ftrace.h
View File

@ -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;
@ -207,6 +210,7 @@ struct ftrace_ops {
struct ftrace_ops_hash old_hash;
unsigned long trampoline;
unsigned long trampoline_size;
struct list_head list;
#endif
};

5
kernel/kallsyms.c
View File

@ -482,6 +482,11 @@ static int get_ksymbol_mod(struct kallsym_iter *iter)
return 1;
}
/*
* ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
* purposes. In that case "__builtin__ftrace" is used as a module name, even
* though "__builtin__ftrace" is not a module.
*/
static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
{
int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,

77
kernel/trace/ftrace.c
View File

@ -2764,6 +2764,38 @@ void __weak arch_ftrace_trampoline_free(struct ftrace_ops *ops)
{
}
/* List of trace_ops that have allocated trampolines */
static LIST_HEAD(ftrace_ops_trampoline_list);
static void ftrace_add_trampoline_to_kallsyms(struct ftrace_ops *ops)
{
lockdep_assert_held(&ftrace_lock);
list_add_rcu(&ops->list, &ftrace_ops_trampoline_list);
}
static void ftrace_remove_trampoline_from_kallsyms(struct ftrace_ops *ops)
{
lockdep_assert_held(&ftrace_lock);
list_del_rcu(&ops->list);
}
/*
* "__builtin__ftrace" is used as a module name in /proc/kallsyms for symbols
* for pages allocated for ftrace purposes, even though "__builtin__ftrace" is
* not a module.
*/
#define FTRACE_TRAMPOLINE_MOD "__builtin__ftrace"
#define FTRACE_TRAMPOLINE_SYM "ftrace_trampoline"
static void ftrace_trampoline_free(struct ftrace_ops *ops)
{
if (ops && (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP) &&
ops->trampoline)
ftrace_remove_trampoline_from_kallsyms(ops);
arch_ftrace_trampoline_free(ops);
}
static void ftrace_startup_enable(int command)
{
if (saved_ftrace_func != ftrace_trace_function) {
@ -2934,7 +2966,7 @@ int ftrace_shutdown(struct ftrace_ops *ops, int command)
synchronize_rcu_tasks();
free_ops:
arch_ftrace_trampoline_free(ops);
ftrace_trampoline_free(ops);
}
return 0;
@ -6178,6 +6210,27 @@ struct ftrace_mod_map {
unsigned int num_funcs;
};
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_TRAMPOLINE_MOD, 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)
@ -6514,6 +6567,7 @@ 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) {
@ -6540,8 +6594,10 @@ 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
@ -6553,6 +6609,18 @@ 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 {
@ -6733,7 +6801,12 @@ void __weak arch_ftrace_update_trampoline(struct ftrace_ops *ops)
static void ftrace_update_trampoline(struct ftrace_ops *ops)
{
unsigned long trampoline = ops->trampoline;
arch_ftrace_update_trampoline(ops);
if (ops->trampoline && ops->trampoline != trampoline &&
(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
ftrace_add_trampoline_to_kallsyms(ops);
}
void ftrace_init_trace_array(struct trace_array *tr)