Commit 1149fcf7 authored by Masami Hiramatsu (Google)'s avatar Masami Hiramatsu (Google)
Browse files

tracing: Add an option to show symbols in _text+offset for function profiler 

Function profiler shows the hit count of each function using its symbol
name. However, there are some same-name local symbols, which we can not
distinguish.
To solve this issue, this introduces an option to show the symbols
in "_text+OFFSET" format. This can avoid exposing the random shift of
KASLR. The functions in modules are shown as "MODNAME+OFFSET" where the
offset is from ".text".

E.g. for the kernel text symbols, specify vmlinux and the output to
 addr2line, you can find the actual function and source info;

  $ addr2line -fie vmlinux _text+3078208
  __balance_callbacks
  kernel/sched/core.c:5064

for modules, specify the module file and .text+OFFSET;

  $ addr2line -fie samples/trace_events/trace-events-sample.ko .text+8224
  do_simple_thread_func
  samples/trace_events/trace-events-sample.c:23

Link: https://lore.kernel.org/all/176187878064.994619.8878296550240416558.stgit@devnote2/



Suggested-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
parent bbec8e28

kernel/trace/ftrace.c

+25 −1
Original line number Diff line number Diff line
@@ -534,7 +534,9 @@ static int function_stat_headers(struct seq_file *m) 


static int function_stat_show(struct seq_file *m, void *v)

{

	struct trace_array *tr = trace_get_global_array();

	struct ftrace_profile *rec = v;

	const char *refsymbol = NULL;

	char str[KSYM_SYMBOL_LEN];

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	static struct trace_seq s;
@@ -554,7 +556,29 @@ static int function_stat_show(struct seq_file *m, void *v) 
		return 0;

#endif



	if (tr->trace_flags & TRACE_ITER(PROF_TEXT_OFFSET)) {

		unsigned long offset;



		if (core_kernel_text(rec->ip)) {

			refsymbol = "_text";

			offset = rec->ip - (unsigned long)_text;

		} else {

			struct module *mod;



			guard(rcu)();

			mod = __module_text_address(rec->ip);

			if (mod) {

				refsymbol = mod->name;

				/* Calculate offset from module's text entry address. */

				offset = rec->ip - (unsigned long)mod->mem[MOD_TEXT].base;

			}

		}

		if (refsymbol)

			snprintf(str, sizeof(str), "  %s+%#lx", refsymbol, offset);

	}

	if (!refsymbol)

		kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);



	seq_printf(m, "  %-30.30s  %10lu", str, rec->counter);



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

kernel/trace/trace.c

+3 −2
Original line number Diff line number Diff line
@@ -522,7 +522,8 @@ EXPORT_SYMBOL_GPL(unregister_ftrace_export); 


/* trace_options that are only supported by global_trace */

#define TOP_LEVEL_TRACE_FLAGS (TRACE_ITER(PRINTK) |			\

	       TRACE_ITER(PRINTK_MSGONLY) | TRACE_ITER(RECORD_CMD))

	       TRACE_ITER(PRINTK_MSGONLY) | TRACE_ITER(RECORD_CMD) |	\

	       TRACE_ITER(PROF_TEXT_OFFSET))



/* trace_flags that are default zero for instances */

#define ZEROED_TRACE_FLAGS \
@@ -11291,7 +11292,7 @@ __init static int tracer_alloc_buffers(void) 


#ifdef CONFIG_FUNCTION_TRACER

/* Used to set module cached ftrace filtering at boot up */

__init struct trace_array *trace_get_global_array(void)

struct trace_array *trace_get_global_array(void)

{

	return &global_trace;

}

kernel/trace/trace.h

+10 −1
Original line number Diff line number Diff line
@@ -1359,6 +1359,14 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 
# define STACK_FLAGS

#endif



#ifdef CONFIG_FUNCTION_PROFILER

# define PROFILER_FLAGS					\

		C(PROF_TEXT_OFFSET,	"prof-text-offset"),

#else

# define PROFILER_FLAGS

# define TRACE_ITER_PROF_TEXT_OFFSET_BIT	-1

#endif



/*

 * trace_iterator_flags is an enumeration that defines bit

 * positions into trace_flags that controls the output.
@@ -1397,7 +1405,8 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 
		FUNCTION_FLAGS					\

		FGRAPH_FLAGS					\

		STACK_FLAGS					\

		BRANCH_FLAGS

		BRANCH_FLAGS					\

		PROFILER_FLAGS



/*

 * By defining C, we can make TRACE_FLAGS a list of bit names