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Commit 3c49b52b authored by Steven Rostedt's avatar Steven Rostedt
Browse files

tracing: Do not do anything special with tracepoint_string when tracing is disabled 

When CONFIG_TRACING is not enabled, there's no reason to save the trace
strings either by the linker or as a static variable that can be
referenced later. Simply pass back the string that is given to
tracepoint_string().

Had to move the define to include/linux/tracepoint.h so that it is still
visible when CONFIG_TRACING is not set.

Link: http://lkml.kernel.org/p/1406318733-26754-2-git-send-email-nicolas.pitre@linaro.org



Suggested-by: default avatarNicolas Pitre <nico@linaro.org>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 19583ca5

include/linux/ftrace_event.h

+0 −34
Original line number Diff line number Diff line
@@ -574,40 +574,6 @@ do { \ 
		__trace_printk(ip, fmt, ##args);			\

} while (0)



/**

 * tracepoint_string - register constant persistent string to trace system

 * @str - a constant persistent string that will be referenced in tracepoints

 *

 * If constant strings are being used in tracepoints, it is faster and

 * more efficient to just save the pointer to the string and reference

 * that with a printf "%s" instead of saving the string in the ring buffer

 * and wasting space and time.

 *

 * The problem with the above approach is that userspace tools that read

 * the binary output of the trace buffers do not have access to the string.

 * Instead they just show the address of the string which is not very

 * useful to users.

 *

 * With tracepoint_string(), the string will be registered to the tracing

 * system and exported to userspace via the debugfs/tracing/printk_formats

 * file that maps the string address to the string text. This way userspace

 * tools that read the binary buffers have a way to map the pointers to

 * the ASCII strings they represent.

 *

 * The @str used must be a constant string and persistent as it would not

 * make sense to show a string that no longer exists. But it is still fine

 * to be used with modules, because when modules are unloaded, if they

 * had tracepoints, the ring buffers are cleared too. As long as the string

 * does not change during the life of the module, it is fine to use

 * tracepoint_string() within a module.

 */

#define tracepoint_string(str)						\

	({								\

		static const char *___tp_str __tracepoint_string = str; \

		___tp_str;						\

	})

#define __tracepoint_string	__attribute__((section("__tracepoint_str")))



#ifdef CONFIG_PERF_EVENTS

struct perf_event;

include/linux/tracepoint.h

+44 −0
Original line number Diff line number Diff line
@@ -249,6 +249,50 @@ extern void syscall_unregfunc(void); 


#endif /* CONFIG_TRACEPOINTS */



#ifdef CONFIG_TRACING

/**

 * tracepoint_string - register constant persistent string to trace system

 * @str - a constant persistent string that will be referenced in tracepoints

 *

 * If constant strings are being used in tracepoints, it is faster and

 * more efficient to just save the pointer to the string and reference

 * that with a printf "%s" instead of saving the string in the ring buffer

 * and wasting space and time.

 *

 * The problem with the above approach is that userspace tools that read

 * the binary output of the trace buffers do not have access to the string.

 * Instead they just show the address of the string which is not very

 * useful to users.

 *

 * With tracepoint_string(), the string will be registered to the tracing

 * system and exported to userspace via the debugfs/tracing/printk_formats

 * file that maps the string address to the string text. This way userspace

 * tools that read the binary buffers have a way to map the pointers to

 * the ASCII strings they represent.

 *

 * The @str used must be a constant string and persistent as it would not

 * make sense to show a string that no longer exists. But it is still fine

 * to be used with modules, because when modules are unloaded, if they

 * had tracepoints, the ring buffers are cleared too. As long as the string

 * does not change during the life of the module, it is fine to use

 * tracepoint_string() within a module.

 */

#define tracepoint_string(str)						\

	({								\

		static const char *___tp_str __tracepoint_string = str; \

		___tp_str;						\

	})

#define __tracepoint_string	__attribute__((section("__tracepoint_str")))

#else

/*

 * tracepoint_string() is used to save the string address for userspace

 * tracing tools. When tracing isn't configured, there's no need to save

 * anything.

 */

# define tracepoint_string(str) str

# define __tracepoint_string

#endif



/*

 * The need for the DECLARE_TRACE_NOARGS() is to handle the prototype

 * (void). "void" is a special value in a function prototype and can