On Thu, 7 Aug 2014, Steven Rostedt wrote:
Because ftrace_events.h is not included when config tracing is not enabled, I got error messages when compiling arm and arm64 without tracing enabled. This is the new patch I'm now testing that moves the tracepoint_string code to include/linux/tracepoint.h as well.
Makes sense.
-- Steve
From 3c49b52b155d0f723792377e1a4480a0e7ca0ba2 Mon Sep 17 00:00:00 2001 From: Steven Rostedt rostedt@goodmis.org Date: Fri, 25 Jul 2014 16:05:29 -0400 Subject: [PATCH] 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@lin...
Suggested-by: Nicolas Pitre nico@linaro.org Signed-off-by: Steven Rostedt rostedt@goodmis.org
include/linux/ftrace_event.h | 34 ---------------------------------- include/linux/tracepoint.h | 44 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+), 34 deletions(-)
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h index cff3106ffe2c..c9f619a2070f 100644 --- a/include/linux/ftrace_event.h +++ b/include/linux/ftrace_event.h @@ -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; diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 2e2a5f7717e5..b1293f15f592 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -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
-- 2.0.1