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Date: Thu, 7 Aug 2014 22:35:53 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Nicolas Pitre <nicolas.pitre@...aro.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Russell King - ARM Linux <linux@....linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH v2 1/5] tracing: Do not do anything special with
tracepoint_string when tracing is disabled
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.
-- Steve
>From 3c49b52b155d0f723792377e1a4480a0e7ca0ba2 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@...dmis.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@linaro.org
Suggested-by: Nicolas Pitre <nico@...aro.org>
Signed-off-by: Steven Rostedt <rostedt@...dmis.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
--
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