tracing: add trace_bprintk()

Impact: add a generic printk() for tracing, like trace_printk()

trace_bprintk() uses the infrastructure to record events on ring_buffer.

[ fweisbec@gmail.com: ported to latest -tip, made it work if
  !CONFIG_MODULES, never free the format strings from modules
  because we can't keep track of them and conditionnaly create
  the ftrace format strings section (reported by Steven Rostedt) ]

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1236356510-8381-4-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 35 insertions, 0 deletions

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 0add6b28c366..48ade3168b13 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -69,6 +69,14 @@
 #define FTRACE_EVENTS()
 #endif
 
+#ifdef CONFIG_TRACING
+#define TRACE_PRINTKS() VMLINUX_SYMBOL(__start___trace_bprintk_fmt) = .;      \
+                         *(__trace_printk_fmt) /* Trace_printk fmt' pointer */ \
+                         VMLINUX_SYMBOL(__stop___trace_bprintk_fmt) = .;
+#else
+#define TRACE_PRINTKS()
+#endif
+
 /* .data section */
 #define DATA_DATA                                                       \
         *(.data)                                                        \
@@ -100,6 +108,7 @@
                 *(__vermagic)           /* Kernel version magic */      \
                 *(__markers_strings)    /* Markers: strings */          \
                 *(__tracepoints_strings)/* Tracepoints: strings */      \
+                TRACE_PRINTKS()                                 \
         }                                                               \
                                                                         \
         .rodata1          : AT(ADDR(.rodata1) - LOAD_OFFSET) {          \
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 1c9cdca02580..1cc8ca453a9b 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -225,6 +225,27 @@ extern int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr);
 
 #ifdef CONFIG_TRACE_BPRINTK
 extern int trace_vbprintk(unsigned long ip, const char *fmt, va_list args);
+extern int __trace_bprintk(unsigned long ip, const char *fmt, ...)
+                __attribute__ ((format (printf, 2, 3)));
+
+static inline void  ____trace_bprintk_check_format(const char *fmt, ...)
+                __attribute__ ((format (printf, 1, 2)));
+static inline void ____trace_bprintk_check_format(const char *fmt, ...) {}
+#define __trace_bprintk_check_format(fmt, args...)                      \
+do {                                                                    \
+        if (0)                                                          \
+                ____trace_bprintk_check_format(fmt, ##args);            \
+} while (0)
+
+#define trace_bprintk(fmt, args...)                                     \
+do {                                                                    \
+        static char *__attribute__((section("__trace_bprintk_fmt")))    \
+                        trace_bprintk_fmt = fmt;                        \
+        __trace_bprintk_check_format(fmt, ##args);                      \
+        __trace_bprintk(_THIS_IP_, trace_bprintk_fmt, ##args);  \
+} while (0)
+#else
+#define trace_bprintk trace_printk
 #endif
 
 /* May be defined in arch */
diff --git a/include/linux/module.h b/include/linux/module.h
index 145a75528cc1..8cbec972d8e7 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -329,6 +329,11 @@ struct module
         unsigned int num_tracepoints;
 #endif
 
+#ifdef CONFIG_TRACE_BPRINTK
+        const char **trace_bprintk_fmt_start;
+        unsigned int num_trace_bprintk_fmt;
+#endif
+
 #ifdef CONFIG_MODULE_UNLOAD
         /* What modules depend on me? */
         struct list_head modules_which_use_me;