tracing/core: bring back raw trace_printk for dynamic formats strings

Impact: fix callsites with dynamic format strings

Since its new binary implementation, trace_printk() internally uses static
containers for the format strings on each callsites. But the value is
assigned once at build time, which means that it can't take dynamic
formats.

So this patch unearthes the raw trace_printk implementation for the callers
that will need trace_printk to be able to carry these dynamic format
strings. The trace_printk() macro will use the appropriate implementation
for each callsite. Most of the time however, the binary implementation will
still be used.

The other impact of this patch is that mmiotrace_printk() will use the old
implementation because it calls the low level trace_vprintk and we can't
guess here whether the format passed in it is dynamic or not.

Some parts of this patch have been written by Steven Rostedt (most notably
the part that chooses the appropriate implementation for each callsites).

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 27 insertions, 13 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 7742798c9208..1daca3b062bb 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -452,32 +452,46 @@ do {									\
 
 #define trace_printk(fmt, args...)                                      \
 do {                                                                    \
-        static const char *trace_printk_fmt                             \
-        __attribute__((section("__trace_printk_fmt")));                 \
-                                                                        \
-        if (!trace_printk_fmt)                                          \
-                trace_printk_fmt = fmt;                                 \
-                                                                        \
         __trace_printk_check_format(fmt, ##args);                       \
-        __trace_printk(_THIS_IP_, trace_printk_fmt, ##args);            \
+        if (__builtin_constant_p(fmt)) {                                \
+                static const char *trace_printk_fmt                     \
+                  __attribute__((section("__trace_printk_fmt"))) =      \
+                        __builtin_constant_p(fmt) ? fmt : NULL;         \
+                                                                        \
+                __trace_bprintk(_THIS_IP_, trace_printk_fmt, ##args);   \
+        } else                                                          \
+                __trace_printk(_THIS_IP_, fmt, ##args);         \
 } while (0)
 
 extern int
+__trace_bprintk(unsigned long ip, const char *fmt, ...)
+        __attribute__ ((format (printf, 2, 3)));
+
+extern int
 __trace_printk(unsigned long ip, const char *fmt, ...)
         __attribute__ ((format (printf, 2, 3)));
 
+/*
+ * The double __builtin_constant_p is because gcc will give us an error
+ * if we try to allocate the static variable to fmt if it is not a
+ * constant. Even with the outer if statement.
+ */
 #define ftrace_vprintk(fmt, vargs)                                      \
 do {                                                                    \
-        static const char *trace_printk_fmt                             \
-        __attribute__((section("__trace_printk_fmt")));                 \
-                                                                        \
-        if (!trace_printk_fmt)                                          \
-                trace_printk_fmt = fmt;                                 \
+        if (__builtin_constant_p(fmt)) {                                \
+                static const char *trace_printk_fmt                     \
+                  __attribute__((section("__trace_printk_fmt"))) =      \
+                        __builtin_constant_p(fmt) ? fmt : NULL;         \
                                                                         \
-        __ftrace_vprintk(_THIS_IP_, trace_printk_fmt, vargs);           \
+                __ftrace_vbprintk(_THIS_IP_, trace_printk_fmt, vargs);  \
+        } else                                                          \
+                __ftrace_vprintk(_THIS_IP_, fmt, vargs);                \
 } while (0)
 
 extern int
+__ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap);
+
+extern int
 __ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap);
 
 extern void ftrace_dump(void);