[PATCH] kernel/trace: Add TRACING_ALLOW_PRINTK config option

Nicolas Boichat
2020-06-24T08:45:41Z

trace_printk is only meant as a debugging tool, and should never be
compiled into production code without source code changes, as
indicated by the warning that shows up on boot if any trace_printk
is called:
** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
** **
** trace_printk() being used. Allocating extra memory. **
** **
** This means that this is a DEBUG kernel and it is **
** unsafe for production use. **

If this option is set to n, the kernel will generate a build-time
error if trace_printk is used.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
---
include/linux/kernel.h | 17 ++++++++++++++++-
kernel/trace/Kconfig | 9 +++++++++
2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 196607aaf653082..b6addc6ba669e85 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -721,10 +721,15 @@ do { \
#define trace_printk(fmt, ...) \
do { \
char _______STR[] = __stringify((__VA_ARGS__)); \
+ \
+ __static_assert( \
+ IS_ENABLED(CONFIG_TRACING_ALLOW_PRINTK),\
+ "trace_printk called, please enable CONFIG_TRACING_ALLOW_PRINTK."); \
+ \
if (sizeof(_______STR) > 3) \
do_trace_printk(fmt, ##__VA_ARGS__); \
else \
- trace_puts(fmt); \
+ do_trace_puts(fmt); \
} while (0)

#define do_trace_printk(fmt, args...) \
@@ -773,6 +778,13 @@ int __trace_printk(unsigned long ip, const char *fmt, ...);
*/

#define trace_puts(str) ({ \
+ __static_assert( \
+ IS_ENABLED(CONFIG_TRACING_ALLOW_PRINTK), \
+ "trace_puts called, please enable CONFIG_TRACING_ALLOW_PRINTK."); \
+ do_trace_puts(str); \
+})
+
+#define do_trace_puts(str) ({ \
static const char *trace_printk_fmt __used \
__attribute__((section("__trace_printk_fmt"))) = \
__builtin_constant_p(str) ? str : NULL; \
@@ -794,6 +806,9 @@ extern void trace_dump_stack(int skip);
*/
#define ftrace_vprintk(fmt, vargs) \
do { \
+ __static_assert( \
+ IS_ENABLED(CONFIG_TRACING_ALLOW_PRINTK), \
+ "ftrace_vprintk called, please enable CONFIG_TRACING_ALLOW_PRINTK."); \
if (__builtin_constant_p(fmt)) { \
static const char *trace_printk_fmt __used \
__attribute__((section("__trace_printk_fmt"))) = \
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index a4020c0b4508c99..89ffddebe1864aa 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -111,6 +111,15 @@ config GENERIC_TRACER
bool
select TRACING

+config TRACING_ALLOW_PRINTK
+ bool "Allow trace_printk"
+ default y if DEBUG_KERNEL
+ depends on TRACING
+ help
+ trace_printk is only meant as a debugging tool. If this option is
+ set to n, the kernel will generate a build-time error if trace_printk
+ is used.
+
#
# Minimum requirements an architecture has to meet for us to
# be able to offer generic tracing facilities:
--
2.27.0.111.gc72c7da667-goog