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Date: Tue, 12 Feb 2019 19:41:57 +0800 From: Mars Cheng <mars.cheng@...iatek.com> To: Steven Rostedt <rostedt@...dmis.org> CC: CC Hwang <cc.hwang@...iatek.com>, <linux-kernel@...r.kernel.org>, <linux-mediatek@...ts.infradead.org>, <linux-arm-kernel@...ts.infradead.org>, Andress Kuo <andress.kuo@...iatek.com>, Mars Cheng <mars.cheng@...iatek.com> Subject: [PATCH 1/1] tracing: Fix event_trace_printk loss on printk_format. From: Andress Kuo <andress.kuo@...iatek.com> If fmt on event_trace_printk is not a constant, It means that something not guaranteed, so the compiler optimizes the fmt out, and then the __trace_printk_fmt section is not filled. if __trace_printk_fmt is not filled, the kernel will not allocate the special buffers needed for the event_trace_printk() and then not shown in the file output sys/kernel/debug/tracing/print_formats. Adding a "__used" to the variable in the __trace_printk_fmt section on event_trace_printk() will keep it around, even though it is set to NULL. This will keep the string from being printed in the sys/kernel/debug/tracing/printk_formats section. We can also refer to commit 3debb0a9ddb1 ("tracing: Fix trace_printk() to print when not using bprintk()")that it had similar issue on path of trace_printk(). Signed-off-by: Andress Kuo <andress.kuo@...iatek.com> Signed-off-by: Mars Cheng <mars.cheng@...iatek.com> --- include/linux/trace_events.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 8a62731..26bd7c4 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -551,7 +551,7 @@ extern int trace_define_field(struct trace_event_call *call, const char *type, __trace_printk_check_format(fmt, ##args); \ tracing_record_cmdline(current); \ if (__builtin_constant_p(fmt)) { \ - static const char *trace_printk_fmt \ + static const char *trace_printk_fmt __used \ __attribute__((section("__trace_printk_fmt"))) = \ __builtin_constant_p(fmt) ? fmt : NULL; \ \ -- 1.7.9.5
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