[PATCH v2 3/3] tracing: simplify printf'ing in seq_print_sym

From: Rasmus Villemoes
Date: Mon Oct 29 2018 - 18:35:59 EST

trace_seq_printf(..., "%s", ...) can be done with trace_seq_puts()
instead, avoiding printf overhead. In the second instance, the string
we're copying was just created from an snprintf() to a stack buffer, so
we might as well do that printf directly. This naturally leads to moving
the declaration of the str buffer inside the CONFIG_KALLSYMS guard,
which in turn will make gcc inline the function for !CONFIG_KALLSYMS (it
only has a single caller, but the huge stack frame seems to make gcc not
inline it for CONFIG_KALLSYMS).

Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
kernel/trace/trace_output.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index f06fb899b746..54373d93e251 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -341,8 +341,8 @@ static inline const char *kretprobed(const char *name)
static void
seq_print_sym(struct trace_seq *s, unsigned long address, bool offset)
- char str[KSYM_SYMBOL_LEN];
+ char str[KSYM_SYMBOL_LEN];
const char *name;

if (offset)
@@ -352,12 +352,11 @@ seq_print_sym(struct trace_seq *s, unsigned long address, bool offset)
name = kretprobed(str);

if (name && strlen(name)) {
- trace_seq_printf(s, "%s", name);
+ trace_seq_puts(s, name);
- snprintf(str, KSYM_SYMBOL_LEN, "0x%08lx", address);
- trace_seq_printf(s, "%s", str);
+ trace_seq_printf(s, "0x%08lx", address);

#ifndef CONFIG_64BIT