linux-kernel - [PATCH] tracing: events_hist: avoid using excessive stack space

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Date:   Fri, 14 May 2021 16:04:25 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Steven Rostedt (VMware)" <rostedt@...mis.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Qiujun Huang <hqjagain@...il.com>, Tom Rix <trix@...hat.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH] tracing: events_hist: avoid using excessive stack space

From: Arnd Bergmann <arnd@...db.de>

In some configurations, clang produces a warning about an overly large
amount of stack space used in hist_trigger_print_key():

kernel/trace/trace_events_hist.c:4594:13: error: stack frame size of 1248 bytes in function 'hist_trigger_print_key' [-Werror,-Wframe-larger-than=]
static void hist_trigger_print_key(struct seq_file *m,

Moving the 'str' variable into a more local scope in the two places
where it gets used actually reduces the the used stack space here
and gets it below the warning limit, because the compiler can now
assume that it is safe to use the same stack slot that it has for
the stack of any inline function.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 kernel/trace/trace_events_hist.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index c1abd63f1d6c..e3fe84f017a8 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -4597,7 +4597,6 @@ static void hist_trigger_print_key(struct seq_file *m,
 				   struct tracing_map_elt *elt)
 {
 	struct hist_field *key_field;
-	char str[KSYM_SYMBOL_LEN];
 	bool multiline = false;
 	const char *field_name;
 	unsigned int i;
@@ -4617,11 +4616,13 @@ static void hist_trigger_print_key(struct seq_file *m,
 			uval = *(u64 *)(key + key_field->offset);
 			seq_printf(m, "%s: %llx", field_name, uval);
 		} else if (key_field->flags & HIST_FIELD_FL_SYM) {
+			char str[KSYM_SYMBOL_LEN];
 			uval = *(u64 *)(key + key_field->offset);
 			sprint_symbol_no_offset(str, uval);
 			seq_printf(m, "%s: [%llx] %-45s", field_name,
 				   uval, str);
 		} else if (key_field->flags & HIST_FIELD_FL_SYM_OFFSET) {
+			char str[KSYM_SYMBOL_LEN];
 			uval = *(u64 *)(key + key_field->offset);
 			sprint_symbol(str, uval);
 			seq_printf(m, "%s: [%llx] %-55s", field_name,
-- 
2.29.2