[for-next][PATCH 05/18] ftrace: Drop a VLA in module_exists()

From: Steven Rostedt
Date: Fri Apr 06 2018 - 09:04:02 EST


From: Salvatore Mesoraca <s.mesoraca16@xxxxxxxxx>

Avoid a VLA by using a real constant expression instead of a variable.
The compiler should be able to optimize the original code and avoid using
an actual VLA. Anyway this change is useful because it will avoid a false
positive with -Wvla, it might also help the compiler generating better
code.

Link: http://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1522399988-8815-1-git-send-email-s.mesoraca16@xxxxxxxxx

Signed-off-by: Salvatore Mesoraca <s.mesoraca16@xxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
kernel/trace/ftrace.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index eac9ce2c57a2..16bbf062018f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3902,14 +3902,13 @@ static bool module_exists(const char *module)
{
/* All modules have the symbol __this_module */
const char this_mod[] = "__this_module";
- const int modname_size = MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 1;
- char modname[modname_size + 1];
+ char modname[MAX_PARAM_PREFIX_LEN + sizeof(this_mod) + 2];
unsigned long val;
int n;

- n = snprintf(modname, modname_size + 1, "%s:%s", module, this_mod);
+ n = snprintf(modname, sizeof(modname), "%s:%s", module, this_mod);

- if (n > modname_size)
+ if (n > sizeof(modname) - 1)
return false;

val = module_kallsyms_lookup_name(modname);
--
2.15.1