[PATCH] locking/lockdep: fix format-truncation compiler-warning

[PATCH] locking/lockdep: fix format-truncation compiler-warning

[Lucy Mielke]

Compiler: gcc x86_64 v13.2.1
Config: allyesconfig, "treat warnings as errors" unset

This fixes a warning emitted by gcc, stating the output may be
truncated. The fix included increasing the buffer size to the one
denoted by gcc.

Signed-off-by: Lucy Mielke <lucymielke@icloud.com>
---
 kernel/locking/lockdep_proc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 15fdc7fa5c68..e2bfb1db589d 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -440,7 +440,7 @@ static void snprint_time(char *buf, size_t bufsiz, s64 nr)
 
 static void seq_time(struct seq_file *m, s64 time)
 {
-	char num[15];
+	char num[22];
 
 	snprint_time(num, sizeof(num), time);
 	seq_printf(m, " %14s", num);
-- 
2.41.0

Re: [PATCH] locking/lockdep: fix format-truncation compiler-warning

[Ingo Molnar]

* Lucy Mielke <lucymielke@icloud.com> wrote:

> Compiler: gcc x86_64 v13.2.1
> Config: allyesconfig, "treat warnings as errors" unset
> 
> This fixes a warning emitted by gcc, stating the output may be
> truncated. The fix included increasing the buffer size to the one
> denoted by gcc.

Mind including the output by GCC in the changelog?

>  static void seq_time(struct seq_file *m, s64 time)
>  {
> -	char num[15];
> +	char num[22];
>  
>  	snprint_time(num, sizeof(num), time);
>  	seq_printf(m, " %14s", num);

Fun.

So this:

static void snprint_time(char *buf, size_t bufsiz, s64 nr)
{
        s64 div;
        s32 rem;

        nr += 5; /* for display rounding */
        div = div_s64_rem(nr, 1000, &rem);
        snprintf(buf, bufsiz, "%lld.%02d", (long long)div, (int)rem/10);
}

... actually needs 21+1 bytes?

Which I suppose is true - longest s64 is "-9223372036854775808"-ish, which 
converted to the fixed-point float format above is "-9223372036854775.80": 
21 bytes, plus termination is another byte: 22.

Maybe put this into the changelog too, instead of relying on magic GCC 
calculations only. :-)

Thanks,

	Ingo

Re: [PATCH] locking/lockdep: fix format-truncation compiler-warning

[Lucy Mielke]

Am Thu, Oct 12, 2023 at 12:11:13AM +0200 schrieb Ingo Molnar:
> 
> Mind including the output by GCC in the changelog?
> 

Sure, let me resend the patch then :)

> ... actually needs 21+1 bytes?
> 
> Which I suppose is true - longest s64 is "-9223372036854775808"-ish, which 
> converted to the fixed-point float format above is "-9223372036854775.80": 
> 21 bytes, plus termination is another byte: 22.
> 
> Maybe put this into the changelog too, instead of relying on magic GCC 
> calculations only. :-)

I can include it as well, of course!

Mit freundlichen Grüßen / Best regards,
	Lucy