Re: [linux-next:master 2296/2770] kernel/bpf/helpers.c:713:43: warning: Uninitialized variable: bufs [uninitvar]

[Florent Revest <revest@chromium.org>]

On Fri, May 14, 2021 at 8:37 AM kernel test robot <lkp@intel.com> wrote:
> cppcheck possible warnings: (new ones prefixed by >>, may not real problems)
>
> >> kernel/bpf/helpers.c:713:43: warning: Uninitialized variable: bufs [uninitvar]
>     if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bufs->tmp_bufs))) {
>                                              ^

I don't think this is a real problem. bufs is not actually
dereferenced, it is only used to give the type information to a
sizeof. This is only evaluated at compilation time.

If this matters, I guess we could silent this cppcheck warning with
something like the following patch. Alexei, what do you think ?

--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -697,8 +697,9 @@ static int bpf_trace_copy_string(char *buf, void
*unsafe_ptr, char fmt_ptype,
 #define MAX_PRINTF_BUF_LEN     512

 /* Support executing three nested bprintf helper calls on a given CPU */
+#define MAX_PRINTF_NEST_LEVEL 3
 struct bpf_bprintf_buffers {
-       char tmp_bufs[3][MAX_PRINTF_BUF_LEN];
+       char tmp_bufs[MAX_PRINTF_NEST_LEVEL][MAX_PRINTF_BUF_LEN];
 };
 static DEFINE_PER_CPU(struct bpf_bprintf_buffers, bpf_bprintf_bufs);
 static DEFINE_PER_CPU(int, bpf_bprintf_nest_level);
@@ -710,7 +711,7 @@ static int try_get_fmt_tmp_buf(char **tmp_buf)

        preempt_disable();
        nest_level = this_cpu_inc_return(bpf_bprintf_nest_level);
-       if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bufs->tmp_bufs))) {
+       if (WARN_ON_ONCE(nest_level > MAX_PRINTF_NEST_LEVEL)) {
                this_cpu_dec(bpf_bprintf_nest_level);
                preempt_enable();
                return -EBUSY;