From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Florent Revest <revest@chromium.org>
Cc: kernel test robot <lkp@intel.com>,
kbuild-all@lists.01.org,
Linux Memory Management List <linux-mm@kvack.org>,
Alexei Starovoitov <ast@kernel.org>
Subject: Re: [linux-next:master 2296/2770] kernel/bpf/helpers.c:713:43: warning: Uninitialized variable: bufs [uninitvar]
Date: Fri, 14 May 2021 07:17:59 -0700 [thread overview]
Message-ID: <CAADnVQ+tYSnbgDP-+6vDG+kmJY3ngp2thoWpnUpT1X17VgqaaA@mail.gmail.com> (raw)
In-Reply-To: <CABRcYmLgV-5eDcuZL_sm95FJsVnjFgQ6b7bsA0o_u9bX5+FRnQ@mail.gmail.com>
On Fri, May 14, 2021 at 7:10 AM Florent Revest <revest@chromium.org> wrote:
>
> 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)) {
Yeah. Why not. I think it's cleaner overall.
WARNING: multiple messages have this Message-ID (diff)
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: kbuild-all@lists.01.org
Subject: Re: [linux-next:master 2296/2770] kernel/bpf/helpers.c:713:43: warning: Uninitialized variable: bufs [uninitvar]
Date: Fri, 14 May 2021 07:17:59 -0700 [thread overview]
Message-ID: <CAADnVQ+tYSnbgDP-+6vDG+kmJY3ngp2thoWpnUpT1X17VgqaaA@mail.gmail.com> (raw)
In-Reply-To: <CABRcYmLgV-5eDcuZL_sm95FJsVnjFgQ6b7bsA0o_u9bX5+FRnQ@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 1746 bytes --]
On Fri, May 14, 2021 at 7:10 AM Florent Revest <revest@chromium.org> wrote:
>
> 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)) {
Yeah. Why not. I think it's cleaner overall.
next prev parent reply other threads:[~2021-05-14 14:18 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-14 6:36 [linux-next:master 2296/2770] kernel/bpf/helpers.c:713:43: warning: Uninitialized variable: bufs [uninitvar] kernel test robot
2021-05-14 6:36 ` kernel test robot
2021-05-14 14:10 ` Florent Revest
2021-05-14 14:10 ` Florent Revest
2021-05-14 14:17 ` Alexei Starovoitov [this message]
2021-05-14 14:17 ` Alexei Starovoitov
2021-05-17 9:30 ` Florent Revest
2021-05-17 9:30 ` Florent Revest
-- strict thread matches above, loose matches on Subject: below --
2021-05-13 16:10 kernel test robot
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