From: Yonghong Song <yonghong.song@linux.dev>
To: "Jose E. Marchesi" <jose.marchesi@oracle.com>, bpf@vger.kernel.org
Cc: david.faust@oracle.com, cupertino.miranda@oracle.com,
Eduard Zingerman <eddyz87@gmail.com>
Subject: Re: [PATCH bpf-next] bpf: avoid uninitialized warnings in verifier_global_subprogs.c
Date: Tue, 7 May 2024 10:41:11 -0700 [thread overview]
Message-ID: <223e5ab8-83da-40b7-b10b-0f6341aacb27@linux.dev> (raw)
In-Reply-To: <20240507140540.3972-1-jose.marchesi@oracle.com>
On 5/7/24 7:05 AM, Jose E. Marchesi wrote:
> The BPF selftest verifier_global_subprogs.c contains code that
> purposedly performs out of bounds access to memory, to check whether
> the kernel verifier is able to catch them. For example:
>
> __noinline int global_unsupp(const int *mem)
> {
> if (!mem)
> return 0;
> return mem[100]; /* BOOM */
> }
>
> With -O1 and higher and no inlining, GCC notices this fact and emits a
> "maybe uninitialized" warning. This is by design. Note that the
> emission of these warnings is highly dependent on the precise
> optimizations that are performed.
Interesting. The error message is 'maybe uninitialized' but not
an error to complain out-of-bound access. But anyway, since gcc
produces a warning, your patch silences it and LGTM.
Acked-by: Yonghong Song <yonghong.song@linux.dev>
>
> This patch adds a compiler pragma to verifier_global_subprogs.c to
> ignore these warnings.
>
> Tested in bpf-next master.
> No regressions.
>
> Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
> Cc: david.faust@oracle.com
> Cc: cupertino.miranda@oracle.com
> Cc: Yonghong Song <yonghong.song@linux.dev>
> Cc: Eduard Zingerman <eddyz87@gmail.com>
> ---
> tools/testing/selftests/bpf/progs/verifier_global_subprogs.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
> index baff5ffe9405..d05dc218b7e9 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
> @@ -8,6 +8,11 @@
> #include "xdp_metadata.h"
> #include "bpf_kfuncs.h"
>
> +/* The compiler may be able to detect the access to uninitialized
> + memory in the routines performing out of bound memory accesses and
> + emit warnings about it. This is the case of GCC. */
> +#pragma GCC diagnostic ignored "-Wuninitialized"
> +
> int arr[1];
> int unkn_idx;
> const volatile bool call_dead_subprog = false;
next prev parent reply other threads:[~2024-05-07 17:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-07 14:05 [PATCH bpf-next] bpf: avoid uninitialized warnings in verifier_global_subprogs.c Jose E. Marchesi
2024-05-07 17:41 ` Yonghong Song [this message]
2024-05-07 18:20 ` Jose E. Marchesi
2024-05-07 19:46 ` Yonghong Song
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=223e5ab8-83da-40b7-b10b-0f6341aacb27@linux.dev \
--to=yonghong.song@linux.dev \
--cc=bpf@vger.kernel.org \
--cc=cupertino.miranda@oracle.com \
--cc=david.faust@oracle.com \
--cc=eddyz87@gmail.com \
--cc=jose.marchesi@oracle.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).