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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Cc: "David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Benjamin Herrenschmidt <benh@amazon.com>,
	Kuniyuki Iwashima <kuni1840@gmail.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>
Subject: Re: [PATCH v5 bpf-next 4/4] selftest/bpf: Extend the bpf_snprintf() test for "%c".
Date: Fri, 13 Aug 2021 16:28:07 -0700	[thread overview]
Message-ID: <CAEf4BzbJC7J9=p9Fh8D7OYPoKMHKg5WyaJUyTkngDcpUhOB_0g@mail.gmail.com> (raw)
In-Reply-To: <20210812164557.79046-5-kuniyu@amazon.co.jp>

On Thu, Aug 12, 2021 at 9:47 AM Kuniyuki Iwashima <kuniyu@amazon.co.jp> wrote:
>
> This patch adds a "positive" pattern for "%c", which intentionally uses a
> __u32 value (0x64636261, "dbca") to print a single character "a".  If the
> implementation went wrong, other 3 bytes might show up as the part of the
> latter "%+05s".
>
> Also, this patch adds two "negative" patterns for wide character.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
> ---
>  tools/testing/selftests/bpf/prog_tests/snprintf.c | 4 +++-
>  tools/testing/selftests/bpf/progs/test_snprintf.c | 7 ++++---
>  2 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/snprintf.c b/tools/testing/selftests/bpf/prog_tests/snprintf.c
> index dffbcaa1ec98..f77d7def7fed 100644
> --- a/tools/testing/selftests/bpf/prog_tests/snprintf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/snprintf.c
> @@ -19,7 +19,7 @@
>  #define EXP_ADDR_OUT "0000000000000000 ffff00000add4e55 "
>  #define EXP_ADDR_RET sizeof(EXP_ADDR_OUT "unknownhashedptr")
>
> -#define EXP_STR_OUT  "str1 longstr"
> +#define EXP_STR_OUT  "str1         a longstr"
>  #define EXP_STR_RET  sizeof(EXP_STR_OUT)
>
>  #define EXP_OVER_OUT "%over"
> @@ -114,6 +114,8 @@ void test_snprintf_negative(void)
>         ASSERT_ERR(load_single_snprintf("%"), "invalid specifier 3");
>         ASSERT_ERR(load_single_snprintf("%12345678"), "invalid specifier 4");
>         ASSERT_ERR(load_single_snprintf("%--------"), "invalid specifier 5");
> +       ASSERT_ERR(load_single_snprintf("%lc"), "invalid specifier 6");
> +       ASSERT_ERR(load_single_snprintf("%llc"), "invalid specifier 7");
>         ASSERT_ERR(load_single_snprintf("\x80"), "non ascii character");
>         ASSERT_ERR(load_single_snprintf("\x1"), "non printable character");
>  }
> diff --git a/tools/testing/selftests/bpf/progs/test_snprintf.c b/tools/testing/selftests/bpf/progs/test_snprintf.c
> index e2ad26150f9b..afc2c583125b 100644
> --- a/tools/testing/selftests/bpf/progs/test_snprintf.c
> +++ b/tools/testing/selftests/bpf/progs/test_snprintf.c
> @@ -40,6 +40,7 @@ int handler(const void *ctx)
>         /* Convenient values to pretty-print */
>         const __u8 ex_ipv4[] = {127, 0, 0, 1};
>         const __u8 ex_ipv6[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1};
> +       const __u32 chr1 = 0x64636261; /* dcba */
>         static const char str1[] = "str1";
>         static const char longstr[] = "longstr";
>
> @@ -59,9 +60,9 @@ int handler(const void *ctx)
>         /* Kernel pointers */
>         addr_ret = BPF_SNPRINTF(addr_out, sizeof(addr_out), "%pK %px %p",
>                                 0, 0xFFFF00000ADD4E55, 0xFFFF00000ADD4E55);
> -       /* Strings embedding */
> -       str_ret  = BPF_SNPRINTF(str_out, sizeof(str_out), "%s %+05s",
> -                               str1, longstr);
> +       /* Strings and single-byte character embedding */
> +       str_ret  = BPF_SNPRINTF(str_out, sizeof(str_out), "%s % 9c %+05s",
> +                               str1, chr1, longstr);


Why this hackery with __u32? You are making an endianness assumption
(it will break on big-endian), and you'd never write real code like
that. Just pass 'a', what's wrong with that?

>         /* Overflow */
>         over_ret = BPF_SNPRINTF(over_out, sizeof(over_out), "%%overflow");
>         /* Padding of fixed width numbers */
> --
> 2.30.2
>

  reply	other threads:[~2021-08-13 23:28 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-12 16:45 [PATCH v5 bpf-next 0/4] BPF iterator for UNIX domain socket Kuniyuki Iwashima
2021-08-12 16:45 ` [PATCH v5 bpf-next 1/4] bpf: af_unix: Implement " Kuniyuki Iwashima
2021-08-12 16:45 ` [PATCH v5 bpf-next 2/4] bpf: Support "%c" in bpf_bprintf_prepare() Kuniyuki Iwashima
2021-08-12 16:45 ` [PATCH v5 bpf-next 3/4] selftest/bpf: Implement sample UNIX domain socket iterator program Kuniyuki Iwashima
2021-08-13 23:25   ` Andrii Nakryiko
2021-08-14  0:21     ` Kuniyuki Iwashima
2021-08-14  0:26       ` Andrii Nakryiko
2021-08-14  1:00         ` Kuniyuki Iwashima
2021-08-15 18:10       ` Yonghong Song
2021-08-16 12:45         ` Kuniyuki Iwashima
2021-08-12 16:45 ` [PATCH v5 bpf-next 4/4] selftest/bpf: Extend the bpf_snprintf() test for "%c" Kuniyuki Iwashima
2021-08-13 23:28   ` Andrii Nakryiko [this message]
2021-08-13 23:30     ` Andrii Nakryiko
2021-08-14  0:37       ` Kuniyuki Iwashima

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