netdev - Re: [PATCH v5 bpf-next 4/4] selftest/bpf: Extend the bpf

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Date:   Fri, 13 Aug 2021 16:30:29 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.co.jp>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Benjamin Herrenschmidt <benh@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH v5 bpf-next 4/4] selftest/bpf: Extend the bpf_snprintf()
 test for "%c".

On Fri, Aug 13, 2021 at 4:28 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Aug 12, 2021 at 9:47 AM Kuniyuki Iwashima <kuniyu@...zon.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@...zon.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);

Can you also add tests for %+2c, %-3c, %04c, %0c? Think outside the box ;)

>
>
> 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
> >