linux-kernel - Re: [PATCH bpf-next v3 2/2] selftests/bpf: activate the OP_NE login in range

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Message-ID: <CAEf4BzZdLvwbh_-GNoqD=ghgK+GxgXwUBKP6yQQH=vWMP4Csqw@mail.gmail.com>
Date: Thu, 14 Dec 2023 15:24:17 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: andrii@...nel.org, eddyz87@...il.com, yonghong.song@...ux.dev, 
	ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com, 
	martin.lau@...ux.dev, song@...nel.org, kpsingh@...nel.org, sdf@...gle.com, 
	haoluo@...gle.com, jolsa@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 2/2] selftests/bpf: activate the OP_NE login
 in range_cond()

On Wed, Dec 13, 2023 at 10:28 PM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> The edge range checking for the registers is supported by the verifier
> now, so we can activate the extended login in
> tools/testing/selftests/bpf/prog_tests/reg_bounds.c/range_cond() to test
> such logic.
>
> Besides, I added some cases to the "crafted_cases" array for this logic.
> These cases are mainly used to test the edge of the src reg and dst reg.
>
> Signed-off-by: Menglong Dong <menglong8.dong@...il.com>
> ---
> v2:
> - add some cases to the "crafted_cases"
> ---
>  .../selftests/bpf/prog_tests/reg_bounds.c     | 25 ++++++++++++++-----
>  1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
> index 0c9abd279e18..53b8711cfd2d 100644
> --- a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
> +++ b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
> @@ -590,12 +590,7 @@ static void range_cond(enum num_t t, struct range x, struct range y,
>                 *newy = range(t, max_t(t, x.a, y.a), min_t(t, x.b, y.b));
>                 break;
>         case OP_NE:
> -               /* generic case, can't derive more information */
> -               *newx = range(t, x.a, x.b);
> -               *newy = range(t, y.a, y.b);
> -               break;
> -
> -               /* below extended logic is not supported by verifier just yet */
> +               /* below logic is supported by the verifier now */
>                 if (x.a == x.b && x.a == y.a) {
>                         /* X is a constant matching left side of Y */
>                         *newx = range(t, x.a, x.b);
> @@ -2101,6 +2096,24 @@ static struct subtest_case crafted_cases[] = {
>         {S32, S64, {(u32)(s32)S32_MIN, (u32)(s32)-255}, {(u32)(s32)-2, 0}},
>         {S32, S64, {0, 1}, {(u32)(s32)S32_MIN, (u32)(s32)S32_MIN}},
>         {S32, U32, {(u32)(s32)S32_MIN, (u32)(s32)S32_MIN}, {(u32)(s32)S32_MIN, (u32)(s32)S32_MIN}},
> +
> +       /* edge overlap testings for BPF_NE */
> +       {U64, U64, {1, 1}, {1, 0x80000000}},
> +       {U64, S64, {1, 1}, {1, 0x80000000}},
> +       {U64, U32, {1, 1}, {1, 0x80000000}},
> +       {U64, S32, {1, 1}, {1, 0x80000000}},
> +       {U64, U64, {0x80000000, 0x80000000}, {1, 0x80000000}},
> +       {U64, S64, {0x80000000, 0x80000000}, {1, 0x80000000}},
> +       {U64, U32, {0x80000000, 0x80000000}, {1, 0x80000000}},
> +       {U64, S32, {0x80000000, 0x80000000}, {1, 0x80000000}},
> +       {U64, U64, {1, 0x80000000}, {1, 1}},
> +       {U64, S64, {1, 0x80000000}, {1, 1}},
> +       {U64, U32, {1, 0x80000000}, {1, 1}},
> +       {U64, S32, {1, 0x80000000}, {1, 1}},
> +       {U64, U64, {1, 0x80000000}, {0x80000000, 0x80000000}},
> +       {U64, S64, {1, 0x80000000}, {0x80000000, 0x80000000}},
> +       {U64, U32, {1, 0x80000000}, {0x80000000, 0x80000000}},
> +       {U64, S32, {1, 0x80000000}, {0x80000000, 0x80000000}},

JNE and JEQ are sign-agnostic, so there is no need to use both U64 and
S64 variants for comparison. As for the choice of values. Wouldn't it
make sense to use really a boundary conditions:

0, 0xffffffffffffffff, and 0x80000000000000 for 64-bit and
0, 0xffffffff, and 0x80000000 for 32-bit? For this one use U32 as the init type?

BTW, all these cases should be tested with auto-generated tests, so
please make sure to run

sudo SLOW_TESTS=1 ./test_progs -t reg_bounds_gen -j

locally. It will take a bit of time, but should help to get confidence
in that everything is working and nothing regressed.

>  };
>
>  /* Go over crafted hard-coded cases. This is fast, so we do it as part of
> --
> 2.39.2
>