On Wed, Jul 17, 2024 at 10:28 PM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
> Add a few reg_bounds selftests to test 32/16/8-bit ldsx and subreg comparison.
> Without the previous patch, all added tests will fail.
>
> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
> .../selftests/bpf/prog_tests/reg_bounds.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
wow, I already forgot most of the things in here... :(
> diff --git a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
> index eb74363f9f70..cd9bafe9c057 100644
> --- a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
> +++ b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
> @@ -441,6 +441,20 @@ static struct range range_refine(enum num_t x_t, struct range x, enum num_t y_t,
> if (t_is_32(y_t) && !t_is_32(x_t)) {
> struct range x_swap;
>
> + /* If we know that
> + * - *x* is in the range of signed 32bit value
> + * - *y_cast* range is 32-bit sign non-negative, and
sign -> signed?
> + * then *x* range can be narrowed to the interaction of
what does it mean "narrowed to the interaction"?
> + * *x* and *y_cast*. Otherwise, if the new range for *x*
> + * allows upper 32-bit 0xffffffff then the eventual new
> + * range for *x* will be out of signed 32-bit range
> + * which violates the origin *x* range.
> + */
> + if (x_t == S64 && y_t == S32 &&
tbh, given this is so specific for x_t == S64 and y_T == S32, I'd move
it out from this if into an independent condition, it doesn't benefit
from being inside
> + !(y_cast.a & 0xffffffff80000000ULL) && !(y_cast.b & 0xffffffff80000000) &&
isn't this just a much more convoluted way of checking:
y_cast.a <= 0x7fffffffULL && y_cast.b <= 0x7fffffffULL
? Is & + negation really easier to follow?...
> + (long long)x.a >= S32_MIN && (long long)x.b <= S32_MAX)
> + return range_improve(x_t, x, y_cast);
> +
> /* some combinations of upper 32 bits and sign bit can lead to
> * invalid ranges, in such cases it's easier to detect them
> * after cast/swap than try to enumerate all the conditions
> @@ -2108,6 +2122,9 @@ static struct subtest_case crafted_cases[] = {
> {S32, U32, {(u32)S32_MIN, 0}, {0, 0}},
> {S32, U32, {(u32)S32_MIN, 0}, {(u32)S32_MIN, (u32)S32_MIN}},
> {S32, U32, {(u32)S32_MIN, S32_MAX}, {S32_MAX, S32_MAX}},
> + {S64, U32, {0x0, 0x1f}, {0xffffffff80000000ULL, 0x000000007fffffffULL}},
> + {S64, U32, {0x0, 0x1f}, {0xffffffffffff8000ULL, 0x0000000000007fffULL}},
> + {S64, U32, {0x0, 0x1f}, {0xffffffffffffff80ULL, 0x000000000000007fULL}},
> };
>
> /* Go over crafted hard-coded cases. This is fast, so we do it as part of
> --
> 2.43.0
>
