From: Vineet Gupta <vineet.gupta@linux.dev>
To: Eduard Zingerman <eddyz87@gmail.com>,
ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
memxor@gmail.com
Cc: martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev,
jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev,
john.fastabend@gmail.com, shuah@kernel.org, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf-next v3 01/12] bpf: Keep the 32-bit range across a sign extension that cannot change it
Date: Wed, 4 Nov 2026 12:53:46 -0800 [thread overview]
Message-ID: <efda3685-8a09-48b2-9592-7a74fdd3238f@linux.dev> (raw)
In-Reply-To: <9720ed1ff19dea17a1b379c02d7dd52ae886d807.camel@gmail.com>
Hi Eduard,
Thx for taking the time to review.
On 10/29/26 3:30 PM, Eduard Zingerman wrote:
> On Tue, 2026-10-20 at 09:18 -0700, Vineet Gupta wrote:
>
> ...
>
>> @@ -6192,6 +6193,27 @@ static void coerce_subreg_to_size_sx(struct bpf_reg_state *reg, int size)
>> if (reg_umax(reg) < (1ULL << (num_bits - 1)))
>> return;
>>
>> + if (size == 1) {
>> + field_smin = S8_MIN;
>> + field_smax = S8_MAX;
>> + } else {
>> + /* size == 2 */
>> + field_smin = S16_MIN;
>> + field_smax = S16_MAX;
>> + }
>> +
>> + /*
>> + * The range already fits the field, so (sN)v == v for every value the
>> + * register can hold and the sign extension changes nothing. The test
>> + * above misses this once the range straddles zero: it only looks at
>> + * reg_umax(), which a negative smin makes huge.
> The `if (reg_umax(reg) < (1ULL << (num_bits - 1))) return` check is no
> longer necessary, the new check below subsumes it.
> Please drop it, otherwise commit lgtm.
Agree. Dropped in v4.
Thx,
-Vineet
>
>> + * This has to precede reg_step_reset() below: the extension is a noop,
>> + * so the base/step line still holds and there is nothing to discard.
>> + */
>> + if (reg_s32_min(reg) >= field_smin && reg_s32_max(reg) <= field_smax)
>> + return;
>> +
>> /* See comment at reg_step_check_unsigned(). */
>> reg_step_reset(reg);
>>
next prev parent reply other threads:[~2026-11-04 20:53 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-20 16:18 [PATCH bpf-next v3 00/12] bpf: track scalar equality across the low 32 bits Vineet Gupta
2026-10-20 16:18 ` [PATCH bpf-next v3 01/12] bpf: Keep the 32-bit range across a sign extension that cannot change it Vineet Gupta
2026-10-29 22:30 ` Eduard Zingerman
2026-11-04 20:53 ` Vineet Gupta [this message]
2026-10-20 16:18 ` [PATCH bpf-next v3 02/12] selftests/bpf: Cover sign extensions that cannot change the range Vineet Gupta
2026-10-20 16:18 ` [PATCH bpf-next v3 03/12] bpf: Prepare linked scalars for relations narrower than 64 bits Vineet Gupta
2026-10-20 17:08 ` bot+bpf-ci
2026-10-26 22:52 ` Vineet Gupta
2026-10-29 22:51 ` Eduard Zingerman
2026-11-04 20:55 ` Vineet Gupta
2026-10-20 16:18 ` [PATCH bpf-next v3 04/12] bpf: Track low-32 scalar equality across zero-extending movs Vineet Gupta
2026-10-20 17:09 ` bot+bpf-ci
2026-10-26 20:30 ` Vineet Gupta
2026-10-29 23:59 ` Eduard Zingerman
2026-10-20 16:19 ` [PATCH bpf-next v3 05/12] selftests/bpf: Cover the low-32 link for " Vineet Gupta
2026-10-20 16:53 ` bot+bpf-ci
2026-10-26 18:36 ` Vineet Gupta
2026-10-20 16:19 ` [PATCH bpf-next v3 06/12] bpf: Track low-32 scalar equality across sign-extending movs Vineet Gupta
2026-10-30 17:52 ` Eduard Zingerman
2026-10-20 16:19 ` [PATCH bpf-next v3 07/12] selftests/bpf: Cover the low-32 link for " Vineet Gupta
2026-10-20 16:19 ` [PATCH bpf-next v3 08/12] bpf: Recover the low 32 bits on the reverse link direction Vineet Gupta
2026-10-20 16:53 ` bot+bpf-ci
2026-10-26 19:57 ` Vineet Gupta
2026-10-20 16:19 ` [PATCH bpf-next v3 09/12] bpf: Track low-32 scalar equality across narrowing stack fills Vineet Gupta
2026-10-30 18:27 ` Eduard Zingerman
2026-10-20 16:19 ` [PATCH bpf-next v3 10/12] selftests/bpf: Cover the low-32 link for " Vineet Gupta
2026-10-20 16:52 ` bot+bpf-ci
2026-10-26 20:21 ` Vineet Gupta
2026-10-20 16:19 ` [PATCH bpf-next v3 11/12] [do not merge] bpf: Track low-32 scalar equality across narrowing stack spills Vineet Gupta
2026-10-30 18:33 ` Eduard Zingerman
2026-10-20 16:19 ` [PATCH bpf-next v3 12/12] [do not merge] selftests/bpf: Cover the low-32 link for " Vineet Gupta
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