linux-kernel - Re: [PATCH v2 2/2] selftests/bpf: Add testcases for BPF_ADD and BPF

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Message-ID: <5b3b620d04fc3bcf4286dc4bb8c6fd995df86a25.camel@gmail.com>
Date: Wed, 18 Jun 2025 14:22:27 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Harishankar Vishwanathan <harishankar.vishwanathan@...il.com>, 
	ast@...nel.org
Cc: m.shachnai@...gers.edu, srinivas.narayana@...gers.edu, 
	santosh.nagarakatte@...gers.edu, Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau	 <martin.lau@...ux.dev>, Song Liu
 <song@...nel.org>, Yonghong Song	 <yonghong.song@...ux.dev>, KP Singh
 <kpsingh@...nel.org>, Stanislav Fomichev	 <sdf@...ichev.me>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,  Mykola Lysenko	
 <mykolal@...com>, Shuah Khan <shuah@...nel.org>, Matan Shachnai	
 <m.shachnai@...il.com>, Luis Gerhorst <luis.gerhorst@....de>, Kumar
 Kartikeya Dwivedi	 <memxor@...il.com>, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, 	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 2/2] selftests/bpf: Add testcases for BPF_ADD and
 BPF_SUB

On Tue, 2025-06-17 at 19:17 -0400, Harishankar Vishwanathan wrote:
> The previous commit improves the precision in scalar(32)_min_max_add,
> and scalar(32)_min_max_sub. The improvement in precision occurs in
> cases when all outcomes overflow or underflow, respectively. This
> commit adds selftests that exercise those cases.
> 
> Co-developed-by: Matan Shachnai <m.shachnai@...gers.edu>
> Signed-off-by: Matan Shachnai <m.shachnai@...gers.edu>
> Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@...il.com>
> ---

Could you please also add test cases when one bound overflows while
another does not? Or these are covered by some other tests?

[...]

> +SEC("socket")
> +__description("64-bit addition overflow, all outcomes overflow")
> +__success __log_level(2)
> +__msg("7: (0f) r5 += r3 {{.*}} R5_w=scalar(smin=0x800003d67e960f7d,umin=0x551ee3d67e960f7d,umax=0xc0149fffffffffff,smin32=0xfe960f7d,umin32=0x7e960f7d,var_off=(0x3d67e960f7d; 0xfffffc298169f082))")

Would it be possible to pick some more "human readable" constants here?
As-is it is hard to make sense what verifier actually computes.

> +__retval(0)
> +__naked void add64_ovf(void)
> +{
> +	asm volatile (
> +	"call %[bpf_get_prandom_u32];"
> +	"r3 = r0;"
> +	"r4 = 0x950a43d67e960f7d ll;"
> +	"r3 |= r4;"
> +	"r5 = 0xc014a00000000000 ll;"
> +	"r5 += r3;"
> +	"r0 = 0;"
> +	"exit"
> +	:
> +	: __imm(bpf_get_prandom_u32)
> +	: __clobber_all);
> +}

[...]