linux-kernel - Re: [PATCH bpf-next v4 2/2] selftests/bpf: Add test for conditional jumps on same scalar register

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Message-ID: <ae64d43491a36fa5efc861be912a615348877d51.camel@gmail.com>
Date: Mon, 03 Nov 2025 10:14:47 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: KaFai Wan <kafai.wan@...ux.dev>, ast@...nel.org, daniel@...earbox.net, 
	john.fastabend@...il.com, andrii@...nel.org, martin.lau@...ux.dev,
 song@...nel.org, 	yonghong.song@...ux.dev, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com, 	jolsa@...nel.org, shuah@...nel.org,
 paul.chaignon@...il.com, m.shachnai@...il.com, 
	harishankar.vishwanathan@...il.com, colin.i.king@...il.com,
 luis.gerhorst@....de, 	bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 2/2] selftests/bpf: Add test for conditional
 jumps on same scalar register

On Mon, 2025-11-03 at 14:31 +0800, KaFai Wan wrote:
> Add test cases to verify the correctness of the BPF verifier's branch analysis
> when conditional jumps are performed on the same scalar register. And make sure
> that JGT does not trigger verifier BUG.
> 
> Signed-off-by: KaFai Wan <kafai.wan@...ux.dev>
> ---

Thank you for adding these.

Acked-by: Eduard Zingerman <eddyz87@...il.com>

(but a comment needs a fix)

[...]

> +SEC("socket")
> +__description("jset on same register, scalar value unknown branch 3")
> +__msg("4: (b7) r0 = 0 {{.*}} R0=0")
> +__msg("6: (b7) r0 = 1 {{.*}} R0=1")
> +__success __log_level(2)
> +__flag(BPF_F_TEST_REG_INVARIANTS)
> +__naked void jset_on_same_register_5(void *ctx)
> +{
> +	asm volatile("			\
> +	/* range [-1;-1] */		\
                     ^^
   Typo, should be [-1;1].

> +	call %[bpf_get_prandom_u32];	\
> +	r0 &= 0x2;			\
> +	r0 -= 1;			\
> +	if r0 & r0 goto l1_%=;		\
> +l0_%=:	r0 = 0;				\
> +	exit;				\
> +l1_%=:	r0 = 1;				\
> +	exit;				\
> +"	:
> +	: __imm(bpf_get_prandom_u32)
> +	: __clobber_all);
> +}
> +
>  char _license[] SEC("license") = "GPL";