Re: [PATCH bpf-next v5 2/3] selftests/bpf: test timed may_goto preserves R0-R5

From: Pu Lehui <pulehui@huawei.com>
To: "Feng Jiang" <jiangfeng@kylinos.cn>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Eduard Zingerman" <eddyz87@gmail.com>,
	"Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
	"Martin KaFai Lau" <martin.lau@linux.dev>,
	"Song Liu" <song@kernel.org>,
	"Yonghong Song" <yonghong.song@linux.dev>,
	"Jiri Olsa" <jolsa@kernel.org>,
	"Emil Tsalapatis" <emil@etsalapatis.com>,
	"Luke Nelson" <luke.r.nels@gmail.com>,
	"Xi Wang" <xi.wang@gmail.com>, "Björn Töpel" <bjorn@kernel.org>,
	"Puranjay Mohan" <puranjay@kernel.org>,
	"Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Alexandre Ghiti" <alex@ghiti.fr>,
	"Shuah Khan" <shuah@kernel.org>,
	"Ihor Solodrai" <ihor.solodrai@linux.dev>
Cc: <bpf@vger.kernel.org>, <linux-riscv@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH bpf-next v5 2/3] selftests/bpf: test timed may_goto preserves R0-R5
Date: Thu, 23 Jul 2026 18:10:35 +0800	[thread overview]
Message-ID: <f8768480-9cbb-4807-bd9c-e2eeea6cdbe0@huawei.com> (raw)
In-Reply-To: <20260723-riscv-bpf-timed-may-goto-v5-2-86acb54e5642@kylinos.cn>


On 2026/7/23 13:41, Feng Jiang wrote:
> Add a test that checks R0-R5 are preserved across
> arch_bpf_timed_may_goto() calls.
> 
> Use bpf_get_prandom_u32() to avoid the verifier removing the checks
> via DCE.
> 
> Suggested-by: Björn Töpel <bjorn@kernel.org>
> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
> ---
>   .../selftests/bpf/progs/verifier_may_goto_1.c      | 58 ++++++++++++++++++++++
>   1 file changed, 58 insertions(+)

Reviewed-by: Pu Lehui <pulehui@huawei.com>

> 
> diff --git a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
> index 4bdf4256a41e..cb1ce4d13cfc 100644
> --- a/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_may_goto_1.c
> @@ -106,4 +106,62 @@ __naked void may_goto_batch_2(void)
>   	: __clobber_all);
>   }
>   
> +/*
> + * Use bpf_get_prandom_u32() to prevent DCE from removing the checks.
> + * retval: 0=all ok, 1-6=R0-R5 clobbered.
> + */
> +SEC("syscall")
> +__description("timed may_goto preserves R0-R5")
> +__arch_x86_64
> +__arch_s390x
> +__arch_arm64
> +__arch_riscv64
> +__success
> +__retval(0)
> +__naked void timed_may_goto_preserves_regs(void)
> +{
> +	asm volatile (
> +	"call %[bpf_get_prandom_u32];"
> +	"r6 = r0;"
> +	"r0 = 0x1111;"
> +	"r0 += r6;"
> +	"r1 = 0x2222;"
> +	"r1 += r6;"
> +	"r2 = 0x3333;"
> +	"r2 += r6;"
> +	"r3 = 0x4444;"
> +	"r3 += r6;"
> +	"r4 = 0x5555;"
> +	"r4 += r6;"
> +	"r5 = 0x6666;"
> +	"r5 += r6;"
> +	".8byte %[may_goto];"
> +	".8byte %[loop];"
> +	"r0 -= r6;"
> +	"r1 -= r6;"
> +	"r2 -= r6;"
> +	"r3 -= r6;"
> +	"r4 -= r6;"
> +	"r5 -= r6;"
> +	"if r0 != 0x1111 goto 1f;"
> +	"if r1 != 0x2222 goto 2f;"
> +	"if r2 != 0x3333 goto 3f;"
> +	"if r3 != 0x4444 goto 4f;"
> +	"if r4 != 0x5555 goto 5f;"
> +	"if r5 != 0x6666 goto 6f;"
> +	"r0 = 0;"
> +	"exit;"
> +	"1: r0 = 1; exit;"
> +	"2: r0 = 2; exit;"
> +	"3: r0 = 3; exit;"
> +	"4: r0 = 4; exit;"
> +	"5: r0 = 5; exit;"
> +	"6: r0 = 6; exit;"
> +	:
> +	: __imm(bpf_get_prandom_u32),
> +	  __imm_insn(may_goto, BPF_RAW_INSN(BPF_JMP | BPF_JCOND, 0, 0, 1, 0)),
> +	  __imm_insn(loop, BPF_RAW_INSN(BPF_JMP | BPF_JA, 0, 0, -2, 0))
> +	: __clobber_all);
> +}
> +
>   char _license[] SEC("license") = "GPL";
>