linux-kernel - Re: [PATCH bpf-next v2 8/9] selftests/bpf: Add selftests for load-acquire and store-release instructions

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Message-ID: <Z6abqWVQRAFHAUZm@google.com>
Date: Fri, 7 Feb 2025 23:47:53 +0000
From: Peilin Ye <yepeilin@...gle.com>
To: bpf@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc: bpf@...f.org, Xu Kuohai <xukuohai@...weicloud.com>,
	Eduard Zingerman <eddyz87@...il.com>,
	David Vernet <void@...ifault.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Puranjay Mohan <puranjay@...nel.org>,
	Ilya Leoshkevich <iii@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Quentin Monnet <qmo@...nel.org>,
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
	Ihor Solodrai <ihor.solodrai@...ux.dev>,
	Yingchi Long <longyingchi24s@....ac.cn>,
	Josh Don <joshdon@...gle.com>, Barret Rhoden <brho@...gle.com>,
	Neel Natu <neelnatu@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 8/9] selftests/bpf: Add selftests for
 load-acquire and store-release instructions

On Fri, Feb 07, 2025 at 02:06:29AM +0000, Peilin Ye wrote:
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/verifier_load_acquire.c
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "../../../include/linux/filter.h"
> +#include "bpf_misc.h"
> +
> +#if defined(ENABLE_ATOMICS_TESTS) && defined(__TARGET_ARCH_arm64)
> +
> +SEC("socket")
> +__description("load-acquire, 8-bit")
> +__success __success_unpriv __retval(0x12)
> +__naked void load_acquire_8(void)
> +{
> +	asm volatile (
> +	"*(u8 *)(r10 - 1) = 0x12;"
                            ~~~~
I realized that I am using STORE_imm<> instructions in load-acquire
tests, and llvm-17 -mcpu=v3 cannot build them.

Can be fixed by simply doing e.g. the following instead:

        "r1 = 0x12;"
	"*(u8 *)(r10 - 1) = r1;"

> +	".8byte %[load_acquire_insn];" // w0 = load_acquire((u8 *)(r10 - 1));
> +	"exit;"
> +	:
> +	: __imm_insn(load_acquire_insn,
> +		     BPF_ATOMIC_OP(BPF_B, BPF_LOAD_ACQ, BPF_REG_0, BPF_REG_10, -1))
> +	: __clobber_all);
> +}

Thanks,
Peilin Ye