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: <Z6ugQ1bd0opoGRYg@google.com>
Date: Tue, 11 Feb 2025 19:09:52 +0000
From: Peilin Ye <yepeilin@...gle.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: bpf@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, bpf@...f.org,
	Xu Kuohai <xukuohai@...weicloud.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 Mon, Feb 10, 2025 at 04:08:44PM -0800, Eduard Zingerman wrote:
> > +++ 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)
> 
> [...]
> 
> > +#else
> > +
> > +SEC("socket")
> > +__description("load-acquire is not supported by compiler or jit, use a dummy test")
> > +__success
> > +int dummy_test(void)
> > +{
> > +	return 0;
> > +}
> 
> Nit: why is dummy_test() necessary?

It's just to make it clear when these tests are (effectively) skipped.
Otherwise, e.g. -cpuv4 runner with LLVM-18 on x86-64 would give:

  #518     verifier_load_acquire:OK

With dummy_test(), we would see:

(FWIW, for v3 I'm planning to change __description() to the following,
since new tests no longer depend on __BPF_FEATURE_LOAD_ACQ_STORE_REL.)

  #518/1   verifier_load_acquire/Clang version < 18, or JIT does not support load-acquire; use a dummy test:OK
  #518     verifier_load_acquire:OK

Commit 147c8f4470ee ("selftests/bpf: Add unit tests for new
sign-extension load insns") did similar thing in verifier_ldsx.c.

> > +
> > +#endif
> > +
> > +char _license[] SEC("license") = "GPL";
> 
> [...]

Thanks,
Peilin Ye