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From: Johan Almbladh <johan.almbladh@anyfinetworks.com>
To: Yonghong Song <yhs@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Tony Ambardar <Tony.Ambardar@gmail.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH 10/14] bpf/tests: Add branch conversion JIT test
Date: Thu, 29 Jul 2021 15:24:29 +0200	[thread overview]
Message-ID: <CAM1=_QRN+aioWWNfeS5Tddo2u6UG86bVj66BJoYyzaUDSkDZ1w@mail.gmail.com> (raw)
In-Reply-To: <6c362bc2-e4cf-321b-89fb-4e20276c0d73@fb.com>

On Thu, Jul 29, 2021 at 2:55 AM Yonghong Song <yhs@fb.com> wrote:
> > +static int bpf_fill_long_jmp(struct bpf_test *self)
> > +{
> > +     unsigned int len = BPF_MAXINSNS;
>
> BPF_MAXINSNS is 4096 as defined in uapi/linux/bpf_common.h.
> Will it be able to trigger a PC relative branch + long
> conditional jump?

It does, on the MIPS32 JIT. The ALU64 MUL instruction with a large
immediate was chosen since it expands to a lot of MIPS32 instructions:
2 to load the immediate, 1 to zero/sign extend it, and then 9 for the
64x64 multiply.

Other JITs will be different of course. On the other hand, other
architectures have other limitations that this test may not trigger
anyway. I added the test because I was implementing a non-trivial
iterative branch conversion logic in the MIPS32 JIT. One can argue
that when such complex JIT mechanisms are added, the test suite should
also be updated to cover that, especially if the mechanism handles
something that almost never occur in practice.

Since I was able to trigger the branch conversion with BPF_MAXINSNS
instructions, and no other test was using more, I left it at that.
However, should I or someone else work on the MIPS64 JIT, I think
updating the test suite so that similar special cases there are
triggered would be a valuable contribution.

  reply	other threads:[~2021-07-29 13:24 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 17:04 [PATCH 00/14] bpf/tests: Extend the eBPF test suite Johan Almbladh
2021-07-28 17:04 ` [PATCH 01/14] bpf/tests: Add BPF_JMP32 test cases Johan Almbladh
2021-07-28 22:31   ` Yonghong Song
2021-07-29 21:30     ` Johan Almbladh
2021-07-28 17:04 ` [PATCH 02/14] bpf/tests: Add BPF_MOV tests for zero and sign extension Johan Almbladh
2021-07-28 22:36   ` Yonghong Song
2021-07-28 17:04 ` [PATCH 03/14] bpf/tests: Fix typos in test case descriptions Johan Almbladh
2021-07-28 22:43   ` Yonghong Song
2021-07-28 17:04 ` [PATCH 04/14] bpf/tests: Add more tests of ALU32 and ALU64 bitwise operations Johan Almbladh
2021-07-28 22:53   ` Yonghong Song
2021-07-28 17:04 ` [PATCH 05/14] bpf/tests: Add more ALU32 tests for BPF_LSH/RSH/ARSH Johan Almbladh
2021-07-28 22:57   ` Yonghong Song
2021-07-28 17:04 ` [PATCH 06/14] bpf/tests: Add more BPF_LSH/RSH/ARSH tests for ALU64 Johan Almbladh
2021-07-28 23:30   ` Yonghong Song
2021-07-29 12:34     ` Johan Almbladh
2021-07-29 15:39       ` Yonghong Song
2021-07-28 17:04 ` [PATCH 07/14] bpf/tests: Add more ALU64 BPF_MUL tests Johan Almbladh
2021-07-28 23:32   ` Yonghong Song
2021-07-29 21:21     ` Johan Almbladh
2021-07-28 17:04 ` [PATCH 08/14] bpf/tests: Add tests for ALU operations implemented with function calls Johan Almbladh
2021-07-28 23:52   ` Yonghong Song
2021-07-29 21:17     ` Johan Almbladh
2021-07-29 22:54       ` Yonghong Song
2021-07-28 17:04 ` [PATCH 09/14] bpf/tests: Add word-order tests for load/store of double words Johan Almbladh
2021-07-28 23:54   ` Yonghong Song
2021-07-28 17:04 ` [PATCH 10/14] bpf/tests: Add branch conversion JIT test Johan Almbladh
2021-07-28 23:58   ` Yonghong Song
2021-07-29 12:45     ` Johan Almbladh
2021-07-29 15:46       ` Yonghong Song
2021-07-29  0:55   ` Yonghong Song
2021-07-29 13:24     ` Johan Almbladh [this message]
2021-07-29 15:50       ` Yonghong Song
2021-07-28 17:04 ` [PATCH 11/14] bpf/tests: Add test for 32-bit context pointer argument passing Johan Almbladh
2021-07-29  0:09   ` Yonghong Song
2021-07-29 13:29     ` Johan Almbladh
2021-07-29 15:50       ` Yonghong Song
2021-07-28 17:05 ` [PATCH 12/14] bpf/tests: Add tests for atomic operations Johan Almbladh
2021-07-29  0:36   ` Yonghong Song
2021-07-28 17:05 ` [PATCH 13/14] bpf/tests: Add tests for BPF_CMPXCHG Johan Almbladh
2021-07-29  0:45   ` Yonghong Song
2021-07-28 17:05 ` [PATCH 14/14] bpf/tests: Add tail call test suite Johan Almbladh
2021-07-29  2:56   ` Yonghong Song
2021-07-29 20:44     ` Johan Almbladh

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