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From: Yonghong Song <yhs@fb.com>
To: Johan Almbladh <johan.almbladh@anyfinetworks.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 08:50:01 -0700	[thread overview]
Message-ID: <0feebbb6-7ba7-fe6e-1854-dd1cebfaf1f2@fb.com> (raw)
In-Reply-To: <CAM1=_QRN+aioWWNfeS5Tddo2u6UG86bVj66BJoYyzaUDSkDZ1w@mail.gmail.com>



On 7/29/21 6:24 AM, Johan Almbladh wrote:
> 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.

Maybe added a comment in the code to mention that with BPF_MAXINSNS
PC relative branch + long conditional jump can be triggered on MIPS32
JIT. Other architecture may need a different/larger number?

> 
> 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 15:50 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
2021-07-29 15:50       ` Yonghong Song [this message]
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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