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From: Yonghong Song <yhs@fb.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Alexei Starovoitov <ast@fb.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 02/10] libbpf: implement BPF CO-RE offset relocation algorithm
Date: Sat, 27 Jul 2019 21:29:22 +0000	[thread overview]
Message-ID: <363f7363-7031-3160-9f5f-583a1662fe25@fb.com> (raw)
In-Reply-To: <CAEf4Bzbt4+mT8GfQG4xMj4tCnWd2ZqJiY3r8cwOankFFQo8wWA@mail.gmail.com>



On 7/27/19 11:24 AM, Andrii Nakryiko wrote:
> On Sat, Jul 27, 2019 at 10:00 AM Alexei Starovoitov <ast@fb.com> wrote:
>>
>> On 7/26/19 11:25 PM, Andrii Nakryiko wrote:
>>>>> +     } else if (class == BPF_ST && BPF_MODE(insn->code) == BPF_MEM) {
>>>>> +             if (insn->imm != orig_off)
>>>>> +                     return -EINVAL;
>>>>> +             insn->imm = new_off;
>>>>> +             pr_debug("prog '%s': patched insn #%d (ST | MEM) imm %d -> %d\n",
>>>>> +                      bpf_program__title(prog, false),
>>>>> +                      insn_idx, orig_off, new_off);
>>>> I'm pretty sure llvm was not capable of emitting BPF_ST insn.
>>>> When did that change?
>>> I just looked at possible instructions that could have 32-bit
>>> immediate value. This is `*(rX) = offsetof(struct s, field)`, which I
>>> though is conceivable. Do you think I should drop it?
>>
>> Just trying to point out that since it's not emitted by llvm
>> this code is likely untested ?
>> Or you've created a bpf asm test for this?
> 
> 
> Yeah, it's untested right now. Let me try to come up with LLVM
> assembly + relocation (not yet sure how/whether builtin works with
> inline assembly), if that works out, I'll leave this, if not, I'll
> drop BPF_ST|BPF_MEM part.

FYI. The llvm does not have assembly code format for BPF_ST instructions 
as it does not generate code for it. So inline asm through llvm won't 
work. llvm disasseembler won't be able to decode BPF_ST either.

>>
>>

  reply	other threads:[~2019-07-27 21:29 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-24 19:27 [PATCH bpf-next 00/10] CO-RE offset relocations Andrii Nakryiko
2019-07-24 19:27 ` [PATCH bpf-next 01/10] libbpf: add .BTF.ext offset relocation section loading Andrii Nakryiko
2019-07-24 21:42   ` Andrii Nakryiko
2019-07-25  0:00   ` Song Liu
2019-07-25  0:37     ` Andrii Nakryiko
2019-07-25  5:20       ` Song Liu
2019-07-27  5:11         ` Andrii Nakryiko
2019-07-29 20:00           ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 02/10] libbpf: implement BPF CO-RE offset relocation algorithm Andrii Nakryiko
2019-07-25 19:32   ` Song Liu
2019-07-27  6:11     ` Andrii Nakryiko
2019-07-27 18:59       ` Song Liu
2019-07-27 19:09         ` Andrii Nakryiko
2019-07-28  0:24           ` Song Liu
2019-07-25 23:18   ` Alexei Starovoitov
2019-07-27  6:25     ` Andrii Nakryiko
2019-07-27 17:00       ` Alexei Starovoitov
2019-07-27 18:24         ` Andrii Nakryiko
2019-07-27 21:29           ` Yonghong Song [this message]
2019-07-27 21:36             ` Andrii Nakryiko
2019-07-29 19:56   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 03/10] selftests/bpf: add CO-RE relocs testing setup Andrii Nakryiko
2019-07-29 20:22   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 04/10] selftests/bpf: add CO-RE relocs struct flavors tests Andrii Nakryiko
2019-07-29 20:37   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 05/10] selftests/bpf: add CO-RE relocs nesting tests Andrii Nakryiko
2019-07-29 21:06   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 06/10] selftests/bpf: add CO-RE relocs array tests Andrii Nakryiko
2019-07-25 23:26   ` Alexei Starovoitov
2019-07-26 23:29     ` Andrii Nakryiko
2019-07-24 19:27 ` [PATCH bpf-next 07/10] selftests/bpf: add CO-RE relocs enum/ptr/func_proto tests Andrii Nakryiko
2019-07-29 21:09   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 08/10] selftests/bpf: add CO-RE relocs modifiers/typedef tests Andrii Nakryiko
2019-07-29 21:11   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 09/10] selftest/bpf: add CO-RE relocs ptr-as-array tests Andrii Nakryiko
2019-07-29 21:14   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 10/10] selftests/bpf: add CO-RE relocs ints tests Andrii Nakryiko
2019-07-29 21:21   ` Song Liu
2019-07-29 20:20 ` [PATCH bpf-next 00/10] CO-RE offset relocations Song Liu
2019-07-29 20:36   ` Song Liu
2019-07-29 23:09     ` Andrii Nakryiko
2019-07-30  5:27       ` Song Liu

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