From: Alexei Starovoitov <ast@fb.com>
To: Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Cong Wang <xiyou.wangcong@gmail.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next v2 08/11] libbpf: support local function pointer relocation
Date: Tue, 23 Feb 2021 11:07:54 -0800 [thread overview]
Message-ID: <a97068b4-2428-bc0b-0978-95d5c1f50752@fb.com> (raw)
In-Reply-To: <b20cf48f-fa7c-1397-fc47-361a9e8edecf@fb.com>
On 2/23/21 10:55 AM, Yonghong Song wrote:
>> BTW, doesn't Clang emit instruction with BPF_PSEUDO_FUNC set properly
>> already? If not, why not?
>
> This is really a contract between libbpf and kernel, similar to
> BPF_PSEUDO_MAP_FD/BPF_PSEUDO_MAP_VALUE/BPF_PSEUDO_BTF_ID.
> Adding encoding in clang is not needed as this is simply a load
> of function address as far as clang concerned.
Andrii, I had the same thought when I first looked at it.
The llvm can be taught to do this, but it would be a change in behavior.
Older llvms will generate relo while new one will not.
To ease adoption libbpf would probably need to support both.
Hence no real need to tweak llvm.
If we go with llvm only approach my ongoing work on naked functions
would require to tweak llvm and libbpf again.
While the llvm does the same relo for naked funcs already.
So I will reuse this libbpf support as-is.
Only for &&label and jmptables the extra llvm work will be needed.
next prev parent reply other threads:[~2021-02-23 19:09 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 18:18 [PATCH bpf-next v2 00/11] bpf: add bpf_for_each_map_elem() helper Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 01/11] bpf: factor out visit_func_call_insn() in check_cfg() Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 02/11] bpf: factor out verbose_invalid_scalar() Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 03/11] bpf: refactor check_func_call() to allow callback function Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 04/11] bpf: add bpf_for_each_map_elem() helper Yonghong Song
2021-02-22 20:59 ` Alexei Starovoitov
2021-02-23 18:39 ` Yonghong Song
2021-02-23 18:46 ` Alexei Starovoitov
2021-02-23 19:37 ` Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 05/11] bpf: add hashtab support for " Yonghong Song
2021-02-22 22:56 ` Alexei Starovoitov
2021-02-23 18:41 ` Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 06/11] bpf: add arraymap " Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 07/11] libbpf: move function is_ldimm64() earlier in libbpf.c Yonghong Song
2021-02-23 8:06 ` Andrii Nakryiko
2021-02-17 18:18 ` [PATCH bpf-next v2 08/11] libbpf: support local function pointer relocation Yonghong Song
2021-02-23 8:03 ` Andrii Nakryiko
2021-02-23 18:55 ` Yonghong Song
2021-02-23 19:07 ` Alexei Starovoitov [this message]
2021-02-23 19:21 ` Andrii Nakryiko
2021-02-23 19:19 ` Andrii Nakryiko
2021-02-23 19:47 ` Yonghong Song
2021-02-23 21:24 ` Andrii Nakryiko
2021-02-17 18:18 ` [PATCH bpf-next v2 09/11] bpftool: print local function pointer properly Yonghong Song
2021-02-23 8:06 ` Andrii Nakryiko
2021-02-23 19:00 ` Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 10/11] selftests/bpf: add hashmap test for bpf_for_each_map_elem() helper Yonghong Song
2021-02-17 18:18 ` [PATCH bpf-next v2 11/11] selftests/bpf: add arraymap " Yonghong Song
2021-02-17 18:29 ` [PATCH bpf-next v2 00/11] bpf: add " Yonghong Song
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