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Date: Sat, 27 Jul 2019 14:36:21 -0700 From: Andrii Nakryiko <andrii.nakryiko@...il.com> To: Yonghong Song <yhs@...com> Cc: Alexei Starovoitov <ast@...com>, Alexei Starovoitov <alexei.starovoitov@...il.com>, Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>, Kernel Team <Kernel-team@...com> Subject: Re: [PATCH bpf-next 02/10] libbpf: implement BPF CO-RE offset relocation algorithm On Sat, Jul 27, 2019 at 2:29 PM Yonghong Song <yhs@...com> wrote: > > > > On 7/27/19 11:24 AM, Andrii Nakryiko wrote: > > On Sat, Jul 27, 2019 at 10:00 AM Alexei Starovoitov <ast@...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. Well then, I'll just drop it for now. Thanks! > > >> > >>
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