From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 79EA8C433EF for ; Sun, 20 Mar 2022 20:09:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343619AbiCTUK0 (ORCPT ); Sun, 20 Mar 2022 16:10:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41334 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236833AbiCTUKY (ORCPT ); Sun, 20 Mar 2022 16:10:24 -0400 Received: from mail-pg1-x52b.google.com (mail-pg1-x52b.google.com [IPv6:2607:f8b0:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CED3E13DEB for ; Sun, 20 Mar 2022 13:09:00 -0700 (PDT) Received: by mail-pg1-x52b.google.com with SMTP id t14so8929716pgr.3 for ; Sun, 20 Mar 2022 13:09:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=2jEbpuKHWGI2at+4mpoQD2yOjBEvPOdppyiOWfPnwQI=; b=QvfzJuerArXUTuDjYjLo8WSNhJNqp7QxbSzIS2KvP3UXvb5eNWXaDHqWSjmM8OUpXQ iWZVeBn3bvs1/HROlpdjw/+Dov+7I3mOCk5MyNi6/aJgMUiNsBGde3Bkz21x9Tr3ehNT JxRppBA0ReRDeKFGq0gyD7LHQRM4LKxyMjC1RB9uzg9dJUgMbuPCERgV+O9qt49hLYQ3 vx8VqcyGUht/N9ddhY7V/1xOL/jlghBd/SG7/7Cst2j27x+YsNtVU4DjQILpzPm0WBKr 46hAHcDn2QgjuVGD72ovrp1o7wBBd2irXZYzj8fdEAIppJp5XSGHMv/3nMCkg1qFKf8O +ePw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=2jEbpuKHWGI2at+4mpoQD2yOjBEvPOdppyiOWfPnwQI=; b=XjnQ6nI3eD0kII3m+zdrmftIBP6G3KTTx/2/foUSsEpyefa1VWECO4y/dBpx2EW/cL NuLD+L7G0yW+NhheQV4h9mkcL9y5G14J0JWEpr7LdR1SHLJ7LaDC6K/fhbytjTkOwxW8 AbsOgQDdSfgAjseFaUKML/15LRNhgVKujqWV3jfFTjS7YzMJv6DkOAhHjnuWC+yQnnuI E8tF0ddSyiNqH+3HWMpiHME1UfrsHwvRz9yIz6YjQC3euyymdkOmwdaX2b20XpCtesMI ykc35v1bg1gS4kqpn9VL9cqg8WFp5Mfb38i9n8sB62MnViN4jVGCqruEYYMgWFN7hzKN TyDg== X-Gm-Message-State: AOAM5330MyLhrKwrSLt5MJwXlqnunefHjibCtuV36Xaw9ckVEmaDXeP2 oLdADp3nHwwJKy5G3v/mdH/TfNEApr/p95cqLJLCXcqLwYw= X-Google-Smtp-Source: ABdhPJwGZjdbe/wFf1DV5xp9vbVEnyLDOfNcwnHe4g/NRO1fsAEFeB9iuOrM70f/DA65AOt4Kthvv6OFCmambf27NAQ= X-Received: by 2002:aa7:805a:0:b0:4f6:dc68:5d41 with SMTP id y26-20020aa7805a000000b004f6dc685d41mr20460596pfm.69.1647806940154; Sun, 20 Mar 2022 13:09:00 -0700 (PDT) MIME-Version: 1.0 References: <20220316004231.1103318-1-kuifeng@fb.com> <20220316004231.1103318-3-kuifeng@fb.com> <20220318190917.tecjespuzkegwb2k@ast-mbp> In-Reply-To: From: Alexei Starovoitov Date: Sun, 20 Mar 2022 13:08:49 -0700 Message-ID: Subject: Re: [PATCH bpf-next v2 2/4] bpf, x86: Create bpf_trace_run_ctx on the caller thread's stack To: Kui-Feng Lee Cc: "daniel@iogearbox.net" , "ast@kernel.org" , "andrii@kernel.org" , "bpf@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Sun, Mar 20, 2022 at 2:31 AM Kui-Feng Lee wrote: > > On Fri, 2022-03-18 at 12:09 -0700, Alexei Starovoitov wrote: > > On Tue, Mar 15, 2022 at 05:42:29PM -0700, Kui-Feng Lee wrote: > > > BPF trampolines will create a bpf_trace_run_ctx on their stacks, > > > and > > > set/reset the current bpf_run_ctx whenever calling/returning from a > > > bpf_prog. > > > > > > Signed-off-by: Kui-Feng Lee > > > --- > > > arch/x86/net/bpf_jit_comp.c | 32 ++++++++++++++++++++++++++++++++ > > > include/linux/bpf.h | 12 ++++++++---- > > > kernel/bpf/syscall.c | 4 ++-- > > > kernel/bpf/trampoline.c | 21 +++++++++++++++++---- > > > 4 files changed, 59 insertions(+), 10 deletions(-) > > > > > > diff --git a/arch/x86/net/bpf_jit_comp.c > > > b/arch/x86/net/bpf_jit_comp.c > > > index 1228e6e6a420..29775a475513 100644 > > > --- a/arch/x86/net/bpf_jit_comp.c > > > +++ b/arch/x86/net/bpf_jit_comp.c > > > @@ -1748,10 +1748,33 @@ static int invoke_bpf_prog(const struct > > > btf_func_model *m, u8 **pprog, > > > { > > > u8 *prog = *pprog; > > > u8 *jmp_insn; > > > + int ctx_cookie_off = offsetof(struct bpf_trace_run_ctx, > > > bpf_cookie); > > > struct bpf_prog *p = l->prog; > > > > > > + EMIT1(0x52); /* push rdx */ > > > > Why save/restore rdx? > > > > > > + > > > + /* mov rdi, 0 */ > > > + emit_mov_imm64(&prog, BPF_REG_1, 0, 0); > > > + > > > + /* Prepare struct bpf_trace_run_ctx. > > > + * sub rsp, sizeof(struct bpf_trace_run_ctx) > > > + * mov rax, rsp > > > + * mov QWORD PTR [rax + ctx_cookie_off], rdi > > > + */ > > > > How about the following instead: > > sub rsp, sizeof(struct bpf_trace_run_ctx) > > mov qword ptr [rsp + ctx_cookie_off], 0 > > ? > > AFAIK, rsp can not be used with the base + displacement addressing > mode. Although, it can be used with base + index + displacement > addressing mode. Where did you find this? 0: 48 c7 44 24 08 00 00 mov QWORD PTR [rsp+0x8],0x0 7: 00 00 > > > > > + EMIT4(0x48, 0x83, 0xEC, sizeof(struct bpf_trace_run_ctx)); > > > + EMIT3(0x48, 0x89, 0xE0); > > > + EMIT4(0x48, 0x89, 0x78, ctx_cookie_off); > > > + > > > + /* mov rdi, rsp */ > > > + EMIT3(0x48, 0x89, 0xE7); > > > + /* mov QWORD PTR [rdi + sizeof(struct bpf_trace_run_ctx)], > > > rax */ > > > + emit_stx(&prog, BPF_DW, BPF_REG_1, BPF_REG_0, sizeof(struct > > > bpf_trace_run_ctx)); > > > > why not to do: > > mov qword ptr[rsp + sizeof(struct bpf_trace_run_ctx)], rsp > > ? > > The same reason as above. 0: 48 89 64 24 08 mov QWORD PTR [rsp+0x8],rsp