From patchwork Mon Jan 27 19:40:30 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Xu X-Patchwork-Id: 1230020 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: incoming-bpf@patchwork.ozlabs.org Delivered-To: patchwork-incoming-bpf@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=bpf-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=dxuuu.xyz Authentication-Results: ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=dxuuu.xyz header.i=@dxuuu.xyz header.a=rsa-sha256 header.s=fm2 header.b=OeZMvKHe; dkim=pass (2048-bit key; unprotected) header.d=messagingengine.com header.i=@messagingengine.com header.a=rsa-sha256 header.s=fm1 header.b=oujBRnSo; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 4860Tv5SrNz9sQp for ; Tue, 28 Jan 2020 06:40:51 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726054AbgA0Tku (ORCPT ); Mon, 27 Jan 2020 14:40:50 -0500 Received: from new1-smtp.messagingengine.com ([66.111.4.221]:43209 "EHLO new1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726004AbgA0Tku (ORCPT ); Mon, 27 Jan 2020 14:40:50 -0500 Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailnew.nyi.internal (Postfix) with ESMTP id E3DE76A26; Mon, 27 Jan 2020 14:40:49 -0500 (EST) Received: from mailfrontend1 ([10.202.2.162]) by compute4.internal (MEProxy); Mon, 27 Jan 2020 14:40:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=dxuuu.xyz; h= from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; s=fm2; bh=ZvSMU6y7wAeb8 /2s/fn5ni9DRfl6SUxPF0nyHzLwl+M=; b=OeZMvKHeRHrtkxVP6Cdhlt28xxPiW CqzXkkeTy0JH6cLGaEENmDfLp36hW9b+eCGRSvH3+gGe5GwdugviO42dvrdxcGom joCoX4fDCE83rlx5Npkj/hGgzpobETTlDeA7sGj8AxBvh4fnsBpDmM+IhmjgwH77 ZC+19XyKMDxVmYBVqz5Bes+twTVDeaV8aIO2EQM2O50LdUcnw3K3cTtbT6hpG/K4 2TVIDRPd4T5cQkvALNEqUplDy0B2aUNFJjBHQIyX1vHMHw5xRta2SpKGipYhzrOq 8MogzR0fuVGq2GQDdsE+QzYJy9bDl9+Lq5XckBOR363e5h6Cbv98iBH1w== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:date:from :in-reply-to:message-id:mime-version:references:subject:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm1; bh=ZvSMU6y7wAeb8/2s/fn5ni9DRfl6SUxPF0nyHzLwl+M=; b=oujBRnSo /e2p/R4sMXdv17/28HS+jAoqYilGnIU73befs9XcvsdIIq9A9d2soYA6/UHEXtNK dgahXcNbYDqiwzRHxS1I6DqbEWli1mgkx7e90PB5Zpjj2CMNOGEPZT5TdLswXbig gaUqnmek2/R0oXzgxkG7AInTPg4vTSveVYz5xqTQgarLiOSUktFoVPUd6+XSv4gn h0kOXGnRrMT1wrgdpG6A2VwE2UhYYIuXr6g+YJWfgIZTp3j84J47ZFYCcmHily0u zKg+6eSegQxJDnNGmYHBWqO4aWQwedI3l9Vc73cGAmkpZjT19fkS/ZHBZikrGy9J HCUBli7xIEiinA== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedugedrfedvgdduvdehucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucgfrhhlucfvnfffucdljedtmdenucfjughrpefhvf fufffkofgjfhgggfestdekredtredttdenucfhrhhomhepffgrnhhivghlucgiuhcuoegu gihusegugihuuhhurdighiiiqeenucfkphepudelledrvddtuddrieegrddufeelnecuve hluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepugiguhesugig uhhuuhdrgiihii X-ME-Proxy: Received: from dlxu-fedora-R90QNFJV.thefacebook.com (unknown [199.201.64.139]) by mail.messagingengine.com (Postfix) with ESMTPA id 881D43280059; Mon, 27 Jan 2020 14:40:48 -0500 (EST) From: Daniel Xu To: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, songliubraving@fb.com, yhs@fb.com, andriin@fb.com Cc: Daniel Xu , linux-kernel@vger.kernel.org, kernel-team@fb.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org Subject: [PATCH v7 bpf-next 1/2] bpf: Add bpf_read_branch_records() helper Date: Mon, 27 Jan 2020 11:40:30 -0800 Message-Id: <20200127194031.19122-2-dxu@dxuuu.xyz> X-Mailer: git-send-email 2.21.1 In-Reply-To: <20200127194031.19122-1-dxu@dxuuu.xyz> References: <20200127194031.19122-1-dxu@dxuuu.xyz> MIME-Version: 1.0 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Branch records are a CPU feature that can be configured to record certain branches that are taken during code execution. This data is particularly interesting for profile guided optimizations. perf has had branch record support for a while but the data collection can be a bit coarse grained. We (Facebook) have seen in experiments that associating metadata with branch records can improve results (after postprocessing). We generally use bpf_probe_read_*() to get metadata out of userspace. That's why bpf support for branch records is useful. Aside from this particular use case, having branch data available to bpf progs can be useful to get stack traces out of userspace applications that omit frame pointers. Signed-off-by: Daniel Xu --- include/uapi/linux/bpf.h | 25 +++++++++++++++++++++++- kernel/trace/bpf_trace.c | 41 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 65 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index f1d74a2bd234..3004470b7269 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -2892,6 +2892,25 @@ union bpf_attr { * Obtain the 64bit jiffies * Return * The 64 bit jiffies + * + * int bpf_read_branch_records(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 flags) + * Description + * For an eBPF program attached to a perf event, retrieve the + * branch records (struct perf_branch_entry) associated to *ctx* + * and store it in the buffer pointed by *buf* up to size + * *buf_size* bytes. + * Return + * On success, number of bytes written to *buf*. On error, a + * negative value. + * + * The *flags* can be set to **BPF_F_GET_BRANCH_RECORDS_SIZE** to + * instead return the number of bytes required to store all the + * branch entries. If this flag is set, *buf* may be NULL. + * + * **-EINVAL** if arguments invalid or **buf_size** not a multiple + * of sizeof(struct perf_branch_entry). + * + * **-ENOENT** if architecture does not support branch records. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -3012,7 +3031,8 @@ union bpf_attr { FN(probe_read_kernel_str), \ FN(tcp_send_ack), \ FN(send_signal_thread), \ - FN(jiffies64), + FN(jiffies64), \ + FN(read_branch_records), /* integer value in 'imm' field of BPF_CALL instruction selects which helper * function eBPF program intends to call @@ -3091,6 +3111,9 @@ enum bpf_func_id { /* BPF_FUNC_sk_storage_get flags */ #define BPF_SK_STORAGE_GET_F_CREATE (1ULL << 0) +/* BPF_FUNC_read_branch_records flags. */ +#define BPF_F_GET_BRANCH_RECORDS_SIZE (1ULL << 0) + /* Mode for BPF_FUNC_skb_adjust_room helper. */ enum bpf_adj_room_mode { BPF_ADJ_ROOM_NET, diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 19e793aa441a..4d3c87a1d215 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1028,6 +1028,45 @@ static const struct bpf_func_proto bpf_perf_prog_read_value_proto = { .arg3_type = ARG_CONST_SIZE, }; +BPF_CALL_4(bpf_read_branch_records, struct bpf_perf_event_data_kern *, ctx, + void *, buf, u32, size, u64, flags) +{ +#ifndef CONFIG_X86 + return -ENOENT; +#else + static const u32 br_entry_size = sizeof(struct perf_branch_entry); + struct perf_branch_stack *br_stack = ctx->data->br_stack; + u32 to_copy; + + if (unlikely(flags & ~BPF_F_GET_BRANCH_RECORDS_SIZE)) + return -EINVAL; + + if (unlikely(!br_stack)) + return -EINVAL; + + if (flags & BPF_F_GET_BRANCH_RECORDS_SIZE) + return br_stack->nr * br_entry_size; + + if (!buf || (size % br_entry_size != 0)) + return -EINVAL; + + to_copy = min_t(u32, br_stack->nr * br_entry_size, size); + memcpy(buf, br_stack->entries, to_copy); + + return to_copy; +#endif +} + +static const struct bpf_func_proto bpf_read_branch_records_proto = { + .func = bpf_read_branch_records, + .gpl_only = true, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_CTX, + .arg2_type = ARG_PTR_TO_MEM_OR_NULL, + .arg3_type = ARG_CONST_SIZE_OR_ZERO, + .arg4_type = ARG_ANYTHING, +}; + static const struct bpf_func_proto * pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) { @@ -1040,6 +1079,8 @@ pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &bpf_get_stack_proto_tp; case BPF_FUNC_perf_prog_read_value: return &bpf_perf_prog_read_value_proto; + case BPF_FUNC_read_branch_records: + return &bpf_read_branch_records_proto; default: return tracing_func_proto(func_id, prog); }