From patchwork Thu May 24 06:56:46 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sandipan Das X-Patchwork-Id: 919643 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 40s0hF010Sz9s0x for ; Thu, 24 May 2018 17:02:53 +1000 (AEST) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.vnet.ibm.com Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 40s0hD5llpzDqG0 for ; Thu, 24 May 2018 17:02:52 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.vnet.ibm.com X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Authentication-Results: lists.ozlabs.org; spf=none (mailfrom) smtp.mailfrom=linux.vnet.ibm.com (client-ip=148.163.156.1; helo=mx0a-001b2d01.pphosted.com; envelope-from=sandipan@linux.vnet.ibm.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.vnet.ibm.com Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40s0Yd6dpQzF1LP for ; Thu, 24 May 2018 16:57:09 +1000 (AEST) Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w4O6sESk142644 for ; Thu, 24 May 2018 02:57:07 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0a-001b2d01.pphosted.com with ESMTP id 2j5rgmr47q-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 24 May 2018 02:57:07 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Thu, 24 May 2018 07:57:01 +0100 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w4O6v1pS8323528; Thu, 24 May 2018 06:57:01 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8A760AE055; Thu, 24 May 2018 07:46:13 +0100 (BST) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 66998AE045; Thu, 24 May 2018 07:46:12 +0100 (BST) Received: from localhost.localdomain (unknown [9.40.193.84]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 24 May 2018 07:46:12 +0100 (BST) From: Sandipan Das To: ast@kernel.org, daniel@iogearbox.net Subject: [PATCH bpf-next v4 02/10] bpf: powerpc64: pad function address loads with NOPs Date: Thu, 24 May 2018 12:26:46 +0530 X-Mailer: git-send-email 2.14.3 In-Reply-To: References: In-Reply-To: References: X-TM-AS-GCONF: 00 x-cbid: 18052406-0044-0000-0000-0000055622B3 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18052406-0045-0000-0000-0000289823F9 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2018-05-24_02:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805240084 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: netdev@vger.kernel.org, naveen.n.rao@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, jakub.kicinski@netronome.com Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" For multi-function programs, loading the address of a callee function to a register requires emitting instructions whose count varies from one to five depending on the nature of the address. Since we come to know of the callee's address only before the extra pass, the number of instructions required to load this address may vary from what was previously generated. This can make the JITed image grow or shrink. To avoid this, we should generate a constant five-instruction when loading function addresses by padding the optimized load sequence with NOPs. Signed-off-by: Sandipan Das --- arch/powerpc/net/bpf_jit_comp64.c | 34 +++++++++++++++++++++++----------- 1 file changed, 23 insertions(+), 11 deletions(-) diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index 1bdb1aff0619..e4582744a31d 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -167,25 +167,37 @@ static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx) static void bpf_jit_emit_func_call(u32 *image, struct codegen_context *ctx, u64 func) { + unsigned int i, ctx_idx = ctx->idx; + + /* Load function address into r12 */ + PPC_LI64(12, func); + + /* For bpf-to-bpf function calls, the callee's address is unknown + * until the last extra pass. As seen above, we use PPC_LI64() to + * load the callee's address, but this may optimize the number of + * instructions required based on the nature of the address. + * + * Since we don't want the number of instructions emitted to change, + * we pad the optimized PPC_LI64() call with NOPs to guarantee that + * we always have a five-instruction sequence, which is the maximum + * that PPC_LI64() can emit. + */ + for (i = ctx->idx - ctx_idx; i < 5; i++) + PPC_NOP(); + #ifdef PPC64_ELF_ABI_v1 - /* func points to the function descriptor */ - PPC_LI64(b2p[TMP_REG_2], func); - /* Load actual entry point from function descriptor */ - PPC_BPF_LL(b2p[TMP_REG_1], b2p[TMP_REG_2], 0); - /* ... and move it to LR */ - PPC_MTLR(b2p[TMP_REG_1]); /* * Load TOC from function descriptor at offset 8. * We can clobber r2 since we get called through a * function pointer (so caller will save/restore r2) * and since we don't use a TOC ourself. */ - PPC_BPF_LL(2, b2p[TMP_REG_2], 8); -#else - /* We can clobber r12 */ - PPC_FUNC_ADDR(12, func); - PPC_MTLR(12); + PPC_BPF_LL(2, 12, 8); + /* Load actual entry point from function descriptor */ + PPC_BPF_LL(12, 12, 0); #endif + + PPC_MTLR(12); PPC_BLRL(); }