Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762436AbcLSNTD (ORCPT ); Mon, 19 Dec 2016 08:19:03 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34647 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759884AbcLSNS5 (ORCPT ); Mon, 19 Dec 2016 08:18:57 -0500 From: Anju T Sudhakar To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: ananth@in.ibm.com, naveen.n.rao@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com, benh@kernel.crashing.org, mpe@ellerman.id.au, mahesh@linux.vnet.ibm.com, mhiramat@kernel.org, anju@linux.vnet.ibm.com Subject: [PATCH V3 2/4] powerpc: add helper to check if offset is within rel branch range Date: Mon, 19 Dec 2016 18:48:27 +0530 X-Mailer: git-send-email 2.7.4 In-Reply-To: <1482153507-17350-1-git-send-email-anju@linux.vnet.ibm.com> References: <1482153507-17350-1-git-send-email-anju@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16121913-0052-0000-0000-000001FFA958 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16121913-0053-0000-0000-0000077401B0 Message-Id: <1482153507-17350-5-git-send-email-anju@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-12-19_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1612050000 definitions=main-1612190184 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2756 Lines: 73 From: "Naveen N. Rao" To permit the use of relative branch instruction in powerpc, the target address has to be relatively nearby, since the address is specified in an immediate field (24 bit filed) in the instruction opcode itself. Here nearby refers to 32MB on either side of the current instruction. This patch verifies whether the target address is within +/- 32MB range or not. Signed-off-by: Naveen N. Rao Signed-off-by: Anju T Sudhakar --- arch/powerpc/include/asm/code-patching.h | 1 + arch/powerpc/lib/code-patching.c | 24 +++++++++++++++++++++++- 2 files changed, 24 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h index 2015b07..75ee4f4 100644 --- a/arch/powerpc/include/asm/code-patching.h +++ b/arch/powerpc/include/asm/code-patching.h @@ -22,6 +22,7 @@ #define BRANCH_SET_LINK 0x1 #define BRANCH_ABSOLUTE 0x2 +bool is_offset_in_branch_range(long offset); unsigned int create_branch(const unsigned int *addr, unsigned long target, int flags); unsigned int create_cond_branch(const unsigned int *addr, diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index d5edbeb..f643451 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -32,6 +32,28 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags) return patch_instruction(addr, create_branch(addr, target, flags)); } +bool is_offset_in_branch_range(long offset) +{ + /* + * Powerpc branch instruction is : + * + * 0 6 30 31 + * +---------+----------------+---+---+ + * | opcode | LI |AA |LK | + * +---------+----------------+---+---+ + * Where AA = 0 and LK = 0 + * + * LI is a signed 24 bits integer. The real branch offset is computed + * by: imm32 = SignExtend(LI:'0b00', 32); + * + * So the maximum forward branch should be: + * (0x007fffff << 2) = 0x01fffffc = 0x1fffffc + * The maximum backward branch should be: + * (0xff800000 << 2) = 0xfe000000 = -0x2000000 + */ + return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3)); +} + unsigned int create_branch(const unsigned int *addr, unsigned long target, int flags) { @@ -43,7 +65,7 @@ unsigned int create_branch(const unsigned int *addr, offset = offset - (unsigned long)addr; /* Check we can represent the target in the instruction format */ - if (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3) + if (!is_offset_in_branch_range(offset)) return 0; /* Mask out the flags and target, so they don't step on each other. */ -- 2.7.4