Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756553Ab2BIGuB (ORCPT ); Thu, 9 Feb 2012 01:50:01 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:44075 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752165Ab2BIGuA (ORCPT ); Thu, 9 Feb 2012 01:50:00 -0500 Date: Thu, 9 Feb 2012 12:07:45 +0530 From: Srikar Dronamraju To: Denys Vlasenko , Masami Hiramatsu Cc: Peter Zijlstra , Linus Torvalds , Oleg Nesterov , Ingo Molnar , Andrew Morton , LKML , Linux-mm , Andi Kleen , Christoph Hellwig , Steven Rostedt , Roland McGrath , Thomas Gleixner , Arnaldo Carvalho de Melo , Anton Arapov , Ananth N Mavinakayanahalli , Jim Keniston , Stephen Rothwell , yrl.pp-manager.tt@hitachi.com Subject: Re: Re: [PATCH v10 3.3-rc2 1/9] uprobes: Install and remove breakpoints. Message-ID: <20120209063745.GB16600@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20120202141840.5967.39687.sendpatchset@srdronam.in.ibm.com> <20120202141851.5967.68000.sendpatchset@srdronam.in.ibm.com> <20120207171707.GA24443@linux.vnet.ibm.com> <4F3320E5.1050707@hitachi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <4F3320E5.1050707@hitachi.com> User-Agent: Mutt/1.5.20 (2009-06-14) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12020906-1780-0000-0000-000002FF1CF3 X-IBM-ISS-SpamDetectors: X-IBM-ISS-DetailInfo: BY=3.00000246; HX=3.00000182; KW=3.00000007; PH=3.00000001; SC=3.00000001; SDB=6.00112197; UDB=6.00027739; UTC=2012-02-09 06:49:58 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3578 Lines: 111 > > No, that is a meaningless operation. > As I originally said, > > > insn_get_length(insn); > > if (insn->rex_prefix.nbytes) { > > cursor = uprobe->insn + insn_offset_rex_prefix(insn); > > *cursor &= 0xfe; /* Clearing REX.B bit */ > > } > I am confused by why we need to call insn_get_length(insn) before checking insn->rex_prefix.nbytes? Is it needed. Denys and Masami, can you please confirm if below is fine. #ifdef CONFIG_X86_64 /* * If uprobe->insn doesn't use rip-relative addressing, return * immediately. Otherwise, rewrite the instruction so that it accesses * its memory operand indirectly through a scratch register. Set * uprobe->arch_info.fixups and uprobe->arch_info.rip_rela_target_address * accordingly. (The contents of the scratch register will be saved * before we single-step the modified instruction, and restored * afterward.) * * We do this because a rip-relative instruction can access only a * relatively small area (+/- 2 GB from the instruction), and the XOL * area typically lies beyond that area. At least for instructions * that store to memory, we can't execute the original instruction * and "fix things up" later, because the misdirected store could be * disastrous. * * Some useful facts about rip-relative instructions: * - There's always a modrm byte. * - There's never a SIB byte. * - The displacement is always 4 bytes. */ static void handle_riprel_insn(struct mm_struct *mm, struct uprobe *uprobe, struct insn *insn) { u8 *cursor; u8 reg; if (mm->context.ia32_compat) return; uprobe->arch_info.rip_rela_target_address = 0x0; if (!insn_rip_relative(insn)) return; /* Clear REX.b bit (extension of MODRM.rm field): * we want to encode rax/rcx, not r8/r9. */ if (insn->rex_prefix.nbytes) { cursor = uprobe->insn + insn_offset_rex_prefix(insn); *cursor &= 0xfe; } /* * Point cursor at the modrm byte. The next 4 bytes are the * displacement. Beyond the displacement, for some instructions, * is the immediate operand. */ cursor = uprobe->insn + insn_offset_modrm(insn); insn_get_length(insn); /* * Convert from rip-relative addressing to indirect addressing * via a scratch register. Change the r/m field from 0x5 (%rip) * to 0x0 (%rax) or 0x1 (%rcx), and squeeze out the offset field. */ reg = MODRM_REG(insn); if (reg == 0) { /* * The register operand (if any) is either the A register * (%rax, %eax, etc.) or (if the 0x4 bit is set in the * REX prefix) %r8. In any case, we know the C register * is NOT the register operand, so we use %rcx (register * #1) for the scratch register. */ uprobe->arch_info.fixups = UPROBES_FIX_RIP_CX; /* Change modrm from 00 000 101 to 00 000 001. */ *cursor = 0x1; } else { /* Use %rax (register #0) for the scratch register. */ uprobe->arch_info.fixups = UPROBES_FIX_RIP_AX; /* Change modrm from 00 xxx 101 to 00 xxx 000 */ *cursor = (reg << 3); } /* Target address = address of next instruction + (signed) offset */ uprobe->arch_info.rip_rela_target_address = (long)insn->length + insn->displacement.value; /* Displacement field is gone; slide immediate field (if any) over. */ if (insn->immediate.nbytes) { cursor++; memmove(cursor, cursor + insn->displacement.nbytes, insn->immediate.nbytes); } return; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/