From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E717714B959 for ; Mon, 6 Jan 2025 09:04:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736154296; cv=none; b=YfynwpIP1TLbmOPtInRKQ6jbxts1YRlQh836iA+LSDGCeP9MRb0OtmLdfeNggSjUMBIo7aCDDjMC9hRjpneR/GBbK7oVKqOmHso5qiDmNy/SV98eU8cFkESD/HhGB7p51DMXJRWbI8bT+aKMMsKOMgLvefMUDLl50zDAu+BbUTA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736154296; c=relaxed/simple; bh=UyGy6SIfUzJoKABrXxh24Z/ikulx1rHPZT9KD/p4iv0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=YCY2KDdmV+L6dHsq+gxGoFAdQJd2vXbQ8xRq3HQBUdtFlMyG97Yz23Qjl7cTgOtuC7Cnr0Fs+Xyt8U7S4aK7e3R69CjuoO5e/XzbwS4z2eARfR2KyHvXEzmc1rzOgaclIoloVph8NKHjZnBex5bAA9cLI1qKWUi3gEFAjvfadeM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=i+GWpOoH; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="i+GWpOoH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D18CC4CED2; Mon, 6 Jan 2025 09:04:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736154295; bh=UyGy6SIfUzJoKABrXxh24Z/ikulx1rHPZT9KD/p4iv0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=i+GWpOoHRFXr2v7D7F6cAmRUeFedy4X+p5alBDGqhJq6B6CnNntGaZdX404iOZp4A 7/zWpkvsPZc3PwKV59Zg33gvZO5abLG29R9W5gMiJTjsTAz6hnxpHEnoTQZoPfFCy6 7J2x2VkQ2SMFyDqpN2BTfCP5O1E6pvUzLOdn3WMy6uLjMKnR5bBtRibsj7ksIMpWBD m3RLCcXGzjatYqvVlF3CFY7iLnZH0OpivDkk0t9pcMSjv/NNEto9Q0Rxs5edGIPOPI GedNFQaQlY6QQmhlamoMzHiAhaDO22jhfflZFojvUN1GlfI51s954sYSpat5TVOzxR aGbrz//2zrfCA== Date: Mon, 6 Jan 2025 18:04:50 +0900 From: Masami Hiramatsu (Google) To: Qinxin Xia Cc: , , , , , , , , , , , Subject: Re: [PATCH v6] arm64: kprobe: Enable OPTPROBE for arm64 Message-Id: <20250106180450.bd589aee885600982a81d488@kernel.org> In-Reply-To: <20250103012753.66988-1-xiaqinxin@huawei.com> References: <20250103012753.66988-1-xiaqinxin@huawei.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Fri, 3 Jan 2025 09:27:53 +0800 Qinxin Xia wrote: > This patch introduce optprobe for ARM64. In optprobe, probed > instruction is replaced by a branch instruction to trampoline. > > Performance of optprobe on Hip08 platform is test using kprobe > example module to analyze the latency of a kernel function, > and here is the result: > > common kprobe: > [280709.846380] do_empty returned 0 and took 1530 ns to execute > [280709.852057] do_empty returned 0 and took 550 ns to execute > [280709.857631] do_empty returned 0 and took 440 ns to execute > [280709.863215] do_empty returned 0 and took 380 ns to execute > [280709.868787] do_empty returned 0 and took 360 ns to execute > [280709.874362] do_empty returned 0 and took 340 ns to execute > [280709.879936] do_empty returned 0 and took 320 ns to execute > [280709.885505] do_empty returned 0 and took 300 ns to execute > [280709.891075] do_empty returned 0 and took 280 ns to execute > [280709.896646] do_empty returned 0 and took 290 ns to execute > > optprobe: > [ 2965.964572] do_empty returned 0 and took 90 ns to execute > [ 2965.969952] do_empty returned 0 and took 80 ns to execute > [ 2965.975332] do_empty returned 0 and took 70 ns to execute > [ 2965.980714] do_empty returned 0 and took 60 ns to execute > [ 2965.986128] do_empty returned 0 and took 80 ns to execute > [ 2965.991507] do_empty returned 0 and took 70 ns to execute > [ 2965.996884] do_empty returned 0 and took 70 ns to execute > [ 2966.002262] do_empty returned 0 and took 80 ns to execute > [ 2966.007642] do_empty returned 0 and took 70 ns to execute > [ 2966.013020] do_empty returned 0 and took 70 ns to execute > [ 2966.018400] do_empty returned 0 and took 70 ns to execute > > As the result shows, optprobe can greatly reduce the latency. Big > latency of common kprobe will significantly impact the real result > while doing performance analysis or debugging performance issues > in lab, so optprobe is useful in this scenario. Looks good result! But this code seems no document about how it works. Can you add the design note in this description and/or comments in the code? It helps us to review it. Thank you, > > Co-developed-by: Qi Liu > Signed-off-by: Qi Liu > Signed-off-by: Qinxin Xia > --- > > Changes since V5: > - Address the comments from Masami, saves stack frames to obtain correct backtrace > and make an array of usage flags to manage the reserved OPT_SLOT_SIZE. > - Link: https://lore.kernel.org/lkml/20211207124002.59877-1-liuqi115@huawei.com/ > > Changes since V4: > - Address the comments from Masami, update arch_prepare_optimized_kprobe， > if the probe address is out of limit return -ERANGE. > - Link: https://lore.kernel.org/lkml/20210818073336.59678-1-liuqi115@huawei.com/ > > Changes since V3: > - Address the comments from Masami, reduce the number of aarch64_insn_patch_text > in arch_optimize_kprobes() and arch_unoptimize_kprobes(). > - Link: https://lore.kernel.org/lkml/20210810055330.18924-1-liuqi115@huawei.com/ > > Changes since V2: > - Address the comments from Masami, prepare another writable buffer in > arch_prepare_optimized_kprobe()and build the trampoline code on it. > - Address the comments from Amit, move save_all_base_regs and > restore_all_base_regs to , as these two macros are reused > in optprobe. > - Link: https://lore.kernel.org/lkml/20210804060209.95817-1-liuqi115@huawei.com/ > > Changes since V1: > - Address the comments from Masami, checks for all branch instructions, and > use aarch64_insn_patch_text_nosync() instead of aarch64_insn_patch_text() > in each probe. > - Link: https://lore.kernel.org/lkml/20210719122417.10355-1-liuqi115@huawei.com/ > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/kprobes.h | 22 ++ > arch/arm64/kernel/probes/Makefile | 2 + > arch/arm64/kernel/probes/opt_arm64.c | 216 ++++++++++++++++++ > .../arm64/kernel/probes/optprobe_trampoline.S | 112 +++++++++ > kernel/kprobes.c | 18 ++ > 6 files changed, 371 insertions(+) > create mode 100644 arch/arm64/kernel/probes/opt_arm64.c > create mode 100644 arch/arm64/kernel/probes/optprobe_trampoline.S > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 100570a048c5..f9c4e2625595 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -244,6 +244,7 @@ config ARM64 > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES > select HAVE_KRETPROBES > + select HAVE_OPTPROBES > select HAVE_GENERIC_VDSO > select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU > select IRQ_DOMAIN > diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h > index be7a3680dadf..bd4973bfb58d 100644 > --- a/arch/arm64/include/asm/kprobes.h > +++ b/arch/arm64/include/asm/kprobes.h > @@ -37,6 +37,28 @@ struct kprobe_ctlblk { > > void arch_remove_kprobe(struct kprobe *); > int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr); > + > +struct arch_optimized_insn { > + kprobe_opcode_t orig_insn[1]; > + kprobe_opcode_t *trampoline; > +}; > + > +#define MAX_OPTIMIZED_LENGTH sizeof(kprobe_opcode_t) > +#define MAX_OPTINSN_SIZE \ > + ((unsigned long)optprobe_template_end - (unsigned long)optprobe_template_entry) > + > +extern __visible kprobe_opcode_t optprobe_template_entry[]; > +extern __visible kprobe_opcode_t optprobe_template_val[]; > +extern __visible kprobe_opcode_t optprobe_template_orig_addr[]; > +extern __visible kprobe_opcode_t optprobe_template_common[]; > +extern __visible kprobe_opcode_t optprobe_template_end[]; > +extern __visible kprobe_opcode_t optprobe_template_restore_begin[]; > +extern __visible kprobe_opcode_t optprobe_template_restore_orig_insn[]; > +extern __visible kprobe_opcode_t optprobe_template_restore_end[]; > +extern __visible kprobe_opcode_t optinsn_slot[]; > + > +void optprobe_common(void); > + > void __kretprobe_trampoline(void); > void __kprobes *trampoline_probe_handler(struct pt_regs *regs); > > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile > index 8e4be92e25b1..7b2885b23ff6 100644 > --- a/arch/arm64/kernel/probes/Makefile > +++ b/arch/arm64/kernel/probes/Makefile > @@ -4,3 +4,5 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \ > simulate-insn.o > obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \ > simulate-insn.o > +obj-$(CONFIG_OPTPROBES) += opt_arm64.o \ > + optprobe_trampoline.o > diff --git a/arch/arm64/kernel/probes/opt_arm64.c b/arch/arm64/kernel/probes/opt_arm64.c > new file mode 100644 > index 000000000000..fa8b68afbbf3 > --- /dev/null > +++ b/arch/arm64/kernel/probes/opt_arm64.c > @@ -0,0 +1,216 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Code for Kernel probes Jump optimization. > + * > + * Copyright (C) 2024 Hisilicon Limited > + */ > + > +#include > +#include > +#include > + > +#include > +#include > +#include > +#include > +#include > + > +#define OPTPROBE_BATCH_SIZE 64 > + > +#define TMPL_VAL_IDX \ > + (optprobe_template_val - optprobe_template_entry) > +#define TMPL_ORIGN_ADDR \ > + (optprobe_template_orig_addr - optprobe_template_entry) > +#define TMPL_CALL_COMMON \ > + (optprobe_template_common - optprobe_template_entry) > +#define TMPL_RESTORE_ORIGN_INSN \ > + (optprobe_template_restore_orig_insn - optprobe_template_entry) > +#define TMPL_RESTORE_END \ > + (optprobe_template_restore_end - optprobe_template_entry) > + > +#define OPT_SLOT_SIZE 65536 > +#define OPT_INSN_PAGES (OPT_SLOT_SIZE / PAGE_SIZE) > + > +static bool insn_page_in_use[OPT_INSN_PAGES]; > + > +void *alloc_optinsn_page(void) > +{ > + int i; > + > + for (i = 0; i < OPT_INSN_PAGES; i++) { > + if (!insn_page_in_use[i]) { > + insn_page_in_use[i] = true; > + return (void *)((unsigned long)optinsn_slot + PAGE_SIZE * i); > + } > + } > + > + return NULL; > +} > + > +void free_optinsn_page(void *page) > +{ > + unsigned long idx = (unsigned long)page - (unsigned long)optinsn_slot; > + > + WARN_ONCE(idx & (PAGE_SIZE - 1), "Invalid idx with wrong align\n"); > + idx >>= PAGE_SHIFT; > + if (WARN_ONCE(idx >= OPT_INSN_PAGES, "Invalid idx with wrong size\n")) > + return; > + insn_page_in_use[idx] = false; > +} > + > +int arch_check_optimized_kprobe(struct optimized_kprobe *op) > +{ > + return 0; > +} > + > +int arch_prepared_optinsn(struct arch_optimized_insn *optinsn) > +{ > + return optinsn->trampoline != NULL; > +} > + > +int arch_within_optimized_kprobe(struct optimized_kprobe *op, kprobe_opcode_t *addr) > +{ > + return op->kp.addr == addr; > +} > + > +static void optprobe_set_pc_value(struct optimized_kprobe *op, struct pt_regs *regs) > +{ > + regs->pc = (unsigned long)op->kp.addr; > +} > + > +static int optprobe_check_branch_limit(unsigned long pc, unsigned long addr) > +{ > + long offset; > + > + if ((pc & 0x3) || (addr & 0x3)) > + return -ERANGE; > + > + offset = (long)addr - (long)pc; > + if (offset < -SZ_128M || offset >= SZ_128M) > + return -ERANGE; > + > + return 0; > +} > + > +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig) > +{ > + kprobe_opcode_t *code, *buf; > + int ret = -ENOMEM; > + u32 insn; > + int i; > + > + buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL); > + if (!buf) > + return ret; > + > + code = get_optinsn_slot(); > + if (!code) > + goto out; > + > + if (optprobe_check_branch_limit((unsigned long)code, (unsigned long)orig->addr + 8)) { > + ret = -ERANGE; > + goto error; > + } > + > + memcpy(buf, optprobe_template_entry, MAX_OPTINSN_SIZE); > + > + insn = aarch64_insn_gen_branch_imm((unsigned long)&code[TMPL_CALL_COMMON], > + (unsigned long)&optprobe_common, > + AARCH64_INSN_BRANCH_LINK); > + buf[TMPL_CALL_COMMON] = insn; > + > + insn = aarch64_insn_gen_branch_imm((unsigned long)&code[TMPL_RESTORE_END], > + (unsigned long)(op->kp.addr + 1), > + AARCH64_INSN_BRANCH_NOLINK); > + buf[TMPL_RESTORE_END] = insn; > + > + buf[TMPL_VAL_IDX] = cpu_to_le32(lower_32_bits((unsigned long)op)); > + buf[TMPL_VAL_IDX + 1] = cpu_to_le32(upper_32_bits((unsigned long)op)); > + buf[TMPL_ORIGN_ADDR] = cpu_to_le32(lower_32_bits((unsigned long)orig->addr)); > + buf[TMPL_ORIGN_ADDR + 1] = cpu_to_le32(upper_32_bits((unsigned long)orig->addr)); > + > + buf[TMPL_RESTORE_ORIGN_INSN] = orig->opcode; > + > + /* Setup template */ > + for (i = 0; i < MAX_OPTINSN_SIZE / MAX_OPTIMIZED_LENGTH; i++) > + aarch64_insn_patch_text_nosync(code + i, buf[i]); > + > + flush_icache_range((unsigned long)code, (unsigned long)(&code[TMPL_VAL_IDX])); > + /* Set op->optinsn.trampoline means prepared. */ > + op->optinsn.trampoline = code; > + > + return 0; > +error: > + free_optinsn_slot(code, 0); > + > +out: > + kfree(buf); > + return ret; > +} > + > +void arch_optimize_kprobes(struct list_head *oplist) > +{ > + struct optimized_kprobe *op, *tmp; > + kprobe_opcode_t insns[OPTPROBE_BATCH_SIZE]; > + void *addrs[OPTPROBE_BATCH_SIZE]; > + int i = 0; > + > + list_for_each_entry_safe(op, tmp, oplist, list) { > + WARN_ON(kprobe_disabled(&op->kp)); > + > + /* > + * Backup instructions which will be replaced > + * by jump address > + */ > + memcpy(op->optinsn.orig_insn, op->kp.addr, AARCH64_INSN_SIZE); > + > + addrs[i] = op->kp.addr; > + insns[i] = aarch64_insn_gen_branch_imm((unsigned long)op->kp.addr, > + (unsigned long)op->optinsn.trampoline, > + AARCH64_INSN_BRANCH_NOLINK); > + > + list_del_init(&op->list); > + if (++i == OPTPROBE_BATCH_SIZE) > + break; > + } > + > + aarch64_insn_patch_text(addrs, insns, i); > +} > + > +void arch_unoptimize_kprobe(struct optimized_kprobe *op) > +{ > + arch_arm_kprobe(&op->kp); > +} > + > +/* > + * Recover original instructions and breakpoints from relative jumps. > + * Caller must call with locking kprobe_mutex. > + */ > +void arch_unoptimize_kprobes(struct list_head *oplist, > + struct list_head *done_list) > +{ > + struct optimized_kprobe *op, *tmp; > + kprobe_opcode_t insns[OPTPROBE_BATCH_SIZE]; > + void *addrs[OPTPROBE_BATCH_SIZE]; > + int i = 0; > + > + list_for_each_entry_safe(op, tmp, oplist, list) { > + addrs[i] = op->kp.addr; > + insns[i] = BRK64_OPCODE_KPROBES; > + list_move(&op->list, done_list); > + > + if (++i == OPTPROBE_BATCH_SIZE) > + break; > + } > + > + aarch64_insn_patch_text(addrs, insns, i); > +} > + > +void arch_remove_optimized_kprobe(struct optimized_kprobe *op) > +{ > + if (op->optinsn.trampoline) { > + free_optinsn_slot(op->optinsn.trampoline, 1); > + op->optinsn.trampoline = NULL; > + } > + > +} > diff --git a/arch/arm64/kernel/probes/optprobe_trampoline.S b/arch/arm64/kernel/probes/optprobe_trampoline.S > new file mode 100644 > index 000000000000..ba936b2efb5e > --- /dev/null > +++ b/arch/arm64/kernel/probes/optprobe_trampoline.S > @@ -0,0 +1,112 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * trampoline entry and return code for optprobes. > + */ > + > +#include > +#include > +#include > + > +#define OPT_SLOT_SIZE 65536 > + > + .global optinsn_slot > +optinsn_slot: > + .space OPT_SLOT_SIZE > + > +SYM_CODE_START(optprobe_common) > + stp x2, x3, [sp, #S_X2] > + stp x4, x5, [sp, #S_X4] > + stp x6, x7, [sp, #S_X6] > + stp x8, x9, [sp, #S_X8] > + stp x10, x11, [sp, #S_X10] > + stp x12, x13, [sp, #S_X12] > + stp x14, x15, [sp, #S_X14] > + stp x16, x17, [sp, #S_X16] > + stp x18, x19, [sp, #S_X18] > + stp x20, x21, [sp, #S_X20] > + stp x22, x23, [sp, #S_X22] > + stp x24, x25, [sp, #S_X24] > + stp x26, x27, [sp, #S_X26] > + stp x28, x29, [sp, #S_X28] > + add x2, sp, #PT_REGS_SIZE > + str x2, [sp, #S_SP] > + /* Construct a useful saved PSTATE */ > + mrs x2, nzcv > + mrs x3, daif > + orr x2, x2, x3 > + mrs x3, CurrentEL > + orr x2, x2, x3 > + mrs x3, SPSel > + orr x2, x2, x3 > + ldr x1, 2f > + stp x1, x2, [sp, #S_PC] > + > + /* set the pt_regs address to x1 */ > + mov x1, sp > + /* store lr of optprobe_common temporary */ > + stp x29, x30, [sp, #-16]! > + mov x29, sp > + > + bl optprobe_optimized_callback > + > + ldp x29, x30, [sp], #16 > + > + ldr x0, [sp, #S_PSTATE] > + and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT) > + msr nzcv, x0 > + > + ldp x0, x1, [sp, #S_X0] > + ldp x2, x3, [sp, #S_X2] > + ldp x4, x5, [sp, #S_X4] > + ldp x6, x7, [sp, #S_X6] > + ldp x8, x9, [sp, #S_X8] > + ldp x10, x11, [sp, #S_X10] > + ldp x12, x13, [sp, #S_X12] > + ldp x14, x15, [sp, #S_X14] > + ldp x16, x17, [sp, #S_X16] > + ldp x18, x19, [sp, #S_X18] > + ldp x20, x21, [sp, #S_X20] > + ldp x22, x23, [sp, #S_X22] > + ldp x24, x25, [sp, #S_X24] > + ldp x26, x27, [sp, #S_X26] > + ldp x28, x29, [sp, #S_X28] > + ret > +SYM_CODE_END(optprobe_common) > + > + .global optprobe_template_entry > +optprobe_template_entry: > + stp x29, x30, [sp, #-16]! > + mov x29, sp > + ldr x30, 2f > + stp x29, x30, [sp, #-16]! > + mov x29, sp > + sub sp, sp, #PT_REGS_SIZE > + str lr, [sp, #S_LR] > + stp x0, x1, [sp, #S_X0] > + /* Get parameters to optimized_callback() */ > + ldr x0, 1f > + .global optprobe_template_common > +optprobe_template_common: > + nop > + ldr lr, [sp, #S_LR] > + add sp, sp, #PT_REGS_SIZE > + ldp x29, x30, [sp], #16 > + ldp x29, x30, [sp], #16 > + .global optprobe_template_restore_orig_insn > +optprobe_template_restore_orig_insn: > + nop > + .global optprobe_template_restore_end > +optprobe_template_restore_end: > + nop > + .balign > + .global optprobe_template_val > +optprobe_template_val: > + 1: .long 0 > + .long 0 > + .balign > + .global optprobe_template_orig_addr > +optprobe_template_orig_addr: > + 2: .long 0 > + .long 0 > + .global optprobe_template_end > +optprobe_template_end: > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index 62b5b08d809d..45287e185ce3 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -425,6 +425,24 @@ void opt_pre_handler(struct kprobe *p, struct pt_regs *regs) > } > NOKPROBE_SYMBOL(opt_pre_handler); > > +void optprobe_optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs) > +{ > + if (kprobe_disabled(&op->kp)) > + return; > + > + guard(preempt)(); > + > + if (kprobe_running()) { > + kprobes_inc_nmissed_count(&op->kp); > + } else { > + __this_cpu_write(current_kprobe, &op->kp); > + get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE; > + opt_pre_handler(&op->kp, regs); > + __this_cpu_write(current_kprobe, NULL); > + } > +} > +NOKPROBE_SYMBOL(optprobe_optimized_callback) > + > /* Free optimized instructions and optimized_kprobe */ > static void free_aggr_kprobe(struct kprobe *p) > { > -- > 2.33.0 > -- Masami Hiramatsu (Google)