From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 3w7MPy2PbMzDqJL for ; Wed, 19 Apr 2017 22:53:58 +1000 (AEST) Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v3JCrqpD081439 for ; Wed, 19 Apr 2017 08:53:56 -0400 Received: from e28smtp05.in.ibm.com (e28smtp05.in.ibm.com [125.16.236.5]) by mx0a-001b2d01.pphosted.com with ESMTP id 29x752uq67-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 19 Apr 2017 08:53:55 -0400 Received: from localhost by e28smtp05.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 19 Apr 2017 18:22:51 +0530 Received: from d28av08.in.ibm.com (d28av08.in.ibm.com [9.184.220.148]) by d28relay10.in.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v3JCpOS220774936 for ; Wed, 19 Apr 2017 18:21:24 +0530 Received: from d28av08.in.ibm.com (localhost [127.0.0.1]) by d28av08.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id v3JCqllJ020294 for ; Wed, 19 Apr 2017 18:22:47 +0530 From: "Naveen N. Rao" To: Michael Ellerman Cc: Ananth N Mavinakayanahalli , Masami Hiramatsu , Ingo Molnar , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 6/6] powerpc: kprobes: prefer ftrace when probing function entry Date: Wed, 19 Apr 2017 18:22:28 +0530 In-Reply-To: References: In-Reply-To: References: Message-Id: <53ebcc66e4a7ccf1c22cd1703afb0e4738f981ea.1492606062.git.naveen.n.rao@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it eliminates the need for a trap, as well as the need to emulate or single-step instructions. Though OPTPROBES provides us with similar performance, we have limited optprobes trampoline slots. As such, when asked to probe at a function entry, default to using the ftrace infrastructure. With: # cd /sys/kernel/debug/tracing # echo 'p _do_fork' > kprobe_events before patch: # cat ../kprobes/list c0000000000daf08 k _do_fork+0x8 [DISABLED] c000000000044fc0 k kretprobe_trampoline+0x0 [OPTIMIZED] and after patch: # cat ../kprobes/list c0000000000d074c k _do_fork+0xc [DISABLED][FTRACE] c0000000000412b0 k kretprobe_trampoline+0x0 [OPTIMIZED] Signed-off-by: Naveen N. Rao --- arch/powerpc/kernel/kprobes.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index df963c6e47b1..d5d6fbd1d788 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -49,8 +49,21 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) #ifdef PPC64_ELF_ABI_v2 /* PPC64 ABIv2 needs local entry point */ addr = (kprobe_opcode_t *)kallsyms_lookup_name(name); - if (addr && !offset) - addr = (kprobe_opcode_t *)ppc_function_entry(addr); + if (addr && !offset) { +#ifdef CONFIG_KPROBES_ON_FTRACE + unsigned long faddr; + /* + * Per livepatch.h, ftrace location is always within the first + * 16 bytes of a function on powerpc with -mprofile-kernel. + */ + faddr = ftrace_location_range((unsigned long)addr, + (unsigned long)addr + 16); + if (faddr) + addr = (kprobe_opcode_t *)faddr; + else +#endif + addr = (kprobe_opcode_t *)ppc_function_entry(addr); + } #elif defined(PPC64_ELF_ABI_v1) /* * 64bit powerpc ABIv1 uses function descriptors: -- 2.12.1