Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758059AbZAVONT (ORCPT ); Thu, 22 Jan 2009 09:13:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754028AbZAVONJ (ORCPT ); Thu, 22 Jan 2009 09:13:09 -0500 Received: from e28smtp02.in.ibm.com ([59.145.155.2]:37943 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753013AbZAVONG (ORCPT ); Thu, 22 Jan 2009 09:13:06 -0500 Date: Thu, 22 Jan 2009 19:42:59 +0530 From: "K.Prasad" To: Linux Kernel Mailing List Cc: Alan Stern , Roland McGrath , akpm@linux-foundation.org, mingo@elte.hu, richardj_moore@uk.ibm.com Subject: [RFC Patch 10/10] Sample HW breakpoint over kernel data address Message-ID: <20090122141259.GI19592@in.ibm.com> Reply-To: prasad@linux.vnet.ibm.com References: <20090122135640.GA11161@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090122135640.GA11161@in.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4815 Lines: 136 This patch introduces a sample kernel module to demonstrate the use of Hardware Breakpoint feature. It places a breakpoint over the kernel variable 'pid_max' to monitor all write operations and emits a function-backtrace when done. Signed-off-by: K.Prasad --- samples/Kconfig | 6 ++ samples/Makefile | 3 - samples/hw_breakpoint/Makefile | 1 samples/hw_breakpoint/data_breakpoint.c | 81 ++++++++++++++++++++++++++++++++ 4 files changed, 90 insertions(+), 1 deletion(-) Index: linux-hbkpt-lkml-29-rc2/samples/Kconfig =================================================================== --- linux-hbkpt-lkml-29-rc2.orig/samples/Kconfig +++ linux-hbkpt-lkml-29-rc2/samples/Kconfig @@ -39,5 +39,11 @@ config SAMPLE_KRETPROBES default m depends on SAMPLE_KPROBES && KRETPROBES +config SAMPLE_HW_BREAKPOINT + tristate "Build kernel hardware breakpoint examples -- loadable modules only" + depends on m + help + This builds kernel hardware breakpoint example modules. + endif # SAMPLES Index: linux-hbkpt-lkml-29-rc2/samples/Makefile =================================================================== --- linux-hbkpt-lkml-29-rc2.orig/samples/Makefile +++ linux-hbkpt-lkml-29-rc2/samples/Makefile @@ -1,3 +1,4 @@ # Makefile for Linux samples code -obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ +obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ \ + hw_breakpoint/ Index: linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/Makefile =================================================================== --- /dev/null +++ linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/Makefile @@ -0,0 +1 @@ +obj-$(CONFIG_SAMPLE_HW_BREAKPOINT) += data_breakpoint.o Index: linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/data_breakpoint.c =================================================================== --- /dev/null +++ linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/data_breakpoint.c @@ -0,0 +1,81 @@ +/* + * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address + * + * This file is a kernel module that places a breakpoint over 'pid_max' kernel + * variable using Hardware Breakpoint register. The corresponding handler which + * prints a backtrace is invoked everytime a write operation is performed on + * that variable. + * + * After inserting this module, invoke a write operation using + * 'echo > /proc/sys/kernel/pid_max' + * to find the function-call backtrace. + * + * Copyright (C) IBM Corporation, 2009 + */ +#include /* Needed by all modules */ +#include /* Needed for KERN_INFO */ +#include /* Needed for the macros */ + +#include + +struct hw_breakpoint pid_max_hw_breakpoint; + +void pid_max_hw_breakpoint_installed(struct hw_breakpoint *temp, struct pt_regs + *temp_regs) +{ + printk(KERN_INFO "pid_max_hw_breakpoint ENABLED\n"); +} + +void pid_max_hw_breakpoint_uninstalled(struct hw_breakpoint *temp, struct + pt_regs *temp_regs) +{ + printk(KERN_INFO "pid_max_hw_breakpoint DISABLED\n"); +} + +void pid_max_hw_breakpoint_handler(struct hw_breakpoint *temp, struct pt_regs + *temp_regs) +{ + printk(KERN_INFO "pid_max value is changed\n"); + dump_stack(); + printk(KERN_INFO "Dump stack from pid_max_hw_breakpoint_handler\n"); +} + +static int __init hw_break_module_init(void) +{ + int ret; + +#ifdef CONFIG_X86 + pid_max_hw_breakpoint.info.name = "pid_max"; + pid_max_hw_breakpoint.info.type = HW_BREAKPOINT_WRITE; + pid_max_hw_breakpoint.info.len = HW_BREAKPOINT_LEN_4; + pid_max_hw_breakpoint.priority = HW_BREAKPOINT_PRIO_NORMAL; + + pid_max_hw_breakpoint.installed = (void*)pid_max_hw_breakpoint_installed; + pid_max_hw_breakpoint.uninstalled = (void*)pid_max_hw_breakpoint_uninstalled; + pid_max_hw_breakpoint.triggered = (void*)pid_max_hw_breakpoint_handler; +#endif /* CONFIG_X86 */ + + ret = register_kernel_hw_breakpoint(&pid_max_hw_breakpoint); + + if (ret < 0) { + printk(KERN_INFO "Breakpoint registration failed\n"); + return ret; + } + else + printk(KERN_INFO "HW Breakpoint for pid_max write installed\n"); + + return 0; +} + +static void __exit hw_break_module_exit(void) +{ + unregister_kernel_hw_breakpoint(&pid_max_hw_breakpoint); + printk(KERN_INFO "HW Breakpoint for pid_max write uninstalled\n"); +} + +module_init(hw_break_module_init); +module_exit(hw_break_module_exit); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("K.Prasad"); +MODULE_DESCRIPTION("pid_max breakpoint"); -- 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/