diff options
| -rw-r--r-- | Documentation/kprobes.txt | 89 |
1 files changed, 56 insertions, 33 deletions
diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt index 2c3b1eae4280..ba26201d5023 100644 --- a/Documentation/kprobes.txt +++ b/Documentation/kprobes.txt @@ -151,9 +151,9 @@ So that you can load and unload Kprobes-based instrumentation modules, make sure "Loadable module support" (CONFIG_MODULES) and "Module unloading" (CONFIG_MODULE_UNLOAD) are set to "y". -You may also want to ensure that CONFIG_KALLSYMS and perhaps even -CONFIG_KALLSYMS_ALL are set to "y", since kallsyms_lookup_name() -is a handy, version-independent way to find a function's address. +Also make sure that CONFIG_KALLSYMS and perhaps even CONFIG_KALLSYMS_ALL +are set to "y", since kallsyms_lookup_name() is used by the in-kernel +kprobe address resolution code. If you need to insert a probe in the middle of a function, you may find it useful to "Compile the kernel with debug info" (CONFIG_DEBUG_INFO), @@ -179,6 +179,27 @@ occurs during execution of kp->pre_handler or kp->post_handler, or during single-stepping of the probed instruction, Kprobes calls kp->fault_handler. Any or all handlers can be NULL. +NOTE: +1. With the introduction of the "symbol_name" field to struct kprobe, +the probepoint address resolution will now be taken care of by the kernel. +The following will now work: + + kp.symbol_name = "symbol_name"; + +(64-bit powerpc intricacies such as function descriptors are handled +transparently) + +2. Use the "offset" field of struct kprobe if the offset into the symbol +to install a probepoint is known. This field is used to calculate the +probepoint. + +3. Specify either the kprobe "symbol_name" OR the "addr". If both are +specified, kprobe registration will fail with -EINVAL. + +4. With CISC architectures (such as i386 and x86_64), the kprobes code +does not validate if the kprobe.addr is at an instruction boundary. +Use "offset" with caution. + register_kprobe() returns 0 on success, or a negative errno otherwise. User's pre-handler (kp->pre_handler): @@ -225,6 +246,12 @@ control to Kprobes.) If the probed function is declared asmlinkage, fastcall, or anything else that affects how args are passed, the handler's declaration must match. +NOTE: A macro JPROBE_ENTRY is provided to handle architecture-specific +aliasing of jp->entry. In the interest of portability, it is advised +to use: + + jp->entry = JPROBE_ENTRY(handler); + register_jprobe() returns 0 on success, or a negative errno otherwise. 4.3 register_kretprobe @@ -251,6 +278,11 @@ of interest: - ret_addr: the return address - rp: points to the corresponding kretprobe object - task: points to the corresponding task struct + +The regs_return_value(regs) macro provides a simple abstraction to +extract the return value from the appropriate register as defined by +the architecture's ABI. + The handler's return value is currently ignored. 4.4 unregister_*probe @@ -369,7 +401,6 @@ stack trace and selected i386 registers when do_fork() is called. #include <linux/kernel.h> #include <linux/module.h> #include <linux/kprobes.h> -#include <linux/kallsyms.h> #include <linux/sched.h> /*For each probe you need to allocate a kprobe structure*/ @@ -403,18 +434,14 @@ int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr) return 0; } -int init_module(void) +static int __init kprobe_init(void) { int ret; kp.pre_handler = handler_pre; kp.post_handler = handler_post; kp.fault_handler = handler_fault; - kp.addr = (kprobe_opcode_t*) kallsyms_lookup_name("do_fork"); - /* register the kprobe now */ - if (!kp.addr) { - printk("Couldn't find %s to plant kprobe\n", "do_fork"); - return -1; - } + kp.symbol_name = "do_fork"; + if ((ret = register_kprobe(&kp) < 0)) { printk("register_kprobe failed, returned %d\n", ret); return -1; @@ -423,12 +450,14 @@ int init_module(void) return 0; } -void cleanup_module(void) +static void __exit kprobe_exit(void) { unregister_kprobe(&kp); printk("kprobe unregistered\n"); } +module_init(kprobe_init) +module_exit(kprobe_exit) MODULE_LICENSE("GPL"); ----- cut here ----- @@ -463,7 +492,6 @@ the arguments of do_fork(). #include <linux/fs.h> #include <linux/uio.h> #include <linux/kprobes.h> -#include <linux/kallsyms.h> /* * Jumper probe for do_fork. @@ -485,17 +513,13 @@ long jdo_fork(unsigned long clone_flags, unsigned long stack_start, } static struct jprobe my_jprobe = { - .entry = (kprobe_opcode_t *) jdo_fork + .entry = JPROBE_ENTRY(jdo_fork) }; -int init_module(void) +static int __init jprobe_init(void) { int ret; - my_jprobe.kp.addr = (kprobe_opcode_t *) kallsyms_lookup_name("do_fork"); - if (!my_jprobe.kp.addr) { - printk("Couldn't find %s to plant jprobe\n", "do_fork"); - return -1; - } + my_jprobe.kp.symbol_name = "do_fork"; if ((ret = register_jprobe(&my_jprobe)) <0) { printk("register_jprobe failed, returned %d\n", ret); @@ -506,12 +530,14 @@ int init_module(void) return 0; } -void cleanup_module(void) +static void __exit jprobe_exit(void) { unregister_jprobe(&my_jprobe); printk("jprobe unregistered\n"); } +module_init(jprobe_init) +module_exit(jprobe_exit) MODULE_LICENSE("GPL"); ----- cut here ----- @@ -530,16 +556,13 @@ report failed calls to sys_open(). #include <linux/kernel.h> #include <linux/module.h> #include <linux/kprobes.h> -#include <linux/kallsyms.h> static const char *probed_func = "sys_open"; /* Return-probe handler: If the probed function fails, log the return value. */ static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) { - // Substitute the appropriate register name for your architecture -- - // e.g., regs->rax for x86_64, regs->gpr[3] for ppc64. - int retval = (int) regs->eax; + int retval = regs_return_value(regs); if (retval < 0) { printk("%s returns %d\n", probed_func, retval); } @@ -552,15 +575,11 @@ static struct kretprobe my_kretprobe = { .maxactive = 20 }; -int init_module(void) +static int __init kretprobe_init(void) { int ret; - my_kretprobe.kp.addr = - (kprobe_opcode_t *) kallsyms_lookup_name(probed_func); - if (!my_kretprobe.kp.addr) { - printk("Couldn't find %s to plant return probe\n", probed_func); - return -1; - } + my_kretprobe.kp.symbol_name = (char *)probed_func; + if ((ret = register_kretprobe(&my_kretprobe)) < 0) { printk("register_kretprobe failed, returned %d\n", ret); return -1; @@ -569,7 +588,7 @@ int init_module(void) return 0; } -void cleanup_module(void) +static void __exit kretprobe_exit(void) { unregister_kretprobe(&my_kretprobe); printk("kretprobe unregistered\n"); @@ -578,6 +597,8 @@ void cleanup_module(void) my_kretprobe.nmissed, probed_func); } +module_init(kretprobe_init) +module_exit(kretprobe_exit) MODULE_LICENSE("GPL"); ----- cut here ----- @@ -590,3 +611,5 @@ messages.) For additional information on Kprobes, refer to the following URLs: http://www-106.ibm.com/developerworks/library/l-kprobes.html?ca=dgr-lnxw42Kprobe http://www.redhat.com/magazine/005mar05/features/kprobes/ +http://www-users.cs.umn.edu/~boutcher/kprobes/ +http://www.linuxsymposium.org/2006/linuxsymposium_procv2.pdf (pages 101-115) |