X-Git-Url: http://pilppa.org/gitweb/?a=blobdiff_plain;f=Documentation%2Fkprobes.txt;h=30c101761d0d54f532122e8a804d376de2aa61d8;hb=877c357e7511395bc923ec9efc2e8b021a17ed79;hp=d71fafffce90de81cba916c5d98dae7db5e9eb63;hpb=6bfe5c9d6f4dcaa998f67e691359cf7b1c4b443d;p=linux-2.6-omap-h63xx.git diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt index d71fafffce9..30c101761d0 100644 --- a/Documentation/kprobes.txt +++ b/Documentation/kprobes.txt @@ -14,6 +14,7 @@ CONTENTS 8. Kprobes Example 9. Jprobes Example 10. Kretprobes Example +Appendix A: The kprobes debugfs interface 1. Concepts: Kprobes, Jprobes, Return Probes @@ -95,7 +96,9 @@ or in registers (e.g., for x86_64 or for an i386 fastcall function). The jprobe will work in either case, so long as the handler's prototype matches that of the probed function. -1.3 How Does a Return Probe Work? +1.3 Return Probes + +1.3.1 How Does a Return Probe Work? When you call register_kretprobe(), Kprobes establishes a kprobe at the entry to the function. When the probed function is called and this @@ -106,9 +109,9 @@ At boot time, Kprobes registers a kprobe at the trampoline. When the probed function executes its return instruction, control passes to the trampoline and that probe is hit. Kprobes' trampoline -handler calls the user-specified handler associated with the kretprobe, -then sets the saved instruction pointer to the saved return address, -and that's where execution resumes upon return from the trap. +handler calls the user-specified return handler associated with the +kretprobe, then sets the saved instruction pointer to the saved return +address, and that's where execution resumes upon return from the trap. While the probed function is executing, its return address is stored in an object of type kretprobe_instance. Before calling @@ -130,6 +133,30 @@ zero when the return probe is registered, and is incremented every time the probed function is entered but there is no kretprobe_instance object available for establishing the return probe. +1.3.2 Kretprobe entry-handler + +Kretprobes also provides an optional user-specified handler which runs +on function entry. This handler is specified by setting the entry_handler +field of the kretprobe struct. Whenever the kprobe placed by kretprobe at the +function entry is hit, the user-defined entry_handler, if any, is invoked. +If the entry_handler returns 0 (success) then a corresponding return handler +is guaranteed to be called upon function return. If the entry_handler +returns a non-zero error then Kprobes leaves the return address as is, and +the kretprobe has no further effect for that particular function instance. + +Multiple entry and return handler invocations are matched using the unique +kretprobe_instance object associated with them. Additionally, a user +may also specify per return-instance private data to be part of each +kretprobe_instance object. This is especially useful when sharing private +data between corresponding user entry and return handlers. The size of each +private data object can be specified at kretprobe registration time by +setting the data_size field of the kretprobe struct. This data can be +accessed through the data field of each kretprobe_instance object. + +In case probed function is entered but there is no kretprobe_instance +object available, then in addition to incrementing the nmissed count, +the user entry_handler invocation is also skipped. + 2. Architectures Supported Kprobes, jprobes, and return probes are implemented on the following @@ -140,6 +167,7 @@ architectures: - ppc64 - ia64 (Does not support probes on instruction slot1.) - sparc64 (Return probes not yet implemented.) +- arm 3. Configuring Kprobes @@ -246,12 +274,6 @@ 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 @@ -278,6 +300,8 @@ of interest: - ret_addr: the return address - rp: points to the corresponding kretprobe object - task: points to the corresponding task struct +- data: points to per return-instance private data; see "Kretprobe + entry-handler" for details. The regs_return_value(regs) macro provides a simple abstraction to extract the return value from the appropriate register as defined by @@ -349,9 +373,12 @@ for instrumentation and error reporting.) If the number of times a function is called does not match the number of times it returns, registering a return probe on that function may -produce undesirable results. We have the do_exit() case covered. -do_execve() and do_fork() are not an issue. We're unaware of other -specific cases where this could be a problem. +produce undesirable results. In such a case, a line: +kretprobe BUG!: Processing kretprobe d000000000041aa8 @ c00000000004f48c +gets printed. With this information, one will be able to correlate the +exact instance of the kretprobe that caused the problem. We have the +do_exit() case covered. do_execve() and do_fork() are not an issue. +We're unaware of other specific cases where this could be a problem. If, upon entry to or exit from a function, the CPU is running on a stack other than that of the current task, registering a return @@ -514,7 +541,7 @@ long jdo_fork(unsigned long clone_flags, unsigned long stack_start, } static struct jprobe my_jprobe = { - .entry = JPROBE_ENTRY(jdo_fork) + .entry = jdo_fork }; static int __init jprobe_init(void) @@ -557,23 +584,52 @@ report failed calls to sys_open(). #include #include #include +#include + +/* per-instance private data */ +struct my_data { + ktime_t entry_stamp; +}; 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) +/* Timestamp function entry. */ +static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs) +{ + struct my_data *data; + + if(!current->mm) + return 1; /* skip kernel threads */ + + data = (struct my_data *)ri->data; + data->entry_stamp = ktime_get(); + return 0; +} + +/* If the probed function failed, log the return value and duration. + * Duration may turn out to be zero consistently, depending upon the + * granularity of time accounting on the platform. */ +static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs) { int retval = regs_return_value(regs); + struct my_data *data = (struct my_data *)ri->data; + s64 delta; + ktime_t now; + if (retval < 0) { - printk("%s returns %d\n", probed_func, retval); + now = ktime_get(); + delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); + printk("%s: return val = %d (duration = %lld ns)\n", + probed_func, retval, delta); } return 0; } static struct kretprobe my_kretprobe = { - .handler = ret_handler, - /* Probe up to 20 instances concurrently. */ - .maxactive = 20 + .handler = return_handler, + .entry_handler = entry_handler, + .data_size = sizeof(struct my_data), + .maxactive = 20, /* probe up to 20 instances concurrently */ }; static int __init kretprobe_init(void) @@ -585,7 +641,7 @@ static int __init kretprobe_init(void) printk("register_kretprobe failed, returned %d\n", ret); return -1; } - printk("Planted return probe at %p\n", my_kretprobe.kp.addr); + printk("Kretprobe active on %s\n", my_kretprobe.kp.symbol_name); return 0; } @@ -595,7 +651,7 @@ static void __exit kretprobe_exit(void) printk("kretprobe unregistered\n"); /* nmissed > 0 suggests that maxactive was set too low. */ printk("Missed probing %d instances of %s\n", - my_kretprobe.nmissed, probed_func); + my_kretprobe.nmissed, probed_func); } module_init(kretprobe_init) @@ -614,3 +670,27 @@ 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) + + +Appendix A: The kprobes debugfs interface + +With recent kernels (> 2.6.20) the list of registered kprobes is visible +under the /debug/kprobes/ directory (assuming debugfs is mounted at /debug). + +/debug/kprobes/list: Lists all registered probes on the system + +c015d71a k vfs_read+0x0 +c011a316 j do_fork+0x0 +c03dedc5 r tcp_v4_rcv+0x0 + +The first column provides the kernel address where the probe is inserted. +The second column identifies the type of probe (k - kprobe, r - kretprobe +and j - jprobe), while the third column specifies the symbol+offset of +the probe. If the probed function belongs to a module, the module name +is also specified. + +/debug/kprobes/enabled: Turn kprobes ON/OFF + +Provides a knob to globally turn registered kprobes ON or OFF. By default, +all kprobes are enabled. By echoing "0" to this file, all registered probes +will be disarmed, till such time a "1" is echoed to this file.