Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756140AbXKUKVN (ORCPT ); Wed, 21 Nov 2007 05:21:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754845AbXKUKU4 (ORCPT ); Wed, 21 Nov 2007 05:20:56 -0500 Received: from rv-out-0910.google.com ([209.85.198.188]:16738 "EHLO rv-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760823AbXKUKUy (ORCPT ); Wed, 21 Nov 2007 05:20:54 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=pzmd/vcGSGd2n2XEbTtzSUgcZJ3hB7dtkva4HFJjDK/PBSG0vWzu6AHo9wsAZw6aG9LyaV0n06iE8k/57vKyVqwIdnV+kXRVjOZkPbX6JQRGnVlb5ZqKK511loBpsUlrsDlVZKTt5MoZS70fzT5PrNkJVz51EzWwX+iQd6RWVK8= Message-ID: <863e9df20711210220i34f0b844u14c79daa54727c21@mail.gmail.com> Date: Wed, 21 Nov 2007 15:50:54 +0530 From: "Abhishek Sagar" To: "Jim Keniston" Subject: Re: [PATCH][RFC] kprobes: Add user entry-handler in kretprobes Cc: "Srinivasa Ds" , linux-kernel@vger.kernel.org, prasanna@in.ibm.com, davem@davemloft.net, anil.s.keshavamurthy@intel.com, "Ananth N Mavinakayanahalli" In-Reply-To: <1195624524.3705.20.camel@dyn9047018096.beaverton.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <47389BEB.1000901@gmail.com> <473ACCBE.9010308@in.ibm.com> <863e9df20711140530h69df9107g38e293aab278686a@mail.gmail.com> <1195080664.5781.78.camel@dyn9047018096.beaverton.ibm.com> <863e9df20711150516w6ee27172j159deaad06d0e5e8@mail.gmail.com> <1195161370.3804.96.camel@dyn9047018096.beaverton.ibm.com> <863e9df20711160950u5a84ddb9wff683d6b405ec94e@mail.gmail.com> <1195260891.8520.104.camel@dyn9047018096.beaverton.ibm.com> <863e9df20711190426t4dca674g54986d1520240894@mail.gmail.com> <1195624524.3705.20.camel@dyn9047018096.beaverton.ibm.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9379 Lines: 244 On 11/21/07, Jim Keniston wrote: > I have one minor suggestion on the code -- see below -- but I'm willing > to ack that with or without the suggested change. Please also see > suggestions on kprobes.txt and the demo program. Thanks...I've made the necessary changes. More comments below. > It would be more consistent with the existing text in kprobes.txt to add > a subsection labeled "User's entry handler (rp->entry_handler):" and > document the entry_handler there. I've moved almost all of the entry_handler discussion in a separate section. > > 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 = 1, /* profile one invocation at a time */ > > I don't like the idea of setting maxactive = 1 here. That's not normal > kretprobes usage, which is what we're trying to illustrate here. This > is no place for splitting hairs about profiling recursive functions. I've reverted back to ".maxactive = 20". In any case, there is no need to protect against recursive instances of sys_open. > > @@ -699,6 +699,14 @@ static int __kprobes pre_handler_kretpro > > struct kretprobe_instance, uflist); > > ri->rp = rp; > > ri->task = current; > > + > > + if (rp->entry_handler) { > > + if (rp->entry_handler(ri, regs)) { > > Could also be > if (rp->entry_handler && rp->entry_handler(ri, regs)) { Done. --- Signed-off-by: Abhishek Sagar diff -upNr linux-2.6.24-rc3/Documentation/kprobes.txt linux-2.6.24-rc3_kp/Documentation/kprobes.txt --- linux-2.6.24-rc3/Documentation/kprobes.txt 2007-11-17 10:46:36.000000000 +0530 +++ linux-2.6.24-rc3_kp/Documentation/kprobes.txt 2007-11-21 15:20:53.000000000 +0530 @@ -96,7 +96,9 @@ or in registers (e.g., for x86_64 or for 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 @@ -107,7 +109,7 @@ At boot time, Kprobes registers a kprobe 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, +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. @@ -131,6 +133,30 @@ zero when the return probe is registered 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 @@ -273,6 +299,8 @@ 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 @@ -555,23 +583,46 @@ report failed calls to sys_open(). #include #include #include +#include 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) +/* per-instance private data */ +struct my_data { + ktime_t entry_stamp; +}; + +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; +} + +static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs) { int retval = regs_return_value(regs); - if (retval < 0) { - printk("%s returns %d\n", probed_func, retval); - } + struct my_data *data = (struct my_data *)ri->data; + s64 delta; + ktime_t now = ktime_get(); + + delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); + if (retval < 0) /* probed function failed; log retval and duration */ + 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) @@ -580,10 +631,10 @@ static int __init kretprobe_init(void) my_kretprobe.kp.symbol_name = (char *)probed_func; if ((ret = register_kretprobe(&my_kretprobe)) < 0) { - printk("register_kretprobe failed, returned %d\n", ret); + printk("Failed to register kretprobe!\n"); 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; } @@ -591,7 +642,7 @@ static void __exit kretprobe_exit(void) { unregister_kretprobe(&my_kretprobe); printk("kretprobe unregistered\n"); - /* nmissed > 0 suggests that maxactive was set too low. */ + /* nmissed > 0 suggests that maxactive was set too low */ printk("Missed probing %d instances of %s\n", my_kretprobe.nmissed, probed_func); } diff -upNr linux-2.6.24-rc3/include/linux/kprobes.h linux-2.6.24-rc3_kp/include/linux/kprobes.h --- linux-2.6.24-rc3/include/linux/kprobes.h 2007-11-17 10:46:36.000000000 +0530 +++ linux-2.6.24-rc3_kp/include/linux/kprobes.h 2007-11-21 13:40:48.000000000 +0530 @@ -152,8 +152,10 @@ static inline int arch_trampoline_kprobe struct kretprobe { struct kprobe kp; kretprobe_handler_t handler; + kretprobe_handler_t entry_handler; int maxactive; int nmissed; + size_t data_size; struct hlist_head free_instances; struct hlist_head used_instances; }; @@ -164,6 +166,7 @@ struct kretprobe_instance { struct kretprobe *rp; kprobe_opcode_t *ret_addr; struct task_struct *task; + char data[0]; }; struct kretprobe_blackpoint { diff -upNr linux-2.6.24-rc3/kernel/kprobes.c linux-2.6.24-rc3_kp/kernel/kprobes.c --- linux-2.6.24-rc3/kernel/kprobes.c 2007-11-17 10:46:36.000000000 +0530 +++ linux-2.6.24-rc3_kp/kernel/kprobes.c 2007-11-21 13:41:57.000000000 +0530 @@ -699,6 +699,12 @@ static int __kprobes pre_handler_kretpro struct kretprobe_instance, uflist); ri->rp = rp; ri->task = current; + + if (rp->entry_handler && rp->entry_handler(ri, regs)) { + spin_unlock_irqrestore(&kretprobe_lock, flags); + return 0; + } + arch_prepare_kretprobe(ri, regs); /* XXX(hch): why is there no hlist_move_head? */ @@ -745,7 +751,8 @@ int __kprobes register_kretprobe(struct INIT_HLIST_HEAD(&rp->used_instances); INIT_HLIST_HEAD(&rp->free_instances); for (i = 0; i < rp->maxactive; i++) { - inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL); + inst = kmalloc(sizeof(struct kretprobe_instance) + + rp->data_size, GFP_KERNEL); if (inst == NULL) { free_rp_inst(rp); return -ENOMEM; - 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/