On Wed, 2007-11-21 at 15:50 +0530, Abhishek Sagar wrote:
> On 11/21/07, Jim Keniston <[email protected]> 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 <[email protected]>
Acked-by: Jim Keniston <[email protected]>
This works for me with the revised kretprobe-example.c and with another
test program I had lying around.
Jim
>
> 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 <linux/kernel.h>
> #include <linux/module.h>
> #include <linux/kprobes.h>
> +#include <linux/ktime.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)
> +/* 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;
-
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