Commit 97f7943d authored by Rusty Lynch's avatar Rusty Lynch Committed by Linus Torvalds
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[PATCH] Return probe redesign: ppc64 specific implementation 



The following is a patch provided by Ananth Mavinakayanahalli that implements
the new PPC64 specific parts of the new function return probe design.

NOTE: Since getting Ananth's patch, I changed trampoline_probe_handler()
      to consume each of the outstanding return probem instances (feedback
      on my original RFC after Ananth cut a patch), and also added the
      arch_init() function (adding arch specific initialization.) I have
      cross compiled but have not testing this on a PPC64 machine.

Changes include:
 * Addition of kretprobe_trampoline to act as a dummy function for instrumented
   functions to return to, and for the return probe infrastructure to place
   a kprobe on on, gaining control so that the return probe handler
   can be called, and so that the instruction pointer can be moved back
   to the original return address.
 * Addition of arch_init(), allowing a kprobe to be registered on
   kretprobe_trampoline
 * Addition of trampoline_probe_handler() which is used as the pre_handler
   for the kprobe inserted on kretprobe_implementation.  This is the function
   that handles the details for calling the return probe handler function
   and returning control back at the original return address
 * Addition of arch_prepare_kretprobe() which is setup as the pre_handler
   for a kprobe registered at the beginning of the target function by
   kernel/kprobes.c so that a return probe instance can be setup when
   a caller enters the target function.  (A return probe instance contains
   all the needed information for trampoline_probe_handler to do it's job.)
 * Hooks added to the exit path of a task so that we can cleanup any left-over
   return probe instances (i.e. if a task dies while inside a targeted function
   then the return probe instance was reserved at the beginning of the function
   but the function never returns so we need to mark the instance as unused.)

Signed-off-by: default avatarRusty Lynch <rusty.lynch@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 9508dbfe

arch/ppc64/kernel/kprobes.c

+99 −0
Original line number Diff line number Diff line
@@ -122,6 +122,23 @@ static inline void restore_previous_kprobe(void) 
	kprobe_saved_msr = kprobe_saved_msr_prev;

}



void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs)

{

	struct kretprobe_instance *ri;



	if ((ri = get_free_rp_inst(rp)) != NULL) {

		ri->rp = rp;

		ri->task = current;

		ri->ret_addr = (kprobe_opcode_t *)regs->link;



		/* Replace the return addr with trampoline addr */

		regs->link = (unsigned long)kretprobe_trampoline;

		add_rp_inst(ri);

	} else {

		rp->nmissed++;

	}

}



static inline int kprobe_handler(struct pt_regs *regs)

{

	struct kprobe *p;
@@ -211,6 +228,78 @@ no_kprobe: 
	return ret;

}



/*

 * Function return probe trampoline:

 * 	- init_kprobes() establishes a probepoint here

 * 	- When the probed function returns, this probe

 * 		causes the handlers to fire

 */

void kretprobe_trampoline_holder(void)

{

	asm volatile(".global kretprobe_trampoline\n"

			"kretprobe_trampoline:\n"

			"nop\n");

}



/*

 * Called when the probe at kretprobe trampoline is hit

 */

int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)

{

        struct kretprobe_instance *ri = NULL;

        struct hlist_head *head;

        struct hlist_node *node, *tmp;

	unsigned long orig_ret_address = 0;

	unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;



        head = kretprobe_inst_table_head(current);



	/*

	 * It is possible to have multiple instances associated with a given

	 * task either because an multiple functions in the call path

	 * have a return probe installed on them, and/or more then one return

	 * return probe was registered for a target function.

	 *

	 * We can handle this because:

	 *     - instances are always inserted at the head of the list

	 *     - when multiple return probes are registered for the same

         *       function, the first instance's ret_addr will point to the

	 *       real return address, and all the rest will point to

	 *       kretprobe_trampoline

	 */

	hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {

                if (ri->task != current)

			/* another task is sharing our hash bucket */

                        continue;



		if (ri->rp && ri->rp->handler)

			ri->rp->handler(ri, regs);



		orig_ret_address = (unsigned long)ri->ret_addr;

		recycle_rp_inst(ri);



		if (orig_ret_address != trampoline_address)

			/*

			 * This is the real return address. Any other

			 * instances associated with this task are for

			 * other calls deeper on the call stack

			 */

			break;

	}



	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));

	regs->nip = orig_ret_address;



	unlock_kprobes();



        /*

         * By returning a non-zero value, we are telling

         * kprobe_handler() that we have handled unlocking

         * and re-enabling preemption.

         */

        return 1;

}



/*

 * Called after single-stepping.  p->addr is the address of the

 * instruction whose first byte has been replaced by the "breakpoint"
@@ -349,3 +438,13 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) 
	memcpy(regs, &jprobe_saved_regs, sizeof(struct pt_regs));

	return 1;

}



static struct kprobe trampoline_p = {

	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,

	.pre_handler = trampoline_probe_handler

};



int __init arch_init(void)

{

	return register_kprobe(&trampoline_p);

}

arch/ppc64/kernel/process.c

+4 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ 
#include <linux/kallsyms.h>

#include <linux/interrupt.h>

#include <linux/utsname.h>

#include <linux/kprobes.h>



#include <asm/pgtable.h>

#include <asm/uaccess.h>
@@ -307,6 +308,8 @@ void show_regs(struct pt_regs * regs) 


void exit_thread(void)

{

	kprobe_flush_task(current);



#ifndef CONFIG_SMP

	if (last_task_used_math == current)

		last_task_used_math = NULL;
@@ -321,6 +324,7 @@ void flush_thread(void) 
{

	struct thread_info *t = current_thread_info();



	kprobe_flush_task(current);

	if (t->flags & _TIF_ABI_PENDING)

		t->flags ^= (_TIF_ABI_PENDING | _TIF_32BIT);

include/asm-ppc64/kprobes.h

+3 −0
Original line number Diff line number Diff line
@@ -42,6 +42,9 @@ typedef unsigned int kprobe_opcode_t; 


#define JPROBE_ENTRY(pentry)	(kprobe_opcode_t *)((func_descr_t *)pentry)



#define ARCH_SUPPORTS_KRETPROBES

void kretprobe_trampoline(void);



/* Architecture specific copy of original instruction */

struct arch_specific_insn {

	/* copy of original instruction */

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