Re: [heiko.carstens@de.ibm.com: Re: [PATCH] kprobes for s390 architecture]

Re: [heiko.carstens@de.ibm.com: Re: [PATCH] kprobes for s390 architecture]

[Michael Grundy]

Heiko Carstens <heiko.carstens@de.ibm.com> wrote on 06/23/2006 08:03:44 AM:

> This won't solve anything. What Martin probably meant is something like a
poor
> man's stop_machine_run() implemented by using smp_call_function(). This
way
> you synchronize all cpus and when all cpus are in a known state, you
change
> the instruction in question and make sure that serialization happens
before
> cpus leave the handler again... Except for the cpu that called
> smp_call_function() you get the serialization for free, since the last
> instruction of the handler is always an lpsw/lpswe instruction.
>
> Otherwise there is still the possibility that a different cpu is fetching
the
> instruction concurrently while you change it. This doesn't sound very
good,
> especially if you take this paragraph of the Principles of Operation into
> account (p.5-89 of SA22-7832-04):
>
> "It is possible, if another CPU or a channel program concurrently
modifies
> the instruction, for one CPU to recognize the changes to some but not all
bit
> positions of an instruction."

(link to doc for anyone following along at home:
 http://publibz.boulder.ibm.com/epubs/pdf/a2278324.pdf)

On the same page it says "All copies of a prefetched instruction are
discarded
when: * A serializing function is performed" Would something like this in a
smp_call_function do it? :

bcr 15,0

if (*p->addr != breakpoint_instruction)
      *p->addr = breakpoint_instruction;


Alternatively, if we did a compare and swap on that location (serializing
instruction) would that be acceptable?

Thanks
Michael

=========================================
If at first you don't succeed, call in an air strike.

Re: [PATCH] kprobes for s390 architecture

[Heiko Carstens]

> On the same page it says "All copies of a prefetched instruction are
> discarded
> when: * A serializing function is performed" Would something like this in a
> smp_call_function do it? :
> 
> bcr 15,0
> 
> if (*p->addr != breakpoint_instruction)
>       *p->addr = breakpoint_instruction;
> 
> 
> Alternatively, if we did a compare and swap on that location (serializing
> instruction) would that be acceptable?
> 
> Thanks
> Michael

The crap below is something that could solve your problem (assumes that "a"
is the address of the instruction to be replaced and 0x42 is the opcode of
the new instruction):

- generates an irq on all other cpus -> prefetched stuff on them discarded
- catches all cpus
- writes the new instruction
- the atomic_inc(&cap.done) is a compare and swap instruction -> serialization

At least this is something that could work... completely untested and might
have some problems that I didn't think of ;)

struct capture_data {
	atomic_t cpus;
	atomic_t done;
};

void capture_wait(void *data)
{ 
	struct capture_data *cap = data;

	atomic_inc(&cap->cpus);
	while(!atomic_read(&cap->done))
		cpu_relax();
	atomic_dec(&cap->cpus);
}

void replace_instr(int *a)
{
	struct capture_data cap;

	preempt_disable();
	atomic_set(&cap.cpus, 0);
	atomic_set(&cap.done, 0);
	smp_call_function(capture_wait, (void *)&cap, 0, 0);
	while (atomic_read(&cap.cpus) != num_online_cpus() - 1)
		cpu_relax();
	*a = 0x42;
	atomic_inc(&cap.done);
	while (atomic_read(&cap.cpus))
		cpu_relax();
	preempt_enable();
}

Re: [PATCH] kprobes for s390 architecture

[Heiko Carstens]

> At least this is something that could work... completely untested and might
> have some problems that I didn't think of ;)
> 
> struct capture_data {
> 	atomic_t cpus;
> 	atomic_t done;
> };
> 
> void capture_wait(void *data)
> { 
> 	struct capture_data *cap = data;
> 
> 	atomic_inc(&cap->cpus);
> 	while(!atomic_read(&cap->done))
> 		cpu_relax();
> 	atomic_dec(&cap->cpus);
> }
> 
> void replace_instr(int *a)
> {
> 	struct capture_data cap;
> 
> 	preempt_disable();
> 	atomic_set(&cap.cpus, 0);
> 	atomic_set(&cap.done, 0);
> 	smp_call_function(capture_wait, (void *)&cap, 0, 0);
> 	while (atomic_read(&cap.cpus) != num_online_cpus() - 1)
> 		cpu_relax();
> 	*a = 0x42;
> 	atomic_inc(&cap.done);
> 	while (atomic_read(&cap.cpus))
> 		cpu_relax();
> 	preempt_enable();
> }

Forget this crap. It can easily cause deadlocks with more than two cpus.

Just do a compare and swap operation on the instruction you want to replace,
then do an smp_call_function() with the wait parameter set to 1 and passing
a pointer to a function that does nothing but return.

The cs/csg instruction will make sure that your cpu has exclusive access
to the memory region in question and will invalidate the cache lines on all
other cpus.
With the following smp_call_function() you can make sure that all other
cpus discard everything they have prefetched. Hence there is only a small
window between the cs/csg and the return of smp_call_function() where you
do not know if other cpus are executing the old or the new instruction.

Re: [PATCH] kprobes for s390 architecture

[Heiko Carstens]

> Just do a compare and swap operation on the instruction you want to replace,
> then do an smp_call_function() with the wait parameter set to 1 and passing
> a pointer to a function that does nothing but return.

Setting wait to 1 isn't necessary as well. Wondering if I get anything right
today...

Re: [PATCH] kprobes for s390 architecture

[Mike Grundy]

On Sat, Jun 24, 2006 at 02:15:41PM +0200, Heiko Carstens wrote:
> > Just do a compare and swap operation on the instruction you want to replace,
> > then do an smp_call_function() with the wait parameter set to 1 and passing
> > a pointer to a function that does nothing but return.
Here's what I came up with Friday before I jumped timezones back east:

void smp_replace_instruction(void *info)
{
	struct ins_replace_args *parms;

	parms = (struct ins_replace_args *) info;
	cmpxchg(parms->addr, parms->oinsn, parms->ninsn);
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
	struct ins_replace_args parms;
	parms.addr = p->addr;
	parms.ninsn = BREAKPOINT_INSTRUCTION;
	parms.oinsn = p->opcode;

	on_each_cpu(smp_replace_instruction, &parms, 0, 1);
} etc...

After reading your notes it's probably overkill doing the cs on each cpu, since
the interrupt will discard the prefetched instructions.

-- 
Thanks
Mike

=========================================
Michael Grundy - grundym@us.ibm.com
Advanced Linux Response Team (ALRT)
http://ltc.linux.ibm.com/teamweb/alrt/
845-435-8842 (T/L 295)

If at first you don't succeed, call in an air strike.

Re: [PATCH] kprobes for s390 architecture

[Heiko Carstens]

> Here's what I came up with Friday before I jumped timezones back east:
> 
> void smp_replace_instruction(void *info)
> {
> 	struct ins_replace_args *parms;
> 
> 	parms = (struct ins_replace_args *) info;
> 	cmpxchg(parms->addr, parms->oinsn, parms->ninsn);
> }
> 
> void __kprobes arch_arm_kprobe(struct kprobe *p)
> {
> 	struct ins_replace_args parms;
> 	parms.addr = p->addr;
> 	parms.ninsn = BREAKPOINT_INSTRUCTION;
> 	parms.oinsn = p->opcode;
> 
> 	on_each_cpu(smp_replace_instruction, &parms, 0, 1);
> } etc...
> 
> After reading your notes it's probably overkill doing the cs on each cpu, since
> the interrupt will discard the prefetched instructions.

Indeed. Another thing that should not be forgotten: it could be that the
whole kernel text segment resides in a shared read only segment. So it can
be shared by multiple z/VM guests.
In that case the cs instruction will fail. Looks like you need to write the
part that replaces the instruction in assembly and supply a fixup section
which in turn makes sure that -EFAULT is returned.

Re: [PATCH] kprobes for s390 architecture

[Martin Schwidefsky]

On Sat, 2006-06-24 at 13:36 +0200, Heiko Carstens wrote:
> > At least this is something that could work... completely untested and might
> > have some problems that I didn't think of ;)
> > 
> > struct capture_data {
> > 	atomic_t cpus;
> > 	atomic_t done;
> > };
> > 
> > void capture_wait(void *data)
> > { 
> > 	struct capture_data *cap = data;
> > 
> > 	atomic_inc(&cap->cpus);
> > 	while(!atomic_read(&cap->done))
> > 		cpu_relax();
> > 	atomic_dec(&cap->cpus);
> > }
> > 
> > void replace_instr(int *a)
> > {
> > 	struct capture_data cap;
> > 
> > 	preempt_disable();
> > 	atomic_set(&cap.cpus, 0);
> > 	atomic_set(&cap.done, 0);
> > 	smp_call_function(capture_wait, (void *)&cap, 0, 0);
> > 	while (atomic_read(&cap.cpus) != num_online_cpus() - 1)
> > 		cpu_relax();
> > 	*a = 0x42;
> > 	atomic_inc(&cap.done);
> > 	while (atomic_read(&cap.cpus))
> > 		cpu_relax();
> > 	preempt_enable();
> > }
> 
> Forget this crap. It can easily cause deadlocks with more than two cpus.

It is not that bad. Instead of preempt_disable/preempt_enable we need a
spinlock. Then only one cpu can do this particular smp_call_function
which will "stop" all other cpus until cap->done has been set.

> Just do a compare and swap operation on the instruction you want to replace,
> then do an smp_call_function() with the wait parameter set to 1 and passing
> a pointer to a function that does nothing but return.

Not good enough. An instruction can be fetched multiple times for a
single execution (see the other mail). So you have a half executed
instruction, the cache line is invalidated, a new instruction is written
and the cache line is recreated to finished the half executed
instruction. That can easiliy happen on millicoded instructions.

> The cs/csg instruction will make sure that your cpu has exclusive access
> to the memory region in question and will invalidate the cache lines on all
> other cpus.

That the cache line is invalidated does not mean that you are safe..

> With the following smp_call_function() you can make sure that all other
> cpus discard everything they have prefetched. Hence there is only a small
> window between the cs/csg and the return of smp_call_function() where you
> do not know if other cpus are executing the old or the new instruction.

The serialization is indeed done by the smp_call_function(). No need to
have a "bcr 15,0" in the called function, the lpsw at the end of the
interrupt already does the serialization.

-- 
blue skies,
  Martin.

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH

"Reality continues to ruin my life." - Calvin.

Re: [PATCH] kprobes for s390 architecture

[Heiko Carstens]

On Tue, Jun 27, 2006 at 05:23:09PM +0200, Martin Schwidefsky wrote:
> On Sat, 2006-06-24 at 13:36 +0200, Heiko Carstens wrote:
> > > At least this is something that could work... completely untested and might
> > > have some problems that I didn't think of ;)
> > > 
> > > struct capture_data {
> > > 	atomic_t cpus;
> > > 	atomic_t done;
> > > };
> > > 
> > > void capture_wait(void *data)
> > > { 
> > > 	struct capture_data *cap = data;
> > > 
> > > 	atomic_inc(&cap->cpus);
> > > 	while(!atomic_read(&cap->done))
> > > 		cpu_relax();
> > > 	atomic_dec(&cap->cpus);
> > > }
> > > 
> > > void replace_instr(int *a)
> > > {
> > > 	struct capture_data cap;
> > > 
> > > 	preempt_disable();
> > > 	atomic_set(&cap.cpus, 0);
> > > 	atomic_set(&cap.done, 0);
> > > 	smp_call_function(capture_wait, (void *)&cap, 0, 0);
> > > 	while (atomic_read(&cap.cpus) != num_online_cpus() - 1)
> > > 		cpu_relax();
> > > 	*a = 0x42;
> > > 	atomic_inc(&cap.done);
> > > 	while (atomic_read(&cap.cpus))
> > > 		cpu_relax();
> > > 	preempt_enable();
> > > }
> > 
> > Forget this crap. It can easily cause deadlocks with more than two cpus.
> 
> It is not that bad. Instead of preempt_disable/preempt_enable we need a
> spinlock. Then only one cpu can do this particular smp_call_function
> which will "stop" all other cpus until cap->done has been set.

CPU0: smp_call_function() -> loops and waits for other cpus
CPU1: [irqs_enabled] - spin_lock(somelock) -> irq -> capture_wait() -> loop
CPU2: [irqs_enabled] ----- spin_lock_irqsave(a,..) -> toasted

CPU2 ends up trying to grab the same lock that CPU1 holds, but has interrupts
disabled and a pending external interrupt because of the smp_call_function()..

> > Just do a compare and swap operation on the instruction you want to replace,
> > then do an smp_call_function() with the wait parameter set to 1 and passing
> > a pointer to a function that does nothing but return.
> Not good enough. An instruction can be fetched multiple times for a
> single execution (see the other mail). So you have a half executed
> instruction, the cache line is invalidated, a new instruction is written
> and the cache line is recreated to finished the half executed
> instruction. That can easiliy happen on millicoded instructions.

Yes, looks like I was too optimistic. Seems like we really have to go for
stop_machine_run() unless somebody comes up with a better idea...

Re: [PATCH] kprobes for s390 architecture

[Mike Grundy]

On Wed, Jun 28, 2006 at 07:58:57AM +0200, Heiko Carstens wrote:
> On Tue, Jun 27, 2006 at 05:23:09PM +0200, Martin Schwidefsky wrote:
> > On Sat, 2006-06-24 at 13:36 +0200, Heiko Carstens wrote:
> > > Just do a compare and swap operation on the instruction you want to replace,
> > > then do an smp_call_function() with the wait parameter set to 1 and passing
> > > a pointer to a function that does nothing but return.
> > Not good enough. An instruction can be fetched multiple times for a
> > single execution (see the other mail). So you have a half executed
> > instruction, the cache line is invalidated, a new instruction is written
> > and the cache line is recreated to finished the half executed
> > instruction. That can easiliy happen on millicoded instructions.
> 
> Yes, looks like I was too optimistic. Seems like we really have to go for
> stop_machine_run() unless somebody comes up with a better idea...

ok, I tried, but my "better ideas" made things worse. stop_machine_run() wins:

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long status = kcb->kprobe_status;
        struct ins_replace_args args;

        args.ptr = p->addr;
        args.old = p->opcode;
        args.new = BREAKPOINT_INSTRUCTION;

        kcb->kprobe_status = KPROBE_SWAP_INST;
        stop_machine_run(swap_instruction, &args, NR_CPUS);
        kcb->kprobe_status = status;
}

It works, and I guess at this point is the only way to do it. I'll send out a 
full patch with this and the other cleanups later.

Mike

Re: [PATCH] kprobes for s390 architecture

[Heiko Carstens]

> ok, I tried, but my "better ideas" made things worse. stop_machine_run() wins:
> 
> void __kprobes arch_arm_kprobe(struct kprobe *p)
> {
>         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>         unsigned long status = kcb->kprobe_status;
>         struct ins_replace_args args;
> 
>         args.ptr = p->addr;
>         args.old = p->opcode;
>         args.new = BREAKPOINT_INSTRUCTION;
> 
>         kcb->kprobe_status = KPROBE_SWAP_INST;
>         stop_machine_run(swap_instruction, &args, NR_CPUS);
>         kcb->kprobe_status = status;
> }
> 
> It works, and I guess at this point is the only way to do it. I'll send out a 
> full patch with this and the other cleanups later.

How fast is this if you have to exchange several hundred instructions?

Re: [PATCH] kprobes for s390 architecture

[Frank Ch. Eigler]

Heiko Carstens <heiko.carstens@de.ibm.com> writes:

> [...]
> > It works, and I guess at this point is the only way to do it. I'll send out a 
> > full patch with this and the other cleanups later.
> 
> How fast is this if you have to exchange several hundred instructions?

That's a very appropriate question.  Related to it is in general how
fast is it to insert and remove ordinary breakpoints on even non-s390
platforms.  Several RH folks recently found that
    probe kernel.function("*") {}
took only a few seconds to insert the probes, but a few *minutes* to
remove them at session shutdown.

- FChE

Re: [PATCH] kprobes for s390 architecture

[Mike Grundy]

On Fri, Jul 07, 2006 at 03:51:23PM -0400, Frank Ch. Eigler wrote:
> Heiko Carstens <heiko.carstens@de.ibm.com> writes:
> 
> > [...]
> > > It works, and I guess at this point is the only way to do it. I'll send out a 
> > > full patch with this and the other cleanups later.
> > 
> > How fast is this if you have to exchange several hundred instructions?
> 
> That's a very appropriate question.  Related to it is in general how
> fast is it to insert and remove ordinary breakpoints on even non-s390
> platforms.  Several RH folks recently found that
>     probe kernel.function("*") {}
> took only a few seconds to insert the probes, but a few *minutes* to
> remove them at session shutdown.

Maybe it would make sense to batch large numbers of arms/disarms? It would be 
up to the module writer to understand that they were inserting a large number
of probes at once and pass a list of probe structures for example.


- Mike

Re: [PATCH] kprobes for s390 architecture

[Mike Grundy]

On Fri, Jul 07, 2006 at 07:25:55PM +0200, Heiko Carstens wrote:
> How fast is this if you have to exchange several hundred instructions?
I'll have to do some timing tests to measure how much overhead it puts on the
system. It's a trade off of safety vs speed. Each increment of safety we've 
put on the swap has had inherent performance penalties. The plus side is the
swaps are only done on activation and deactivation, and don't have this kind
of overhead during operations. 

The latest patch is attached.

Thanks
Mike


Signed-off-by: Michael Grundy <grundym@us.ibm.com>

 arch/s390/Kconfig              |   14
 arch/s390/kernel/Makefile      |    1
 arch/s390/kernel/entry.S       |   12
 arch/s390/kernel/entry64.S     |   12
 arch/s390/kernel/kprobes.c     |  692 +++++++++++++++++++++++++++++++++++++++++
 arch/s390/kernel/traps.c       |   42 ++
 arch/s390/kernel/vmlinux.lds.S |    1
 arch/s390/mm/fault.c           |   40 ++
 include/asm-s390/kdebug.h      |   57 +++
 include/asm-s390/kprobes.h     |  111 ++++++
 10 files changed, 976 insertions(+), 6 deletions(-)

diff -Nurp linux-2.6.17-git25/arch/s390/Kconfig linux-2.6.17-git25-kp390/arch/s390/Kconfig
--- linux-2.6.17-git25/arch/s390/Kconfig	2006-07-08 13:05:48.000000000 -0400
+++ linux-2.6.17-git25-kp390/arch/s390/Kconfig	2006-07-08 13:06:46.000000000 -0400
@@ -490,8 +490,22 @@ source "drivers/net/Kconfig"
 
 source "fs/Kconfig"
 
+menu "Instrumentation Support"
+	depends on EXPERIMENTAL
+
 source "arch/s390/oprofile/Kconfig"
 
+config KPROBES
+	bool "Kprobes (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && MODULES
+	help
+	  Kprobes allows you to trap at almost any kernel address and
+	  execute a callback function.  register_kprobe() establishes
+	  a probepoint and specifies the callback.  Kprobes is useful
+	  for kernel debugging, non-intrusive instrumentation and testing.
+	  If in doubt, say "N".
+endmenu
+
 source "arch/s390/Kconfig.debug"
 
 source "security/Kconfig"
diff -Nurp linux-2.6.17-git25/arch/s390/kernel/entry64.S linux-2.6.17-git25-kp390/arch/s390/kernel/entry64.S
--- linux-2.6.17-git25/arch/s390/kernel/entry64.S	2006-07-08 13:05:48.000000000 -0400
+++ linux-2.6.17-git25-kp390/arch/s390/kernel/entry64.S	2006-07-08 13:06:46.000000000 -0400
@@ -518,6 +518,8 @@ pgm_no_vtime2:
 #endif
 	lg	%r9,__LC_THREAD_INFO	# load pointer to thread_info struct
 	lg	%r1,__TI_task(%r9)
+	tm	__LC_PGM_OLD_PSW+1(%r15),0x01	# kernel per event ?
+	jz	kernel_per
 	mvc	__THREAD_per+__PER_atmid(2,%r1),__LC_PER_ATMID
 	mvc	__THREAD_per+__PER_address(8,%r1),__LC_PER_ADDRESS
 	mvc	__THREAD_per+__PER_access_id(1,%r1),__LC_PER_ACCESS_ID
@@ -553,6 +555,16 @@ pgm_no_vtime3:
 	stosm	__SF_EMPTY(%r15),0x03	# reenable interrupts
 	j	sysc_do_svc
 
+#
+# per was called from kernel, must be kprobes
+#
+kernel_per:
+	lhi	%r0,__LC_PGM_OLD_PSW
+	sth	%r0,SP_TRAP(%r15)	# set trap indication to pgm check
+	la	%r2,SP_PTREGS(%r15)	# address of register-save area
+	larl	%r14,sysc_leave		# load adr. of system ret, no work
+	jg	do_single_step		# branch to do_single_step
+
 /*
  * IO interrupt handler routine
  */
diff -Nurp linux-2.6.17-git25/arch/s390/kernel/entry.S linux-2.6.17-git25-kp390/arch/s390/kernel/entry.S
--- linux-2.6.17-git25/arch/s390/kernel/entry.S	2006-07-08 13:05:48.000000000 -0400
+++ linux-2.6.17-git25-kp390/arch/s390/kernel/entry.S	2006-07-08 13:06:46.000000000 -0400
@@ -505,6 +505,8 @@ pgm_no_vtime2:
 	mvc	__THREAD_per+__PER_address(4,%r1),__LC_PER_ADDRESS
 	mvc	__THREAD_per+__PER_access_id(1,%r1),__LC_PER_ACCESS_ID
 	oi	__TI_flags+3(%r9),_TIF_SINGLE_STEP # set TIF_SINGLE_STEP
+	tm	__LC_PGM_OLD_PSW+1(%r15),0x01	# kernel per event ?
+	bz	BASED(kernel_per)
 	l	%r3,__LC_PGM_ILC	 # load program interruption code
 	la	%r8,0x7f
 	nr	%r8,%r3                  # clear per-event-bit and ilc
@@ -536,6 +538,16 @@ pgm_no_vtime3:
 	stosm	__SF_EMPTY(%r15),0x03	# reenable interrupts
 	b	BASED(sysc_do_svc)
 
+#
+# per was called from kernel, must be kprobes
+#
+kernel_per:
+	mvi	SP_TRAP+1(%r15),0x28	# set trap indication to pgm check
+	la	%r2,SP_PTREGS(%r15)	# address of register-save area
+	l	%r1,BASED(.Lhandle_per)	# load adr. of per handler
+	la	%r14,BASED(sysc_leave)	# load adr. of system return
+	br	%r1			# branch to do_single_step
+
 /*
  * IO interrupt handler routine
  */
diff -Nurp linux-2.6.17-git25/arch/s390/kernel/kprobes.c linux-2.6.17-git25-kp390/arch/s390/kernel/kprobes.c
--- linux-2.6.17-git25/arch/s390/kernel/kprobes.c	1969-12-31 19:00:00.000000000 -0500
+++ linux-2.6.17-git25-kp390/arch/s390/kernel/kprobes.c	2006-07-08 13:06:46.000000000 -0400
@@ -0,0 +1,692 @@
+/*
+ *  Kernel Probes (KProbes)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2002, 2006
+ *
+ * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
+ */
+
+#include <linux/config.h>
+#include <linux/kprobes.h>
+#include <linux/ptrace.h>
+#include <linux/preempt.h>
+#include <linux/stop_machine.h>
+#include <asm/cacheflush.h>
+#include <asm/kdebug.h>
+#include <asm/sections.h>
+#include <asm/uaccess.h>
+#include <linux/module.h>
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+int __kprobes arch_prepare_kprobe(struct kprobe *p)
+{
+	/* Make sure the probe isn't going on a difficult instruction */
+	if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
+		return -EINVAL;
+
+	if ((unsigned long)p->addr & 0x01) {
+		printk("Attempt to register kprobe at an unaligned address\n");
+		return -EINVAL;
+		}
+
+	/* Use the get_insn_slot() facility for correctness */
+	if (!(p->ainsn.insn = get_insn_slot()))
+		return -ENOMEM;
+
+	memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+
+	get_instruction_type(&p->ainsn);
+	p->opcode = *p->addr;
+	return 0;
+}
+
+int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
+{
+	switch (*(__u8 *) instruction) {
+	case 0x0c:      /* bassm */
+	case 0x0b:      /* bsm   */
+	case 0x83:      /* diag  */
+	case 0x44:      /* ex    */
+		return -EINVAL;
+	}
+	switch (*(__u16 *) instruction) {
+	case 0x0101:    /* pr    */
+	case 0xb25a:    /* bsa   */
+	case 0xb240:    /* bakr  */
+	case 0xb258:    /* bsg   */
+	case 0xb218:    /* pc    */
+	case 0xb228:    /* pt    */
+		return -EINVAL;
+	}
+	return 0;
+}
+
+void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
+{
+	/* default fixup method */
+	ainsn->fixup = FIXUP_PSW_NORMAL;
+
+	/* save r1 operand */
+	ainsn->reg = *(__u8 *) (ainsn->insn + 1) & 0xf0;
+
+	/* save the instruction length (pop 5-5) in bytes */
+	switch (*(__u8 *) (ainsn->insn) >> 4) {
+	case 0:
+		ainsn->ilen = 2;
+		break;
+	case 1:
+	case 2:
+		ainsn->ilen = 4;
+		break;
+	case 3:
+		ainsn->ilen = 6;
+		break;
+	}
+
+	switch (*(__u8 *) ainsn->insn) {
+	case 0x05:	/* balr	*/
+	case 0x0d:	/* basr */
+		ainsn->fixup = FIXUP_RETURN_REGISTER;
+		/* if r2 = 0, no branch will be taken */
+		if ((*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0)
+			ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
+		break;
+	case 0x06:	/* bctr	*/
+	case 0x07:	/* bcr	*/
+		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		break;
+	case 0x45:	/* bal	*/
+	case 0x4d:	/* bas	*/
+		ainsn->fixup = FIXUP_RETURN_REGISTER;
+		break;
+	case 0x47:	/* bc	*/
+	case 0x46:	/* bct	*/
+	case 0x86:	/* bxh	*/
+	case 0x87:	/* bxle	*/
+		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		break;
+	case 0x82:	/* lpsw	*/
+		ainsn->fixup = FIXUP_NOT_REQUIRED;
+		break;
+	case 0xb2:	/* lpswe */
+		if (*(__u8 *) (ainsn->insn + 1) == 0xb2) {
+			ainsn->fixup = FIXUP_NOT_REQUIRED;
+		}
+		break;
+	case 0xa7:	/* bras	*/
+		if ((*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0x05) {
+			ainsn->fixup = FIXUP_RETURN_REGISTER;
+		}
+		break;
+	case 0xc0:
+		if ((*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0x00 ||    /*larl */
+			(*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0x05){ /*brasl*/
+			ainsn->fixup = FIXUP_RETURN_REGISTER;
+		}
+		break;
+	case 0xeb:
+		if (*(__u8 *) (ainsn->insn + 5) == 0x44 ||	/* bxhg  */
+			*(__u8 *) (ainsn->insn + 5) == 0x45) {	/* bxleg */
+			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		}
+		break;
+	case 0xe3:	/* bctg	*/
+		if (*(__u8 *) (ainsn->insn + 5) == 0x46) {
+			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		}
+		break;
+	}
+}
+static int __kprobes swap_instruction(void *aref)
+{
+	unsigned long addr, prev, tmp;
+	int shift;
+	struct ins_replace_args *args = aref;
+
+	addr = (unsigned long) args->ptr;
+	shift = (2 ^ (addr & 2)) << 3;
+	addr ^= addr & 2;
+	asm volatile(
+		"    l   %0,0(%4)\n"
+		"    nr  %0,%5\n"
+                "    lr  %1,%0\n"
+		"    or  %0,%2\n"
+		"    or  %1,%3\n"
+		"0:  cs  %0,%1,0(%4)\n"
+		"    jnl 1f\n"
+		"    xr  %1,%0\n"
+		"    nr  %1,%5\n"
+		"    jnz 0b\n"
+		"1:"
+#ifndef __s390x__
+		".section .fixup,\"ax\"\n"
+		"2: lhi    %0,%6\n"
+		"   bras   1,3f\n"
+		"   .long  1b\n"
+		"3: l      1,0(1)\n"
+		"   br     1\n"
+		".previous\n"
+		".section __ex_table,\"a\"\n"
+		"   .align 4\n"
+		"   .long  0b,2b\n"
+		".previous"
+#else /* __s390x__ */
+		".section .fixup,\"ax\"\n"
+		"2: lghi   %0,%6\n"
+		"   jg     1b\n"
+		".previous\n"
+		".section __ex_table,\"a\"\n"
+		"   .align 8\n"
+		"   .quad  0b,2b\n"
+		".previous"
+#endif /* __s390x__ */
+		: "=&d" (prev), "=&d" (tmp)
+		: "d" (args->old << shift), "d" (args->new << shift),
+		  "a" (args->ptr), "d" (~(65535 << shift)), "K" (-EFAULT)
+		: "memory", "cc" );
+	return prev >> shift;
+}
+
+void __kprobes arch_arm_kprobe(struct kprobe *p)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long status = kcb->kprobe_status;
+	struct ins_replace_args args;
+
+	args.ptr = p->addr;
+	args.old = p->opcode;
+	args.new = BREAKPOINT_INSTRUCTION;
+
+	kcb->kprobe_status = KPROBE_SWAP_INST;
+	stop_machine_run(swap_instruction, &args, NR_CPUS);
+	kcb->kprobe_status = status;
+}
+
+void __kprobes arch_disarm_kprobe(struct kprobe *p)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long status = kcb->kprobe_status;
+	struct ins_replace_args args;
+
+	args.ptr = p->addr;
+	args.old = BREAKPOINT_INSTRUCTION;
+	args.new = p->opcode;
+
+	kcb->kprobe_status = KPROBE_SWAP_INST;
+	stop_machine_run(swap_instruction, &args, NR_CPUS);
+	kcb->kprobe_status = status;
+}
+
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+	mutex_lock(&kprobe_mutex);
+	free_insn_slot(p->ainsn.insn);
+	mutex_unlock(&kprobe_mutex);
+}
+
+static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+	per_cr_bits kprobe_per_regs[1];
+
+	memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
+	regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
+
+	/* Set up the per control reg info, will pass to lctl */
+	kprobe_per_regs[0].em_instruction_fetch = 1;
+	kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
+	kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
+
+	/* Set the PER control regs, turns on single step for this address */
+	__ctl_load(kprobe_per_regs, 9, 11);
+	regs->psw.mask |= PSW_MASK_PER;
+	regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
+}
+
+static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	kcb->prev_kprobe.kp = kprobe_running();
+	kcb->prev_kprobe.status = kcb->kprobe_status;
+	kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
+	memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
+					sizeof(kcb->kprobe_saved_ctl));
+}
+
+static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
+	kcb->kprobe_status = kcb->prev_kprobe.status;
+	kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
+	memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
+					sizeof(kcb->kprobe_saved_ctl));
+}
+
+static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
+						struct kprobe_ctlblk *kcb)
+{
+	__get_cpu_var(current_kprobe) = p;
+	/* Save the interrupt and per flags */
+	kcb->kprobe_saved_imask = regs->psw.mask &
+	    (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
+	/* Save the control regs that govern PER */
+	__ctl_store(kcb->kprobe_saved_ctl, 9, 11);
+}
+
+/* Called with kretprobe_lock held */
+void __kprobes 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->gprs[14];
+
+		/* Replace the return addr with trampoline addr */
+		regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
+
+		add_rp_inst(ri);
+	} else {
+		rp->nmissed++;
+	}
+}
+
+static int __kprobes kprobe_handler(struct pt_regs *regs)
+{
+	struct kprobe *p;
+	int ret = 0;
+	unsigned long *addr = (unsigned long *)
+		((regs->psw.addr & PSW_ADDR_INSN) - 2);
+	struct kprobe_ctlblk *kcb;
+
+	/*
+	 * We don't want to be preempted for the entire
+	 * duration of kprobe processing
+	 */
+	preempt_disable();
+	kcb = get_kprobe_ctlblk();
+
+	/* Check we're not actually recursing */
+	if (kprobe_running()) {
+		p = get_kprobe(addr);
+		if (p) {
+			if (kcb->kprobe_status == KPROBE_HIT_SS &&
+			    *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
+				regs->psw.mask &= ~PSW_MASK_PER;
+				regs->psw.mask |= kcb->kprobe_saved_imask;
+				goto no_kprobe;
+			}
+			/* We have reentered the kprobe_handler(), since
+			 * another probe was hit while within the handler.
+			 * We here save the original kprobes variables and
+			 * just single step on the instruction of the new probe
+			 * without calling any user handlers.
+			 */
+			save_previous_kprobe(kcb);
+			set_current_kprobe(p, regs, kcb);
+			kprobes_inc_nmissed_count(p);
+			prepare_singlestep(p, regs);
+			kcb->kprobe_status = KPROBE_REENTER;
+			return 1;
+		} else {
+			p = __get_cpu_var(current_kprobe);
+			if (p->break_handler && p->break_handler(p, regs)) {
+				goto ss_probe;
+			}
+		}
+		goto no_kprobe;
+	}
+
+	p = get_kprobe(addr);
+	if (!p) {
+		if (*addr != BREAKPOINT_INSTRUCTION) {
+			/*
+			 * The breakpoint instruction was removed right
+			 * after we hit it.  Another cpu has removed
+			 * either a probepoint or a debugger breakpoint
+			 * at this address.  In either case, no further
+			 * handling of this interrupt is appropriate.
+			 *
+			 */
+			ret = 1;
+		}
+		/* Not one of ours: let kernel handle it */
+		goto no_kprobe;
+	}
+
+	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+	set_current_kprobe(p, regs, kcb);
+	if (p->pre_handler && p->pre_handler(p, regs))
+		/* handler has already set things up, so skip ss setup */
+		return 1;
+
+ss_probe:
+	prepare_singlestep(p, regs);
+	kcb->kprobe_status = KPROBE_HIT_SS;
+	return 1;
+
+no_kprobe:
+	preempt_enable_no_resched();
+	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" "bcr 0,0\n");
+}
+
+/*
+ * Called when the probe at kretprobe trampoline is hit
+ */
+int __kprobes 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 flags, orig_ret_address = 0;
+	unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
+
+	spin_lock_irqsave(&kretprobe_lock, flags);
+	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->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
+
+	reset_current_kprobe();
+	spin_unlock_irqrestore(&kretprobe_lock, flags);
+	preempt_enable_no_resched();
+
+	/*
+	 * By returning a non-zero value, we are telling
+	 * kprobe_handler() that we don't want the post_handler
+	 * to run (and have re-enabled preemption)
+	 */
+	return 1;
+}
+
+/*
+ * Called after single-stepping.  p->addr is the address of the
+ * instruction whose first byte has been replaced by the "breakpoint"
+ * instruction.  To avoid the SMP problems that can occur when we
+ * temporarily put back the original opcode to single-step, we
+ * single-stepped a copy of the instruction.  The address of this
+ * copy is p->ainsn.insn.
+ */
+static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	regs->psw.addr &= PSW_ADDR_INSN;
+
+	if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
+		regs->psw.addr = (unsigned long)p->addr +
+				((unsigned long)regs->psw.addr -
+				 (unsigned long)p->ainsn.insn);
+
+	if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
+		if ((unsigned long)regs->psw.addr -
+		    (unsigned long)p->ainsn.insn == p->ainsn.ilen)
+			regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
+
+	if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
+		regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
+						(regs->gprs[p->ainsn.reg] -
+						(unsigned long)p->ainsn.insn))
+						| PSW_ADDR_AMODE;
+
+	regs->psw.addr |= PSW_ADDR_AMODE;
+	/* turn off PER mode */
+	regs->psw.mask &= ~PSW_MASK_PER;
+	/* Restore the original per control regs */
+	__ctl_load(kcb->kprobe_saved_ctl, 9, 11);
+	regs->psw.mask |= kcb->kprobe_saved_imask;
+}
+
+static int __kprobes post_kprobe_handler(struct pt_regs *regs)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	if (!cur)
+		return 0;
+
+	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
+		kcb->kprobe_status = KPROBE_HIT_SSDONE;
+		cur->post_handler(cur, regs, 0);
+	}
+
+	resume_execution(cur, regs);
+
+	/*Restore back the original saved kprobes variables and continue. */
+	if (kcb->kprobe_status == KPROBE_REENTER) {
+		restore_previous_kprobe(kcb);
+		goto out;
+	}
+	reset_current_kprobe();
+out:
+	preempt_enable_no_resched();
+
+	/*
+	 * if somebody else is singlestepping across a probe point, psw mask
+	 * will have PER set, in which case, continue the remaining processing
+	 * of do_single_step, as if this is not a probe hit.
+	 */
+	if (regs->psw.mask & PSW_MASK_PER) {
+		return 0;
+	}
+
+	return 1;
+}
+
+static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	const struct exception_table_entry *entry;
+
+	switch(kcb->kprobe_status) {
+	case KPROBE_SWAP_INST:
+		/* We are here because the instruction replacement failed */
+		return 0;
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		/*
+		 * We are here because the instruction being single
+		 * stepped caused a page fault. We reset the current
+		 * kprobe and the nip points back to the probe address
+		 * and allow the page fault handler to continue as a
+		 * normal page fault.
+		 */
+		regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
+		regs->psw.mask &= ~PSW_MASK_PER;
+		regs->psw.mask |= kcb->kprobe_saved_imask;
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			restore_previous_kprobe(kcb);
+		else
+			reset_current_kprobe();
+		preempt_enable_no_resched();
+		break;
+	case KPROBE_HIT_ACTIVE:
+	case KPROBE_HIT_SSDONE:
+		/*
+		 * We increment the nmissed count for accounting,
+		 * we can also use npre/npostfault count for accouting
+		 * these specific fault cases.
+		 */
+		kprobes_inc_nmissed_count(cur);
+
+		/*
+		 * We come here because instructions in the pre/post
+		 * handler caused the page_fault, this could happen
+		 * if handler tries to access user space by
+		 * copy_from_user(), get_user() etc. Let the
+		 * user-specified handler try to fix it first.
+		 */
+		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
+			return 1;
+
+		/*
+		 * In case the user-specified fault handler returned
+		 * zero, try to fix up.
+		 */
+		entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
+		if (entry) {
+			regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
+			return 1;
+		}
+
+		/*
+		 * fixup_exception() could not handle it,
+		 * Let do_page_fault() fix it.
+		 */
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
+/*
+ * Wrapper routine to for handling exceptions.
+ */
+int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
+				       unsigned long val, void *data)
+{
+	struct die_args *args = (struct die_args *)data;
+	int ret = NOTIFY_DONE;
+
+	switch (val) {
+	case DIE_BPT:
+		if (kprobe_handler(args->regs))
+			ret = NOTIFY_STOP;
+		break;
+	case DIE_SSTEP:
+		if (post_kprobe_handler(args->regs))
+			ret = NOTIFY_STOP;
+		break;
+	case DIE_TRAP:
+	case DIE_PAGE_FAULT:
+		/* kprobe_running() needs smp_processor_id() */
+		preempt_disable();
+		if (kprobe_running() &&
+		    kprobe_fault_handler(args->regs, args->trapnr))
+			ret = NOTIFY_STOP;
+		preempt_enable();
+		break;
+	default:
+		break;
+	}
+	return ret;
+}
+
+int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct jprobe *jp = container_of(p, struct jprobe, kp);
+	unsigned long addr;
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
+
+	/* setup return addr to the jprobe handler routine */
+	regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;
+
+	/* r14 is the function return address */
+	kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
+	/* r15 is the stack pointer */
+	kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
+	addr = (unsigned long)kcb->jprobe_saved_r15;
+
+	memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
+	       MIN_STACK_SIZE(addr));
+	return 1;
+}
+
+void __kprobes jprobe_return(void)
+{
+	asm volatile (".word 0x0002");
+}
+
+void __kprobes jprobe_return_end(void)
+{
+	asm volatile ("bcr 0,0");
+}
+
+int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);
+
+	/* Put the regs back */
+	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
+	/* put the stack back */
+	memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
+	       MIN_STACK_SIZE(stack_addr));
+	preempt_enable_no_resched();
+	return 1;
+}
+
+static struct kprobe trampoline_p = {
+	.addr = (kprobe_opcode_t *) & kretprobe_trampoline,
+	.pre_handler = trampoline_probe_handler
+};
+
+int __init arch_init_kprobes(void)
+{
+	return register_kprobe(&trampoline_p);
+}
diff -Nurp linux-2.6.17-git25/arch/s390/kernel/Makefile linux-2.6.17-git25-kp390/arch/s390/kernel/Makefile
--- linux-2.6.17-git25/arch/s390/kernel/Makefile	2006-07-08 13:05:48.000000000 -0400
+++ linux-2.6.17-git25-kp390/arch/s390/kernel/Makefile	2006-07-08 13:08:41.000000000 -0400
@@ -22,6 +22,7 @@ obj-$(CONFIG_BINFMT_ELF32)	+= binfmt_elf
 
 obj-$(CONFIG_VIRT_TIMER)	+= vtime.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
+obj-$(CONFIG_KPROBES)		+= kprobes.o
 
 # Kexec part
 S390_KEXEC_OBJS := machine_kexec.o crash.o
diff -Nurp linux-2.6.17-git25/arch/s390/kernel/traps.c linux-2.6.17-git25-kp390/arch/s390/kernel/traps.c
--- linux-2.6.17-git25/arch/s390/kernel/traps.c	2006-07-08 13:05:48.000000000 -0400
+++ linux-2.6.17-git25-kp390/arch/s390/kernel/traps.c	2006-07-08 13:06:47.000000000 -0400
@@ -29,6 +29,7 @@
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/reboot.h>
+#include <linux/kprobes.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -39,6 +40,7 @@
 #include <asm/s390_ext.h>
 #include <asm/lowcore.h>
 #include <asm/debug.h>
+#include <asm/kdebug.h>
 
 /* Called from entry.S only */
 extern void handle_per_exception(struct pt_regs *regs);
@@ -74,6 +76,20 @@ static int kstack_depth_to_print = 12;
 static int kstack_depth_to_print = 20;
 #endif /* CONFIG_64BIT */
 
+ATOMIC_NOTIFIER_HEAD(s390die_chain);
+
+int register_die_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_register(&s390die_chain, nb);
+}
+EXPORT_SYMBOL(register_die_notifier);
+
+int unregister_die_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_unregister(&s390die_chain, nb);
+}
+EXPORT_SYMBOL(unregister_die_notifier);
+
 /*
  * For show_trace we have tree different stack to consider:
  *   - the panic stack which is used if the kernel stack has overflown
@@ -305,8 +321,9 @@ report_user_fault(long interruption_code
 #endif
 }
 
-static void inline do_trap(long interruption_code, int signr, char *str,
-                           struct pt_regs *regs, siginfo_t *info)
+static void __kprobes inline do_trap(long interruption_code, int signr,
+					char *str, struct pt_regs *regs,
+					siginfo_t *info)
 {
 	/*
 	 * We got all needed information from the lowcore and can
@@ -315,6 +332,10 @@ static void inline do_trap(long interrup
         if (regs->psw.mask & PSW_MASK_PSTATE)
 		local_irq_enable();
 
+	if (notify_die(DIE_TRAP, str, regs, interruption_code,
+				interruption_code, signr) == NOTIFY_STOP)
+		return;
+
         if (regs->psw.mask & PSW_MASK_PSTATE) {
                 struct task_struct *tsk = current;
 
@@ -336,8 +357,12 @@ static inline void *get_check_address(st
 	return (void *)((regs->psw.addr-S390_lowcore.pgm_ilc) & PSW_ADDR_INSN);
 }
 
-void do_single_step(struct pt_regs *regs)
+void __kprobes do_single_step(struct pt_regs *regs)
 {
+	if (notify_die(DIE_SSTEP, "sstep", regs, 0, 0,
+					SIGTRAP) == NOTIFY_STOP){
+		return;
+	}
 	if ((current->ptrace & PT_PTRACED) != 0)
 		force_sig(SIGTRAP, current);
 }
@@ -463,8 +488,15 @@ asmlinkage void illegal_op(struct pt_reg
 #endif
 		} else
 			signal = SIGILL;
-	} else
-		signal = SIGILL;
+	} else {
+		/*
+		 * If we get an illegal op in kernel mode, send it through the
+		 * kprobes notifier. If kprobes doesn't pick it up, SIGILL
+		 */
+		if (notify_die(DIE_BPT, "bpt", regs, interruption_code,
+					3, SIGTRAP) != NOTIFY_STOP)
+			signal = SIGILL;
+	}
 
 #ifdef CONFIG_MATHEMU
         if (signal == SIGFPE)
diff -Nurp linux-2.6.17-git25/arch/s390/kernel/vmlinux.lds.S linux-2.6.17-git25-kp390/arch/s390/kernel/vmlinux.lds.S
--- linux-2.6.17-git25/arch/s390/kernel/vmlinux.lds.S	2006-07-08 13:05:48.000000000 -0400
+++ linux-2.6.17-git25-kp390/arch/s390/kernel/vmlinux.lds.S	2006-07-08 13:06:47.000000000 -0400
@@ -24,6 +24,7 @@ SECTIONS
 	*(.text)
 	SCHED_TEXT
 	LOCK_TEXT
+	KPROBES_TEXT
 	*(.fixup)
 	*(.gnu.warning)
 	} = 0x0700
diff -Nurp linux-2.6.17-git25/arch/s390/mm/fault.c linux-2.6.17-git25-kp390/arch/s390/mm/fault.c
--- linux-2.6.17-git25/arch/s390/mm/fault.c	2006-07-08 13:05:48.000000000 -0400
+++ linux-2.6.17-git25-kp390/arch/s390/mm/fault.c	2006-07-08 14:25:56.000000000 -0400
@@ -25,10 +25,12 @@
 #include <linux/console.h>
 #include <linux/module.h>
 #include <linux/hardirq.h>
+#include <linux/kprobes.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
+#include <asm/kdebug.h>
 
 #ifndef CONFIG_64BIT
 #define __FAIL_ADDR_MASK 0x7ffff000
@@ -48,6 +50,38 @@ extern int sysctl_userprocess_debug;
 
 extern void die(const char *,struct pt_regs *,long);
 
+#ifdef CONFIG_KPROBES
+ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
+int register_page_fault_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
+}
+
+int unregister_page_fault_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
+}
+
+static inline int notify_page_fault(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	struct die_args args = {
+		.regs = regs,
+		.str = str,
+		.err = err,
+		.trapnr = trap,
+		.signr = sig
+	};
+	return atomic_notifier_call_chain(&notify_page_fault_chain, val, &args);
+}
+#else
+static inline int notify_page_fault(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	return NOTIFY_DONE;
+}
+#endif
+
 extern spinlock_t timerlist_lock;
 
 /*
@@ -159,7 +193,7 @@ static void do_sigsegv(struct pt_regs *r
  *   11       Page translation     ->  Not present       (nullification)
  *   3b       Region third trans.  ->  Not present       (nullification)
  */
-static inline void
+static inline void __kprobes
 do_exception(struct pt_regs *regs, unsigned long error_code, int is_protection)
 {
         struct task_struct *tsk;
@@ -173,6 +207,10 @@ do_exception(struct pt_regs *regs, unsig
         tsk = current;
         mm = tsk->mm;
 	
+	if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
+					SIGSEGV) == NOTIFY_STOP)
+		return;
+
 	/* 
          * Check for low-address protection.  This needs to be treated
 	 * as a special case because the translation exception code 
diff -Nurp linux-2.6.17-git25/include/asm-s390/kdebug.h linux-2.6.17-git25-kp390/include/asm-s390/kdebug.h
--- linux-2.6.17-git25/include/asm-s390/kdebug.h	1969-12-31 19:00:00.000000000 -0500
+++ linux-2.6.17-git25-kp390/include/asm-s390/kdebug.h	2006-07-08 13:06:47.000000000 -0400
@@ -0,0 +1,57 @@
+#ifndef _S390_KDEBUG_H
+#define _S390_KDEBUG_H
+
+/*
+ * Feb 2006 Ported to s390 <grundym@us.ibm.com>
+ */
+#include <linux/notifier.h>
+
+struct pt_regs;
+
+struct die_args {
+	struct pt_regs *regs;
+	const char *str;
+	long err;
+	int trapnr;
+	int signr;
+};
+
+/* Note - you should never unregister because that can race with NMIs.
+ * If you really want to do it first unregister - then synchronize_sched
+ *  - then free.
+ */
+extern int register_die_notifier(struct notifier_block *);
+extern int unregister_die_notifier(struct notifier_block *);
+extern struct atomic_notifier_head s390die_chain;
+
+
+enum die_val {
+	DIE_OOPS = 1,
+	DIE_BPT,
+	DIE_SSTEP,
+	DIE_PANIC,
+	DIE_NMI,
+	DIE_DIE,
+	DIE_NMIWATCHDOG,
+	DIE_KERNELDEBUG,
+	DIE_TRAP,
+	DIE_GPF,
+	DIE_CALL,
+	DIE_NMI_IPI,
+	DIE_PAGE_FAULT,
+};
+
+static inline int notify_die(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	struct die_args args = {
+		.regs = regs,
+		.str = str,
+		.err = err,
+		.trapnr = trap,
+		.signr = sig
+	};
+	return atomic_notifier_call_chain(&s390die_chain, val, &args);
+}
+
+#endif
diff -Nurp linux-2.6.17-git25/include/asm-s390/kprobes.h linux-2.6.17-git25-kp390/include/asm-s390/kprobes.h
--- linux-2.6.17-git25/include/asm-s390/kprobes.h	1969-12-31 19:00:00.000000000 -0500
+++ linux-2.6.17-git25-kp390/include/asm-s390/kprobes.h	2006-07-08 13:39:00.000000000 -0400
@@ -0,0 +1,111 @@
+#ifndef _ASM_S390_KPROBES_H
+#define _ASM_S390_KPROBES_H
+/*
+ *  Kernel Probes (KProbes)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2002, 2006
+ *
+ * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
+ *		Probes initial implementation ( includes suggestions from
+ *		Rusty Russell).
+ * 2004-Nov	Modified for PPC64 by Ananth N Mavinakayanahalli
+ *		<ananth@in.ibm.com>
+ * 2005-Dec	Used as a template for s390 by Mike Grundy
+ * 		<grundym@us.ibm.com>
+ */
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/percpu.h>
+
+#define  __ARCH_WANT_KPROBES_INSN_SLOT
+struct pt_regs;
+struct kprobe;
+
+typedef u16 kprobe_opcode_t;
+#define BREAKPOINT_INSTRUCTION	0x0002
+
+/* Maximum instruction size is 3 (16bit) halfwords: */
+#define MAX_INSN_SIZE		0x0003
+#define MAX_STACK_SIZE 		64
+#define MIN_STACK_SIZE(ADDR) (((MAX_STACK_SIZE) < \
+	(((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR))) \
+	? (MAX_STACK_SIZE) \
+	: (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
+
+#define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)((func_descr_t *)pentry)
+
+#define ARCH_SUPPORTS_KRETPROBES
+#define  ARCH_INACTIVE_KPROBE_COUNT 0
+
+#define KPROBE_SWAP_INST	0x10
+
+#define FIXUP_PSW_NORMAL	0x08
+#define FIXUP_BRANCH_NOT_TAKEN	0x04
+#define FIXUP_RETURN_REGISTER	0x02
+#define FIXUP_NOT_REQUIRED	0x01
+
+/* Architecture specific copy of original instruction */
+struct arch_specific_insn {
+	/* copy of original instruction */
+	kprobe_opcode_t *insn;
+	int fixup;
+	int ilen;
+	int reg;
+};
+
+struct ins_replace_args {
+	kprobe_opcode_t *ptr;
+	kprobe_opcode_t old;
+	kprobe_opcode_t new;
+};
+struct prev_kprobe {
+	struct kprobe *kp;
+	unsigned long status;
+	unsigned long saved_psw;
+	unsigned long kprobe_saved_imask;
+	unsigned long kprobe_saved_ctl[3];
+};
+
+/* per-cpu kprobe control block */
+struct kprobe_ctlblk {
+	unsigned long kprobe_status;
+	unsigned long kprobe_saved_imask;
+	unsigned long kprobe_saved_ctl[3];
+	struct pt_regs jprobe_saved_regs;
+	unsigned long jprobe_saved_r14;
+	unsigned long jprobe_saved_r15;
+	struct prev_kprobe prev_kprobe;
+	kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE];
+};
+
+void arch_remove_kprobe(struct kprobe *p);
+void kretprobe_trampoline(void);
+int  is_prohibited_opcode(kprobe_opcode_t *instruction);
+void get_instruction_type(struct arch_specific_insn *ainsn);
+#endif	/* _ASM_S390_KPROBES_H */
+
+#ifdef CONFIG_KPROBES
+
+extern int kprobe_exceptions_notify(struct notifier_block *self,
+					unsigned long val, void *data);
+#else	/* !CONFIG_KPROBES */
+static inline int kprobe_exceptions_notify(struct notifier_block *self,
+						unsigned long val, void *data)
+{
+	return 0;
+}
+#endif

Re: [PATCH] kprobes for s390 architecture

[Mike Grundy]

On Sat, Jul 08, 2006 at 02:54:28PM -0400, Michael Grundy wrote:
> The latest patch is attached.

Yeah, I wasn't paying attention, the 2.6.18-rc1 version is attached, no 
difference really (other than testing it with the -rc1 code)

Thanks
Mike

--

Signed-off-by: Michael Grundy <grundym@us.ibm.com>

 arch/s390/Kconfig              |   14
 arch/s390/kernel/Makefile      |    1
 arch/s390/kernel/entry.S       |   12
 arch/s390/kernel/entry64.S     |   12
 arch/s390/kernel/kprobes.c     |  692 +++++++++++++++++++++++++++++++++++++++++
 arch/s390/kernel/traps.c       |   42 ++
 arch/s390/kernel/vmlinux.lds.S |    1
 arch/s390/mm/fault.c           |   40 ++
 include/asm-s390/kdebug.h      |   57 +++
 include/asm-s390/kprobes.h     |  111 ++++++
 10 files changed, 976 insertions(+), 6 deletions(-)

diff -Nurp linux-2.6.18-rc1/arch/s390/Kconfig linux-2.6.18-rc1-kp390/arch/s390/Kconfig
--- linux-2.6.18-rc1/arch/s390/Kconfig	2006-07-06 00:09:49.000000000 -0400
+++ linux-2.6.18-rc1-kp390/arch/s390/Kconfig	2006-07-08 15:07:32.000000000 -0400
@@ -490,8 +490,22 @@ source "drivers/net/Kconfig"
 
 source "fs/Kconfig"
 
+menu "Instrumentation Support"
+	depends on EXPERIMENTAL
+
 source "arch/s390/oprofile/Kconfig"
 
+config KPROBES
+	bool "Kprobes (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && MODULES
+	help
+	  Kprobes allows you to trap at almost any kernel address and
+	  execute a callback function.  register_kprobe() establishes
+	  a probepoint and specifies the callback.  Kprobes is useful
+	  for kernel debugging, non-intrusive instrumentation and testing.
+	  If in doubt, say "N".
+endmenu
+
 source "arch/s390/Kconfig.debug"
 
 source "security/Kconfig"
diff -Nurp linux-2.6.18-rc1/arch/s390/kernel/entry64.S linux-2.6.18-rc1-kp390/arch/s390/kernel/entry64.S
--- linux-2.6.18-rc1/arch/s390/kernel/entry64.S	2006-07-06 00:09:49.000000000 -0400
+++ linux-2.6.18-rc1-kp390/arch/s390/kernel/entry64.S	2006-07-08 15:07:32.000000000 -0400
@@ -518,6 +518,8 @@ pgm_no_vtime2:
 #endif
 	lg	%r9,__LC_THREAD_INFO	# load pointer to thread_info struct
 	lg	%r1,__TI_task(%r9)
+	tm	__LC_PGM_OLD_PSW+1(%r15),0x01	# kernel per event ?
+	jz	kernel_per
 	mvc	__THREAD_per+__PER_atmid(2,%r1),__LC_PER_ATMID
 	mvc	__THREAD_per+__PER_address(8,%r1),__LC_PER_ADDRESS
 	mvc	__THREAD_per+__PER_access_id(1,%r1),__LC_PER_ACCESS_ID
@@ -553,6 +555,16 @@ pgm_no_vtime3:
 	stosm	__SF_EMPTY(%r15),0x03	# reenable interrupts
 	j	sysc_do_svc
 
+#
+# per was called from kernel, must be kprobes
+#
+kernel_per:
+	lhi	%r0,__LC_PGM_OLD_PSW
+	sth	%r0,SP_TRAP(%r15)	# set trap indication to pgm check
+	la	%r2,SP_PTREGS(%r15)	# address of register-save area
+	larl	%r14,sysc_leave		# load adr. of system ret, no work
+	jg	do_single_step		# branch to do_single_step
+
 /*
  * IO interrupt handler routine
  */
diff -Nurp linux-2.6.18-rc1/arch/s390/kernel/entry.S linux-2.6.18-rc1-kp390/arch/s390/kernel/entry.S
--- linux-2.6.18-rc1/arch/s390/kernel/entry.S	2006-07-06 00:09:49.000000000 -0400
+++ linux-2.6.18-rc1-kp390/arch/s390/kernel/entry.S	2006-07-08 15:07:32.000000000 -0400
@@ -505,6 +505,8 @@ pgm_no_vtime2:
 	mvc	__THREAD_per+__PER_address(4,%r1),__LC_PER_ADDRESS
 	mvc	__THREAD_per+__PER_access_id(1,%r1),__LC_PER_ACCESS_ID
 	oi	__TI_flags+3(%r9),_TIF_SINGLE_STEP # set TIF_SINGLE_STEP
+	tm	__LC_PGM_OLD_PSW+1(%r15),0x01	# kernel per event ?
+	bz	BASED(kernel_per)
 	l	%r3,__LC_PGM_ILC	 # load program interruption code
 	la	%r8,0x7f
 	nr	%r8,%r3                  # clear per-event-bit and ilc
@@ -536,6 +538,16 @@ pgm_no_vtime3:
 	stosm	__SF_EMPTY(%r15),0x03	# reenable interrupts
 	b	BASED(sysc_do_svc)
 
+#
+# per was called from kernel, must be kprobes
+#
+kernel_per:
+	mvi	SP_TRAP+1(%r15),0x28	# set trap indication to pgm check
+	la	%r2,SP_PTREGS(%r15)	# address of register-save area
+	l	%r1,BASED(.Lhandle_per)	# load adr. of per handler
+	la	%r14,BASED(sysc_leave)	# load adr. of system return
+	br	%r1			# branch to do_single_step
+
 /*
  * IO interrupt handler routine
  */
diff -Nurp linux-2.6.18-rc1/arch/s390/kernel/kprobes.c linux-2.6.18-rc1-kp390/arch/s390/kernel/kprobes.c
--- linux-2.6.18-rc1/arch/s390/kernel/kprobes.c	1969-12-31 19:00:00.000000000 -0500
+++ linux-2.6.18-rc1-kp390/arch/s390/kernel/kprobes.c	2006-07-08 15:07:32.000000000 -0400
@@ -0,0 +1,692 @@
+/*
+ *  Kernel Probes (KProbes)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2002, 2006
+ *
+ * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
+ */
+
+#include <linux/config.h>
+#include <linux/kprobes.h>
+#include <linux/ptrace.h>
+#include <linux/preempt.h>
+#include <linux/stop_machine.h>
+#include <asm/cacheflush.h>
+#include <asm/kdebug.h>
+#include <asm/sections.h>
+#include <asm/uaccess.h>
+#include <linux/module.h>
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+int __kprobes arch_prepare_kprobe(struct kprobe *p)
+{
+	/* Make sure the probe isn't going on a difficult instruction */
+	if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
+		return -EINVAL;
+
+	if ((unsigned long)p->addr & 0x01) {
+		printk("Attempt to register kprobe at an unaligned address\n");
+		return -EINVAL;
+		}
+
+	/* Use the get_insn_slot() facility for correctness */
+	if (!(p->ainsn.insn = get_insn_slot()))
+		return -ENOMEM;
+
+	memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+
+	get_instruction_type(&p->ainsn);
+	p->opcode = *p->addr;
+	return 0;
+}
+
+int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
+{
+	switch (*(__u8 *) instruction) {
+	case 0x0c:      /* bassm */
+	case 0x0b:      /* bsm   */
+	case 0x83:      /* diag  */
+	case 0x44:      /* ex    */
+		return -EINVAL;
+	}
+	switch (*(__u16 *) instruction) {
+	case 0x0101:    /* pr    */
+	case 0xb25a:    /* bsa   */
+	case 0xb240:    /* bakr  */
+	case 0xb258:    /* bsg   */
+	case 0xb218:    /* pc    */
+	case 0xb228:    /* pt    */
+		return -EINVAL;
+	}
+	return 0;
+}
+
+void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
+{
+	/* default fixup method */
+	ainsn->fixup = FIXUP_PSW_NORMAL;
+
+	/* save r1 operand */
+	ainsn->reg = *(__u8 *) (ainsn->insn + 1) & 0xf0;
+
+	/* save the instruction length (pop 5-5) in bytes */
+	switch (*(__u8 *) (ainsn->insn) >> 4) {
+	case 0:
+		ainsn->ilen = 2;
+		break;
+	case 1:
+	case 2:
+		ainsn->ilen = 4;
+		break;
+	case 3:
+		ainsn->ilen = 6;
+		break;
+	}
+
+	switch (*(__u8 *) ainsn->insn) {
+	case 0x05:	/* balr	*/
+	case 0x0d:	/* basr */
+		ainsn->fixup = FIXUP_RETURN_REGISTER;
+		/* if r2 = 0, no branch will be taken */
+		if ((*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0)
+			ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
+		break;
+	case 0x06:	/* bctr	*/
+	case 0x07:	/* bcr	*/
+		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		break;
+	case 0x45:	/* bal	*/
+	case 0x4d:	/* bas	*/
+		ainsn->fixup = FIXUP_RETURN_REGISTER;
+		break;
+	case 0x47:	/* bc	*/
+	case 0x46:	/* bct	*/
+	case 0x86:	/* bxh	*/
+	case 0x87:	/* bxle	*/
+		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		break;
+	case 0x82:	/* lpsw	*/
+		ainsn->fixup = FIXUP_NOT_REQUIRED;
+		break;
+	case 0xb2:	/* lpswe */
+		if (*(__u8 *) (ainsn->insn + 1) == 0xb2) {
+			ainsn->fixup = FIXUP_NOT_REQUIRED;
+		}
+		break;
+	case 0xa7:	/* bras	*/
+		if ((*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0x05) {
+			ainsn->fixup = FIXUP_RETURN_REGISTER;
+		}
+		break;
+	case 0xc0:
+		if ((*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0x00 ||    /*larl */
+			(*(__u8 *) (ainsn->insn + 1) & 0x0f) == 0x05){ /*brasl*/
+			ainsn->fixup = FIXUP_RETURN_REGISTER;
+		}
+		break;
+	case 0xeb:
+		if (*(__u8 *) (ainsn->insn + 5) == 0x44 ||	/* bxhg  */
+			*(__u8 *) (ainsn->insn + 5) == 0x45) {	/* bxleg */
+			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		}
+		break;
+	case 0xe3:	/* bctg	*/
+		if (*(__u8 *) (ainsn->insn + 5) == 0x46) {
+			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+		}
+		break;
+	}
+}
+static int __kprobes swap_instruction(void *aref)
+{
+	unsigned long addr, prev, tmp;
+	int shift;
+	struct ins_replace_args *args = aref;
+
+	addr = (unsigned long) args->ptr;
+	shift = (2 ^ (addr & 2)) << 3;
+	addr ^= addr & 2;
+	asm volatile(
+		"    l   %0,0(%4)\n"
+		"    nr  %0,%5\n"
+                "    lr  %1,%0\n"
+		"    or  %0,%2\n"
+		"    or  %1,%3\n"
+		"0:  cs  %0,%1,0(%4)\n"
+		"    jnl 1f\n"
+		"    xr  %1,%0\n"
+		"    nr  %1,%5\n"
+		"    jnz 0b\n"
+		"1:"
+#ifndef __s390x__
+		".section .fixup,\"ax\"\n"
+		"2: lhi    %0,%6\n"
+		"   bras   1,3f\n"
+		"   .long  1b\n"
+		"3: l      1,0(1)\n"
+		"   br     1\n"
+		".previous\n"
+		".section __ex_table,\"a\"\n"
+		"   .align 4\n"
+		"   .long  0b,2b\n"
+		".previous"
+#else /* __s390x__ */
+		".section .fixup,\"ax\"\n"
+		"2: lghi   %0,%6\n"
+		"   jg     1b\n"
+		".previous\n"
+		".section __ex_table,\"a\"\n"
+		"   .align 8\n"
+		"   .quad  0b,2b\n"
+		".previous"
+#endif /* __s390x__ */
+		: "=&d" (prev), "=&d" (tmp)
+		: "d" (args->old << shift), "d" (args->new << shift),
+		  "a" (args->ptr), "d" (~(65535 << shift)), "K" (-EFAULT)
+		: "memory", "cc" );
+	return prev >> shift;
+}
+
+void __kprobes arch_arm_kprobe(struct kprobe *p)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long status = kcb->kprobe_status;
+	struct ins_replace_args args;
+
+	args.ptr = p->addr;
+	args.old = p->opcode;
+	args.new = BREAKPOINT_INSTRUCTION;
+
+	kcb->kprobe_status = KPROBE_SWAP_INST;
+	stop_machine_run(swap_instruction, &args, NR_CPUS);
+	kcb->kprobe_status = status;
+}
+
+void __kprobes arch_disarm_kprobe(struct kprobe *p)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long status = kcb->kprobe_status;
+	struct ins_replace_args args;
+
+	args.ptr = p->addr;
+	args.old = BREAKPOINT_INSTRUCTION;
+	args.new = p->opcode;
+
+	kcb->kprobe_status = KPROBE_SWAP_INST;
+	stop_machine_run(swap_instruction, &args, NR_CPUS);
+	kcb->kprobe_status = status;
+}
+
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+	mutex_lock(&kprobe_mutex);
+	free_insn_slot(p->ainsn.insn);
+	mutex_unlock(&kprobe_mutex);
+}
+
+static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+	per_cr_bits kprobe_per_regs[1];
+
+	memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
+	regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
+
+	/* Set up the per control reg info, will pass to lctl */
+	kprobe_per_regs[0].em_instruction_fetch = 1;
+	kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
+	kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
+
+	/* Set the PER control regs, turns on single step for this address */
+	__ctl_load(kprobe_per_regs, 9, 11);
+	regs->psw.mask |= PSW_MASK_PER;
+	regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
+}
+
+static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	kcb->prev_kprobe.kp = kprobe_running();
+	kcb->prev_kprobe.status = kcb->kprobe_status;
+	kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
+	memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
+					sizeof(kcb->kprobe_saved_ctl));
+}
+
+static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
+	kcb->kprobe_status = kcb->prev_kprobe.status;
+	kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
+	memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
+					sizeof(kcb->kprobe_saved_ctl));
+}
+
+static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
+						struct kprobe_ctlblk *kcb)
+{
+	__get_cpu_var(current_kprobe) = p;
+	/* Save the interrupt and per flags */
+	kcb->kprobe_saved_imask = regs->psw.mask &
+	    (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
+	/* Save the control regs that govern PER */
+	__ctl_store(kcb->kprobe_saved_ctl, 9, 11);
+}
+
+/* Called with kretprobe_lock held */
+void __kprobes 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->gprs[14];
+
+		/* Replace the return addr with trampoline addr */
+		regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
+
+		add_rp_inst(ri);
+	} else {
+		rp->nmissed++;
+	}
+}
+
+static int __kprobes kprobe_handler(struct pt_regs *regs)
+{
+	struct kprobe *p;
+	int ret = 0;
+	unsigned long *addr = (unsigned long *)
+		((regs->psw.addr & PSW_ADDR_INSN) - 2);
+	struct kprobe_ctlblk *kcb;
+
+	/*
+	 * We don't want to be preempted for the entire
+	 * duration of kprobe processing
+	 */
+	preempt_disable();
+	kcb = get_kprobe_ctlblk();
+
+	/* Check we're not actually recursing */
+	if (kprobe_running()) {
+		p = get_kprobe(addr);
+		if (p) {
+			if (kcb->kprobe_status == KPROBE_HIT_SS &&
+			    *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
+				regs->psw.mask &= ~PSW_MASK_PER;
+				regs->psw.mask |= kcb->kprobe_saved_imask;
+				goto no_kprobe;
+			}
+			/* We have reentered the kprobe_handler(), since
+			 * another probe was hit while within the handler.
+			 * We here save the original kprobes variables and
+			 * just single step on the instruction of the new probe
+			 * without calling any user handlers.
+			 */
+			save_previous_kprobe(kcb);
+			set_current_kprobe(p, regs, kcb);
+			kprobes_inc_nmissed_count(p);
+			prepare_singlestep(p, regs);
+			kcb->kprobe_status = KPROBE_REENTER;
+			return 1;
+		} else {
+			p = __get_cpu_var(current_kprobe);
+			if (p->break_handler && p->break_handler(p, regs)) {
+				goto ss_probe;
+			}
+		}
+		goto no_kprobe;
+	}
+
+	p = get_kprobe(addr);
+	if (!p) {
+		if (*addr != BREAKPOINT_INSTRUCTION) {
+			/*
+			 * The breakpoint instruction was removed right
+			 * after we hit it.  Another cpu has removed
+			 * either a probepoint or a debugger breakpoint
+			 * at this address.  In either case, no further
+			 * handling of this interrupt is appropriate.
+			 *
+			 */
+			ret = 1;
+		}
+		/* Not one of ours: let kernel handle it */
+		goto no_kprobe;
+	}
+
+	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+	set_current_kprobe(p, regs, kcb);
+	if (p->pre_handler && p->pre_handler(p, regs))
+		/* handler has already set things up, so skip ss setup */
+		return 1;
+
+ss_probe:
+	prepare_singlestep(p, regs);
+	kcb->kprobe_status = KPROBE_HIT_SS;
+	return 1;
+
+no_kprobe:
+	preempt_enable_no_resched();
+	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" "bcr 0,0\n");
+}
+
+/*
+ * Called when the probe at kretprobe trampoline is hit
+ */
+int __kprobes 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 flags, orig_ret_address = 0;
+	unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
+
+	spin_lock_irqsave(&kretprobe_lock, flags);
+	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->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
+
+	reset_current_kprobe();
+	spin_unlock_irqrestore(&kretprobe_lock, flags);
+	preempt_enable_no_resched();
+
+	/*
+	 * By returning a non-zero value, we are telling
+	 * kprobe_handler() that we don't want the post_handler
+	 * to run (and have re-enabled preemption)
+	 */
+	return 1;
+}
+
+/*
+ * Called after single-stepping.  p->addr is the address of the
+ * instruction whose first byte has been replaced by the "breakpoint"
+ * instruction.  To avoid the SMP problems that can occur when we
+ * temporarily put back the original opcode to single-step, we
+ * single-stepped a copy of the instruction.  The address of this
+ * copy is p->ainsn.insn.
+ */
+static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	regs->psw.addr &= PSW_ADDR_INSN;
+
+	if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
+		regs->psw.addr = (unsigned long)p->addr +
+				((unsigned long)regs->psw.addr -
+				 (unsigned long)p->ainsn.insn);
+
+	if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
+		if ((unsigned long)regs->psw.addr -
+		    (unsigned long)p->ainsn.insn == p->ainsn.ilen)
+			regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
+
+	if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
+		regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
+						(regs->gprs[p->ainsn.reg] -
+						(unsigned long)p->ainsn.insn))
+						| PSW_ADDR_AMODE;
+
+	regs->psw.addr |= PSW_ADDR_AMODE;
+	/* turn off PER mode */
+	regs->psw.mask &= ~PSW_MASK_PER;
+	/* Restore the original per control regs */
+	__ctl_load(kcb->kprobe_saved_ctl, 9, 11);
+	regs->psw.mask |= kcb->kprobe_saved_imask;
+}
+
+static int __kprobes post_kprobe_handler(struct pt_regs *regs)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	if (!cur)
+		return 0;
+
+	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
+		kcb->kprobe_status = KPROBE_HIT_SSDONE;
+		cur->post_handler(cur, regs, 0);
+	}
+
+	resume_execution(cur, regs);
+
+	/*Restore back the original saved kprobes variables and continue. */
+	if (kcb->kprobe_status == KPROBE_REENTER) {
+		restore_previous_kprobe(kcb);
+		goto out;
+	}
+	reset_current_kprobe();
+out:
+	preempt_enable_no_resched();
+
+	/*
+	 * if somebody else is singlestepping across a probe point, psw mask
+	 * will have PER set, in which case, continue the remaining processing
+	 * of do_single_step, as if this is not a probe hit.
+	 */
+	if (regs->psw.mask & PSW_MASK_PER) {
+		return 0;
+	}
+
+	return 1;
+}
+
+static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	const struct exception_table_entry *entry;
+
+	switch(kcb->kprobe_status) {
+	case KPROBE_SWAP_INST:
+		/* We are here because the instruction replacement failed */
+		return 0;
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		/*
+		 * We are here because the instruction being single
+		 * stepped caused a page fault. We reset the current
+		 * kprobe and the nip points back to the probe address
+		 * and allow the page fault handler to continue as a
+		 * normal page fault.
+		 */
+		regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
+		regs->psw.mask &= ~PSW_MASK_PER;
+		regs->psw.mask |= kcb->kprobe_saved_imask;
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			restore_previous_kprobe(kcb);
+		else
+			reset_current_kprobe();
+		preempt_enable_no_resched();
+		break;
+	case KPROBE_HIT_ACTIVE:
+	case KPROBE_HIT_SSDONE:
+		/*
+		 * We increment the nmissed count for accounting,
+		 * we can also use npre/npostfault count for accouting
+		 * these specific fault cases.
+		 */
+		kprobes_inc_nmissed_count(cur);
+
+		/*
+		 * We come here because instructions in the pre/post
+		 * handler caused the page_fault, this could happen
+		 * if handler tries to access user space by
+		 * copy_from_user(), get_user() etc. Let the
+		 * user-specified handler try to fix it first.
+		 */
+		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
+			return 1;
+
+		/*
+		 * In case the user-specified fault handler returned
+		 * zero, try to fix up.
+		 */
+		entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
+		if (entry) {
+			regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
+			return 1;
+		}
+
+		/*
+		 * fixup_exception() could not handle it,
+		 * Let do_page_fault() fix it.
+		 */
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
+/*
+ * Wrapper routine to for handling exceptions.
+ */
+int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
+				       unsigned long val, void *data)
+{
+	struct die_args *args = (struct die_args *)data;
+	int ret = NOTIFY_DONE;
+
+	switch (val) {
+	case DIE_BPT:
+		if (kprobe_handler(args->regs))
+			ret = NOTIFY_STOP;
+		break;
+	case DIE_SSTEP:
+		if (post_kprobe_handler(args->regs))
+			ret = NOTIFY_STOP;
+		break;
+	case DIE_TRAP:
+	case DIE_PAGE_FAULT:
+		/* kprobe_running() needs smp_processor_id() */
+		preempt_disable();
+		if (kprobe_running() &&
+		    kprobe_fault_handler(args->regs, args->trapnr))
+			ret = NOTIFY_STOP;
+		preempt_enable();
+		break;
+	default:
+		break;
+	}
+	return ret;
+}
+
+int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct jprobe *jp = container_of(p, struct jprobe, kp);
+	unsigned long addr;
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
+
+	/* setup return addr to the jprobe handler routine */
+	regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;
+
+	/* r14 is the function return address */
+	kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
+	/* r15 is the stack pointer */
+	kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
+	addr = (unsigned long)kcb->jprobe_saved_r15;
+
+	memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
+	       MIN_STACK_SIZE(addr));
+	return 1;
+}
+
+void __kprobes jprobe_return(void)
+{
+	asm volatile (".word 0x0002");
+}
+
+void __kprobes jprobe_return_end(void)
+{
+	asm volatile ("bcr 0,0");
+}
+
+int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);
+
+	/* Put the regs back */
+	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
+	/* put the stack back */
+	memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
+	       MIN_STACK_SIZE(stack_addr));
+	preempt_enable_no_resched();
+	return 1;
+}
+
+static struct kprobe trampoline_p = {
+	.addr = (kprobe_opcode_t *) & kretprobe_trampoline,
+	.pre_handler = trampoline_probe_handler
+};
+
+int __init arch_init_kprobes(void)
+{
+	return register_kprobe(&trampoline_p);
+}
diff -Nurp linux-2.6.18-rc1/arch/s390/kernel/Makefile linux-2.6.18-rc1-kp390/arch/s390/kernel/Makefile
--- linux-2.6.18-rc1/arch/s390/kernel/Makefile	2006-07-06 00:09:49.000000000 -0400
+++ linux-2.6.18-rc1-kp390/arch/s390/kernel/Makefile	2006-07-08 15:07:32.000000000 -0400
@@ -22,6 +22,7 @@ obj-$(CONFIG_BINFMT_ELF32)	+= binfmt_elf
 
 obj-$(CONFIG_VIRT_TIMER)	+= vtime.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
+obj-$(CONFIG_KPROBES)		+= kprobes.o
 
 # Kexec part
 S390_KEXEC_OBJS := machine_kexec.o crash.o
diff -Nurp linux-2.6.18-rc1/arch/s390/kernel/traps.c linux-2.6.18-rc1-kp390/arch/s390/kernel/traps.c
--- linux-2.6.18-rc1/arch/s390/kernel/traps.c	2006-07-06 00:09:49.000000000 -0400
+++ linux-2.6.18-rc1-kp390/arch/s390/kernel/traps.c	2006-07-08 15:07:32.000000000 -0400
@@ -29,6 +29,7 @@
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/reboot.h>
+#include <linux/kprobes.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -39,6 +40,7 @@
 #include <asm/s390_ext.h>
 #include <asm/lowcore.h>
 #include <asm/debug.h>
+#include <asm/kdebug.h>
 
 /* Called from entry.S only */
 extern void handle_per_exception(struct pt_regs *regs);
@@ -74,6 +76,20 @@ static int kstack_depth_to_print = 12;
 static int kstack_depth_to_print = 20;
 #endif /* CONFIG_64BIT */
 
+ATOMIC_NOTIFIER_HEAD(s390die_chain);
+
+int register_die_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_register(&s390die_chain, nb);
+}
+EXPORT_SYMBOL(register_die_notifier);
+
+int unregister_die_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_unregister(&s390die_chain, nb);
+}
+EXPORT_SYMBOL(unregister_die_notifier);
+
 /*
  * For show_trace we have tree different stack to consider:
  *   - the panic stack which is used if the kernel stack has overflown
@@ -305,8 +321,9 @@ report_user_fault(long interruption_code
 #endif
 }
 
-static void inline do_trap(long interruption_code, int signr, char *str,
-                           struct pt_regs *regs, siginfo_t *info)
+static void __kprobes inline do_trap(long interruption_code, int signr,
+					char *str, struct pt_regs *regs,
+					siginfo_t *info)
 {
 	/*
 	 * We got all needed information from the lowcore and can
@@ -315,6 +332,10 @@ static void inline do_trap(long interrup
         if (regs->psw.mask & PSW_MASK_PSTATE)
 		local_irq_enable();
 
+	if (notify_die(DIE_TRAP, str, regs, interruption_code,
+				interruption_code, signr) == NOTIFY_STOP)
+		return;
+
         if (regs->psw.mask & PSW_MASK_PSTATE) {
                 struct task_struct *tsk = current;
 
@@ -336,8 +357,12 @@ static inline void *get_check_address(st
 	return (void *)((regs->psw.addr-S390_lowcore.pgm_ilc) & PSW_ADDR_INSN);
 }
 
-void do_single_step(struct pt_regs *regs)
+void __kprobes do_single_step(struct pt_regs *regs)
 {
+	if (notify_die(DIE_SSTEP, "sstep", regs, 0, 0,
+					SIGTRAP) == NOTIFY_STOP){
+		return;
+	}
 	if ((current->ptrace & PT_PTRACED) != 0)
 		force_sig(SIGTRAP, current);
 }
@@ -463,8 +488,15 @@ asmlinkage void illegal_op(struct pt_reg
 #endif
 		} else
 			signal = SIGILL;
-	} else
-		signal = SIGILL;
+	} else {
+		/*
+		 * If we get an illegal op in kernel mode, send it through the
+		 * kprobes notifier. If kprobes doesn't pick it up, SIGILL
+		 */
+		if (notify_die(DIE_BPT, "bpt", regs, interruption_code,
+					3, SIGTRAP) != NOTIFY_STOP)
+			signal = SIGILL;
+	}
 
 #ifdef CONFIG_MATHEMU
         if (signal == SIGFPE)
diff -Nurp linux-2.6.18-rc1/arch/s390/kernel/vmlinux.lds.S linux-2.6.18-rc1-kp390/arch/s390/kernel/vmlinux.lds.S
--- linux-2.6.18-rc1/arch/s390/kernel/vmlinux.lds.S	2006-07-06 00:09:49.000000000 -0400
+++ linux-2.6.18-rc1-kp390/arch/s390/kernel/vmlinux.lds.S	2006-07-08 15:07:32.000000000 -0400
@@ -24,6 +24,7 @@ SECTIONS
 	*(.text)
 	SCHED_TEXT
 	LOCK_TEXT
+	KPROBES_TEXT
 	*(.fixup)
 	*(.gnu.warning)
 	} = 0x0700
diff -Nurp linux-2.6.18-rc1/arch/s390/mm/fault.c linux-2.6.18-rc1-kp390/arch/s390/mm/fault.c
--- linux-2.6.18-rc1/arch/s390/mm/fault.c	2006-07-06 00:09:49.000000000 -0400
+++ linux-2.6.18-rc1-kp390/arch/s390/mm/fault.c	2006-07-08 15:07:32.000000000 -0400
@@ -25,10 +25,12 @@
 #include <linux/console.h>
 #include <linux/module.h>
 #include <linux/hardirq.h>
+#include <linux/kprobes.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
+#include <asm/kdebug.h>
 
 #ifndef CONFIG_64BIT
 #define __FAIL_ADDR_MASK 0x7ffff000
@@ -48,6 +50,38 @@ extern int sysctl_userprocess_debug;
 
 extern void die(const char *,struct pt_regs *,long);
 
+#ifdef CONFIG_KPROBES
+ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
+int register_page_fault_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
+}
+
+int unregister_page_fault_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
+}
+
+static inline int notify_page_fault(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	struct die_args args = {
+		.regs = regs,
+		.str = str,
+		.err = err,
+		.trapnr = trap,
+		.signr = sig
+	};
+	return atomic_notifier_call_chain(&notify_page_fault_chain, val, &args);
+}
+#else
+static inline int notify_page_fault(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	return NOTIFY_DONE;
+}
+#endif
+
 extern spinlock_t timerlist_lock;
 
 /*
@@ -159,7 +193,7 @@ static void do_sigsegv(struct pt_regs *r
  *   11       Page translation     ->  Not present       (nullification)
  *   3b       Region third trans.  ->  Not present       (nullification)
  */
-static inline void
+static inline void __kprobes
 do_exception(struct pt_regs *regs, unsigned long error_code, int is_protection)
 {
         struct task_struct *tsk;
@@ -173,6 +207,10 @@ do_exception(struct pt_regs *regs, unsig
         tsk = current;
         mm = tsk->mm;
 	
+	if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
+					SIGSEGV) == NOTIFY_STOP)
+		return;
+
 	/* 
          * Check for low-address protection.  This needs to be treated
 	 * as a special case because the translation exception code 
diff -Nurp linux-2.6.18-rc1/include/asm-s390/kdebug.h linux-2.6.18-rc1-kp390/include/asm-s390/kdebug.h
--- linux-2.6.18-rc1/include/asm-s390/kdebug.h	1969-12-31 19:00:00.000000000 -0500
+++ linux-2.6.18-rc1-kp390/include/asm-s390/kdebug.h	2006-07-08 15:07:32.000000000 -0400
@@ -0,0 +1,57 @@
+#ifndef _S390_KDEBUG_H
+#define _S390_KDEBUG_H
+
+/*
+ * Feb 2006 Ported to s390 <grundym@us.ibm.com>
+ */
+#include <linux/notifier.h>
+
+struct pt_regs;
+
+struct die_args {
+	struct pt_regs *regs;
+	const char *str;
+	long err;
+	int trapnr;
+	int signr;
+};
+
+/* Note - you should never unregister because that can race with NMIs.
+ * If you really want to do it first unregister - then synchronize_sched
+ *  - then free.
+ */
+extern int register_die_notifier(struct notifier_block *);
+extern int unregister_die_notifier(struct notifier_block *);
+extern struct atomic_notifier_head s390die_chain;
+
+
+enum die_val {
+	DIE_OOPS = 1,
+	DIE_BPT,
+	DIE_SSTEP,
+	DIE_PANIC,
+	DIE_NMI,
+	DIE_DIE,
+	DIE_NMIWATCHDOG,
+	DIE_KERNELDEBUG,
+	DIE_TRAP,
+	DIE_GPF,
+	DIE_CALL,
+	DIE_NMI_IPI,
+	DIE_PAGE_FAULT,
+};
+
+static inline int notify_die(enum die_val val, const char *str,
+			struct pt_regs *regs, long err, int trap, int sig)
+{
+	struct die_args args = {
+		.regs = regs,
+		.str = str,
+		.err = err,
+		.trapnr = trap,
+		.signr = sig
+	};
+	return atomic_notifier_call_chain(&s390die_chain, val, &args);
+}
+
+#endif
diff -Nurp linux-2.6.18-rc1/include/asm-s390/kprobes.h linux-2.6.18-rc1-kp390/include/asm-s390/kprobes.h
--- linux-2.6.18-rc1/include/asm-s390/kprobes.h	1969-12-31 19:00:00.000000000 -0500
+++ linux-2.6.18-rc1-kp390/include/asm-s390/kprobes.h	2006-07-08 15:07:32.000000000 -0400
@@ -0,0 +1,111 @@
+#ifndef _ASM_S390_KPROBES_H
+#define _ASM_S390_KPROBES_H
+/*
+ *  Kernel Probes (KProbes)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2002, 2006
+ *
+ * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
+ *		Probes initial implementation ( includes suggestions from
+ *		Rusty Russell).
+ * 2004-Nov	Modified for PPC64 by Ananth N Mavinakayanahalli
+ *		<ananth@in.ibm.com>
+ * 2005-Dec	Used as a template for s390 by Mike Grundy
+ * 		<grundym@us.ibm.com>
+ */
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/percpu.h>
+
+#define  __ARCH_WANT_KPROBES_INSN_SLOT
+struct pt_regs;
+struct kprobe;
+
+typedef u16 kprobe_opcode_t;
+#define BREAKPOINT_INSTRUCTION	0x0002
+
+/* Maximum instruction size is 3 (16bit) halfwords: */
+#define MAX_INSN_SIZE		0x0003
+#define MAX_STACK_SIZE 		64
+#define MIN_STACK_SIZE(ADDR) (((MAX_STACK_SIZE) < \
+	(((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR))) \
+	? (MAX_STACK_SIZE) \
+	: (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
+
+#define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)((func_descr_t *)pentry)
+
+#define ARCH_SUPPORTS_KRETPROBES
+#define  ARCH_INACTIVE_KPROBE_COUNT 0
+
+#define KPROBE_SWAP_INST	0x10
+
+#define FIXUP_PSW_NORMAL	0x08
+#define FIXUP_BRANCH_NOT_TAKEN	0x04
+#define FIXUP_RETURN_REGISTER	0x02
+#define FIXUP_NOT_REQUIRED	0x01
+
+/* Architecture specific copy of original instruction */
+struct arch_specific_insn {
+	/* copy of original instruction */
+	kprobe_opcode_t *insn;
+	int fixup;
+	int ilen;
+	int reg;
+};
+
+struct ins_replace_args {
+	kprobe_opcode_t *ptr;
+	kprobe_opcode_t old;
+	kprobe_opcode_t new;
+};
+struct prev_kprobe {
+	struct kprobe *kp;
+	unsigned long status;
+	unsigned long saved_psw;
+	unsigned long kprobe_saved_imask;
+	unsigned long kprobe_saved_ctl[3];
+};
+
+/* per-cpu kprobe control block */
+struct kprobe_ctlblk {
+	unsigned long kprobe_status;
+	unsigned long kprobe_saved_imask;
+	unsigned long kprobe_saved_ctl[3];
+	struct pt_regs jprobe_saved_regs;
+	unsigned long jprobe_saved_r14;
+	unsigned long jprobe_saved_r15;
+	struct prev_kprobe prev_kprobe;
+	kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE];
+};
+
+void arch_remove_kprobe(struct kprobe *p);
+void kretprobe_trampoline(void);
+int  is_prohibited_opcode(kprobe_opcode_t *instruction);
+void get_instruction_type(struct arch_specific_insn *ainsn);
+#endif	/* _ASM_S390_KPROBES_H */
+
+#ifdef CONFIG_KPROBES
+
+extern int kprobe_exceptions_notify(struct notifier_block *self,
+					unsigned long val, void *data);
+#else	/* !CONFIG_KPROBES */
+static inline int kprobe_exceptions_notify(struct notifier_block *self,
+						unsigned long val, void *data)
+{
+	return 0;
+}
+#endif

Re: [PATCH] kprobes for s390 architecture

[Heiko Carstens]

> +static int __kprobes swap_instruction(void *aref)
> +{
> +	unsigned long addr, prev, tmp;
> +	int shift;
> +	struct ins_replace_args *args = aref;
> +
> +	addr = (unsigned long) args->ptr;
> +	shift = (2 ^ (addr & 2)) << 3;
> +	addr ^= addr & 2;
> +	asm volatile(
> +		"    l   %0,0(%4)\n"
> +		"    nr  %0,%5\n"
> +                "    lr  %1,%0\n"

Whitespace :)

> +		"    or  %0,%2\n"
> +		"    or  %1,%3\n"
> +		"0:  cs  %0,%1,0(%4)\n"
> +		"    jnl 1f\n"
> +		"    xr  %1,%0\n"
> +		"    nr  %1,%5\n"
> +		"    jnz 0b\n"
> +		"1:"
> +#ifndef __s390x__
> +		".section .fixup,\"ax\"\n"
> +		"2: lhi    %0,%6\n"
> +		"   bras   1,3f\n"
> +		"   .long  1b\n"
> +		"3: l      1,0(1)\n"
> +		"   br     1\n"
> +		".previous\n"
> +		".section __ex_table,\"a\"\n"
> +		"   .align 4\n"
> +		"   .long  0b,2b\n"
> +		".previous"
> +#else /* __s390x__ */
> +		".section .fixup,\"ax\"\n"
> +		"2: lghi   %0,%6\n"
> +		"   jg     1b\n"
> +		".previous\n"
> +		".section __ex_table,\"a\"\n"
> +		"   .align 8\n"
> +		"   .quad  0b,2b\n"
> +		".previous"
> +#endif /* __s390x__ */
> +		: "=&d" (prev), "=&d" (tmp)
> +		: "d" (args->old << shift), "d" (args->new << shift),
> +		  "a" (args->ptr), "d" (~(65535 << shift)), "K" (-EFAULT)
> +		: "memory", "cc" );
> +	return prev >> shift;

You need a label behind the cs instruction and put that into the __ex_table,
since the PSW will point to the instruction after cs if it fails.

Also, on failure this function seems to return -EFAULT >> shift, which
seems to be wrong.

> +EXPORT_SYMBOL(register_die_notifier);
> +EXPORT_SYMBOL(unregister_die_notifier);

_GPL?

Re: [PATCH] kprobes for s390 architecture

[Mike Grundy]

On Mon, Jul 10, 2006 at 11:28:52AM +0200, Heiko Carstens wrote:
> Whitespace :)
d'oh.
> You need a label behind the cs instruction and put that into the __ex_table,
> since the PSW will point to the instruction after cs if it fails.
Yeah, thought that was a nullify not a terminate. d'oh. d'oh.

> Also, on failure this function seems to return -EFAULT >> shift, which
> seems to be wrong.
Yeah. I think just returning the value without the shift would be ok. kprobes
never checks to see if the instruction swap was successful (which seems even
more wrong)

> > +EXPORT_SYMBOL(register_die_notifier);
> > +EXPORT_SYMBOL(unregister_die_notifier);
> _GPL?
Makes sense, but I kept it consistent with the rest of kprobes.

-- 
Thanks
Mike

=========================================
Michael Grundy - grundym@us.ibm.com

If at first you don't succeed, call in an air strike.

Re: [PATCH] kprobes for s390 architecture

[Frank Ch. Eigler]

grundym wrote:

> > How fast is this if you have to exchange several hundred instructions?
>
> I'll have to do some timing tests to measure how much overhead it
> puts on the system. It's a trade off of safety vs speed. [...] 

No question, safety has to be paramount.

> The plus side is the swaps are only done on activation and
> deactivation, and don't have this kind of overhead during
> operations. [...]

Even though infrequent, we should nevertheless measure
activation/deactivation times, since it is not hard to insert and
remove thousands of kprobes in a single script.  If those times are on
the order of milliseconds, and if batching them into one operation can
allow sharing of synchronization overhead, then we will need to adopt
that.

- FChE

Re: [PATCH] kprobes for s390 architecture

[Frank Ch. Eigler]

I wrote:

> grundym wrote:
> > I'll have to do some timing tests to measure how much overhead it
> > puts on the system. It's a trade off of safety vs speed. [...] 
> 
> No question, safety has to be paramount.

To elaborate: safety here would mean system stability.  If a method of
probe insertion/removal can be found that does not risk stability,
merely may cause unpredictable early/late probe hits, or gradual
deferred cleanup that would be fine.  For example, it may likely be
fine if different processors on an SMP start or stop to see the kprobe
breakpoints at different times.  A "softer" method analogous to RCU
may work for us here.

- FChE

Re: [PATCH] kprobes for s390 architecture

[Mike Grundy]

On Fri, Jul 07, 2006 at 07:25:55PM +0200, Heiko Carstens wrote:
> > ok, I tried, but my "better ideas" made things worse. stop_machine_run() wins:
> How fast is this if you have to exchange several hundred instructions?

I did a little measuring. On average stop_machine_run() adds 8.7 msec of
overhead on a 4-way config. Of that %57 was sub-msec overhead. For the times
where overhead was measurable, the average was 20.2 msec, lowest at 10msec
highest at 100msec. That's on a z800 under vm and I have no idea how many real
cpus the machine has :-)

-- 
Thanks
Mike

=========================================
Michael Grundy - grundym@us.ibm.com
Advanced Linux Response Team (ALRT)
http://ltc.linux.ibm.com/teamweb/alrt/
845-435-8842 (T/L 295)

If at first you don't succeed, call in an air strike.

Re: [PATCH] kprobes for s390 architecture

[Martin Schwidefsky]

On Tue, 2006-07-11 at 09:54 -0400, Mike Grundy wrote:
> I did a little measuring. On average stop_machine_run() adds 8.7 msec of
> overhead on a 4-way config. Of that %57 was sub-msec overhead. For the times
> where overhead was measurable, the average was 20.2 msec, lowest at 10msec
> highest at 100msec. That's on a z800 under vm and I have no idea how many real
> cpus the machine has :-)

So adding 100 probes will roughly take 1 second. Not too bad, I expected it
to take longer.

-- 
blue skies,
  Martin.

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH

"Reality continues to ruin my life." - Calvin.

Re: [heiko.carstens@de.ibm.com: Re: [PATCH] kprobes for s390 architecture]

[Michael Grundy]

Heiko Carstens <heiko.carstens@de.ibm.com> wrote on 06/23/2006 08:03:44 AM:

> This won't solve anything. What Martin probably meant is something like a
poor
> man's stop_machine_run() implemented by using smp_call_function(). This
way
> you synchronize all cpus and when all cpus are in a known state, you
change
> the instruction in question and make sure that serialization happens
before
> cpus leave the handler again... Except for the cpu that called
> smp_call_function() you get the serialization for free, since the last
> instruction of the handler is always an lpsw/lpswe instruction.
>
> Otherwise there is still the possibility that a different cpu is fetching
the
> instruction concurrently while you change it. This doesn't sound very
good,
> especially if you take this paragraph of the Principles of Operation into
> account (p.5-89 of SA22-7832-04):
>
> "It is possible, if another CPU or a channel program concurrently
modifies
> the instruction, for one CPU to recognize the changes to some but not all
bit
> positions of an instruction."

(link to doc for anyone following along at home:
 http://publibz.boulder.ibm.com/epubs/pdf/a2278324.pdf)

On the same page it says "All copies of a prefetched instruction are
discarded
when: * A serializing function is performed" Would something like this in a
smp_call_function do it? :

bcr 15,0

if (*p->addr != breakpoint_instruction)
      *p->addr = breakpoint_instruction;


Alternatively, if we did a compare and swap on that location (serializing
instruction) would that be acceptable?

Thanks
Michael

=========================================
If at first you don't succeed, call in an air strike.

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