Date:	Thu, 24 May 2012 21:35:52 +0800
From:	Hui Zhu <teawater@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Geoff Levand <geoff@...radead.org>, jason.wessel@...driver.com
Subject: Re: [PATCH]KGTP (Linux Kernel debugger and tracer) lite patch for
 review

On Fri, May 11, 2012 at 1:38 AM, Andi Kleen <andi@...stfloor.org> wrote:
> On Thu, May 10, 2012 at 08:15:36PM +0800, Hui Zhu wrote:
>> On 05/09/12 22:05, Andi Kleen wrote:
>> >Please provide better explanation of the use case for this module.
>> >One paragraph why someone would want it in their kernel.
>>
>> sudo insmod kernel/gtp.ko
>
> Thanks. Please put that into the change log for the next iteration.

OK.  I will add them.

>
>> >>+#ifndef _ASM_ARM_GTP_H_
>> >>+#define _ASM_ARM_GTP_H_
>> >>+
>> >>+#define ULONGEST           uint64_t
>> >
>> >So u64 in kernel. Just use that.
>> >
>> >>+#define CORE_ADDR          unsigned long
>> >
>> >In linux kernel CORE_ADDR is always unsigned long. Use that.
>> >
>>
>> ULONGEST and CORE_ADDR is the type from GDB rsp packet.  I use it to parse
>> the package from GDB.  Then want to add add a new arch to KGTP, just need
>> set this two type same with GDB.  So do you mind I keep it?
>
> I was just aiming to eliminate the asm files. Is that possible?
> If you can't please reuse stuff from kgdb.

I remove them from asm files, and add:
#ifndef ULONGEST
#define ULONGEST		uint64_t
#endif
#ifndef CORE_ADDR
#define CORE_ADDR		unsigned long
#endif
in gtp.c
Then if not need, the arch didn't define ULONGEST and CORE_ADDR for itself.

>
>> OK.  I changed hex2ulongest to simple_strtoull in new patch.
>> But I meet a issue is checkpatch told me that "simple_strtoull is
>> obsolete, use kstrtoull instead".  But kstrtoull cannot get the address
>> that where this convert stop at.  Do you have some comments on it?
>
> Keep using simple_strtoull.  Ignore checkpatch when it's wrong.
>
>> +static inline void
>> +gtp_regs2ascii(struct pt_regs *regs, char *buf)
>> +{
>> +#ifdef CONFIG_32BIT
>
> BITS_PER_LONG == 32 ? Then it would work on other archs and you could
> move it out from asm/

That is hard becuase the different arch's format of reg is so different.
For example ARM and MIPS have a lot of special reg that cannot be converted by a for loop.

After check the code the kgdb, I thought that good ways is use dbg_reg_def of kgdb to convert the reg to gdb rsp format.  But use it directly will make kgtp depend on kgdb.
What I thought is move this part of code out from kgdb, when kgdb or kgtp need, select it too.  But I am not sure Jason is OK with that.

>
>> +#define OUTFORMAT    "%08lx"
>> +#define REGSIZE              8
>> +#define SWAB(a)              ntohl(a)
>> +#else
>> +#define OUTFORMAT    "%016lx"
>> +#define REGSIZE              16
>> +#ifdef __LITTLE_ENDIAN
>> +#define SWAB(a)              swab64(a)
>> +#else
>> +#define SWAB(a)              (a)
>> +#endif
>
> be64_to_cpu()

OK.

>
>> @@ -0,0 +1,914 @@
>> +/*
>> + * Kernel GDB tracepoint module.
>
> add one sentence here what this file does.

OK.

>
>> +     memcpy(&freg->regs, regs, sizeof(struct pt_regs));
>> +#ifdef CONFIG_X86_32
>> +     freg->regs.sp = (unsigned long)&regs->sp;
>> +#endif       /* CONFIG_X86_32 */
>> +#ifdef CONFIG_X86
>> +     freg->regs.ip -= 1;
>> +#endif       /* CONFIG_X86 */
>
> What is that for? - 1?

That is because when kprobe, the ip of X86 point will have a offset with current ip.

>
>> +
>> +static void
>> +gtp_action_release(struct action *ae)
>
> Standard style is type on the same line.

OK.  Fixed them all in the patch.

>
>> +{
>> +     struct action   *ae2;
>> +
>> +     while (ae) {
>> +             ae2 = ae;
>> +             ae = ae->next;
>> +             /* Release ae2.  */
>> +             kfree(ae2);
>> +     }
>
> Better use a list_head from list.h and list_for_each_entry_safe() etc.
> This will simplify some of the list code.

OK.  I changed both gtp_list and action to list_head.

>
>> +static int
>> +gtp_gdbrsp_qtstart(void)
>> +{
>> +     struct gtp_entry        *tpe;
>> +
>> +     if (gtp_start)
>> +             return -EBUSY;
>
> This is in a lot of places. Can you put it somewhere more central?

Sorry I don't understand this part.  Do you want I change all "struct gtp_entry        *tpe;" to "struct gtp_entry *tpe;"?

>> +     if (!gtp_frame) {
>> +             gtp_frame = vmalloc(GTP_FRAME_SIZE);
>> +             if (!gtp_frame)
>> +                     return -ENOMEM;
>> +
>> +             gtp_frame_reset();
>> +     }
>> +
>> +     for (tpe = gtp_list; tpe; tpe = tpe->next) {
>> +             if (tpe->action_list) {
>> +                     int     ret = register_kprobe(&tpe->kp);
>> +                     if (ret < 0) {
>> +                             gtp_gdbrsp_qtstop();
>> +                             return ret;
>
> memory leak with frame?

Use this because I don't want alloc frame each time tracepoint start.
It will be release in gtp_release.

>
>> +     pr_devel("gtp_gdbrsp_QT: %s\n", pkg);
>> +
>> +     if (strcmp("init", pkg) == 0)
>> +             ret = gtp_gdbrsp_qtinit();
>
> This if cascade should be probably a table walk

I cannot find the examle about it in the Kernel, could you give me a example?

>
>> +     else if (strcmp("Stop", pkg) == 0)
>> +             ret = gtp_gdbrsp_qtstop();
>> +
>> +     return ret;
>> +}
>> +
>> +static unsigned char gtp_m_buffer[0xffff];
>
> Ok so what lock protects this buffer?

No.  The gtp_frame_lock protects the vars that follow it:
static int			gtp_frame_num;
static char			*gtp_frame;
static char			*gtp_frame_r_start;
static char			*gtp_frame_w_start;
static char			*gtp_frame_w_end;
static char			*gtp_frame_r_cache;
static int			gtp_frame_is_circular;
It protects them all.

gtp_m_buffer is protected by gtp_rw_lock that I just add in new patch.

>
>> +     struct gtp_frame_reg    *fr = NULL;
>> +
>> +     if (GTP_RW_MAX - 4 - gtp_rw_size < GTP_REG_ASCII_SIZE)
>> +             return -E2BIG;
>
> The magic 4 should be a define

Done.
>
>> +     next = gtp_frame_current->next;
>> +     while (next) {
>> +             switch (next[0]) {
>> +             case 'r':
>> +                     fr = (struct gtp_frame_reg *) (next + 1);
>> +                     goto check;
>> +                     break;
>
> either check or break, but not both
>
>> +             default:
>> +                     next = NULL;
>
> Not needed
>> +                     break;
>> +             }
>> +     }

This part is fixed.

>> +check:
>> +     if (fr)
>> +             gtp_regs2ascii(&fr->regs, gtp_rw_bufp);
>> +     else
>> +             memset(gtp_rw_bufp, '0', GTP_REG_ASCII_SIZE);
>
> No 0 termination?

No, it don't need becuase it will add head and tail in gtp_write.
>
>> +
>> +static int
>> +gtp_open(struct inode *inode, struct file *file)
>> +{
>> +     if (atomic_inc_return(&gtp_count) > 1) {
>> +             atomic_dec(&gtp_count);
>> +             return -EBUSY;
>> +     }
>
> This looks racy. Better use a try mutex lock

Fixed.

>
>> +static int __init gtp_init(void)
>> +{
>> +     atomic_set(&gtp_count, 0);
>> +     gtp_read_ack = 0;
>> +     gtp_rw_buf = NULL;
>> +     gtp_rw_bufp = NULL;
>> +     gtp_rw_size = 0;
>> +     gtp_start = 0;
>> +     gtp_disconnected_tracing = 0;
>> +     gtp_circular = 0;
>> +     gtp_frame_num = 0;
>> +     gtp_frame = NULL;
>> +     gtp_frame_r_start = NULL;
>> +     gtp_frame_w_start = NULL;
>> +     gtp_frame_w_end = NULL;
>> +     gtp_frame_r_cache = NULL;
>> +     gtp_frame_is_circular = 0;
>> +     gtp_frame_current = NULL;
>
> Globals don't need to be initialized with 0

OK.  Fixed.

>
>>
>> +config GTP
>> +     tristate "GDB tracepoint support"
>> +     depends on X86 || ARM || MIPS
>> +     select KPROBES
>> +     select DEBUG_FS
>> +     ---help---
>> +       Supply GDB tracepoint interface in /sys/kernel/debug/gtp.
>
> Need far more description here. Write 1-2 paragraphs why a user
> wants this. checkpatch should have warned.

OK.  Add some introduce.  checkpatch is OK with it.

>
> -Andi
> --
> ak@...ux.intel.com -- Speaking for myself only.

Thanks for your help.

Best,
Hui

sudo insmod kernel/gtp.ko
sudo gdb ./vmlinux
#Connect KGTP interface
(gdb) target remote /sys/kernel/debug/gtp
Remote debugging using /sys/kernel/debug/gtp
0x0000000000000000 in irq_stack_union ()
#Access memory directly
(gdb) p jiffies_64
$1 = 4332444293
(gdb) p jiffies_64
$2 = 4332444591
(gdb) p *((struct module *)((char *)modules->next - ((size_t) &(((struct module *)0)->list))))
$3 = {state = MODULE_STATE_LIVE, list = {next = 0xffffffffa0964188, prev = 0xffffffff81c345f0},
  name = "gtp", '\000' <repeats 52 times>, mkobj = {kobj = {name = 0xffff88011f5c49c8 "gtp", entry = {
        next = 0xffff880221cd6420, prev = 0xffffffffa09641d8}, parent = 0xffff880221cd6438, kset = 0xffff880221cd6420,
...
(gdb) p *(struct device *)(__per_cpu_offset[0]+(uint64_t)(&mce_device))
$4 = {parent = 0xffff8802212f8000, p = 0x1fe, kobj = {name = 0x0, entry = {next = 0x0, prev = 0xffffffff8102ae70},
    parent = 0x0, kset = 0x0, ktype = 0x0, sd = 0x0, kref = {refcount = {counter = 0}}, state_initialized = 0,
...
#Set tracepoint to collect the register info of function vfs_read
(gdb) trace vfs_read
Tracepoint 1 at 0xffffffff8117a3d0: file /home/teawater/kernel2/linux/fs/read_write.c, line 365.
(gdb) actions
Enter actions for tracepoint 1, one per line.
End with a line saying just "end".
collect $reg
end
(gdb) tstart
(gdb) tstop
(gdb) tfind
Found trace frame 0, tracepoint 1
#0  vfs_read (file=0xffff880070bb6100,
    buf=0x31cb8f0 "$2aa6178136313733#331bb700088ffff481fe4450188ffff002", '0' <repeats 13 times>, "f0b81c03000000000061bb700088ffff781fe4450188ffff301fe4450188ffff606944030000000058f19a010288ffff01", '0' <repeats 14 times>, "4602", '0' <repeats 12 times>, "f0b81c0"..., count=8192, pos=0xffff880145e41f48) at /home/teawater/kernel2/linux/fs/read_write.c:365
365     {
(gdb) info reg
rax            0x0      0
rbx            0xffff880070bb6100       -131939504004864
rcx            0xffff880145e41f48       -131935927787704
rdx            0x2000   8192
rsi            0x31cb8f0        52214000
rdi            0xffff880070bb6100       -131939504004864
rbp            0xffff880145e41f78       0xffff880145e41f78
rsp            0xffff880145e41f30       0xffff880145e41f30
r8             0x3446960        54815072
r9             0xffff8802019af158       -131932778466984
r10            0x1      1
r11            0x246    582
r12            0x31cb8f0        52214000
r13            0x2000   8192
r14            0xa      10
r15            0xa      10
rip            0xffffffff8117a3d0       0xffffffff8117a3d0 <vfs_read>
eflags         0x286    [ PF SF IF ]
cs             0x10     16
ss             0x18     24
ds             *value not available*
es             *value not available*
fs             *value not available*
gs             *value not available*

Because this is a lite patch, so this patch doesn't support other functions of KGTP.

Signed-off-by: Hui Zhu <teawater@...il.com>
---
  arch/arm/include/asm/gtp.h  |   24 +
  arch/mips/include/asm/gtp.h |   56 ++
  arch/x86/include/asm/gtp.h  |   92 ++++
  kernel/Makefile             |    2
  kernel/gtp.c                |  892 ++++++++++++++++++++++++++++++++++++++++++++
  lib/Kconfig.debug           |   12
  6 files changed, 1078 insertions(+)

--- /dev/null
+++ b/arch/arm/include/asm/gtp.h
@@ -0,0 +1,24 @@
+#ifndef _ASM_ARM_GTP_H_
+#define _ASM_ARM_GTP_H_
+
+#define GTP_REG_ASCII_SIZE	336
+
+static inline void gtp_regs2ascii(struct pt_regs *regs, char *buf)
+{
+	int	i;
+
+	for (i = 0; i < 16; i++) {
+		sprintf(buf, "%08lx", (unsigned long) ntohl(regs->uregs[i]));
+		buf += 8;
+	}
+
+	/* f0-f7 fps */
+	memset(buf, '0', 200);
+	buf += 200;
+
+	sprintf(buf, "%08lx",
+		 (unsigned long) ntohl(regs->uregs[16]));
+	buf += 8;
+}
+
+#endif
--- /dev/null
+++ b/arch/mips/include/asm/gtp.h
@@ -0,0 +1,56 @@
+#ifndef _ASM_MIPS_GTP_H_
+#define _ASM_MIPS_GTP_H_
+
+#ifdef CONFIG_32BIT
+#define GTP_REG_ASCII_SIZE	304
+#else
+#define GTP_REG_ASCII_SIZE	608
+#endif
+
+#define GTP_SP_NUM		29
+
+static inline void gtp_regs2ascii(struct pt_regs *regs, char *buf)
+{
+#ifdef CONFIG_32BIT
+#define OUTFORMAT	"%08lx"
+#define REGSIZE		8
+#define SWAB(a)		ntohl(a)
+#else
+#define OUTFORMAT	"%016lx"
+#define REGSIZE		16
+#define SWAB(a)		be64_to_cpu(a)
+#endif
+	{
+		int	i;
+
+		for (i = 0; i < 32; i++) {
+			sprintf(buf, OUTFORMAT,
+				 (unsigned long) SWAB(regs->regs[i]));
+			buf += REGSIZE;
+		}
+	}
+
+	sprintf(buf, OUTFORMAT,
+		 (unsigned long) SWAB(regs->cp0_status));
+	buf += REGSIZE;
+	sprintf(buf, OUTFORMAT,
+		 (unsigned long) SWAB(regs->lo));
+	buf += REGSIZE;
+	sprintf(buf, OUTFORMAT,
+		 (unsigned long) SWAB(regs->hi));
+	buf += REGSIZE;
+	sprintf(buf, OUTFORMAT,
+		 (unsigned long) SWAB(regs->cp0_badvaddr));
+	buf += REGSIZE;
+	sprintf(buf, OUTFORMAT,
+		 (unsigned long) SWAB(regs->cp0_cause));
+	buf += REGSIZE;
+	sprintf(buf, OUTFORMAT,
+		 (unsigned long) SWAB(regs->cp0_epc));
+	buf += REGSIZE;
+#undef OUTFORMAT
+#undef REGSIZE
+#undef SWAB
+}
+
+#endif
--- /dev/null
+++ b/arch/x86/include/asm/gtp.h
@@ -0,0 +1,92 @@
+#ifndef _ASM_X86_GTP_H_
+#define _ASM_X86_GTP_H_
+
+#ifdef CONFIG_X86_32
+#define GTP_REG_ASCII_SIZE	128
+#else
+#define GTP_REG_ASCII_SIZE	296
+#endif
+
+static inline void gtp_regs2ascii(struct pt_regs *regs, char *buf)
+{
+#ifdef CONFIG_X86_32
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->ax));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->cx));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->dx));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->bx));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->sp));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->bp));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->si));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->di));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->ip));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->flags));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->cs));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->ss));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->ds));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->es));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->fs));
+	buf += 8;
+	sprintf(buf, "%08x", (unsigned int) swab32(regs->gs));
+	buf += 8;
+#else
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->ax));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->bx));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->cx));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->dx));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->si));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->di));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->bp));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->sp));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r8));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r9));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r10));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r11));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r12));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r13));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r14));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->r15));
+	buf += 16;
+	sprintf(buf, "%016lx", (unsigned long) swab64(regs->ip));
+	buf += 16;
+	sprintf(buf, "%08x",
+		(unsigned int) swab32((unsigned int)regs->flags));
+	buf += 8;
+	sprintf(buf, "%08x",
+		(unsigned int) swab32((unsigned int)regs->cs));
+	buf += 8;
+	sprintf(buf, "%08x",
+		(unsigned int) swab32((unsigned int)regs->ss));
+	buf += 8;
+#endif
+}
+
+#endif
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -108,6 +108,8 @@ obj-$(CONFIG_PADATA) += padata.o
  obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
  obj-$(CONFIG_JUMP_LABEL) += jump_label.o
  
+obj-$(CONFIG_GTP) += gtp.o
+
  $(obj)/configs.o: $(obj)/config_data.h
  
  # config_data.h contains the same information as ikconfig.h but gzipped.
--- /dev/null
+++ b/kernel/gtp.c
@@ -0,0 +1,892 @@
+/*
+ * KGTP is a realtime and lightweight Linux debugger and tracer.
+ * It makes Linux Kernel supply a GDB remote debug interface.
+ *
+ * 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) KGTP team (https://code.google.com/p/kgtp/), 2010, 2011, 2012
+ *
+ */
+
+#include <linux/version.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/vmalloc.h>
+#include <linux/poll.h>
+#include <linux/kprobes.h>
+#include <linux/interrupt.h>
+#include <linux/debugfs.h>
+#include <linux/slab.h>
+#include <asm/gtp.h>
+
+#ifndef ULONGEST
+#define ULONGEST		uint64_t
+#endif
+#ifndef CORE_ADDR
+#define CORE_ADDR		unsigned long
+#endif
+
+#define GTP_RW_MAX		16384
+#define GTP_RW_BUFP_MAX		(GTP_RW_MAX - 4 - gtp_rw_size)
+
+#define GTP_FRAME_SIZE		5242880
+#define GTP_FRAME_HEAD_SIZE	(1 + sizeof(struct gtp_frame_head))
+#define GTP_FRAME_REG_SIZE	(1 + sizeof(struct gtp_frame_reg))
+
+#define TOHEX(h)		((h) > 9 ? (h) + 'a' - 10 : (h) + '0')
+
+struct action {
+	struct list_head	node;
+	char			type;
+	union {
+		ULONGEST	reg_mask;
+	} u;
+};
+
+struct gtp_entry {
+	struct list_head	node;
+	ULONGEST		num;
+	ULONGEST		addr;
+	ULONGEST		step;
+	ULONGEST		pass;
+	int			nopass;
+	int			kpreg;
+	struct kprobe		kp;
+	struct list_head	action_list;
+};
+
+static LIST_HEAD(gtp_list);
+
+struct gtp_frame_head {
+	int		frame_num;
+	ULONGEST	trace_num;
+	char		*next;
+};
+
+struct gtp_frame_reg {
+	struct pt_regs	regs;
+	char		*next;
+};
+
+static char			gtp_read_ack;
+static char			*gtp_rw_buf;
+static char			*gtp_rw_bufp;
+static size_t			gtp_rw_size;
+
+static int			gtp_start;
+
+static int			gtp_disconnected_tracing;
+static int			gtp_circular;
+
+/* This spin_lock protects the gtp_frame.  */
+static DEFINE_SPINLOCK(gtp_frame_lock);
+static int			gtp_frame_num;
+static char			*gtp_frame;
+static char			*gtp_frame_r_start;
+static char			*gtp_frame_w_start;
+static char			*gtp_frame_w_end;
+static char			*gtp_frame_r_cache;
+static int			gtp_frame_is_circular;
+static struct gtp_frame_head	*gtp_frame_current;
+
+static DEFINE_SEMAPHORE(gtp_rw_lock);
+static int	gtp_rw_count;
+
+static char *gtp_frame_alloc(size_t size)
+{
+	char	*ret = NULL;
+
+	if (size > GTP_FRAME_SIZE)
+		return NULL;
+
+	spin_lock(&gtp_frame_lock);
+
+	if (gtp_frame_w_start + size > gtp_frame_w_end) {
+		if (gtp_circular) {
+			gtp_frame_is_circular = 1;
+			gtp_frame_w_start = gtp_frame;
+			gtp_frame_r_start = gtp_frame;
+		} else
+			goto out;
+	}
+
+	if (gtp_frame_is_circular) {
+		/* Release some frame entry to get some place.
+		   XXX:  When support new frame type, need add new handler
+		   to switch.  */
+		while (gtp_frame_w_start + size > gtp_frame_r_start) {
+			switch (gtp_frame_r_start[0]) {
+			case 'h':
+				gtp_frame_r_start += GTP_FRAME_HEAD_SIZE;
+				break;
+			case 'r':
+				gtp_frame_r_start += GTP_FRAME_REG_SIZE;
+				break;
+			default:
+				goto out;
+			}
+		}
+	}
+
+	ret = gtp_frame_w_start;
+	gtp_frame_w_start += size;
+
+out:
+	spin_unlock(&gtp_frame_lock);
+	return ret;
+}
+
+static inline char **gtp_action_r(struct pt_regs *regs, struct action *ae,
+				  char **next)
+{
+	struct gtp_frame_reg	*freg;
+	char			*tmp;
+
+	tmp = gtp_frame_alloc(GTP_FRAME_REG_SIZE);
+	if (!tmp)
+		return NULL;
+
+	*next = tmp;
+	tmp[0] = 'r';
+	freg = (struct gtp_frame_reg *) (tmp + 1);
+	memcpy(&freg->regs, regs, sizeof(struct pt_regs));
+#ifdef CONFIG_X86_32
+	freg->regs.sp = (unsigned long)&regs->sp;
+#endif	/* CONFIG_X86_32 */
+#ifdef CONFIG_X86
+	freg->regs.ip -= 1;
+#endif	/* CONFIG_X86 */
+	freg->next = NULL;
+
+	return &freg->next;
+}
+
+static int gtp_kp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct gtp_entry	*tpe = container_of(p, struct gtp_entry, kp);
+	struct gtp_frame_head	*head;
+	char			*tmp;
+	struct action		*ae;
+	struct list_head	*cur;
+	char			**next;
+
+	pr_devel("gtp_kp_pre_handler: tracepoint %d\n", (int)tpe->num);
+
+	/* Get the head.  */
+	tmp = gtp_frame_alloc(GTP_FRAME_HEAD_SIZE);
+	if (!tmp)
+		goto no_memory;
+	tmp[0] = 'h';
+	head = (struct gtp_frame_head *) (tmp + 1);
+	/* Get a new frame num from gtp_frame_num.  */
+	spin_lock(&gtp_frame_lock);
+	if (gtp_frame_num < 0)
+		gtp_frame_num = head->frame_num = 0;
+	else
+		head->frame_num = gtp_frame_num++;
+	spin_unlock(&gtp_frame_lock);
+	head->trace_num = tpe->num;
+	head->next = NULL;
+	next = &head->next;
+
+	/* Handle actions.  */
+	list_for_each(cur, &tpe->action_list) {
+		ae = list_entry(cur, struct action, node);
+		switch (ae->type) {
+		case 'r':
+			next = gtp_action_r(regs, ae, next);
+			if (!next)
+				goto no_memory;
+			break;
+		}
+	}
+
+	return 0;
+
+no_memory:
+	pr_devel("gtp_kp_pre_handler: tracepoint %d no memory.\n",
+		 (int)tpe->num);
+	return 0;
+}
+
+static struct action *gtp_action_alloc(char type)
+{
+	struct action	*ret;
+
+	ret = kzalloc(sizeof(struct action), GFP_KERNEL);
+	if (!ret)
+		goto out;
+
+	ret->type = type;
+
+out:
+	return ret;
+}
+
+static struct gtp_entry *gtp_list_add(ULONGEST num, ULONGEST addr)
+{
+	struct gtp_entry	*ret = kzalloc(sizeof(struct gtp_entry),
+					       GFP_KERNEL);
+
+	if (!ret)
+		goto out;
+	ret->num = num;
+	ret->addr = addr;
+	ret->kp.addr = (kprobe_opcode_t *) (CORE_ADDR)addr;
+	ret->kp.pre_handler = gtp_kp_pre_handler;
+	INIT_LIST_HEAD(&ret->action_list);
+
+	list_add(&ret->node, &gtp_list);
+
+out:
+	return ret;
+}
+
+static struct gtp_entry *gtp_list_find(ULONGEST num, ULONGEST addr)
+{
+	struct gtp_entry	*tpe;
+	struct list_head	*cur;
+
+	list_for_each(cur, &gtp_list) {
+		tpe = list_entry(cur, struct gtp_entry, node);
+		if (tpe->num == num && tpe->addr == addr)
+			return tpe;
+	}
+
+	return NULL;
+}
+
+static void gtp_list_release(void)
+{
+	struct gtp_entry	*tpe;
+	struct list_head	*cur, *next;
+
+	list_for_each_safe(cur, next, &gtp_list) {
+		struct action		*ae;
+		struct list_head	*cur_ae, *next_ae;
+
+		tpe = list_entry(cur, struct gtp_entry, node);
+
+		list_for_each_safe(cur_ae, next_ae, &tpe->action_list) {
+			ae = list_entry(cur_ae, struct action, node);
+			kfree(ae);
+		}
+
+		kfree(tpe);
+	}
+}
+
+static void gtp_frame_reset(void)
+{
+	gtp_frame_num = 0;
+	gtp_frame_r_start = gtp_frame;
+	gtp_frame_w_start = gtp_frame;
+	gtp_frame_w_end = gtp_frame + GTP_FRAME_SIZE;
+	gtp_frame_is_circular = 0;
+	gtp_frame_r_cache = NULL;
+	gtp_frame_current = NULL;
+}
+
+static int gtp_gdbrsp_qtinit(void)
+{
+	if (gtp_start)
+		return -EBUSY;
+
+	gtp_list_release();
+
+	if (gtp_frame)
+		gtp_frame_reset();
+
+	return 0;
+}
+
+static int gtp_gdbrsp_qtdp(char *pkg)
+{
+	int			addnew = 1;
+	ULONGEST		num, addr;
+	struct gtp_entry	*tpe;
+
+	pr_devel("gtp_gdbrsp_qtdp: %s\n", pkg);
+
+	if (gtp_start)
+		return -EBUSY;
+
+	if (pkg[0] == '-') {
+		pkg++;
+		addnew = 0;
+	}
+
+	/* Get num and addr.  */
+	if (pkg[0] == '\0')
+		return -EINVAL;
+	num = simple_strtoull(pkg, &pkg, 16);
+	if (pkg[0] == '\0')
+		return -EINVAL;
+	pkg++;
+	addr = simple_strtoull(pkg, &pkg, 16);
+	if (pkg[0] == '\0')
+		return -EINVAL;
+	pkg++;
+
+	tpe = gtp_list_find(num, addr);
+	if (addnew) {
+		if (tpe)
+			return -EINVAL;
+		if (pkg[0] == 'D')
+			return 0;
+		if (pkg[0] == '\0')
+			return -EINVAL;
+		pkg++;
+
+		tpe = gtp_list_add(num, addr);
+		if (tpe == NULL)
+			return -ENOMEM;
+
+		/* Get step and pass.  */
+		if (pkg[0] == '\0')
+			return -EINVAL;
+		pkg++;
+		tpe->step = simple_strtoull(pkg, &pkg, 16);
+		if (pkg[0] == '\0')
+			return -EINVAL;
+		pkg++;
+		tpe->pass = simple_strtoull(pkg, &pkg, 16);
+		if (tpe->pass == 0)
+			tpe->nopass = 1;
+	} else if (tpe) {
+		/* Add action to tpe.  */
+		int	step_action = 0;
+
+		if (pkg[0] == 'S') {
+			pkg++;
+			step_action = 1;
+			/* XXX: Still not support step.  */
+			return 1;
+		}
+		while (pkg[0]) {
+			struct action	*ae;
+
+			switch (pkg[0]) {
+			case 'R':
+				/* XXX: reg_mask is ignore.  */
+				ae = gtp_action_alloc(pkg[0]);
+				if (!ae)
+					return -ENOMEM;
+				pkg++;
+				ae->type = 'r';
+				ae->u.reg_mask = simple_strtoull(pkg, &pkg, 16);
+				break;
+			default:
+				/* XXX: Not support.  */
+				return 1;
+			}
+
+			if (ae)
+				list_add(&ae->node, &tpe->action_list);
+		}
+	} else
+		return -EINVAL;
+
+	return 0;
+}
+
+static int gtp_gdbrsp_qtdisconnected(char *pkg)
+{
+	ULONGEST setting;
+
+	if (gtp_start)
+		return -EBUSY;
+	if (pkg[0] == '\0')
+		return -EINVAL;
+
+	setting = simple_strtoull(pkg, NULL, 16);
+	gtp_disconnected_tracing = (int) setting;
+
+	return 0;
+}
+
+static int gtp_gdbrsp_qtbuffer(char *pkg)
+{
+	if (strncmp("circular:", pkg, 9) == 0) {
+		ULONGEST setting;
+
+		pkg += 9;
+		if (pkg[0] == '\0')
+			return -EINVAL;
+		setting = simple_strtoull(pkg, NULL, 16);
+		gtp_circular = (int)setting;
+
+		return 0;
+	}
+
+	return 1;
+}
+
+static struct gtp_frame_head *gtp_frame_head_find(int num)
+{
+	struct gtp_frame_head	*ret = NULL;
+	char			*tmp;
+
+	if (gtp_frame_r_cache) {
+		tmp = gtp_frame_r_cache;
+
+		while (tmp < gtp_frame_w_start) {
+			switch (tmp[0]) {
+			case 'h':
+				ret = (struct gtp_frame_head *)(tmp + 1);
+				goto cache_check;
+				break;
+			case 'r':
+				tmp += GTP_FRAME_REG_SIZE;
+				break;
+			default:
+				goto cache_check;
+				break;
+			}
+		}
+
+cache_check:
+		if (ret && ret->frame_num == num)
+			goto out;
+	}
+
+	tmp = gtp_frame_r_start;
+	while (tmp < gtp_frame_w_start) {
+		switch (tmp[0]) {
+		case 'h':
+			ret = (struct gtp_frame_head *) (tmp + 1);
+			if (ret->frame_num == num)
+				goto out;
+			ret = NULL;
+			tmp += GTP_FRAME_HEAD_SIZE;
+			break;
+		case 'r':
+			tmp += GTP_FRAME_REG_SIZE;
+			break;
+		default:
+			goto out;
+		}
+	}
+
+out:
+	return ret;
+}
+
+static int gtp_gdbrsp_qtframe(char *pkg)
+{
+	if (gtp_start)
+		return -EBUSY;
+
+	if (strncmp(pkg, "pc:", 3) == 0)	/* XXX */
+		return 1;
+	else if (strncmp(pkg, "tdp:", 4) == 0)	/* XXX */
+		return 1;
+	else if (strncmp(pkg, "range:", 6) == 0)	/* XXX */
+		return 1;
+	else if (strncmp(pkg, "outside:", 8) == 0)	/* XXX */
+		return 1;
+	else {
+		ULONGEST		num;
+		struct gtp_frame_head	*ret;
+
+		if (pkg[0] == '\0')
+			return -EINVAL;
+		num = simple_strtoull(pkg, NULL, 16);
+
+		pr_devel("gtp_gdbrsp_qtframe: %d\n", (int) num);
+
+		if (((int) num) < 0) {
+			/* Return to current.  */
+			gtp_frame_current = NULL;
+
+			return 0;
+		}
+		ret = gtp_frame_head_find((int) num);
+		if (ret) {
+			gtp_frame_current = ret;
+			gtp_frame_r_cache = (char *)ret;
+			gtp_frame_r_cache += sizeof(struct gtp_frame_head);
+			sprintf(gtp_rw_bufp, "F%xT%x",
+				gtp_frame_current->frame_num,
+				(unsigned int)gtp_frame_current->trace_num);
+			gtp_rw_size += strlen(gtp_rw_bufp);
+			gtp_rw_bufp += strlen(gtp_rw_bufp);
+		} else {
+			strcpy(gtp_rw_bufp, "F-1");
+			gtp_rw_bufp += 3;
+			gtp_rw_size += 3;
+		}
+	}
+
+	return 1;
+}
+
+static int gtp_gdbrsp_qtstop(void)
+{
+	struct gtp_entry	*tpe;
+	struct list_head	*cur;
+
+	if (!gtp_start)
+		return -EBUSY;
+
+	list_for_each(cur, &gtp_list) {
+		tpe = list_entry(cur, struct gtp_entry, node);
+		if (tpe->kpreg) {
+			unregister_kprobe(&tpe->kp);
+			tpe->kpreg = 0;
+		}
+	}
+
+	gtp_start = 0;
+
+	return 0;
+}
+
+static int gtp_gdbrsp_qtstart(void)
+{
+	struct gtp_entry	*tpe;
+	struct list_head	*cur;
+
+	if (gtp_start)
+		return -EBUSY;
+
+	if (!gtp_frame) {
+		gtp_frame = vmalloc(GTP_FRAME_SIZE);
+		if (!gtp_frame)
+			return -ENOMEM;
+
+		gtp_frame_reset();
+	}
+
+	list_for_each(cur, &gtp_list) {
+		tpe = list_entry(cur, struct gtp_entry, node);
+		if (!list_empty(&tpe->action_list)) {
+			int	ret = register_kprobe(&tpe->kp);
+			if (ret < 0) {
+				gtp_gdbrsp_qtstop();
+				return ret;
+			}
+			tpe->kpreg = 1;
+		}
+	}
+
+	gtp_start = 1;
+
+	return 0;
+}
+
+static int gtp_gdbrsp_QT(char *pkg)
+{
+	int	ret = 1;
+
+	pr_devel("gtp_gdbrsp_QT: %s\n", pkg);
+
+	if (strcmp("init", pkg) == 0)
+		ret = gtp_gdbrsp_qtinit();
+	else if (strncmp("DP:", pkg, 3) == 0)
+		ret = gtp_gdbrsp_qtdp(pkg + 3);
+	else if (strncmp("Disconnected:", pkg, 13) == 0)
+		ret = gtp_gdbrsp_qtdisconnected(pkg + 13);
+	else if (strncmp("Buffer:", pkg, 7) == 0)
+		ret = gtp_gdbrsp_qtbuffer(pkg + 7);
+	else if (strncmp("Frame:", pkg, 6) == 0)
+		ret = gtp_gdbrsp_qtframe(pkg + 6);
+	else if (strcmp("Start", pkg) == 0)
+		ret = gtp_gdbrsp_qtstart();
+	else if (strcmp("Stop", pkg) == 0)
+		ret = gtp_gdbrsp_qtstop();
+
+	return ret;
+}
+
+static unsigned char	gtp_m_buffer[0xffff];
+
+static int gtp_gdbrsp_m(char *pkg)
+{
+	int		i;
+	ULONGEST	addr, len;
+
+	/* Get add and len.  */
+	if (pkg[0] == '\0')
+		return -EINVAL;
+	addr = simple_strtoull(pkg, &pkg, 16);
+	if (pkg[0] != ',')
+		return -EINVAL;
+	pkg++;
+	len = simple_strtoull(pkg, &pkg, 16);
+	if (len == 0)
+		return -EINVAL;
+	len &= 0xffff;
+	len = (ULONGEST) min((int)(GTP_RW_BUFP_MAX / 2),
+			     (int)len);
+
+	pr_devel("gtp_gdbrsp_m: addr = 0x%lx len = %d\n",
+		 (unsigned long) addr, (int) len);
+
+	if (probe_kernel_read(gtp_m_buffer, (void *)(CORE_ADDR)addr,
+			      (size_t)len))
+		return -EFAULT;
+
+	for (i = 0; i < (int)len; i++) {
+		sprintf(gtp_rw_bufp, "%02x", gtp_m_buffer[i]);
+		gtp_rw_bufp += 2;
+		gtp_rw_size += 2;
+	}
+
+	return 1;
+}
+
+static int gtp_gdbrsp_g(void)
+{
+	char			*next;
+	struct gtp_frame_reg	*fr = NULL;
+
+	if (GTP_RW_BUFP_MAX < GTP_REG_ASCII_SIZE)
+		return -E2BIG;
+
+	if (gtp_start || !gtp_frame_current)
+		goto empty_out;
+
+	/* Get the fr.  */
+	next = gtp_frame_current->next;
+	if (next[0] == 'r') {
+		fr = (struct gtp_frame_reg *) (next + 1);
+		gtp_regs2ascii(&fr->regs, gtp_rw_bufp);
+	} else {
+empty_out:
+		memset(gtp_rw_bufp, '0', GTP_REG_ASCII_SIZE);
+	}
+	gtp_rw_bufp += GTP_REG_ASCII_SIZE;
+	gtp_rw_size += GTP_REG_ASCII_SIZE;
+	return 1;
+}
+
+static int gtp_open(struct inode *inode, struct file *file)
+{
+	int	ret = 0;
+
+	down(&gtp_rw_lock);
+
+	if (gtp_rw_count > 0) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	gtp_read_ack = 0;
+	gtp_rw_buf = vmalloc(GTP_RW_MAX);
+	if (!gtp_rw_buf) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	gtp_rw_count++;
+
+out:
+	up(&gtp_rw_lock);
+	return ret;
+}
+
+static int gtp_release(struct inode *inode, struct file *file)
+{
+	down(&gtp_rw_lock);
+	vfree(gtp_rw_buf);
+
+	/* XXX:  not handle gtp_disconnected_tracing.  */
+	gtp_gdbrsp_qtstop();
+	gtp_gdbrsp_qtinit();
+	vfree(gtp_frame);
+	gtp_frame = NULL;
+
+	gtp_rw_count--;
+
+	up(&gtp_rw_lock);
+
+	return 0;
+}
+
+static long gtp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	/* This function will make GDB happy.  */
+	pr_devel("gtp_ioctl: %x\n", cmd);
+
+	return 0;
+}
+
+static ssize_t gtp_write(struct file *file, const char __user *buf,
+			 size_t size, loff_t *ppos)
+{
+	char		*rsppkg = NULL;
+	int		i, ret;
+	unsigned char	csum = 0;
+
+	down(&gtp_rw_lock);
+
+	size = min_t(size_t, size, GTP_RW_MAX);
+	if (copy_from_user(gtp_rw_buf, buf, size)) {
+		size = -EFAULT;
+		goto out;
+	}
+
+	if (gtp_rw_buf[0] == '+' || gtp_rw_buf[0] == '-'
+	    || gtp_rw_buf[0] == '\3')
+		goto out;
+
+	/* Check format and crc and get the rsppkg.  */
+	for (i = 0; i < size - 2; i++) {
+		if (rsppkg == NULL) {
+			if (gtp_rw_buf[i] == '$')
+				rsppkg = gtp_rw_buf + i + 1;
+		} else {
+			if (gtp_rw_buf[i] == '#')
+				break;
+			else
+				csum += gtp_rw_buf[i];
+		}
+	}
+	if (rsppkg && gtp_rw_buf[i] == '#') {
+		/* Format is OK.  Check crc.  */
+		unsigned char	c1, c2;
+
+		gtp_rw_buf[i] = '\0';
+
+		c1 = gtp_rw_buf[i+1];
+		c2 = gtp_rw_buf[i+2];
+		if (csum == (c1 << 4) + c2) {
+			pr_devel("gtp_write: crc error\n");
+			gtp_read_ack = '-';
+			goto out;
+		}
+	} else {
+		pr_devel("gtp_write: format error\n");
+		gtp_read_ack = '-';
+		goto out;
+	}
+	gtp_read_ack = '+';
+
+	pr_devel("gtp_write: %s\n", rsppkg);
+
+	/* Handle rsppkg and put return to gtp_rw_buf.  */
+	gtp_rw_buf[0] = '$';
+	gtp_rw_bufp = gtp_rw_buf + 1;
+	gtp_rw_size = 0;
+	ret = 1;
+	switch (rsppkg[0]) {
+	case '?':
+		strcpy(gtp_rw_bufp, "S05");
+		gtp_rw_bufp += 3;
+		gtp_rw_size += 3;
+		break;
+	case 'g':
+		ret = gtp_gdbrsp_g();
+		break;
+	case 'm':
+		ret = gtp_gdbrsp_m(rsppkg + 1);
+		break;
+	case 'Q':
+		if (rsppkg[1] == 'T')
+			ret = gtp_gdbrsp_QT(rsppkg + 2);
+		break;
+	}
+	if (ret == 0) {
+		strcpy(gtp_rw_bufp, "OK");
+		gtp_rw_bufp += 2;
+		gtp_rw_size += 2;
+	} else if (ret < 0) {
+		sprintf(gtp_rw_bufp, "E%02x", -ret);
+		gtp_rw_bufp += 3;
+		gtp_rw_size += 3;
+	}
+
+	gtp_rw_bufp[0] = '#';
+	csum = 0;
+	for (i = 1; i < gtp_rw_size + 1; i++)
+		csum += gtp_rw_buf[i];
+	gtp_rw_bufp[1] = TOHEX(csum >> 4);
+	gtp_rw_bufp[2] = TOHEX(csum & 0x0f);
+	gtp_rw_bufp = gtp_rw_buf;
+	gtp_rw_size += 4;
+
+out:
+	up(&gtp_rw_lock);
+	return size;
+}
+
+static ssize_t gtp_read(struct file *file, char __user *buf, size_t size,
+	 loff_t *ppos)
+{
+	if (size == 0)
+		return 0;
+
+	down(&gtp_rw_lock);
+
+	if (gtp_read_ack) {
+		int err = put_user(gtp_read_ack, buf);
+		if (err) {
+			size = -err;
+			goto out;
+		}
+		gtp_read_ack = 0;
+		size = 1;
+		goto out;
+	}
+
+	size = min(gtp_rw_size, size);
+
+	if (copy_to_user(buf, gtp_rw_bufp, size)) {
+		size = -EFAULT;
+		goto out;
+	}
+	gtp_rw_bufp += size;
+	gtp_rw_size -= size;
+
+out:
+	up(&gtp_rw_lock);
+	return size;
+}
+
+static const struct file_operations gtp_operations = {
+	.owner		= THIS_MODULE,
+	.open		= gtp_open,
+	.release	= gtp_release,
+	.unlocked_ioctl	= gtp_ioctl,
+	.compat_ioctl	= gtp_ioctl,
+	.read		= gtp_read,
+	.write		= gtp_write,
+};
+
+struct dentry	*gtp_dir;
+
+static int __init gtp_init(void)
+{
+	gtp_dir = debugfs_create_file("gtp", S_IFIFO | S_IRUSR | S_IWUSR, NULL,
+				      NULL, &gtp_operations);
+	if (gtp_dir == NULL || gtp_dir == ERR_PTR(-ENODEV))
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void __exit gtp_exit(void)
+{
+	if (gtp_dir)
+		debugfs_remove_recursive(gtp_dir);
+}
+
+module_init(gtp_init)
+module_exit(gtp_exit)
+
+MODULE_AUTHOR("Hui Zhu <teawater@...il.com>");
+MODULE_LICENSE("GPL");
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1307,6 +1307,18 @@ config ASYNC_RAID6_TEST
  
  	  If unsure, say N.
  
+config GTP
+	tristate "GDB tracepoint support"
+	depends on X86 || ARM || MIPS
+	select KPROBES
+	select DEBUG_FS
+	---help---
+	  KGTP is a realtime and lightweight Linux debugger and tracer.
+	  It makes Linux Kernel supply a GDB remote debug interface.
+	  Then GDB in current machine can debug and trace Linux through
+	  GDB tracepoint and some other functions without stopping the
+	  Linux Kernel.
+
  source "samples/Kconfig"
  
  source "lib/Kconfig.kgdb"

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