KGTP is a realtime and lightweight Linux Kernel GDB debugger and tracer. It makes Linux Kernel supply a GDB remote debug interface. Then GDB in current machine or remote machine can debug and trace Linux through GDB tracepoint without stopping the Linux Kernel. And even if the board doesn’t have GDB on it and doesn’t have interface for remote debug. It can debug the Linux Kernel using offline debug. Now, it supports X86-32, X86-64, MIPS and ARM.

This article describes how to use kgtp debug linux kernel on android.

Kernel Building

 General setup  --->
     [ * ] Prompt for development and/or incomplete code/drivers
     [ * ] Kprobe
Kernel hacking  --->
     [ * ] Compile the kernel with debug info
     [ * ] Compile the kernel with frame pointers

Building KGTP

Config KGTP Makefile

KERNELDIR := /work/vc1000/src/kernel-vc1000-2.3
ARCH=arm
CROSS_COMPILE=/usr/local/arm/arm-2009q3/bin/arm-none-linux-gnueabi-

error: ‘GTP_VAR_RDTSC_ID’ undeclared(latest version fixed By: teawater )

  CC [M]  /home/border/work/kernel/kgtp/trunk/gtp.o
/home/border/work/kernel/kgtp/trunk/gtp.c: In function 'gtp_gdbrsp_qtv':
/home/border/work/kernel/kgtp/trunk/gtp.c:6318: error: 'GTP_VAR_RDTSC_ID' undeclared (first use in this function)
/home/border/work/kernel/kgtp/trunk/gtp.c:6318: error: (Each undeclared identifier is reported only once
/home/border/work/kernel/kgtp/trunk/gtp.c:6318: error: for each function it appears in.)
/home/border/work/kernel/kgtp/trunk/gtp.c:6320: error: implicit declaration of function 'rdtscll'

* solution:

diff --git a/trunk/gtp.c b/trunk/gtp.c
index 4d0c9a2..75c145e 100644
--- a/trunk/gtp.c
+++ b/trunk/gtp.c
@@ -6315,11 +6315,13 @@ gtp_gdbrsp_qtv(char *pkg)
                if (num == GTP_VAR_CLOCK_ID) {
                        val = (uint64_t)GTP_LOCAL_CLOCK;
                        goto output_value;
+#ifdef CONFIG_X86
                } else if (num == GTP_VAR_RDTSC_ID) {
                        unsigned long long a;
                        rdtscll(a);
                        val = (uint64_t)a;
                        goto output_value;
+#endif
                } else if (num == GTP_VAR_XTIME_SEC_ID
                           || num == GTP_VAR_XTIME_NSEC_ID) {
                        struct timespec time

Complie and Install KGTP

make
sudo su
adb push gtp.ko /system/vendor/lib
exit

KGTP Running On Android

#Open the KGTP interface in current machine.
su
cd /system/vendor/lib
insmod gtp.ko
lsmod
nc -l -p 1234 < /sys/kernel/debug/gtp > /sys/kernel/debug/gtp

Host PC

cd /work/vc1000/src/kernel-vc1000-2.3
make -j8

Network connect to gtp

# symbian use "set gnutarget elf32-littlearm-symbian"
# vxworks use "set gnutarget elf32-littlearm-vxworks"
gdb-release -ex "set gnutarget elf32-littlearm" -ex "file ./vmlinux"

# if you want see the debug info
(gdb) set debug remote 1

# connection your remote device
(gdb) target remote 192.168.2.213:1234

USB connect to gtp

sudo su
# forward socket(adb forward <local> <remote>)
adb forward tcp:1234 tcp:1234
exit
gdb-release -ex "set gnutarget elf32-littlearm" -ex "file ./vmlinux"
# connection your remote device
(gdb) target remote 127.0.0.1:1234

Debugging with gtp

(gdb) trace vfs_readdir
Tracepoint 1 at 0xc02289f0: file /build/buildd/linux-2.6.35/fs/readdir.c, line 23.
(gdb) actions
Enter actions for tracepoint 1, one per line.
End with a line saying just "end".
>collect $reg
>end
(gdb) tstart

Change To Android Device Shell And Run ls Command * Android Device

$ ls

Back To Host PC GDB Shell * Host PC

(gdb) shell ls
vmlinux-2.6.35-30-generic
(gdb) tstop
(gdb) tfind
Found trace frame 0, tracepoint 1
#0  vfs_readdir (file=0x0, filler=0x163d8ae3, buf=0x18c0) at /build/buildd/linux-2.6.35/fs/readdir.c:23
23      {

Good luck, Happy Hacking…

Very grateful for teawater

References

* kgtp Linux Kernel GDB Tracepoint module

* kgtp Quick start

* kgtp How to

* How To Use KGTP In Android

* GDB Tracepoints