LTRACE
=========================================
from the Man page
ltrace is a program that simply runs the specified command until it exits. It intercepts and records the dynamic library calls which are called by the executed process and the signals which are received by that process. It can also intercept and print the system calls executed by the program.
STRACE
===========================================
In the simplest case strace runs the specified command until it exits. It intercepts and records the system calls which are called by a process and the signals which are received by a process. The name of each system call, its arguments and its return value are printed on standard error or to the file specified with the -o option.
nemesis@nemesis-laptop:~/test_code$ strace ./crashcourse
execve("./crashcourse", ["./crashcourse"], [/* 42 vars */]) = 0
brk(0) = 0x80ba000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7846000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=72786, ...}) = 0
mmap2(NULL, 72786, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7834000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/tls/i686/cmov/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260l\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1319364, ...}) = 0
mmap2(NULL, 1325416, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x626000
mmap2(0x764000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x13e) = 0x764000
mmap2(0x767000, 10600, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x767000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7833000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb78336c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0x764000, 8192, PROT_READ) = 0
mprotect(0x8049000, 4096, PROT_READ) = 0
mprotect(0x3d0000, 4096, PROT_READ) = 0
munmap(0xb7834000, 72786) = 0
--- SIGSEGV (Segmentation fault) @ 0 (0) ---
+++ killed by SIGSEGV +++
MTRACE
=============================================
nemesis@nemesis-laptop:~/test_code$ mtrace ./crashcourse
No memory leaks
Friday, December 18, 2009
LibC
nemesis@nemesis-laptop:/lib$ ./libc.so.6
GNU C Library (EGLIBC) stable release version 2.10.1, by Roland McGrath et al.
Copyright (C) 2009 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.4.1.
Compiled on a Linux >>2.6.24-23-server<< system on 2009-10-07.
Available extensions:
crypt add-on version 2.1 by Michael Glad and others
GNU Libidn by Simon Josefsson
Native POSIX Threads Library by Ulrich Drepper et al
BIND-8.2.3-T5B
For bug reporting instructions, please see:
.
GNU C Library (EGLIBC) stable release version 2.10.1, by Roland McGrath et al.
Copyright (C) 2009 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.4.1.
Compiled on a Linux >>2.6.24-23-server<< system on 2009-10-07.
Available extensions:
crypt add-on version 2.1 by Michael Glad and others
GNU Libidn by Simon Josefsson
Native POSIX Threads Library by Ulrich Drepper et al
BIND-8.2.3-T5B
For bug reporting instructions, please see:
Core Dump : how to enable & Debug
1. find out if core will be dumped.
nemesis@nemesis-laptop:~/test_code$ ulimit -c
0
This means that core will NOT be dumped. ulimit specifies the maximum size of the core file.
2. Now set the value of ulimit to whatever you want it to be
ulimit -c [size]
3. you can also specify the directory in which core files will be placed
root@nemesis-laptop:/home/nemesis/test_code# echo "/tmp/corefiles/core" > /proc/sys/kernel/core_pattern
4. small program to cause the segmentation fault
###########################################
#include
void func2(void)
{
int *p = NULL;
*p = 0xdeadcafe;
}
void func1(void)
{
func2();
}
int main (int argc, char **argv)
{
func1();
int *p = NULL;
*p = 0xdeadcafe;
}
##############################################
nemesis@nemesis-laptop:~/test_code$ gcc -g -o crashcourse crash_core.c
5. now generate the core file
nemesis@nemesis-laptop:~/test_code$ ./corefile
Segmentation fault (core dumped)
6. a bit more details from the file command [Tells you the program which generated the core dump]
nemesis@nemesis-laptop:~/test_code$ file /tmp/corefiles/core
/tmp/corefiles/core: ELF 32-bit LSB core file Intel 80386, version 1 (SYSV), SVR4-style, from './corefile'
7. gdb [executable_file] [core_file]
##################################################
nemesis@nemesis-laptop:~/test_code$ gdb crashcourse /tmp/corefiles/core
GNU gdb (GDB) 7.0-ubuntu
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
...
Reading symbols from /home/nemesis/test_code/crashcourse...done.
warning: Can't read pathname for load map: Input/output error.
Reading symbols from /lib/tls/i686/cmov/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/tls/i686/cmov/libc.so.6
Reading symbols from /lib/ld-linux.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib/ld-linux.so.2
Core was generated by `./crashcourse'.
Program terminated with signal 11, Segmentation fault.
#0 0x080483c4 in func2 () at crash_core.c:6
6 *p = 0xdeadcafe;
##################################################
8. Get the backtrace
(gdb) bt
#0 0x080483c4 in func2 () at crash_core.c:6
#1 0x080483d4 in func1 () at crash_core.c:11
#2 0x080483e1 in main (argc=1, argv=0xbfe81b44) at crash_core.c:17
9. use the "up" and "down" commands to go through the code. (you can't run the code remember :) )
==============================================
UP
==============================================
(gdb) up
#1 0x080483d4 in func1 () at crash_core.c:11
11 func2();
(gdb) up
#2 0x080483e1 in main (argc=1, argv=0xbfe81b44) at crash_core.c:17
17 func1();
(gdb) up
Initial frame selected; you cannot go up.
===============================================
DOWN
===============================================
(gdb) down
#1 0x080483d4 in func1 () at crash_core.c:11
11 func2();
(gdb) down
#0 0x080483c4 in func2 () at crash_core.c:6
6 *p = 0xdeadcafe;
=========================================
NOTE: What if somebody handed you a core file and you don't the crashing process ? Happens a lot of times when the test team would pass you the core file and wash their hands off the issue altogether :)
Answer:
1. from the (file) following command
file [CORE-FILE]
2. just load the core file in gdb with "any" program name.
nemesis@nemesis-laptop:~/test_code$ gdb /bin/ps /tmp/corefiles/core
GNU gdb (GDB) 7.0-ubuntu
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
...
Reading symbols from /bin/ps...(no debugging symbols found)...done.
warning: core file may not match specified executable file.
Core was generated by `./crashcourse'.
Program terminated with signal 11, Segmentation fault.
#0 0x080483c4 in ?? ()
GDB is intelligent enough to catch your bluff but the good that comes out of it is that it tells you the correct name of the program that core-d. (GDB can't tell if your bluffing or plain ignorant :))
nemesis@nemesis-laptop:~/test_code$ ulimit -c
0
This means that core will NOT be dumped. ulimit specifies the maximum size of the core file.
2. Now set the value of ulimit to whatever you want it to be
ulimit -c [size]
3. you can also specify the directory in which core files will be placed
root@nemesis-laptop:/home/nemesis/test_code# echo "/tmp/corefiles/core" > /proc/sys/kernel/core_pattern
4. small program to cause the segmentation fault
###########################################
#include
void func2(void)
{
int *p = NULL;
*p = 0xdeadcafe;
}
void func1(void)
{
func2();
}
int main (int argc, char **argv)
{
func1();
int *p = NULL;
*p = 0xdeadcafe;
}
##############################################
nemesis@nemesis-laptop:~/test_code$ gcc -g -o crashcourse crash_core.c
5. now generate the core file
nemesis@nemesis-laptop:~/test_code$ ./corefile
Segmentation fault (core dumped)
6. a bit more details from the file command [Tells you the program which generated the core dump]
nemesis@nemesis-laptop:~/test_code$ file /tmp/corefiles/core
/tmp/corefiles/core: ELF 32-bit LSB core file Intel 80386, version 1 (SYSV), SVR4-style, from './corefile'
7. gdb [executable_file] [core_file]
##################################################
nemesis@nemesis-laptop:~/test_code$ gdb crashcourse /tmp/corefiles/core
GNU gdb (GDB) 7.0-ubuntu
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
Reading symbols from /home/nemesis/test_code/crashcourse...done.
warning: Can't read pathname for load map: Input/output error.
Reading symbols from /lib/tls/i686/cmov/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/tls/i686/cmov/libc.so.6
Reading symbols from /lib/ld-linux.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib/ld-linux.so.2
Core was generated by `./crashcourse'.
Program terminated with signal 11, Segmentation fault.
#0 0x080483c4 in func2 () at crash_core.c:6
6 *p = 0xdeadcafe;
##################################################
8. Get the backtrace
(gdb) bt
#0 0x080483c4 in func2 () at crash_core.c:6
#1 0x080483d4 in func1 () at crash_core.c:11
#2 0x080483e1 in main (argc=1, argv=0xbfe81b44) at crash_core.c:17
9. use the "up" and "down" commands to go through the code. (you can't run the code remember :) )
==============================================
UP
==============================================
(gdb) up
#1 0x080483d4 in func1 () at crash_core.c:11
11 func2();
(gdb) up
#2 0x080483e1 in main (argc=1, argv=0xbfe81b44) at crash_core.c:17
17 func1();
(gdb) up
Initial frame selected; you cannot go up.
===============================================
DOWN
===============================================
(gdb) down
#1 0x080483d4 in func1 () at crash_core.c:11
11 func2();
(gdb) down
#0 0x080483c4 in func2 () at crash_core.c:6
6 *p = 0xdeadcafe;
=========================================
NOTE: What if somebody handed you a core file and you don't the crashing process ? Happens a lot of times when the test team would pass you the core file and wash their hands off the issue altogether :)
Answer:
1. from the (file) following command
file [CORE-FILE]
nemesis@nemesis-laptop:~/test_code$ file /tmp/corefiles/core
/tmp/corefiles/core: ELF 32-bit LSB core file Intel 80386, version 1 (SYSV), SVR4-style, from './corefile'
2. just load the core file in gdb with "any" program name.
nemesis@nemesis-laptop:~/test_code$ gdb /bin/ps /tmp/corefiles/core
GNU gdb (GDB) 7.0-ubuntu
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
Reading symbols from /bin/ps...(no debugging symbols found)...done.
warning: core file may not match specified executable file.
Core was generated by `./crashcourse'.
Program terminated with signal 11, Segmentation fault.
#0 0x080483c4 in ?? ()
GDB is intelligent enough to catch your bluff but the good that comes out of it is that it tells you the correct name of the program that core-d. (GDB can't tell if your bluffing or plain ignorant :))
Sunday, December 13, 2009
GIT Guide --- update
Before your commits make sure you have these variables defined. :)
==================================================
nemesis@nemesis-laptop:~/qemu/qemu$ git config --global user.name "nemesisofstate"
nemesis@nemesis-laptop:~/qemu/qemu$ git config --global user.email "nemesisofstate@gmail.com"
-s --signoff
==================================================
nemesis@nemesis-laptop:~/qemu/qemu$ git config --global user.name "nemesisofstate"
nemesis@nemesis-laptop:~/qemu/qemu$ git config --global user.email "nemesisofstate@gmail.com"
for checkin
========
edit [file]
git add [file]
git commit -m "your-message-here" -s
Add Signed-off-by line by the committer at the end of the commit log message.
======================
see your patch
git format-patch origin/master
your messages
===============
git show
gitk ===> graphic tool for git
Send out your patch
================
I use gmail to send my patches ...so u need msmtp for it [http://msmtp.sourceforge.net]. Install the file and configure your ~/.msmtprc file
git-config --global sendemail.smtpserver /usr/local/bin/msmtp
sudo apt-get install git-email
git email-send
e.g
nemesis@nemesis-laptop:~/qemu/qemu$ git send-email 0001-correcting-ARM-CPSR-register-bit-position-comment.patch
Saturday, December 12, 2009
QEMU + U-BOOT
1. Get the U-Boot sources
However this would need mkimage. Where do we get it from--- Easy:) ---- after running make you can find the mkimage in [u-boot-dir]/tools directory.
3. Launch
sudo qemu-system-arm -nographic -m 256 -M versatileab -kernel u-boot.bin
The above command is good if your testing u-boot as a standalone app. However it would be wonderful to have networking between host and target to boot a linux kernel
sudo qemu-system-arm -M versatileab -kernel u-boot -net nic -net tap -nographic -serial stdio
Don't worry about the error message we will get to it.
===================================================
nemesis@nemesis-laptop:~/u-boot-2009.08$ sudo qemu-system-arm -nographic -m 256 -M versatileab -kernel u-boot.bin
U-Boot 2009.08 (Dec 13 2009 - 00:28:50)
DRAM: 0 kB
## Unknown FLASH on Bank 1 - Size = 0x00000000 = 0 MB
Flash: 0 kB
*** Warning - bad CRC, using default environment
In: serial
Out: serial
Err: serial
===================================================
Build linux kernel Image for U-boot
nemesis@nemesis-laptop:~/linux_kernel/linux-2.6.32$ make uImage
CHK include/linux/version.h
make[1]: `include/asm-arm/mach-types.h' is up to date.
CHK include/linux/utsrelease.h
SYMLINK include/asm -> include/asm-arm
CALL scripts/checksyscalls.sh
MKELF scripts/mod/elfconfig.h
HOSTCC scripts/mod/file2alias.o
HOSTCC scripts/mod/modpost.o
scripts/mod/modpost.c: In function ‘get_markers’:
scripts/mod/modpost.c:1562: warning: ignoring return value of ‘asprintf’, declared with attribute warn_unused_result
scripts/mod/modpost.c: In function ‘add_marker’:
scripts/mod/modpost.c:1982: warning: ignoring return value of ‘asprintf’, declared with attribute warn_unused_result
HOSTCC scripts/mod/sumversion.o
HOSTLD scripts/mod/modpost
CHK include/linux/compile.h
GEN lib/crc32table.h
CC lib/crc32.o
LD lib/built-in.o
LD vmlinux.o
MODPOST vmlinux.o
GEN .version
CHK include/linux/compile.h
UPD include/linux/compile.h
CC init/version.o
LD init/built-in.o
LD .tmp_vmlinux1
KSYM .tmp_kallsyms1.S
AS .tmp_kallsyms1.o
LD .tmp_vmlinux2
KSYM .tmp_kallsyms2.S
AS .tmp_kallsyms2.o
LD vmlinux
SYSMAP System.map
SYSMAP .tmp_System.map
OBJCOPY arch/arm/boot/Image
Kernel: arch/arm/boot/Image is ready
GZIP arch/arm/boot/compressed/piggy.gz
AS arch/arm/boot/compressed/piggy.o
LD arch/arm/boot/compressed/vmlinux
OBJCOPY arch/arm/boot/zImage
Kernel: arch/arm/boot/zImage is ready
UIMAGE arch/arm/boot/uImage
Image Name: Linux-2.6.32
Created: Sun Dec 13 02:29:45 2009
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 1535396 Bytes = 1499.41 kB = 1.46 MB
Load Address: 00008000
Entry Point: 00008000
Image arch/arm/boot/uImage is ready
GET READY TO BOOT YOUR LINUX KERNEL
======================================
VersatilePB # setenv ipaddr 10.0.2.16
VersatilePB # setenv serverip 10.0.2.15
VersatilePB # ping 10.0.2.15
SMC91111: PHY auto-negotiate timed out
Using MAC Address 52:54:00:12:34:56
host 10.0.2.15 is alive
VersatilePB # tftp 8000 uImage
SMC91111: PHY auto-negotiate timed out
Using MAC Address 52:54:00:12:34:56
TFTP from server 10.0.2.15; our IP address is 10.0.2.16
Filename 'uImage'.
Load address: 0x8000
Loading: T T T T T T T #################################################################
###T #####################################
done
Bytes transferred = 1535460 (176de4 hex)
PROBLEM: There seems to be a bug in the sense that DRAM setting are not correct for versatile.
Switching to Integrator platform. [build uboot and linux image for integrator]
(uboot config =====> integratorcp_config)
nemesis@nemesis-laptop:~/u-boot-2009.08$ sudo qemu-system-arm -kernel u-boot -net nic -net tap -nographic -serial stdio
[sudo] password for nemesis:
U-Boot 2009.08 (Dec 13 2009 - 04:00:17)
DRAM: 128 MB
## Unknown FLASH on Bank 1 - Size = 0x00000000 = 0 MB
Flash: 0 kB
*** Warning - bad CRC, using default environment
In: serial
Out: serial
Err: serial
Hit any key to stop autoboot: 0
Integrator-CP # setenv serverip 10.0.2.15
Integrator-CP # setenv ipaddr 10.0.2.16
Integrator-CP # tftp 8000 uImage
SMC91111: PHY auto-negotiate timed out
Using MAC Address 52:54:00:12:34:56
TFTP from server 10.0.2.15; our IP address is 10.0.2.16
Filename 'uImage'.
Load address: 0x8000
Loading: T T #################################################################
################################
done
Bytes transferred = 1411276 (1588cc hex)
Integrator-CP # bootm
## Booting kernel from Legacy Image at 00008000 ...
Image Name: Linux-2.6.32
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 1411212 Bytes = 1.3 MB
Load Address: 00008000
Entry Point: 00008000
XIP Kernel Image ... OK
OK
Starting kernel ...
qemu: fatal: Trying to execute code outside RAM or ROM at 0xfffff1c2
R00=00000000 R01=00000107 R02=00000100 R03=00000002
R04=00fddfc0 R05=00000000 R06=00008000 R07=00000113
R08=00fddfdc R09=010172c0 R10=010176ac R11=00fddced
R12=0100f750 R13=00000000 R14=00008008 R15=fffff1c2
PSR=600001db -ZC- A und32
Aborted
nemesis@nemesis-laptop:~/u-boot-2009.08$
============================================
So far so good...Uboot passes control to linux kernel but the kernel boot does a crash and burn. Will need to solve this one now....
2. sudo apt-get install qemu-kvm-extras [for qemu-system-arm]
We will compile for ARM (needless to say) target---ARM versatile board (needless again)
[NOTE]: [u-boot-dir]/include/configs contains the default configs for most of the platforms. It almost corresponds to the one in linux kernel sources.
STEPS
=======
1. make versatile_config
2. make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi-
make ....make....make...
[NOTE]: Uboot needs the linux with uboot specific headers in order to boot it. This u-boot specific image can be generated using "make uImage".
STEPS
=======
1. make versatile_config
2. make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi-
make ....make....make...
[NOTE]: Uboot needs the linux with uboot specific headers in order to boot it. This u-boot specific image can be generated using "make uImage".
---- Or get it from sudo apt-get install uboot-mkimage
3. Launch
sudo qemu-system-arm -nographic -m 256 -M versatileab -kernel u-boot.bin
The above command is good if your testing u-boot as a standalone app. However it would be wonderful to have networking between host and target to boot a linux kernel
sudo qemu-system-arm -M versatileab -kernel u-boot -net nic -net tap -nographic -serial stdio
Don't worry about the error message we will get to it.
===================================================
nemesis@nemesis-laptop:~/u-boot-2009.08$ sudo qemu-system-arm -nographic -m 256 -M versatileab -kernel u-boot.bin
U-Boot 2009.08 (Dec 13 2009 - 00:28:50)
DRAM: 0 kB
## Unknown FLASH on Bank 1 - Size = 0x00000000 = 0 MB
Flash: 0 kB
*** Warning - bad CRC, using default environment
In: serial
Out: serial
Err: serial
===================================================
Build linux kernel Image for U-boot
nemesis@nemesis-laptop:~/linux_kernel/linux-2.6.32$ make uImage
CHK include/linux/version.h
make[1]: `include/asm-arm/mach-types.h' is up to date.
CHK include/linux/utsrelease.h
SYMLINK include/asm -> include/asm-arm
CALL scripts/checksyscalls.sh
MKELF scripts/mod/elfconfig.h
HOSTCC scripts/mod/file2alias.o
HOSTCC scripts/mod/modpost.o
scripts/mod/modpost.c: In function ‘get_markers’:
scripts/mod/modpost.c:1562: warning: ignoring return value of ‘asprintf’, declared with attribute warn_unused_result
scripts/mod/modpost.c: In function ‘add_marker’:
scripts/mod/modpost.c:1982: warning: ignoring return value of ‘asprintf’, declared with attribute warn_unused_result
HOSTCC scripts/mod/sumversion.o
HOSTLD scripts/mod/modpost
CHK include/linux/compile.h
GEN lib/crc32table.h
CC lib/crc32.o
LD lib/built-in.o
LD vmlinux.o
MODPOST vmlinux.o
GEN .version
CHK include/linux/compile.h
UPD include/linux/compile.h
CC init/version.o
LD init/built-in.o
LD .tmp_vmlinux1
KSYM .tmp_kallsyms1.S
AS .tmp_kallsyms1.o
LD .tmp_vmlinux2
KSYM .tmp_kallsyms2.S
AS .tmp_kallsyms2.o
LD vmlinux
SYSMAP System.map
SYSMAP .tmp_System.map
OBJCOPY arch/arm/boot/Image
Kernel: arch/arm/boot/Image is ready
GZIP arch/arm/boot/compressed/piggy.gz
AS arch/arm/boot/compressed/piggy.o
LD arch/arm/boot/compressed/vmlinux
OBJCOPY arch/arm/boot/zImage
Kernel: arch/arm/boot/zImage is ready
UIMAGE arch/arm/boot/uImage
Image Name: Linux-2.6.32
Created: Sun Dec 13 02:29:45 2009
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 1535396 Bytes = 1499.41 kB = 1.46 MB
Load Address: 00008000
Entry Point: 00008000
Image arch/arm/boot/uImage is ready
GET READY TO BOOT YOUR LINUX KERNEL
======================================
VersatilePB # setenv ipaddr 10.0.2.16
VersatilePB # setenv serverip 10.0.2.15
VersatilePB # ping 10.0.2.15
SMC91111: PHY auto-negotiate timed out
Using MAC Address 52:54:00:12:34:56
host 10.0.2.15 is alive
VersatilePB # tftp 8000 uImage
SMC91111: PHY auto-negotiate timed out
Using MAC Address 52:54:00:12:34:56
TFTP from server 10.0.2.15; our IP address is 10.0.2.16
Filename 'uImage'.
Load address: 0x8000
Loading: T T T T T T T #################################################################
###T #####################################
done
Bytes transferred = 1535460 (176de4 hex)
PROBLEM: There seems to be a bug in the sense that DRAM setting are not correct for versatile.
Switching to Integrator platform. [build uboot and linux image for integrator]
(uboot config =====> integratorcp_config)
nemesis@nemesis-laptop:~/u-boot-2009.08$ sudo qemu-system-arm -kernel u-boot -net nic -net tap -nographic -serial stdio
[sudo] password for nemesis:
U-Boot 2009.08 (Dec 13 2009 - 04:00:17)
DRAM: 128 MB
## Unknown FLASH on Bank 1 - Size = 0x00000000 = 0 MB
Flash: 0 kB
*** Warning - bad CRC, using default environment
In: serial
Out: serial
Err: serial
Hit any key to stop autoboot: 0
Integrator-CP # setenv serverip 10.0.2.15
Integrator-CP # setenv ipaddr 10.0.2.16
Integrator-CP # tftp 8000 uImage
SMC91111: PHY auto-negotiate timed out
Using MAC Address 52:54:00:12:34:56
TFTP from server 10.0.2.15; our IP address is 10.0.2.16
Filename 'uImage'.
Load address: 0x8000
Loading: T T #################################################################
################################
done
Bytes transferred = 1411276 (1588cc hex)
Integrator-CP # bootm
## Booting kernel from Legacy Image at 00008000 ...
Image Name: Linux-2.6.32
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 1411212 Bytes = 1.3 MB
Load Address: 00008000
Entry Point: 00008000
XIP Kernel Image ... OK
OK
Starting kernel ...
qemu: fatal: Trying to execute code outside RAM or ROM at 0xfffff1c2
R00=00000000 R01=00000107 R02=00000100 R03=00000002
R04=00fddfc0 R05=00000000 R06=00008000 R07=00000113
R08=00fddfdc R09=010172c0 R10=010176ac R11=00fddced
R12=0100f750 R13=00000000 R14=00008008 R15=fffff1c2
PSR=600001db -ZC- A und32
Aborted
nemesis@nemesis-laptop:~/u-boot-2009.08$
============================================
So far so good...Uboot passes control to linux kernel but the kernel boot does a crash and burn. Will need to solve this one now....
Sunday, December 6, 2009
Busybox
1. Download the source and patches from the busybox website.
http://www.busybox.net/download.html
The version at the time of writing this is 1.14.1.
2. untar the sources to the directory where you will run the build.
3. patch the sources
patch -p0 <>.patch
e.g patch -p0 <>
4. config the busybox using your favourite config method. I prefer to use xconfig.
5. make your day :) -------- run make
6. once the make has run successful , you would want to install the busybox in a seperate directory which you can later ready to use as the rootfs.
make CONFIG_PREFIX=~/busybox/target install
where I am installing busybox in the /home/nemesis/busybox/target directory
7 cd to the install directory
cd ~/busybox/target
8. There isn't a great deal there
ls -al would return
sbin, bin , usr and linuxrc (a symbolic link to /bin/busybox)
9. Create the dev, dev/pts, etc, etc/init.d, lib, mnt, opt, proc, root, sys, tmp, var, and var/log directories. Also create the device node for the initial console
mkdir dev etc lib mnt opt proc root sys tmp var debug
mkdir etc/init.d
mkdir var/log
sudo mknod dev/console c 5 1
sudo mknod dev/null c 1 3
10. Mount proc and /dev/pts at boot time
===========================
edit /etc/fstab for these filesystems
11. Shared library and library loader
==========================
We still need the
---------- shared libraries (from your toolchain)
---------- library loader (e.g ld-linux.so.3 in the listing below)
nemesis@nemesis-laptop:~/codesourcery/arm-2009q3/arm-none-linux-gnueabi/libc/lib$ ls
ld-2.10.1.so libdl-2.10.1.so libnss_dns.so.2 libresolv-2.10.1.so
ld-linux.so.3 libdl.so.2 libnss_files-2.10.1.so libresolv.so.2
libanl-2.10.1.so libgcc_s.so libnss_files.so.2 librt-2.10.1.so
libanl.so.1 libgcc_s.so.1 libnss_hesiod-2.10.1.so librt.so.1
libBrokenLocale-2.10.1.so libm-2.10.1.so libnss_hesiod.so.2 libSegFault.so
libBrokenLocale.so.1 libmemusage.so libnss_nis-2.10.1.so libthread_db-1.0.so
libc-2.10.1.so libm.so.6 libnss_nisplus-2.10.1.so libthread_db.so.1
libcidn-2.10.1.so libnsl-2.10.1.so libnss_nisplus.so.2 libutil-2.10.1.so
libcidn.so.1 libnsl.so.1 libnss_nis.so.2 libutil.so.1
libcrypt-2.10.1.so libnss_compat-2.10.1.so libpcprofile.so
libcrypt.so.1 libnss_compat.so.2 libpthread-2.10.1.so
libc.so.6 libnss_dns-2.10.1.so libpthread.so.0
--- that's an aweful lot. Copying them indiscriminately will cause our rootfs to be bloated (something we don't want). So just pick what you need. And And And ofcourse strip these libraries :)
nemesis@nemesis-laptop:~/busybox/target/lib$ ~/codesourcery/arm-2009q3/bin/arm-none-linux-gnueabi-strip *
Thats the minimal set for the rootfs
12. Kernel Modules
=================
Now it is time to get our dear modules.
--- go to the kernel build directory
--- issue the following command : make modules
after it has completed successfully , we need to install the modules in our rootfs. Elementary my dear watson!
http://www.busybox.net/download.html
The version at the time of writing this is 1.14.1.
2. untar the sources to the directory where you will run the build.
3. patch the sources
patch -p0 <>.patch
e.g patch -p0 <>
4. config the busybox using your favourite config method. I prefer to use xconfig.
5. make your day :) -------- run make
6. once the make has run successful , you would want to install the busybox in a seperate directory which you can later ready to use as the rootfs.
make CONFIG_PREFIX=~/busybox/target install
where I am installing busybox in the /home/nemesis/busybox/target directory
7 cd to the install directory
cd ~/busybox/target
8. There isn't a great deal there
ls -al would return
sbin, bin , usr and linuxrc (a symbolic link to /bin/busybox)
9. Create the dev, dev/pts, etc, etc/init.d, lib, mnt, opt, proc, root, sys, tmp, var, and var/log directories. Also create the device node for the initial console
mkdir dev etc lib mnt opt proc root sys tmp var debug
mkdir etc/init.d
mkdir var/log
sudo mknod dev/console c 5 1
sudo mknod dev/null c 1 3
10. Mount proc and /dev/pts at boot time
===========================
edit /etc/fstab for these filesystems
11. Shared library and library loader
==========================
We still need the
---------- shared libraries (from your toolchain)
---------- library loader (e.g ld-linux.so.3 in the listing below)
nemesis@nemesis-laptop:~/codesourcery/arm-2009q3/arm-none-linux-gnueabi/libc/lib$ ls
ld-2.10.1.so libdl-2.10.1.so libnss_dns.so.2 libresolv-2.10.1.so
ld-linux.so.3 libdl.so.2 libnss_files-2.10.1.so libresolv.so.2
libanl-2.10.1.so libgcc_s.so libnss_files.so.2 librt-2.10.1.so
libanl.so.1 libgcc_s.so.1 libnss_hesiod-2.10.1.so librt.so.1
libBrokenLocale-2.10.1.so libm-2.10.1.so libnss_hesiod.so.2 libSegFault.so
libBrokenLocale.so.1 libmemusage.so libnss_nis-2.10.1.so libthread_db-1.0.so
libc-2.10.1.so libm.so.6 libnss_nisplus-2.10.1.so libthread_db.so.1
libcidn-2.10.1.so libnsl-2.10.1.so libnss_nisplus.so.2 libutil-2.10.1.so
libcidn.so.1 libnsl.so.1 libnss_nis.so.2 libutil.so.1
libcrypt-2.10.1.so libnss_compat-2.10.1.so libpcprofile.so
libcrypt.so.1 libnss_compat.so.2 libpthread-2.10.1.so
libc.so.6 libnss_dns-2.10.1.so libpthread.so.0
--- that's an aweful lot. Copying them indiscriminately will cause our rootfs to be bloated (something we don't want). So just pick what you need. And And And ofcourse strip these libraries :)
nemesis@nemesis-laptop:~/busybox/target/lib$ ~/codesourcery/arm-2009q3/bin/arm-none-linux-gnueabi-strip *
Thats the minimal set for the rootfs
12. Kernel Modules
=================
Now it is time to get our dear modules.
--- go to the kernel build directory
--- issue the following command : make modules
after it has completed successfully , we need to install the modules in our rootfs. Elementary my dear watson!
make INSTALL_MOD_PATH=/path/to/rootfs modules_install
Once we are out of the debugging phase, we would like to strip the modules to slim down.
cd /path/to/rootfs/lib/modules
arm-none-linux-gnueabi-strip `find . –name “*.ko”`
Root File System
Umpteen ways to get this done :-
1. NFS Mounted. [One of the most popular methods ]
2. Initial RAMDISK (Initrd) ====> Will cover this in more detail in a later post
3. JFFS/JFFS2
4. CRAMFS (Read-only)
We will use busybox -- the veritable "Swiss Army Knife" for embedded systems.
Each of these will be explained in seperate posts, starting with Busybox
Each of these will be explained in seperate posts, starting with Busybox
Saturday, December 5, 2009
ARM on QEMU
Goal : Run linux on a verstaline board (simulated by QEMU)
why : Because it is not always possible to have the real board available for development.
Prerequisites:
==============
1. QEMU : ofcourse
on debian systems : sudo apt-get install qemu
on RH systems : sudo yum install qemu
2. This one depends on what kind of communication mechanism is used between the host (your development) system and the guest sytem on QEMU. I prefer to use networking.
---- Have DHCP running so that guest system on qemu can use it to get an IP address.
---- host TAP devices used to connect to QEMU. The kernel config of the host should have TAP/TUN networking enabled. The switch for this is CONFIG_TUN.
grep CONFIG_TUN= /boot/config-`uname -r`
This should return you the state of the switch.
nemesis@nemesis-laptop:~$ grep CONFIG_TUN= /boot/config-`uname -r`
CONFIG_TUN=m
nemesis@nemesis-laptop:~$ ls -al /dev/net/tun
crw-rw-rw- 1 root root 10, 200 2009-11-03 11:46 /dev/net/tun
This verifies that the device exists indeed. If not, create it manually.
mknod /dev/net/tun c 10 200
Configure bridge-control
==================
Add the following to a script file
#!/bin/sh
/usr/sbin/brctl addbr br0 ### Add a bridge
/sbin/ifconfig eth0 0.0.0.0 promisc up ### set up eth0
/usr/sbin/brctl addif br0 eth0 ### add an intf(eth0) to the bridge (br0)
/sbin/dhclient br0 ### enable dhcp
/sbin/iptables -F FORWARD
Build kernel
=========
The quickest way is to use the default config file for the versatile platform.
Simply copy the config file from configs directory for ARM arch and rename it as .config
cp/arch/arm/configs/versatile_defconfig /.config
Config the Linux kernel (xconfig, menuconfig or simply using vim to edit..have it your way)
1. Enable ARM EABI support : switch CONFIG_AEABI (part of kernel features)
2. Enable DHCP : Switch CONFIG_IP_PNP_DHCP
3. Enable Universal TUN/TAP driver : switch CONFIG_TUN
4. Enable tmpfs : Switch CONFIG_TMPFS
Now we are ready to make (my day)
Ofcourse ARCH = arm
and CROSS_COMPILE = your_cross_compiler (I use codesourcery and for me it is
arm-none-linux-gnueabi-)
What about the Root File System ?
=======================
We will NFS mount the root filesystem. Build your rootfs.
1. edit /etc/exports ===> Add the following line
/mnt/arm-linux-rootfs / *(rw,sync,no_root_squash)
Here the untarred rootfs is at /mnt/arm-linux-rootfs and it is accessible as rw filesystem from any systems (indicated by *). If static ip-addresses are assigned, use the ip-address of the peer here.
2. restart the nfs service so that our changes come into effect.
/etc/init.d/nfs restart
Boot into Linux on QEMU
======================
qemu-ifup
=============================
#!/bin/sh
echo "Executing /etc/qemu-ifup"
echo "Bringing up $1 for bridged mode..."
sudo /sbin/ifconfig $1 0.0.0.0 promisc up
echo "Adding $1 to br0..."
sudo /usr/sbin/brctl addif br0 $1
sleep 2
Source : http://fedoraproject.org/wiki/Architectures/ARM/HowToQemu
http://www.aurel32.net/info/debian_arm_qemu.php
why : Because it is not always possible to have the real board available for development.
Prerequisites:
==============
1. QEMU : ofcourse
on debian systems : sudo apt-get install qemu
on RH systems : sudo yum install qemu
2. This one depends on what kind of communication mechanism is used between the host (your development) system and the guest sytem on QEMU. I prefer to use networking.
---- Have DHCP running so that guest system on qemu can use it to get an IP address.
---- host TAP devices used to connect to QEMU. The kernel config of the host should have TAP/TUN networking enabled. The switch for this is CONFIG_TUN.
grep CONFIG_TUN= /boot/config-`uname -r`
This should return you the state of the switch.
nemesis@nemesis-laptop:~$ grep CONFIG_TUN= /boot/config-`uname -r`
CONFIG_TUN=m
nemesis@nemesis-laptop:~$ ls -al /dev/net/tun
crw-rw-rw- 1 root root 10, 200 2009-11-03 11:46 /dev/net/tun
This verifies that the device exists indeed. If not, create it manually.
mknod /dev/net/tun c 10 200
Configure bridge-control
==================
Add the following to a script file
#!/bin/sh
/usr/sbin/brctl addbr br0 ### Add a bridge
/sbin/ifconfig eth0 0.0.0.0 promisc up ### set up eth0
/usr/sbin/brctl addif br0 eth0 ### add an intf(eth0) to the bridge (br0)
/sbin/dhclient br0 ### enable dhcp
/sbin/iptables -F FORWARD
Build kernel
=========
The quickest way is to use the default config file for the versatile platform.
Simply copy the config file from configs directory for ARM arch and rename it as .config
cp
Config the Linux kernel (xconfig, menuconfig or simply using vim to edit..have it your way)
1. Enable ARM EABI support : switch CONFIG_AEABI (part of kernel features)
2. Enable DHCP : Switch CONFIG_IP_PNP_DHCP
3. Enable Universal TUN/TAP driver : switch CONFIG_TUN
4. Enable tmpfs : Switch CONFIG_TMPFS
Now we are ready to make (my day)
Ofcourse ARCH = arm
and CROSS_COMPILE = your_cross_compiler (I use codesourcery and for me it is
arm-none-linux-gnueabi-)
What about the Root File System ?
=======================
We will NFS mount the root filesystem. Build your rootfs.
1. edit /etc/exports ===> Add the following line
/mnt/arm-linux-rootfs / *(rw,sync,no_root_squash)
Here the untarred rootfs is at /mnt/arm-linux-rootfs and it is accessible as rw filesystem from any systems (indicated by *). If static ip-addresses are assigned, use the ip-address of the peer here.
2. restart the nfs service so that our changes come into effect.
/etc/init.d/nfs restart
Boot into Linux on QEMU
======================
qemu-system-arm -M versatilepb -kernel zImage-versatile -append root="/dev/nfs nfsroot=:/mnt/arm-linux-rootfs rw ip=dhcp" \
-net nic,vlan=0 -net tap,vlan=0,ifname=tap0,script=./qemu-ifup
qemu-ifup
=============================
#!/bin/sh
echo "Executing /etc/qemu-ifup"
echo "Bringing up $1 for bridged mode..."
sudo /sbin/ifconfig $1 0.0.0.0 promisc up
echo "Adding $1 to br0..."
sudo /usr/sbin/brctl addif br0 $1
sleep 2
Source : http://fedoraproject.org/wiki/Architectures/ARM/HowToQemu
http://www.aurel32.net/info/debian_arm_qemu.php
Sunday, November 29, 2009
Cross Toolchains : PART2 (Kernel Headers)
1. Download the kernel sources from kernel.org
2. cd to the sources root directory
3. run the following command to extract the headers for ARM
To see a list of all supported architectures
make headers_install_all exports headers for all architectures simultaneously. Not very useful for the average embedded programmer.
#Decribe the API for the user space programs wishing to use kernel services
#Used by system's C library (glibc or uClibc) to define available system calls as well as constants and structures to be used with these system calls.
#Kernel headers are backward compatible.
[Sources : 1. Documentation/make/headers_install.txt ]
2. cd to the sources root directory
3. run the following command to extract the headers for ARM
make headers_install ARCH=arm INSTALL_HDR_PATH=/usr/include/arm-linux-headersWhere ARCH specifies the architecture for which the headers are to be generated. INSTALL_HDR_PATH is the path on the local system where the header files will be placed. The default is /usr/include
To see a list of all supported architectures
ls -d include/asm-* | sed 's/.*-//'
make headers_install_all exports headers for all architectures simultaneously. Not very useful for the average embedded programmer.
#Decribe the API for the user space programs wishing to use kernel services
#Used by system's C library (glibc or uClibc) to define available system calls as well as constants and structures to be used with these system calls.
#Kernel headers are backward compatible.
[Sources : 1. Documentation/make/headers_install.txt ]
nemesis@nemesis-laptop:~/arm-linux-kernel/linux-2.6.31.6$ sudo make headers_install ARCH=arm INSTALL_HDR_PATH=/usr/include/arm-linux
CHK include/linux/version.h
make[1]: `scripts/unifdef' is up to date.
INSTALL include/asm-generic (34 files)
INSTALL include/drm (12 files)
INSTALL include/linux/byteorder (2 files)
INSTALL include/linux/can (4 files)
INSTALL include/linux/dvb (8 files)
INSTALL include/linux/hdlc (1 file)
INSTALL include/linux/isdn (1 file)
INSTALL include/linux/netfilter (58 files)
INSTALL include/linux/netfilter_arp (2 files)
INSTALL include/linux/netfilter_bridge (16 files)
INSTALL include/linux/netfilter_ipv4 (46 files)
INSTALL include/linux/netfilter_ipv6 (21 files)
INSTALL include/linux/nfsd (6 files)
INSTALL include/linux/raid (2 files)
INSTALL include/linux/spi (1 file)
INSTALL include/linux/sunrpc (1 file)
INSTALL include/linux/tc_act (6 files)
INSTALL include/linux/tc_ematch (4 files)
INSTALL include/linux/usb (8 files)
INSTALL include/linux/wimax (1 file)
INSTALL include/linux (352 files)
INSTALL include/mtd (5 files)
INSTALL include/rdma (1 file)
INSTALL include/scsi (4 files)
INSTALL include/sound (9 files)
INSTALL include/video (3 files)
INSTALL include/xen (1 file)
INSTALL include (0 file)
INSTALL include/asm (32 files)
Cross Toolchains : PART 1 (Binutils)
Components of crosstoolchain
===================
1. Binutils
2. Kernel header
3. C library
4. Compiler [e.g gcc]
optional : gdb debugger etc
Binutils
=====
The target architecture needs to have its own set of tools to generate binary files for it. Also it would be nice to have some tools to enable examining these.
ld ---> linker
strip --> to strip the object file of a particular section. e.g strip the comments to reduce the code size.
as --> assembler
objdump
objcopy
readelf: very useful tool. I invariably use it with -a switch to retrieve the max info.
nm : lists all the symbols in an object file.
===========
Extract from IBM's website
objdump & nm
=================================
addr2line : very important for debugging. E.g lets say you get a core dump with a backtrace. You can use the backtrace info to go to the code directly
void test_funk()
{
printf("#NEMESIS: testing funky func \n");
printf("#NEMESIS: address of test_funk [%p]", &test_funk);
}
Output: in the output the addess printed is 0x845c. Pass this as an input to the addr2line.]
nemesis@nemesis-laptop:~/test_code$ arm-none-linux-gnueabi-addr2line 0x845c
/home/adikumar/test_code/test_3.c:5 ===> Lo and behold.You have the line in the code.
strings: Lists all string in an object file. use it with grep to find a particular string
nemesis@nemesis-laptop:~/codesourcery/arm-2009q3/bin$ arm-none-linux-gnueabi-strings test2
/lib/ld-linux.so.3
libgcc_s.so.1
__aeabi_unwind_cpp_pr0
__gmon_start__
_Jv_RegisterClasses
__aeabi_unwind_cpp_pr1
libc.so.6
abort
printf
__libc_start_main
GCC_3.5
GLIBC_2.4
###!Nemesis: LittleEndian =========> my prints
###!Nemesis: BigEndian =========> my prints
0x%x
===================
1. Binutils
2. Kernel header
3. C library
4. Compiler [e.g gcc]
optional : gdb debugger etc
Binutils
=====
The target architecture needs to have its own set of tools to generate binary files for it. Also it would be nice to have some tools to enable examining these.
ld ---> linker
strip --> to strip the object file of a particular section. e.g strip the comments to reduce the code size.
strip [ -F BFDNAME | --target=BFDNAME ]
[ -I BFDNAME | --input-target=BFDNAME ]
[ -O BFDNAME | --output-target=BFDNAME ]
[ -s | --strip-all ] [ -S | -g | --strip-debug ]
[ -K SYMBOLNAME | --keep-symbol=SYMBOLNAME ]
[ -N SYMBOLNAME | --strip-symbol=SYMBOLNAME ]
[ -x | --discard-all ] [ -X | --discard-locals ]
[ -R SECTIONNAME | --remove-section=SECTIONNAME ]
[ -o FILE ] [ -p | --preserve-dates ]
[ -v | --verbose ] [ -V | --version ] [ --help ]
OBJFILE...
e.g strip --remove section=.comment
as --> assembler
objdump
objcopy
readelf: very useful tool. I invariably use it with -a switch to retrieve the max info.
nm : lists all the symbols in an object file.
===========
Extract from IBM's website
objdump & nm
The commands objdump and nm both display information about object files. If a crash occurs and a corefile is produced, these commands help you analyze the file.
- objdump
- Use this command to disassemble shared objects and libraries. After you have discovered which library or object has caused the problem, use objdump to locate the method in which the problem originates. To invoke objdump, type: objdump
- nm
- This command lists symbol names from object files. These symbol names can be either functions, global variables, or static variables. For each symbol, the value, symbol type, and symbol name are displayed. Lower case symbol types mean the symbol is local, while upper case means the symbol is global or external. To use this tool, type: nm
You can see a complete list of options by typing objdump -H. The -d option disassembles contents of executable sections
Run these commands on the same machine as the one that produced the core files to get the most accurate symbolic information available. This output (together with the core file, if small enough) is used by the IBM® support team for Java™ to diagnose a problem.
addr2line : very important for debugging. E.g lets say you get a core dump with a backtrace. You can use the backtrace info to go to the code directly
void test_funk()
{
printf("#NEMESIS: testing funky func \n");
printf("#NEMESIS: address of test_funk [%p]", &test_funk);
}
Output: in the output the addess printed is 0x845c. Pass this as an input to the addr2line.]
nemesis@nemesis-laptop:~/test_code$ arm-none-linux-gnueabi-addr2line 0x845c
/home/adikumar/test_code/test_3.c:5 ===> Lo and behold.You have the line in the code.
strings: Lists all string in an object file. use it with grep to find a particular string
nemesis@nemesis-laptop:~/codesourcery/arm-2009q3/bin$ arm-none-linux-gnueabi-strings test2
/lib/ld-linux.so.3
libgcc_s.so.1
__aeabi_unwind_cpp_pr0
__gmon_start__
_Jv_RegisterClasses
__aeabi_unwind_cpp_pr1
libc.so.6
abort
printf
__libc_start_main
GCC_3.5
GLIBC_2.4
###!Nemesis: LittleEndian =========> my prints
###!Nemesis: BigEndian =========> my prints
0x%x
Wednesday, November 25, 2009
Whats your Endian-ness ?
int i= 0x1;
*((char*)&i) ? printf("###!Nemesis: LittleEndian\n"):printf("###!Nemesis: BigEndian\n");
printf("0x%x \n", *((char*)&i));
Wednesday, November 18, 2009
Forthcoming Embedded Articles
1. Building cross compiled linux kernel [With debug support]. Explain various configuration options.
2. Building a customized root filesystem
3. initial Ram disk
4. Uboot Bootloader: Internals, porting
5. Linux kernel start code walk through [ARM perspective]
6. Busybox
7. Using emulators [Qemu]
8. Linux device driver Serial : ARM Primecell UART
9. Linux Network driver
10. Linux Serial Driver
11. Gnu Tool chain [ gdb, gcc etc ]. binutils Making your own toolchain
12. ucLinux , ucLibc
13. NFS mounting
14. Remote debugging with gdbserver
15. Integrating Eclipse into your embedded development system
16. Misc tools : valgrind, profiling tools etc
17. kernel boot parameters. Explain nfs boot [ ip assigned by DHCP]
18. Various kernel image formats...zImage, uImage, vmlinux etc [ explain the linking and image components]
19. uClibC vs glibc
20. different filesystems (esp squashfs )
21. scratchbox, Buildroot
Wednesday, July 8, 2009
Difference between "su" and "su -"
A lot of people don't know the difference [and there is a day light of difference :) ]
==================
su
==================
1. ENVIRONMENT : The environment is the same as that of the user's from which you entered root. In the following example, the environment would be the same as that of user nemesis.
e.g nemesis@tantra:~/device-drivers$su
================================
su -
================================
1. shell reads a relevant startup files and simulates a login
2. ENVIRONMENT: The enviroment is that of the superuser/root and NOT that of the account from you you invoked "su".
For more detailed information, please refer to the man pages.
Monday, July 6, 2009
Strings: Single Quote Vs Double Quotes
In UNIX Shell
============
Double Quotes : In (Most ) UNIX shells and other scripting languages like perl, the interpreter would parse through the string inorder to perform substitutions for any variables in the string.
Single Quotes: Interpreter leaves the string alone. It is treated as a string literal.
In C
===========
Double Quotes: For strings
Single Quotes : For single character literals.
e.g
char c[];
c = 'c'; ==> SINGLE Quotes
c = "char"; ==> DOUBLE quotes
Tuesday, January 13, 2009
Minimal GIT guide
1. Create a new branch on the remote git repository
git push origin origin:refs/heads/
e.g git push origin origin:/refs/heads/nemesis-debug
creates a branch called nemesis-debug on the remote repository.
Confirm this by typing git branch -r. Your new respository should appear there.
2. create a local branch to track the newly created remote branch.
git checkout --track -b
e.g git checkout --track -b nemesis-debug origin/nemesis-debug
3. make all necessary changes.
4. commit your changes
a.add files/directories you want to commit
git add
git add . # adds all the files in the directory recursively
b. commit
git commit -m "commit-message"
c. push all your changes to the repository
git push origin
e.g git push origin nemesis-debug
5. In case you screwed up and want to delete the remote branch
git push origin :heads/
e.g git push origin :heads/nemesis-debug
Tuesday, January 6, 2009
Memory Optimizations: Kernel Programming
UNLIKE User-space code/data, kernel code/data reside PERMANENTLY in memory. They are NOT swapped Out.
>>> module_init : RUN Time Optimization. Executed when the associated module is loaded. If the module is statically included in the kernel, the kernel can free the module_init routine right at the boot time, after it runs.
>>> module_exit: LINK Time Optimization. It is never executed if the modules are statically included in the kernel. In such cases, it is not needed to include module_exit routines into the kernel image and are discarded at Link Time.
Monday, January 5, 2009
SSH: Logging without Passwords
Here is what to do :-
1. generate a public and private key pair.
ssh-keygen -t rsa -b 4096 -C "comment"
This would generate a 4096 bit long key using RSA encryption mechanism. You can choose to use DSA instead of RSA.
2. When prompted save the key to your home directory.
In my case it would be /home/nemesis/.ssh/id_rsa.pub
3. When prompted for a passphrase, just press enter. Press enter to confirm again. This means a blank password.
4. scp the above generated password file to the remote server.
e.g scp /home/nemesis/.ssh/id_rsa.pub nemesis@remote-server.org:/home/nemesis/
where remote-server.org is the remote machine that I want to login to without using passwords.
5. ON THE Remote machine now.
>Check to see if there is a .ssh folder. If it doesnt exist in your home directory, create it
mkdir -p /home/nemesis/.ssh
Now add your credentials to the authorized lists. Here is how to do it.
cat id_rsa.pub >> .ssh/authorized_keys
6.Logout
7. ssh nemesis@remote-server.org
Voila!!! You are in. No password required.
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