Remote Kernel Compilation: Custom Installation Path

make a directory myinstall

#> make modules_install INSTALL_MOD_PATH=myinstall
#> make install INSTALL_PATH=myinstall
#> make headers_install INSTALL_HDR_PATH=myinstall

everything will be neatly under myinstall directory :-)

now make the ramdisk by
mkinitramfs -o initrd.img-3.1.6 -r (myinstall) -v 3.1.6

on the remote machine,
copy myinstall/lib into /lib and fix the build and source symbolic links to actual source code directory. if there is no source directory, then only copy the headers. into /lib/modules/<version>/build/include...

/lib/modules/<version>/kernel contains all the .ko files
/lib/modules/<version>/build and source points to the headers, or you can keep the actual source files here... all it cares is the include directory inside build :-)

copy myinstall/config, map and vmlinuz into /boot and configure grub.

that's how we transfer a kernel from remote machine to target machine. do not forget to copy the .config file from target to remote before building kernel on remote.

Breakpoints in modules

I am working in modframe

Inside Host, connect gdb via pts to VM. 

Inside VM,
put the module in /root/Desktop/modexperiments/mf
make the module with all debugging info
    add this line in Makefile... EXTRA_CFLAGS += -ggdb3
modframe.ko will be created

insert the module. then it will have a /sys/modules/modframe/sections/.text entry.
track that 0xf8031000
or try this
grep function_name /proc/kallsyms ... track that address

Inside Host,

copy mf directory into /root/Desktop/modexperiments/ ... so that the files are there.

Now we will add breakpoints. 

Inside VM,

echo g > /proc/sysrq-trigger
This will hand transfer to gdb in host

Inside Host,
fire up gdb in host,
  # add-symbol-file modframe.ko 0x########
               -s .data 0x########
               -s .bss   0x########
you can view listing, or put a break point b *0xf8031000

Inside VM,
or remove the modules... that will hit the breakpoint :)
Other interesting utilities
objdump is another utility (use -h flag)

 $ nm modframe.ko -- view symbols 

or

 $ objdump -t modframe.ko            (all sections)
 $ objdump -t -j data modframe.ko    (data section)
 $ objdump -t -j bss modframe.ko     (BSS section)  

Ref:

https://www.linux.com/learn/linux-career-center/33991-the-kernel-newbie-corner-

kernel-and-module-debugging-with-gdb 

http://linux-hacks.blogspot.com/2009/07/using-gdb-for-debugging-kernel-modules.html

Commands Saturday Oct 15 2011

viewing information
info program, info sttck, info registers, info break

setting a breakpoint
break <function name>
break <line number>

clearing breakpoint
clear <function_name>
delete <breakpoint number>

viewing paramters
print <name>

Compile Kernel in a Remote Machine

compile remote kernel
http://web.archive.org/web/20000823075731/http://www.mindspring.com/~rgolan/lula/moving_kernels.html

preparing kvm ubuntu

install ubuntu mini in kvm VM.

then install ssh, gcc, vim, libncurses5-dev

then build and install the kernel

links link links

http://people.freebsd.org/~jhb/papers/bsdcan/2008/article/article.html
http://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug.html
http://issaris.blogspot.com/2007/12/download-linux-kernel-sourcecode-from.html

loading kernel in gdb

compile kernel with everything about tracing and kernel hacking (DYNAMIC, FTRACE, OPTIMIZE)

then vmlinux file is copied from remote to host

now start gdb/ddd
    > file vmlinux
    > target remote /dev/pts/X

that's it

Sysrq

echo g > /proc/sysrq-trigger

enable/disable sysrq

echo 0 > /proc/sys/kernel/sysrq

echo 1 > /proc/sys/kernel/sysrq 

Finding a symbol
grep alloc_pages /proc/kallsyms -- more symbols because of the loadable modules
or grep alloc_pages /boot/System.map-XXX -- only built-in symbols


kgdb ref:
http://elinux.org/Debugging_The_Linux_Kernel_Using_Gdb