building a RHEL4 kernel w/ kdb support

fytzzh

Sometimes I have a need to reproduce bugs on other platforms. When that platform uses a heavily patched kernel, it makes it hard to debug. Below are some notes I took while building a RHEL4 kernel with
kdb support
.
1. get the kernel
It's not easy to find the kernel sources for RHEL4 if you don't have the CDs. I was working off-site so I didn't.
I finally found
a security article
on
LinuxSecurity.com
that talked about a security fix and referenced the FTP source for
kernel-2.6.9-22.EL.src.rpm
. I grabbed that.
2. install the rpm
This step is easy, just run rpm -i kernel-2.6.9-22.EL.src.rpm. The sources are unpacked into /usr/src/redhat directories.
3. prepare the kernel
This step unpacks the tarball and applies the millions of patches packages with the redhat kernel:
    $ rpmbuild --target=i686 -bp /usr/src/redhat/SPECS/kernel-2.6.spec
The kernel is now in /usr/src/redhat/BUILD/kernel-2.6.9/linux-2.6.9
4. getting the KDB patches
If you need help, read the
README
.
You need to get two KDB patches. One common, and one for your architecture. In my case that's i386.
(I hope that is your case too, if not email me and maybe I can help you with the conversion of the patches)
The original patches (see below) require some manual fixing.
    $ cd /usr/src/redhat/SOURCES/
    $ wget http://jukie.net/~bart/kernel/2.6.9-22+kdb/kdb-v4.4-2.6.9-22.EL-common-2.patch.bz2
    $ bunzip2 kdb-v4.4-2.6.9-22.EL-common-2.patch.bz2
    $ wget http://jukie.net/~bart/kernel/2.6.9-22+kdb/kdb-v4.4-2.6.9-22.EL-i386-1.patch.bz2
    $ bunzip2 kdb-v4.4-2.6.9-22.EL-i386-1.patch.bz2
here are the links:
kdb-v4.4-2.6.9-22.EL-common-2.patch.bz2
,
kdb-v4.4-2.6.9-22.EL-i386-1.patch.bz2
For reference, these are the original patches I started with:
    $ wget ftp://oss.sgi.com/projects/kdb/download/v4.4/kdb-v4.4-2.6.9-common-2.bz2
    $ wget ftp://oss.sgi.com/projects/kdb/download/v4.4/kdb-v4.4-2.6.9-i386-1.bz2
5. patching the .spec file
To build an RPM you need a spec file. The spec file shipped with the .src.rpm contains a list of all the patches that will be applied, so we just need to add the two kdb patches. Here is the diff you will have to make:

add the patches into the list of patches at the end:
after Patch10001 add:
+Patch10002: kdb-v4.4-2.6.9-22.EL-common-2.patch
+Patch10003: kdb-v4.4-2.6.9-22.EL-i386-1.patch

add the options to pass to patch when applying our kdb patches:
after %patch10001 add:
+# kdb-v4.4-2.6.9-22.EL-common-2.patch
+%patch10002 -p1
+# kdb-v4.4-2.6.9-22.EL-i386-1.patch
+%patch10003 -p1
You can just get my spec patch:
    $ cd /usr/src/redhat/SPECS/
    $ wget http://jukie.net/~bart/kernel/2.6.9-22+kdb/kernel-2.6.spec.patch
here is the link:
kernel-2.6.spec.patch
Then apply it by running
    $ cd /usr/src/redhat/SPECS/
    $ patch -p0
8. patching the configs
I added 4 lines to each of the i686 config files in /usr/src/redhat/SOURCES:
    +CONFIG_KDB=y
    +# CONFIG_KDB_MODULES is not set
    +# CONFIG_KDB_OFF is not set
    +CONFIG_KDB_CONTINUE_CATASTROPHIC=0
You can just get my config patch:
    $ wget http://jukie.net/~bart/kernel/2.6.9-22+kdb/kernel-2.6.9-i686-configs.patch
here is the link:
kernel-2.6.9-i686-configs.patch
Then apply it by running
    $ cd /usr/src/redhat/SOURCES/
    $ patch -p0
7. building the rpm packages
To build both source and binary packages run:
    $ rpmbuild --target=i686 -ba /usr/src/redhat/SPECS/kernel-2.6.spec
The final products will be stored in /usr/src/redhat/RPMS/i686/ and /usr/src/redhat/SRPMS/. Should something fail you can review the tree in /usr/src/redhat/BUILD/kernel-2.6.9/linux-2.6.9 to see if you can fix it.
Note that this will build a 2.6.9-22.EL.root kernel. There is probably a good reason for including the user name of who built it. Eh, whatever.
This is what I get:
    $ ls /usr/src/redhat/{RPMS/i686/,SRPMS}
    /usr/src/redhat/RPMS/i686/:
    total 40M
    9.9M kernel-2.6.9-22.EL.root.i686.rpm
    3.7M kernel-devel-2.6.9-22.EL.root.i686.rpm
    9.5M kernel-hugemem-2.6.9-22.EL.root.i686.rpm
    3.8M kernel-hugemem-devel-2.6.9-22.EL.root.i686.rpm
    9.6M kernel-smp-2.6.9-22.EL.root.i686.rpm
    3.7M kernel-smp-devel-2.6.9-22.EL.root.i686.rpm
    /usr/src/redhat/SRPMS:
    total 40M
    40M kernel-2.6.9-22.EL.root.src.rpm
8. installing the new rpms
To install the new package simply run
    $ cd /usr/src/redhat/RPMS/i686/
    $ rpm -i kernel-2.6.9-22.EL.root.i686.rpm kernel-devel-2.6.9-22.EL.root.i686.rpm
(I install the devel packages because I am building 3rd party modules against it)
I am not sure if this updates /etc/grub.conf. Check it. Make sure you have something like this:
    title Red Hat Enterprise Linux AS (2.6.9-22.EL.root)
            root (hd0,0)
            kernel /boot/vmlinuz-2.6.9-22.EL.root ro root=LABEL=/1 rhgb quiet
            initrd /boot/initrd-2.6.9-22.EL.root.img
Then cross your fingers and reboot.
9. using kdb
Read the
Inside the Linux kernel debugger
article from IBM.


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