Linux: How to check the IO address space on your Linux machine

The parallel port is at address 0x0378?

This is the IO address space and this information is provided under the /proc file system as:

$> cat /proc/ioports

Sample output is as follows:

Linux: Implementing tftpboot with Linux u-boot

If your u-boot is not running tftpboot, for any reason as is the case with my board, you can always fool it into doing tftpboot for you by leveraging the run support in the u-boot bootloader.

U-boot is a very popular bootloader and you can learn more about it here: http://www.denx.de/wiki/U-Boot

Here is the trick to implement it:

setenv bootcmd 'dhcp; run cmd'
setenv cmd 'tftp LOADADDR PATH_TO_TFTPIMAGE'

 In the above set of commands you will have to replace LOADADDR with the correct address in memory where you want to load the image. The PATH_TO_TFTPIMAGE is the path to the image on the tftpserver.

Which Linux Kernel timing or delay APIs to use for what?

I classify the waiting or timing API in the Linux kernel in two categories:
1. Which blocks the current thread of execution.
2. Something which has to be scheduled for later but we want the current thread to continue.
In most cases, the distinction between 1 and 2 is clear, but the techniques used to implement 2 can also be manipulated to behave like 1.

1. Blocking current thread of execution (Inline delays)
The API for 1. in the above case are:

Why Linux Kernel KASLR is not very effective

Recently, with more time on hand  I am reading about security in the Linux kernel. A common mode of attack on any program is using buffer overflow to implement return oriented programming (ROP) blobs. Return oriented programming is a mechanism of overwriting return addresses in a library to implement code blobs (or gadgets) that will perform the desired functionality.

Linux: Why to drop caches and how? Host or virtual machine

Repost of an old post

Excerpt from stackoverflow: "The reason to drop caches like this is for benchmarking disk performance, and is the only reason it exists. When running an I/O-intensive benchmark, you want to be sure that the various settings you try are all actually doing disk I/O, so Linux allows you to drop caches rather than do a full reboot."

How to drop caches on the host?