Cross Compile Environment - Practical Raspberry Pi - page 116

This should also produce no errors. Normally the next step would be to run make install but that won't be very
helpful. Change into the src directory and run the file command:
# file hello
Now take a look at Figure 6-15 and you can see why it's not helpful.
Figure 6-15. Why running make install would be bad
It's now quite clear why make install would not go as planned. It's always a good idea to run the file tool across
your cross compiled binary files: this will make sure that you have in fact cross compiled the application and not just
used the local version of GCC. Now copy the hello application across to your Raspberry Pi by whatever means fits
best. I like to use scp to copy the file from my build machine to my Raspberry Pi. You could also insert the SD card
back into your host machine if you wanted to. Now it's time to see if it really worked. Run the hello application.
The GNU hello application supports a few options; in Figure 6-16 you can see my favorite option and its output.
Figure 6-16. The output of the GNU hello application
Congratulations! You have your first cross compiled application. Unfortunately, GNU hello is not very useful.
I do use it to test my tool chains; after all, I know the source code is in a well-maintained and working state.
Now that you have tested your tool chain, try and compile a small simple application. I will show you another
example for the application called netcat . You will be surprised at how easy it is. Listing 6-2 shows the build process.
Listing 6-2. Commands to Build netcat
# CC=arm-unknown-linux-gnueabi-gcc ./configure --host=arm-unknown-linux-gnueabi
# make
Look familiar? Those are the exact same commands you used to build the hello application. It's not hard to cross
compile a program if that program depends on nothing else. What would happen if you wanted to compile a more
complex program when you can't use the system library files (after all, they are compiled for an x86 architecture)?
Cross Compiling with Dependencies
A good example of a program that uses system library files is nmap, which depends on the pcap library files. For you
to be able to build nmap you're going to need to build libpcap for the ARM architecture first.
The first step will be to download libpcap into your build directory. You can download libpcap from
http://www.tcpdump.org/ . I will be using libpcap-1.3.0 . Extract the source once the download is finished. I like to
keep the source tarballs as well just in case I make a mess of the compile and install. In Figure 6-17 you can see the
source and its tarballs in my build directory.