How to recompile a FreeBSD kernel with SSE support

Newer versions of ZXTM are built using newer versions of RSA's Crypto-library. Unfortunately, this library tries to be clever when optimizing itself for better performance, and will enable performance enhancements (such as, in this case, SSE support) when the processor supports them. Unfortunately, in the case of FreeBSD 4, while the processor does support these enhanced instructions, the default kernel doesn't!

So what is happening is that the RSA code and the processor agree between themselves to use (perfectly valid) enhanced codepaths, which thoroughly confuses the OS.

Since the code which does this is RSA's and not ours, we cannot fix this directly. However, the good news is that even the FreeBSD kernel can be rebuilt *with* SSE support.

To do this, you need to ensure that you have the kernel sources installed, and then add "options CPU_ENABLE_SSE" to your kernel configuration ("/usr/src/sys/i386/conf/{NAME}" - where NAME is "GENERIC" by default, but it's best practise to copy this file to a new name, and modify this).

This value is defined in /sys/i386/conf/LINT line 178, and is the default setting in FreeBSD 5.

Once set, use the following command:

make buildkernel KERNCONF={NAME} && make installkernel
KERNCONF={NAME}

as root in /usr/src should build and install your new kernel and, after a reboot, ZXTM should now work correctly!

Stuart Shelton [Zeus Support] 01 July 2005 2 comments