Splack Linux is Slackware for Sparc.
Splack supports all Sun4c, Sun4d, and Sun4m hardware.
Most Sun4U (Ultrasparc) machines are supported, but the more modern SunBlade and SunFire systems are not supported in the 2.2.20 kernel.
As a workaround you may be able to move the boot disk to a supported UltraSparc machine, install Splack 8.0, upgrade to Splack-current, and build a 2.4.27 or later kernel.
Sun4m SMP requires kernel 2.4.27 or later. Sun4d SMP requires 2.4.27 plus patches, the patches should be included in 2.4.28. Sun4d SMP will not work with serial console: install a framebuffer, monitor, and keyboard.