I may be the odd man out here, but the spring is tied to the frame rail by the center pin. The floorpan over the spring mount is relatively thin gauge sheet metal and can simply be replaced.
Weld in a hefty plate if you feel better about it, but as long as the frame rail where the spring is attached is solid and sound (make sure of this before putting effort into repairs), replace the floorpans and call it a day.

Good thought.
Radi,does it look like the floor has rusted thru more than the mount has poked thru?
If that the case,firm up the mount as Radi suggests.
Either way,I think having it looked at by someone who really knows XJs would be helpful.

^This from the pics (it can always be hard to know for sure from pics though) it looks like the mount itself is intact and the floor pan just rotted off the top of it. If this is the case it should be a relatively easy repair. The uni-frame rail takes most of the weight/stress so if that is solid you should be good, but you should still fix the floor ASAP as it does provide some re-enforcement and leaving it like that risks that additional stress will crack the welds that hold the mount to the uni-frame which would be a major issue (and much more difficult to repair).

agree^^

sorry for not replying sooner but yes the rest of this cherokee is mint this is the only rust ive found on this thing but I and in the next couple of weeks I will be replacing the floor pan

X2 on the above. What I was seeing in my head was way worse than those pics. Fixing it seems to be well within reason.