Replacing the C runtime library?

Hi,
 
I'm running into strange behavior with the C runtime library, e.g. crashes in sprintf and bizarre results from gmtime. I'm not able to reproduce it in a small program, and I may well be stomping on memory somewhere. But it's really tough to debug without the library source code.
 
Has anyone had experience replacing the C runtime with an open source version? Is there any documentation on the procedure?
 
- Bob
 

The buffer I provide for sprintf is twice as big as it needs to be. And I initialize it to 0xff so I can see that, after the crash, the entire buffer was not in use. I can even see how far sprintf got before it crashed: it was processing a %02d.
 
I'm not calling gmtime from a interrupt. I discovered, though, that other time functions use the same buffer as gmtime. Again, that's not what's happening here.
 

You should be able to just add a user command line flag depending how much you want to replace. You take out the default lib you will have to provide a vector table and clear the BSS.
-nodefaultlibs
-nostdlib