Well, I finally found the cause of a bug that's been troubling me
for some time without really creating big trouble.
Consider the following program:

#include <stdio.h>
int main(void)
{
 if (stat("/foo/bar/baz")) perror("stat");
 if (rename("/foo/bar/baz", "/qux/quux/quuux")) perror("rename");
 exit(0);
}

compile with  "cc t.c -o t -lposix", run, and observe:
# ./t
stat: No such file or directory
Segmentation fault

This happens because the program will call the libposix.so "rename",
the system call fails, the "rename" stub calls the common "cerror",
which is in libc.so, but the "cerror" routing doesn't set the pointer
to the libc.so GOT (?) as it should.  Here is the (quite simple) fix:

--- /usr/src/lib/libc/arch/mips/sys/cerror.S	Mon Oct 14 17:37:39 1996
+++ cerror.S.fix	Sat Jul 25 03:57:22 1998
@@ -50,6 +50,9 @@
 	.globl	_C_LABEL(errno)
 LEAF(cerror)
 	.set	noreorder
+#ifdef ABICALLS
+        .cpload t9
+#endif
 	sw	v0, _C_LABEL(errno)
 	li	v0, -1
 	j	ra

It was a bit hard to find out what's wrong, but looking at the the other
assembly files in the same directory this fix looks safe.

  -  Arne H. J.