- * find the return address for mcount,
- * and the return address for mcount's caller.
+ * selfpc = pc pushed by mcount jsr,
+ * frompcindex = pc pushed by jsr into self.
+ * In GCC the caller's stack frame has already been built so we
+ * have to chase a6 to find caller's raddr. This assumes that all
+ * routines we are profiling were built with GCC and that all
+ * profiled routines use link/unlk.