The location of the vectors file object is critical.

From the comments at the head of vectors.s:

  The issue with this file is getting it loaded at the right place.
  The first vector MUST be at address 0x????0100.
  How this is achieved is dependant on the tool chain.

  However the basic mechanism for ELF assemblers is to create a
  section called ".vectors", which will be loaded to an address
  between 0x????0000 and 0x????0100 (inclusive) via a link script.

  The basic mechanism for XCOFF assemblers is to place it in the
  normal text section, and arrange for this file to be located
  at an appropriate position on the linker command line.

  The variable 'PPC_VECTOR_FILE_BASE' must be defined to be the
  offset from 0x????0000 to the first location in the file.  This
  will usually be 0x0000 or 0x0100.

Andrew Bray 18/8/1995
