Re: Linker overlay pages strategy [Q]

[Ian Lance Taylor <ian@zembu.com>]

   Date: Thu, 19 Aug 1999 22:37:23 -0400
   From: Timothy Wall <twall@tiac.net>

   I'm trying to figure out the best way to handle a processor's dual
   address space as it relates to the linker and script files.  Fortunately
   I don't have to do compatibility with the other vendor's linker scripts,
   but there are a few options I need to include.  First is being able to
   specify separate allocations for load-time and run-time addresses of
   sections, and second, being able to map into two overlapping addrss
   spaces.

Separate load and run time addresses are normally handled via the AT
modifier in the linker script.

The linker does nothing to stop you from mapping into overlapping
address spaces.

   Some sections may be designated to have a different "run time"
   allocation, which may be on the same or a different page.  e.g.

   MEMORY
   {
       PAGE 0: PROG: ORIGIN 0x0000 LENGTH 0xFF00
      PAGE 1: DATA: ORIGIN 0x0080 LENGTH 0xFF80
   }

   SECTIONS
   {
       .text: load = PROG, run = 0x800
       .cinit: load = PROG, run = DATA
   }

   So what this does is effectively allocate two sections per section.  The
   text section is expected to be relocated before running (so all
   relocations are done for the "run" address).

You just need to use the AT modifier for the .text section.  Do
something like
    .text 0x800 : AT (0) { *(.text) }
or
    .text : AT (0) { *(.text) } > PROG

   Note that the memory "pages" have overlapping address space.

I don't think the linker will care.

Note that you don't have to use MEMORY regions.  If you find them
inconvenient, just specify the addresses directly.  The main advantage
of MEMORY regions is that they cause the linker to warn when you
overflow memory.

Ian