Overlay Sample Program (Debugging with GDB)

### 14.4 Overlay Sample Program ¶

When linking a program which uses overlays, you must place the overlays at their load addresses, while relocating them to run at their mapped addresses. To do this, you must write a linker script (see Overlay Description in Using ld: the GNU linker). Unfortunately, since linker scripts are specific to a particular host system, target architecture, and target memory layout, this manual cannot provide portable sample code demonstrating GDB’s overlay support.

However, the GDB source distribution does contain an overlaid program, with linker scripts for a few systems, as part of its test suite. The program consists of the following files from `gdb/testsuite/gdb.base`:

`overlays.c`

  The main program file.

`ovlymgr.c`

  A simple overlay manager, used by `overlays.c`.

`foo.c`
`bar.c`
`baz.c`
`grbx.c`

  Overlay modules, loaded and used by `overlays.c`.

`d10v.ld`
`m32r.ld`

  Linker scripts for linking the test program on the `d10v-elf` and `m32r-elf` targets.

You can build the test program using the `d10v-elf` GCC cross-compiler like this:

    $ d10v-elf-gcc -g -c overlays.c
    $ d10v-elf-gcc -g -c ovlymgr.c
    $ d10v-elf-gcc -g -c foo.c
    $ d10v-elf-gcc -g -c bar.c
    $ d10v-elf-gcc -g -c baz.c
    $ d10v-elf-gcc -g -c grbx.c
    $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
                      baz.o grbx.o -Wl,-Td10v.ld -o overlays

The build process is identical for any other architecture, except that you must substitute the appropriate compiler and linker script for the target system for `d10v-elf-gcc` and `d10v.ld`.