13.4. 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 (). 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
The main program file.
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.