The stub files provided with GDB implement the target side of the
communication protocol, and the GDB side is implemented in the
GDB source file remote.c. Normally, you can simply allow
these subroutines to communicate, and ignore the details. (If you're
implementing your own stub file, you can still ignore the details: start
with one of the existing stub files. sparc-stub.c is the best
organized, and therefore the easiest to read.)
To debug a program running on another machine (the debugging target machine), you must first arrange for all the usual prerequisites for the program to run by itself. For example, for a C program, you need:
crt0. The startup routine may be supplied by
your hardware supplier, or you may have to write your own.
The next step is to arrange for your program to use a serial port to communicate with the machine where GDB is running (the host machine). In general terms, the scheme looks like this:
target remote command
(see Specifying a Debugging Target).
On certain remote targets, you can use an auxiliary program
gdbserver instead of linking a stub into your program.
See Using the gdbserver program, for details.
The debugging stub is specific to the architecture of the remote
machine; for example, use sparc-stub.c to debug programs on
SPARC boards.
These working remote stubs are distributed with GDB:
i386-stub.c
m68k-stub.c
sh-stub.c
sparc-stub.c
sparcl-stub.c
The README file in the GDB distribution may list other
recently added stubs.