Red Hat ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE, Manual

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158 Chapter 19. Debugging remote programs
int getDebugChar()
Write this subroutine to read a single character from the serial port. It may be identical to
getchar
for your target system; a different name is used to allow you to distinguish the two
if you wish.
void putDebugChar(int)
Write this subroutine to write a single character to the serial port. It may be identical to
putchar
for your target system; a different name is used to allow you to distinguish the two if you wish.
If you want gdb to be able to stop your program while it is running, you need to use an interrupt-driven
serial driver, and arrange for it to stop when it receives a
^C
(
\003
, the control-C character). That is
the character which gdb uses to tell the remote system to stop.
Getting the debugging target to return the proper status to gdb probably requires changes to the stan-
dard stub; one quick and dirty way is to just execute a breakpoint instruction (the "dirty" part is that
gdb reports a
SIGTRAP
instead of a
SIGINT
).
Other routines you need to supply are:
void exceptionHandler (int
exception_number
, void *
exception_address
)
Write this function to install
exception_address
in the exception handling tables. You need to
do this because the stub does not have any way of knowing what the exception handling tables on
your target system are like (for example, the processor’s table might be in rom, containing entries
which point to a table in ram).
exception_number
is the exception number which should be
changed; its meaning is architecture-dependent (for example, different numbers might represent
divide by zero, misaligned access, etc). When this exception occurs, control should be transferred
directly to
exception_address
, and the processor state (stack, registers, and so on) should be
just as it is when a processor exception occurs. So if you want to use a jump instruction to reach
exception_address
, it should be a simple jump, not a jump to subroutine.
For the 386,
exception_address
should be installed as an interrupt gate so that interrupts
are masked while the handler runs. The gate should be at privilege level 0 (the most privi-
leged level). The sparc and 68k stubs are able to mask interrupts themselves without help from
exceptionHandler
.
void flush_i_cache()
On sparc and sparclite only, write this subroutine to flush the instruction cache, if any, on your
target machine. If there is no instruction cache, this subroutine may be a no-op.
On target machines that have instruction caches, gdb requires this function to make certain that
the state of your program is stable.
You must also make sure this library routine is available:
void *memset(void *, int, int)
This is the standard library function
memset
that sets an area of memory to a known value. If
you have one of the free versions of
libc.a
,
memset
can be found there; otherwise, you must
either obtain it from your hardware manufacturer, or write your own.
If you do not use the GNU C compiler, you may need other standard library subroutines as well; this
varies from one stub to another, but in general the stubs are likely to use any of the common library
subroutines which
gcc
generates as inline code.