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( Vector Definition

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Target Vector Definition

   The target vector defines the interface between GDB's abstract
handling of target systems, and the nitty-gritty code that actually
exercises control over a process or a serial port.  GDB includes some
30-40 different target vectors; however, each configuration of GDB
includes only a few of them.

File Targets

   Both executables and core files have target vectors.

Standard Protocol and Remote Stubs

   GDB's file `remote.c' talks a serial protocol to code that runs in
the target system.  GDB provides several sample "stubs" that can be
integrated into target programs or operating systems for this purpose;
they are named `*-stub.c'.

   The GDB user's manual describes how to put such a stub into your
target code.  What follows is a discussion of integrating the SPARC
stub into a complicated operating system (rather than a simple
program), by Stu Grossman, the author of this stub.

   The trap handling code in the stub assumes the following upon entry
to `trap_low':

  1. %l1 and %l2 contain pc and npc respectively at the time of the

  2. traps are disabled;

  3. you are in the correct trap window.

   As long as your trap handler can guarantee those conditions, then
there is no reason why you shouldn't be able to "share" traps with the
stub.  The stub has no requirement that it be jumped to directly from
the hardware trap vector.  That is why it calls `exceptionHandler()',
which is provided by the external environment.  For instance, this could
set up the hardware traps to actually execute code which calls the stub
first, and then transfers to its own trap handler.

   For the most point, there probably won't be much of an issue with
"sharing" traps, as the traps we use are usually not used by the kernel,
and often indicate unrecoverable error conditions.  Anyway, this is all
controlled by a table, and is trivial to modify.  The most important
trap for us is for `ta 1'.  Without that, we can't single step or do
breakpoints.  Everything else is unnecessary for the proper operation
of the debugger/stub.

   From reading the stub, it's probably not obvious how breakpoints
work.  They are simply done by deposit/examine operations from GDB.

ROM Monitor Interface

Custom Protocols

Transport Layer

Builtin Simulator

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