WDB Support for GNU gdb-5.0

Introduction

One among the supported targets is the vxWorks (tm) real-time kernel. vxWorks features a so called "remote agent", which, among other things can be used for remote debugging. gdb (running on a host computer) talks to the remote agent speaking a dedicated network protocol. Until version 5.3 of vxWorks, there were two different agents and protocols: RDB and WDB. WindRiver had written and released to the public, the RDB client for gdb which enabled the debugger to connect to vxWorks targets. However, as of version 5.4, vxWorks no longer supports RDB and the RDB server is no longer present.

This page describes a patch for gdb which provides WDB (the newer protocol) support.

WDB Support

• small architecture specific piece of code (read/write registers), see: 'remote-vx<arch>.c'. Currently, I have only implemented remote-vxppc.c (PowerPC); however adding support for other architectures should be straightforward (you'd need to tweak the config/<arch>/vxworks.h, configure.in and maybe Makefile.in file also.)

• the wdb library source code (distributed by WindRiver with vxWorks). We should ask them if they are willing to release this code to the public...
• my 'tillRdb' package. There is some functionality lacking in WDB. Therefore, I created code that implements the necessary subset of the RDB protocol. You need to compile it for and load it to the target. Then issue 'startRdb' (on the target).


Note: you can still use vxgdb without my rdb server but some functionality will be missing (i.e. essentially everything that deals with files: uploading files, guessing path names etc.) Without tillRdb, you have to specify an additional parameter to the "target vxworks" command if you want to use symbols exported by vxWorks:

target vxworks <vxworks_image_file_path>

also, you have to tell gdb explicitely what modules are loaded (because it connot ask the target):

file <path_to_my_module>

New Features / TODO

• nice new feature:

attach 0

command. If you set a breakpoint and attach to task id 0, the first task that hits the breakpoint will stop, i.e. you don't have to know its id in advance.
• semantics of the 'run' command: 'run' takes (almost) the same arguments like the target shell's 'taskSpawn', i.e.

run <name> <priority> <options> <stack_size> <arg> <arg> ...

(note that no task name can be given; <name> is the text-symbol of the code you want to run). If you omit parameters, vxgdb uses default values (prio=100, options=0, stack=20000), hence

run helloWorld 50

starts 'helloWord' in a new task context on the target with a priority of 50, no options and a stack size of 20000.

IMPORTANT: you can _only_ pass integer arguments to the created task, i.e.

run printf 100 0 20000 "hello world\n"

does not work. (vxgdb does not allocate a string on the target and pass its address to the created task but creates a string locally [on the host] passing the local address to the target).
• Lacking functionality: WDB does not allow for multiple (simultaneous) connections. Therefore, it is currently not possible to concurrently run multiple vxgdb sessions (connected to the same target). However, I heard of somebody having created a "WDB multiplexor" for this purpose. I do not know whether it would be hard to integrate it with my software.

Notes

GUI Front End

Object File Path

Installation

What you need

• gdb-5.0 source distribution
• this patch file
• the WDB host interface. This consists of a couple of source and header files distributed by WindRiver with vxWorks. In vxWorks-5.4 the necessary files are located in <WIND_HOME>/share/src/agents/wdb
• native compiler and utilites for compiling gdb.
• cross-compiler and utilities for building the mini-RDB server that runs on the target. (see README.wdb).

Building the Package

• unpack the sources for gdb-5.0
• 'cd' to the <TOP>/gdb subdirectory.
• create a directory 'vx-wdb' and copy or symlink the following files from the vxworks tree (at WIND_HOME/share/src/agents/wdb) to the new directory 'vx-wdb': ctx.c ctxstep.c evtpoint.c memory.c rpccksum.c xdrcore.c ctxcreat.c evtdata.c regs.c wrapper.c wdb.h wdbP.h
• 'cd' to the gdb-5.0 top directory and apply the patch:

patch -p1 < patch_file

Note that the -p1 option is important.
• create a directory for the build e.g.

mkdir build-powerpc-vxgdb 

• 'cd' to the build directory and configure the package:

../configure --target=powerpc-vxworks --enable-vxwdb

(NOTE: by default WDB support is not enabled).
• 'make' and 'make install' etc...

Building the RDB Server

Download

• tillRdb, a tiny RDB server which implements the functionality lacking in WDB
• patch for gdb-5.0 which implements WDB support