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171 lines
No EOL
6.5 KiB
Text
171 lines
No EOL
6.5 KiB
Text
GDB Stub for DJGPP 0.2 Readme File
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==================================
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Copyright
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---------
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GDB Stub for DJGPP is distributed under the terms of the GNU Library
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General Public License (GNU LGPL) - please see the document LICENSE,
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which should be found in the same directory as this file.
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Copyright (c) 2000 by Jonathan Brogdon, 2002 by Gordon Schumacher
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What It Does
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------------
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The GDB stub is used to debug a DJGPP target remotely over a one of
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the PC COM ports. GDB, running on a host machine, communicates with
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the target using the GDB serial protocol over the serial link. For
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more information on the GDB stub, see "Debugging with GDB, The GNU
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Source-Level Debugger", by Richard M. Stallman and Roland H. Pesch
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(http://sources.redhat.com/gdb/download/onlinedocs/gdb.html)
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How It Works
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------------
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Exceptions:
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The GDB stub needs to handle all processor exceptions. Since these
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exceptions already handled by DJGPP, we cannot handle them directly.
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DJGPP maps all processor exceptions to signals. Therefore, we can
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install the GDB stub handler as the signal handler for those signals
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that represent processor exceptions. The following table shows the
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processor exception to signal mapping:
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Exception/Interrupt: Exception #: Signal:
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------------------- ----------- ------
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Divide Error 0 SIGFPE
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Debug Exception 1 SIGTRAP
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NMI Interrupt 2 No signal defined
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Breakpoint 3 SIGTRAP
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INTO-detected overflow 4 SIGFPE
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BOUND Range Exceeded 5 SIGSEGV
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Invalid Opcode 6 No signal defined
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Coprocessor not available 7 SIGNOFP
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Double Fault 8 SIGSEGV
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Coprocessor Seg overrun 9 SIGSEGV
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Invalid Task State Seg 10 No signal defined
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Segment not present 11 SIGSEGV
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Stack Fault 12 SIGSEGV
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General Protection Fault 13 SIGSEGV
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Page Fault 14 SIGSEGV
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Intel Reserved 15 No signal defined
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Coprocessor Error 16 SIGFPE
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The GDB stub handler services requests from the GDB host. These
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requests are seen by the GDB stub handler as command messages from
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the GDB host. These commands and command formats are defined in
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"Debugging with GDB, The GNU Source-Level Debugger", by Richard M.
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Stallman and Roland H. Pesch (http://sources.redhat.com/gdb/
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download/onlinedocs/gdb.html -- one of many sources).
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Serial Interface:
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Interface functions for sending and receiving characters from the
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serial interface must be provided by the engineer porting the GDB
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stub. The following funtions must be provided to support the
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implementation.
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int getDebugChar(void);
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void putDebugChar(int c);
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There are a variety of serial libraries for DJGPP. The user may
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already be using one of these libraries in their application, and
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installing more than one serial library often causes conflicts.
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To this end, a modular function layer was written that allows any
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serial library to be used with the GDB stub. Layers have been
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written to support SVAsync, DZComm, and the _bios_serialcom()
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function. At the time of this writing, DZComm appears to work the
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best for serial debugging.
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Hard Coded Breakpoint:
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A breakpoint() function is provided to manually invoke the stub.
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This function, inserts a breakpoint instruction directly in the code
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to invoke the GDB stub handler.
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How You Use It
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--------------
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First, you need to select a serial library. In the i386-supp.c file,
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there are lines of the form
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// #include "some_layer.h"
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Uncomment the line for the serial library you intend to use - or add
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a new include line for a file written for some other library.
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In the main() function of your target program, you should initilize
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the GDB serial handlers and the GDB stub. The following functions
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are provided in the GDB stub library for this purpose.
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gdb_serial_init(unsigned int port, unsigned int speed);
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gdb_target_init(void);
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Where, port is the COM port number, and speed is the baud rate for
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the serial link.
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After initialing the GDB serial interface and target, you should
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invoke the breakpoint() function somewhere. You may choose to do
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this immediately after initialization, or at a specific location in
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your code where you wish to set a breakpoint. By putting the
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breakpoint() function in the beginning of main(), you can use the
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GDB host to set a breakpoint at any place in your code.
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Make sure that you use the '-g' option when compiling your files with
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gcc.
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After the target executable is running, start up gdb on the host,
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passing the target executable as an argument.
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Example: gdb demo.exe
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Now, tell gdb which serial interface to use for communicating to
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the target.
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Example: (gdb) target remote COM1
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This example uses COM1 on the host to communicate with the target.
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GDB is now 'listening' on COM for a valid GDB serial packet.
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Once your GDB host finds your target, you may need to tell GDB where
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to find any source files which were used to generate your program.
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Use the directory command to do this.
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Example: (gdb) directory ../src/demo
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That's it. You should now be able to single step through code, set
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breakpoints, set variables, examine variables, any anthing else that
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you would normally use GDB to accomplish.
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What You Build
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--------------
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Read the INSTALL file for more information on installing the GDB stub
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library. After installing the library, your code should include
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i386-stub.h for function prototypes. In addition, your code should
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link against the libgdb.a library. The source for a demonstration
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program has been included with this distributias an example.
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As an alternative, you can simply include the i386-stub and i386-supp
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files and the layer header for the serial library you plan to use into
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your project and link them in directly.
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For More Info
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-------------
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See "Debugging with GDB, The GNU Source-Level Debugger", by Richard
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M. Stallman and Roland H. Pesch (http://sources.redhat.com/gdb/
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download/onlinedocs/gdb.html -- one of many sources).
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TODO
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----
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Port for network operation.
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Contact Info
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------------
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My contact info is below. If you have any comments, suggestions, bug
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reports or problems, please mail me, and I'll see what I can do.
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Regards,
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Jonathan Brogdon
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<brogdon@austin.rr.com>
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6th June 2000
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Modular update:
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Gordon Schumacher
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<gordons@valleyhold.org>
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12th February 2002 |