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152 lines
4.7 KiB
Plaintext
152 lines
4.7 KiB
Plaintext
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Debugging your code using VICE
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Ullrich von Bassewitz, March 1999
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Contents
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--------
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1. Overview
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2. What is VICE?
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3. How to prepare your sources
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4. How to use the label file
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5. Problems and workarounds
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1. Overview
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-----------
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This document describes how to debug your programs using the cc65
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development tools and the VICE CBM emulator.
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2. What is VICE?
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----------------
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VICE is an emulator for many of the CBM machines. It runs on Unix, DOS and
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Windows 95. It emulates the Commodore 64, 128, VIC20, PET and the 600/700
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machines. For more information see the VICE home page:
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http://www.cs.cmu.edu/~dsladic/vice/vice.html
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VICE has a builtin machine language monitor that may be used for debugging
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your programs. Using an emulator for debugging has some advantages:
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- Since you're using a crossassembler/-compiler anyway, you don't need
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to transfer the program to the real machine until it is done.
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- An emulator allows many things that are almost impossible one of the
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original machines. You may set watchpoints (detect read or write
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access to arbitary addresses), debug interrupt handlers and even debug
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routines that run inside the 1541 floppy.
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- You may use the label file generated by the linker to make much more
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use from the monitor.
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Please note that you need at least VICE version 0.16 for the label file
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feature to work. This version has still some problems (see section 5 for
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descriptions and some workarounds), but older versions had even more
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problems and do NOT work correctly.
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3. How to prepare your programs
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-------------------------------
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VICE support is mostly done via a label file that is generated by the
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linker and that may be read by the VICE monitor, so it knows about your
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program. Source level debugging is *not* available, you have to debug your
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programs in the assembler view.
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The first step is to generate object files that contain information about
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ALL labels in your sources, not just the exported ones. This can be done
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by several means:
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- Use the -g switch on the assembler command line.
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- Use the
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.debuginfo +
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command in your source.
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- Use the -g switch when invoking the compiler. The compiler will then
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put the .debuginfo command into the generated assembler source.
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So, if you have just C code, all you need is to invoke the compiler with
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-g. If you're using assembler code, you have to use -g for the assembler,
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or add ".debuginfo +" to your source files. Since the generated debug info
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is not appended to the generated executables, it is a good idea to always
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use -g. It makes the object files and libraries slightly larger (~30%),
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but this is usually not a problem.
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The second step is to tell the linker that it should generate a VICE label
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file. This is done by the -L switch followed by the name of the label file
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(I'm usually using a .lbl extension for these files). An example for a
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linker command line would be:
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ld65 -t c64 -L hello.lbl -m hello.map -o hello crt0 hello.o c64.lib
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This will generate a file named hello.lbl that contains all symbols used
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in your program.
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Note: The runtime libraries and startup files were generated with debug
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info, so you don't have to care about this.
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4. How to use the label file
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----------------------------
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Load your program, then enter the monitor and use the "pb" command to load
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your label file like this:
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pb "hello.lbl"
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You will get lots of warnings and even a few errors. You may ignore safely
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all these warnings and errors as long as they reference any problems VICE
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thinks it has with the labels.
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After loading the labels, they are used by VICE in the disassembler
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listing, and you may use them whereever you need to specify an address.
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Try
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d ._main
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as an example (note that VICE needs a leading dot before all labels, and
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that the compiler prepends an underline under most named labels).
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5. Problems and workarounds
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---------------------------
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Unfortunately, the VICE monitor has several problems with labels. However,
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it is still tremendously useful, and I think that most problems are gone
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in the next version. So, here is a list of the problems known to me as of
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version 0.16.1:
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* The "ll" command does not work. Worse, it seems that internal memory
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gets corrupted when using this command, so VICE will crash after use.
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Be sure to use the "pb" command to load the label file.
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* VICE will crash if you use a label that is undefined. This is probably
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the worst problem of all, since it needs just one typo to kill VICE.
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So, watch your steps:-)
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* Cheap labels, that is, labels starting with '@' or '?' are not
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accepted.
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* The disassembly output is somewhat suboptimal. However, most things are
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just cosmetical, e.g. labels appended to the right side of the
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disassembled code.
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