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showed how to disassemble a prodos file

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Sean 2018-08-29 13:22:43 -07:00
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@ -8,11 +8,14 @@ This is a set of command-line tools designed specifically to reverse engineer Ap
`2mg` extracts .2mg and .po prodos disk images. You can also just list the contents of the disk image with the `-l` or `--list` command line argument. Otherwise, it will create a folder with the name of the disk and extract all the files into that folder.
Listing out the files will also give you the metadata associated with each
file. In particular, it will tell you the type and auxiliary type for
the files.
## omf
`omf` is a rather complicated tool which is designed to extract relocatable segments from OMF files. Apple IIgs executables (.sys16 files) and system tools (ex. SYSTEM/TOOLS/TOOL025) are in OMF format.
`omf` is a rather complicated tool which is designed to extract relocatable segments from OMF files. Apple IIgs executables (.s16 files) and system tools (ex. SYSTEM/TOOLS/TOOL025) are in OMF format.
You first run this tool and pass it an OMF file and it will generate a .map file. This map file is a simple text file that you may edit. Each line is in the format:
@ -172,4 +175,32 @@ Look up the dword in that location and I find that the toolset is located at `$f
At that location, we discover the offset to the tool entry point is `$ff/41a4` so we'll add `$ff/41a5`to the map file and rerun the disassembly.
Boom, we have just disassembled a specific tool call from ram.
Boom, we have just disassembled a specific tool call from ram.
### Disassembling a simple ProDOS executable
ProDOS binaries aren't relocatable and don't have anything inside them that
specifies where in RAM they should be loaded. However, the filesystem
itself does have that information.
Using `2mg` with the `-l` or `--list` argument will give a list of the
files along with metadata associated with the files. Let's use `BASIC.SYSTEM`
as an example.
You'll see that `BASIC.SYSTEM` has a type of `$ff` and auxtype of
`$2000`, and `2mg` identifies it as a "sys/ProDOS System File". This is
indeed a simple executable.
The aux type specifies where in RAM to load this executable, in this
case, it's `$2000`.
It is also important to note that these executables should start with 8-bit
registers.
So we can use all of that information to disassemble this file.
`$ regs --org=2000 -m -x BASIC.SYSTEM > basic.s`
This tells regs to start with 8-bit accumulator and indices, and load the
file starting at `$2000` before disassembling it.