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l80

l80 is a linker for CP/M and MS-DOS COM executables.

It reads in object files and libraries created by a80 and produces executable CP/M-80 binaries from them.

There are not (yet) any assemblers or compilers that produce 8086 object code for l80. But when such programs appear, l80 will already be able to handle them.

You can read an in-depth explanation of how the linker and object file format work here.

Building

l80 should build with any D compiler for any supported platform. I use GDC on OpenBSD and that works well.

There is a port of l80 to C that can be compiled for CP/M, MS-DOS, and Unix. The C port has the following differences:

  • Only the first 15 characters of symbol names are unique.
  • On CP/M, the binary is named ld to avoid conflict with Microsoft L80.

You can build this C version for CP/M with:

$ make cpm

For MS-DOS with:

$ make dos

And for Unix with:

$ make c

Running

usage: l80 binary file1.obj [file2.obj ...]

All object files must end in .obj or .lib.

The .com extension will automatically be appended to binary.

Object format

l80 uses the most simple object format I could devise.

Object files are comprised of control codes and data. There are three control codes:

  • 00: The following byte is literal data.
  • 01: The following bytes are a symbol declaration.
  • 02: The following bytes are a symbol reference.

l80 uses two passes to generate the final execuatable binary. The first pass writes all object files and libraries into a single buffer and then collects all the symbol declarations and calculates the address of each symbol. The second pass writes out the executable, replacing references with the addresses calculated during the first pass.

Libraries are simply collections of object files. They can be created with the ar80 utility.

Caveats

l80 does not recognize nor remove the code of unused symbols. Doing so is planned.

The order of the object files and libraries can be very important.

Compilers should implement name mangling for symbols not destined to be globals to prevent spurious duplicate symbol errors.

Bugs

Probably lots. Test and let me know.

License

ISC License. See LICENSE for details.

Note

This l80 is in no way related to the linker of the same name produced by Microsoft, also targeting CP/M-80.

That one uses a very different file format.