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MOSS
``A Soft Blanket over the Rocky Slopes of DOS''
A DOS extender based on the Flux OS toolkit

Bryan Ford
baford@cs.utah.edu
Sleepless Software
420 South 1100 East
Salt Lake City, UT 84102
and the
Computer Systems Laboratory
Department of Computer Science
University of Utah
Salt Lake City, UT 84112

Abstract:

MOSS is a new DOS extender with the following major features:

• Can be used royalty-free in commercial and non-commercial products.
• Full support for DPMI, VCPI, XMS, and ``raw'' DOS modes.
• Supports up to 2GB of virtual and physical memory.
• Demand-loading of executables for quick startup times.
• Supports POSIX low-level file I/O as well as ANSI C I/O.
• Processor exceptions can be delivered as POSIX signals.
• Hardware interrupts can be delivered as POSIX.1b real-time queued signals (except under DPMI).
• Traditional-DOS-extender-like interrupt revectoring also available under all environments.
• Supports the POSIX.1b memory locking API (mlock et al).
• Remote source-level debugging over a serial line using GDB.
• Full cross-development from Linux and other Unix-compatible OS's.
• Uses i386 ELF object files and executables.
• Allows a program and any associated data files to be attached to MOSS, forming one big DOS executable.
• Written almost entirely in easy-to-modify C code.
• Can be compiled completely using the freely-available GNU development tools (i.e. doesn't require a commercial compiler/assembler to handle the 16-bit x86 code).

• Contents
• Introduction
  • License
  • Support
• Using MOSS
  • Tools required
  • Building and running MOSS applications
  • Example MOSS application
• Building MOSS
  • Building binutils
  • Building GCC
  • Building MOSS
  • Building the rest of GCC
  • MOSS directory structure
  • Compile-time options
• Attaching files to MOSS.EXE
• Remote debugging
  • Preparing to debug
  • Running applications under the remote debugger
  • Features supported by MOSS's remote GDB stub
• MOSS system calls
  • alloc_dma: allocate DMA memory
  • alloc_dos: allocate low DOS memory
  • close: close an open file descriptor
  • _exit: terminate the program without cleanup
  • fstat: return statistics on a file descriptor
  • gettimeofday: read the current system time
  • irq_free: free a previously-allocated hardware interrupt
  • irq_request: allocate and handle a hardware interrupt vector
  • kill: send a signal to a process
  • lseek: reposition current offset in a file
  • mlock: lock a region of memory
  • mlockall: lock all memory
  • mmap: map a file's contents into memory
  • munlock: unlock a region of memory
  • open: open a file
  • read: read from a file
  • rename: rename a file
  • sbrk: low-level memory allocator
  • sigaction: change the action for a signal
  • sigpending: find the set of currently pending signals
  • sigprocmask: change the signal mask of the current process
  • unlink: delete a file
  • write: write to a file
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