[Michael Schmitt]
Attached is a patch to SheepShaver to fix memory allocation problems when OS X 10.5 is the host. It also relaxes the 512 MB RAM limit on OS X hosts.


Problem
-------
Some users have been unable to run SheepShaver on OS X 10.5 (Leopard) hosts. The symptom is error "ERROR: Cannot map RAM: File already exists".

SheepShaver allocates RAM at fixed addresses. If it is running in "Real" addressing mode, and can't allocate at address 0, then it was hard-coded to allocate the RAM area at 0x20000000. The ROM area as allocated at 0x40800000.

The normal configuration is for SheepShaver to run under SDL, which is a Cocoa wrapper. By the time SheepShaver does its memory allocations, the Cocoa application has already started. The result is the SheepShaver memory address space already contains libraries, fonts, Input Managers, and IOKit areas.

On Leopard hosts these areas can land on the same addresses SheepShaver needs, so SheepShaver's memory allocation fails.


Solution
--------
The approach is to change SheepShaver (on Unix & OS X hosts) to allocate the RAM area anywhere it can find the space, rather than at a fixed address.

This could result in the RAM allocated higher than the ROM area, which causes a crash. To prevent this from occurring, the RAM and ROM areas are allocated contiguously.

Previously the ROM starting address was a constant ROM_BASE, which was used throughout the source files. The ROM start address is now a variable ROMBase. ROMBase is allocated and set by main_*.cpp just like RAMBase.

A side-effect of this change is that it lifts the 512 MB RAM limit for OS X hosts. The limit was because the fixed RAM and ROM addresses were such that the RAM could only be 512 MB before it overlapped the ROM area.


Impact
------
The change to make ROMBase a variable is throughout all hosts & addressing modes.

The RAM and ROM areas will only shift when run on Unix & OS X hosts, otherwise the same fixed allocation address is used as before.

This change is limited to "Real" addressing mode. Unlike Basilisk II, SheepShaver *pre-calculates* the offset for "Direct" addressing mode; the offset is compiled into the program. If the RAM address were allowed to shift, it could result in the RAM area wrapping around address 0.


Changes to main_unix.cpp
------------------------
1. Real addressing mode no longer defines a RAM_BASE constant.

2. The base address of the Mac ROM (ROMBase) is defined and exported by this program.

3. Memory management helper vm_mac_acquire is renamed to vm_mac_acquire_fixed. Added a new memory management helper vm_mac_acquire, which allocates memory at any address.

4. Changed and rearranged the allocation of RAM and ROM areas.

Before it worked like this:

  - Allocate ROM area
  - If can, attempt to allocate RAM at address zero
  - If RAM not allocated at 0, allocate at fixed address

We still want to try allocating the RAM at zero, and if using DIRECT addressing we're still going to use the fixed addresses. So we don't know where the ROM should be until after we do the RAM. The new logic is:

  - If can, attempt to allocate RAM at address zero
  - If RAM not allocated at 0
      if REAL addressing
         allocate RAM and ROM together. The ROM address is aligned to a 1 MB boundary
      else (direct addressing)
         allocate RAM at fixed address
  - If ROM hasn't been allocated yet, allocate at fixed address

5. Calculate ROMBase and ROMBaseHost based on where the ROM was loaded.

6. There is a crash if the RAM is allocated too high. To try and catch this, check if it was allocated higher than the kernel data address.

7. Change subsequent code from using constant ROM_BASE to variable ROMBase.


Changes to Other Programs
-------------------------
emul_op.cpp, main.cpp, name_registery.cpp, rom_patches.cpp, rsrc_patches.cpp, emul_ppc.cpp, sheepshaver_glue.cpp, ppc-translate-cpp:
Change from constant ROM_BASE to variable ROMBase.

ppc_asm.S: It was setting register to a hard-coded literal address: 0x40b0d000. Changed to set it to ROMBase + 0x30d000.

ppc_asm.tmpl: It defined a macro ASM_LO16 but it assumed that the macro would always be used with operands that included a register specification. This is not true. Moved the register specification from the macro to the macro invocations.

main_beos.cpp, main_windows.cpp: Since the subprograms are all expecting a variable ROMBase, all the main_*.cpp pgrams have to define and export it. The ROM_BASE constant is moved here for consistency. The mains for beos and windows just allocate the ROM at the same fixed address as before, set ROMBaseHost and ROMBase to that address, and then use ROMBase for the subsequent code.

cpu_emulation.h: removed ROM_BASE constant. This value is moved to the main_*.cpp modules, to be consistent with RAM_BASE.

user_strings_unix.cpp, user_strings_unix.h: Added new error messages related to errors that occur when the RAM and ROM are allocated anywhere.

Fix for DIRECT_ADDRESSING mode (Windows)

avoid unaligned memory accessed when patching the ROM (IRIX/mips)

Happy New Year 2005!

disable power management for now (opcode fe0f)

Implement Direct Addressing mode similarly to Basilisk II. This is to get
SheepShaver working on OSes that don't support maipping of Low Memory globals
at 0x00000000, e.g. Windows.

More accurate Gestalt 'cput' values (G4, 750FX)

Fix Gestalt for PowerPC 745x processors.

Don't handle XLM_IRQ_NEST atomically in emulated mode. That's useless since
this variable is modified only within a single thread and interrupts are
not handled asynchronously.

"idlewait" support for Linux and NewWorld ROMs

Now that we have AltiVec emulation, we can pretend for a G4 processor
Also make sure to actually fix PVR code for 7400

Happy New Year! :)

There may be extra instructions before moving stuff to SCC registers.

Generic ROM patches from ROMTYPE_PARCELS experiments, no apparent
regession. There is no improvement either.

Add new thunking system for 64-bit fixes.

fix parcels decoder

- Add checks against ROM patches space
- Make sure to also load the floppy disk driver with Gossamer ROMs so
  that exfs feature can work too

fix tm_task patch for Gossamer ROMs

Little endian fixes to Serial trampolines.

Try to handle XLM_IRQ_NEST atomically in emulated PPC views. Fix placement
of fake SCSIGlobals (disabled for now). Switch back to mono core emulation
until things are debugged enough. Implement get_resource() et al.

Don't call FE0A opcode in Shutdown Manager: handle better NewWorld ROMs.
i.e. don't force a "bra" if there was no "beq" beforehand.

Finally enable boot on MacOS 8.6 Update CD from iMac DV
- Don't read PVR at ROM_BASE + 0x314600
- Generated code for FC1E and FE0A don't really match comments
- Move FC1E routine base to ROM_BASE + 0x36fb00
- Recognize iMacUpdate 1.1 ROM (nwrom v1.2.1)

Add support to decode parcels-based ROMs
- include/rom_patches.h (DecodeROM): Declare.
- rom_patches.cpp (DecodeROM): Define.
- Unix/main_unix.cpp, BeOS/main_beos.cpp (decode_lzss): Move to...
- rom_patches.cpp (decode_lzss): ... here.
- Unix/main_unix.cpp (main): Call DecodeROM().
- BeOS/main_beos.cpp (SheepShaver::load_rom): Call DecodeROM().