Attached is a patch to SheepShaver, to fix a SIGSEGV crash that occurs when booting a new machine with OS 7.5.
One of the bytes in the xPRAM portion of the NVRAM controls which version of the system memory manager is used by OS 7.5: the legacy 680x0 memory manager or the PPC memory manager (aka the "Modern Memory Manager"). OS 7.5 is supposed to be able to use either one, but for some reason SheepShaver crashes on boot if the 680x0 version is used.
Later Mac OS versions don't have this problem. They don't support the 680x0 version, so they force the PPC version to be used.
The fix is to have SheepShaver initialize the NVRAM to use the PPC memory manager. Note: This is supposed to be the default in OS 7.5.
This affects when a new NVRAM file is used, or when it is initialized after doing zapping the PRAM.
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
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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
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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
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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
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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
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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.
migrate the Ethernet driver to the MacOS side. This is enabled for
DIRECT_ADDRESSING cases. I didn't want to alter much of ether.cpp (as it
would have required to support that mode). Of course, in REAL_ADDRESSING
mode (the default) and for debugging purposes, the old driver is still
available.
in that case. Tell me if I broke other arches, e.g. r13 is no longer saved
in Video and Ethernet stubs, though it seems to be OK.
Colateral feature: SheepShaver should now run on Linux/ppc64 with relevant
32-bit runtime. Native Linux/ppc64 support is harder as low mem globals are
32-bit in mind and e.g. the TLS register there is %r13, %r2 is the TOC
(PowerOpen/AIX ABI)
