mwccgap AKA "MWCC Global Assembly Processor"

mwccgap is a tool that enables individual functions within a C file to be replaced with assembly code, drawing heavy inspiration from asm-processor.

While the MWCC compiler does support embedding raw assembly within a C file, it requires that all variables and functions be fully defined. This limitation makes the traditional Ship of Theseus approach to matching decompiled code slow and cumbersome.

Unlike asm-processor, which uses a GLOBAL_ASM pragma, mwccgap adopts an INCLUDE_ASM macro to align with the needs of its first supported project, which uses GCC. Future updates may add support for both approaches.

When a function in a C file is marked defined using the INCLUDE_ASM macro, it is replaced with a series of nop instructions of the appropriate size during compilation. The C file is then compiled as usual. Separately, the assembly code for these functions is compiled, and the resulting object data is transplanted back into the C object. Symbols and relocations are updated as needed to ensure correctness.

Any .rodata sections within the assembly code will also be transplanted into the C object.

Usage

mwccgap input.c output.o [ -O4,p -sym on ... ]

mwccgap supports the following arguments:

--mwcc-path (path)

The path to the MWCC executable, defaults to mwccpsp.exe

--as-path (path)

The path to GNU as, defaults to mipsel-linux-gnu-as

--as-march

The -march= value to pass to GNU as, defaults to allegrex

--as-mabi

The -mabi= value to pass to GNU as, defaults to 32

--use-wibo

Whether or not to prefix the call to the MWCC executable with wibo, defaults to false.

--wibo-path

Path to wibo (i.e. if wibo is not on your path, or you wish to use wine instead), defaults to wibo.

--asm-dir-prefix

Optional prefix for INCLUDE_ASM files.

--macro-inc-path

Optional path to your macro.inc file.

--target-encoding [sjis, ujis, etc]

Optional encoding that the input c file should be converted to, before being passed to the compiler.

All additional arguments will be passed to the MWCC executable.

Limitations

Known limitations:

• .rodata alignment set to 0x8 for all INCLUDE_RODATA sections.

Bugs

This project is in its infancy and is full of assumptions, and therefore likely riddled with bugs; PRs are welcomed!

Examples

Projects that use mwccgap include:

• Castlevania: Symphony of the Night Decompilation
• Street Fighter III: 3rd Strike