oot/docs/compilers.md

Compilers

Ocarina of Time was written mostly in C, compiled to MIPS machine code. For the N64 and GameCube versions, all code was compiled with the IDO compiler. For the iQue Player versions, some of the code (namely libultra, and some game files such as those related to Chinese text) was compiled with the EGCS compiler instead.

IDO

Ocarina of Time was originally developed on Silicon Graphics "Indy" workstations, and IDO (IRIS Development Option) was the C compiler toolchain that shipped with these. Two different versions of IDO were used for Ocarina of Time: IDO 5.3 was used for some libraries (namely libultra, libleo, and the JPEG library) while IDO 7.1 was used for the other libraries and all of the "main" game code.

These Silicon Graphics workstations ran the MIPS-based IRIX operating system, so the original compiler binaries can't run on modern systems. Originally this project used qemu-irix (now unmaintained) to run emulate IRIX on modern systems, but nowadays we use the more lightweight ido-static-recomp instead.

EGCS

EGCS (Experimental/Enhanced GNU Compiler System) was a fork of the GCC compiler. The Linux-based iQue SDK included a patched version of EGCS release 1.1.2. The original compiler can still run on modern Linux systems, but we use a modified version that includes Mac support and a few other minor improvements (such as anonymous struct/union support).

This version of the EGCS compiler has a bug where code that indexes into an array member can fail to compile if the array member is at a large (>= 0x8000) offset in a struct. For example, when run on the source code

struct Foo {
    char a[0x8000];
    int b[1];
};

int test(struct Foo* foo, int i) {
    return foo->b[i];
}

the compiler errors with

Compiler error: src.c: In function `test':
src.c:8: internal error--unrecognizable insn:
(insn 20 18 22 (set (reg:SI 85)
        (plus:SI (reg:SI 81)
            (const_int 32768))) -1 (nil)
    (nil))
../../gcc/toplev.c:1367: Internal compiler error in function fatal_insn

In some recompiled files, the game developers had to modify the code to work around this bug, for example by storing a pointer to the array in a temporary variable before indexing into it.