Overview and Predefined Variables

Overview and Predefined Variables

There are two sets of issues: the LP64 model, and the new calling conventions. Each of these issues is solved by a combination of predefined variables that the compiler emits, and macros in <sys/asm.h> and <sys/regdef.h>, that use those predefine variables to define macros appropriately.
The predefines that the assembler emits are:

For MIPS1/2 executables:

-D_MIPS_FPSET=16
-D_MIPS_ISA=_MIPS_ISA_MIPS1
-D_MIPS_SIM=_MIPS_SIM_ABI32
-D_MIPS_SZINT=32
-D_MIPS_SZLONG=32
-D_MIPS_SZPTR=32

For MIPS3 executables:

-D_MIPS_FPSET=32
-D_MIPS_ISA=_MIPS_ISA_MIPS3
-D_MIPS_SIM=_MIPS_SIM_ABI64
-D_MIPS_SZINT=32
-D_MIPS_SZLONG=64
-D_MIPS_SZPTR=64

For MIPS4 executables:

-D_MIPS_FPSET=32
-D_MIPS_ISA=_MIPS_ISA_MIPS4
-D_MIPS_SIM=_MIPS_SIM_ABI64
-D_MIPS_SZINT=32
-D_MIPS_SZLONG=64
-D_MIPS_SZPTR=64

The explanation of these predefined variables is as follows:

MIPS_ISA is MIPS Instruction Set Architecture. MIPS_ISA_MIPS1 and MIPS_ISA_MIPS3 would be the most common variants for kernel-level assembler code.
MIPS_ISA_MIPS4 is the ISA for R8000 applications. MIPS_SIM is MIPS Subprogram Interface Model - this describes the subroutine linkage convention and register naming/usage convention.
_MIPS_FPSET describes the number of floating point registers. The MipsIII compilation model makes use of the extended floating point registers available on the R4000.
_MIPS_SZINT, _MIPS_SZLONG, and _MIPS_SZPTR describe the size of each of those types.

An example of the use of these macros:

 #if (_MIPS_ISA == _MIPS_ISA_MIPS1 || _MIPS_ISA == _MIPS_ISA_MIPS2)
 #define SZREG           4
 #endif

 #if (_MIPS_ISA == _MIPS_ISA_MIPS3 || _MIPS_ISA == _MIPS_ISA_MIPS4)
 #define SZREG           8
 #endif