The calling sequence and stack frame

After the callee performs the save statement, the stack frame looks like:

[%fp]	Caller's frame
	variable size local scratch
	(if needed) strg for wrd8
$\lbrack$%sp+92$\rbrack$	(if needed) strg for wrd7
[%sp+68]	storage for words 1-6
[%sp+64]	struct/union return ptr
[%sp]	ireg window save

32 bit ABI

[%fp+2047]	Caller's frame
	variable size local scratch
	(if needed) strg for wrd8
$\lbrack$%sp+176+2047$\rbrack$	(if needed) strg for wrd7
[%sp+128+2047]	storage for words 1-6
[%sp+2047]	ireg window save

64 bit ABI

The callee's arguments are stored in the caller's stack frame. Note that the address of %sp must be kept 8-byte aligned for the 32 bit ABI, and 16-byte aligned for 64 bit.

For the 64-bit frame, the 2047 offset is called the BIAS, and it allow system libs to know which ABI is in effect (if 1 in last binary digit, 64 bit). Integers are stored in 64 bit slots, with the last 4 bytes holding the good value. Therefore, to load an int stored at 176 you do a ldsw [%sp+2047+176+4], reg.

For the 32-bit ABIs, floating point args are passed in the integer regs (2 regs for double) and floating point functions return their value in %f0.

For the 64 bit v9 ABI, there is a complicated memory-slot/register mapping which determines how things are passed in registers, as shown in 2 (note that after the callee executes the save statement, the %o registers will of course be the %i registers). Note that v9a is just v9 with VIS extensions, and v9b also includes some UltraSPARC-III extensions, so all v9 ABIs are the same for the information discussed here.

Figure 2: Argument passing for 64-bit SPARC v9 ABI