150 lines
3.9 KiB
Plaintext
150 lines
3.9 KiB
Plaintext
=========================
|
|
MN10300 FUNCTION CALL ABI
|
|
=========================
|
|
|
|
=======
|
|
GENERAL
|
|
=======
|
|
|
|
The MN10300/AM33 kernel runs in little-endian mode; big-endian mode is not
|
|
supported.
|
|
|
|
The stack grows downwards, and should always be 32-bit aligned. There are
|
|
separate stack pointer registers for userspace and the kernel.
|
|
|
|
|
|
================
|
|
ARGUMENT PASSING
|
|
================
|
|
|
|
The first two arguments (assuming up to 32-bits per argument) to a function are
|
|
passed in the D0 and D1 registers respectively; all other arguments are passed
|
|
on the stack.
|
|
|
|
If 64-bit arguments are being passed, then they are never split between
|
|
registers and the stack. If the first argument is a 64-bit value, it will be
|
|
passed in D0:D1. If the first argument is not a 64-bit value, but the second
|
|
is, the second will be passed entirely on the stack and D1 will be unused.
|
|
|
|
Arguments smaller than 32-bits are not coalesced within a register or a stack
|
|
word. For example, two byte-sized arguments will always be passed in separate
|
|
registers or word-sized stack slots.
|
|
|
|
|
|
=================
|
|
CALLING FUNCTIONS
|
|
=================
|
|
|
|
The caller must allocate twelve bytes on the stack for the callee's use before
|
|
it inserts a CALL instruction. The CALL instruction will write into the TOS
|
|
word, but won't actually modify the stack pointer; similarly, the RET
|
|
instruction reads from the TOS word of the stack, but doesn't move the stack
|
|
pointer beyond it.
|
|
|
|
|
|
Stack:
|
|
| |
|
|
| |
|
|
|---------------| SP+20
|
|
| 4th Arg |
|
|
|---------------| SP+16
|
|
| 3rd Arg |
|
|
|---------------| SP+12
|
|
| D1 Save Slot |
|
|
|---------------| SP+8
|
|
| D0 Save Slot |
|
|
|---------------| SP+4
|
|
| Return Addr |
|
|
|---------------| SP
|
|
| |
|
|
| |
|
|
|
|
|
|
The caller must leave space on the stack (hence an allocation of twelve bytes)
|
|
in which the callee may store the first two arguments.
|
|
|
|
|
|
============
|
|
RETURN VALUE
|
|
============
|
|
|
|
The return value is passed in D0 for an integer (or D0:D1 for a 64-bit value),
|
|
or A0 for a pointer.
|
|
|
|
If the return value is a value larger than 64-bits, or is a structure or an
|
|
array, then a hidden first argument will be passed to the callee by the caller:
|
|
this will point to a piece of memory large enough to hold the result of the
|
|
function. In this case, the callee will return the value in that piece of
|
|
memory, and no value will be returned in D0 or A0.
|
|
|
|
|
|
===================
|
|
REGISTER CLOBBERING
|
|
===================
|
|
|
|
The values in certain registers may be clobbered by the callee, and other
|
|
values must be saved:
|
|
|
|
Clobber: D0-D1, A0-A1, E0-E3
|
|
Save: D2-D3, A2-A3, E4-E7, SP
|
|
|
|
All other non-supervisor-only registers are clobberable (such as MDR, MCRL,
|
|
MCRH).
|
|
|
|
|
|
=================
|
|
SPECIAL REGISTERS
|
|
=================
|
|
|
|
Certain ordinary registers may carry special usage for the compiler:
|
|
|
|
A3: Frame pointer
|
|
E2: TLS pointer
|
|
|
|
|
|
==========
|
|
KERNEL ABI
|
|
==========
|
|
|
|
The kernel may use a slightly different ABI internally.
|
|
|
|
(*) E2
|
|
|
|
If CONFIG_MN10300_CURRENT_IN_E2 is defined, then the current task pointer
|
|
will be kept in the E2 register, and that register will be marked
|
|
unavailable for the compiler to use as a scratch register.
|
|
|
|
Normally the kernel uses something like:
|
|
|
|
MOV SP,An
|
|
AND 0xFFFFE000,An
|
|
MOV (An),Rm // Rm holds current
|
|
MOV (yyy,Rm) // Access current->yyy
|
|
|
|
To find the address of current; but since this option permits current to
|
|
be carried globally in an register, it can use:
|
|
|
|
MOV (yyy,E2) // Access current->yyy
|
|
|
|
instead.
|
|
|
|
|
|
===============
|
|
SYSTEM CALL ABI
|
|
===============
|
|
|
|
System calls are called with the following convention:
|
|
|
|
REGISTER ENTRY EXIT
|
|
=============== ======================= =======================
|
|
D0 Syscall number Return value
|
|
A0 1st syscall argument Saved
|
|
D1 2nd syscall argument Saved
|
|
A3 3rd syscall argument Saved
|
|
A2 4th syscall argument Saved
|
|
D3 5th syscall argument Saved
|
|
D2 6th syscall argument Saved
|
|
|
|
All other registers are saved. The layout is a consequence of the way the MOVM
|
|
instruction stores registers onto the stack.
|