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Based on kernel version 3.13. Page generated on 2014-01-20 22:03 EST.

1				   =========================
2				   MN10300 FUNCTION CALL ABI
3				   =========================
4	
5	=======
6	GENERAL
7	=======
8	
9	The MN10300/AM33 kernel runs in little-endian mode; big-endian mode is not
10	supported.
11	
12	The stack grows downwards, and should always be 32-bit aligned. There are
13	separate stack pointer registers for userspace and the kernel.
14	
15	
16	================
17	ARGUMENT PASSING
18	================
19	
20	The first two arguments (assuming up to 32-bits per argument) to a function are
21	passed in the D0 and D1 registers respectively; all other arguments are passed
22	on the stack.
23	
24	If 64-bit arguments are being passed, then they are never split between
25	registers and the stack. If the first argument is a 64-bit value, it will be
26	passed in D0:D1. If the first argument is not a 64-bit value, but the second
27	is, the second will be passed entirely on the stack and D1 will be unused.
28	
29	Arguments smaller than 32-bits are not coalesced within a register or a stack
30	word. For example, two byte-sized arguments will always be passed in separate
31	registers or word-sized stack slots.
32	
33	
34	=================
35	CALLING FUNCTIONS
36	=================
37	
38	The caller must allocate twelve bytes on the stack for the callee's use before
39	it inserts a CALL instruction. The CALL instruction will write into the TOS
40	word, but won't actually modify the stack pointer; similarly, the RET
41	instruction reads from the TOS word of the stack, but doesn't move the stack
42	pointer beyond it.
43	
44	
45		Stack:
46		|		|
47		|		|
48		|---------------| SP+20
49		| 4th Arg	|
50		|---------------| SP+16
51		| 3rd Arg	|
52		|---------------| SP+12
53		| D1 Save Slot	|
54		|---------------| SP+8
55		| D0 Save Slot	|
56		|---------------| SP+4
57		| Return Addr	|
58		|---------------| SP
59		|		|
60		|		|
61	
62	
63	The caller must leave space on the stack (hence an allocation of twelve bytes)
64	in which the callee may store the first two arguments.
65	
66	
67	============
68	RETURN VALUE
69	============
70	
71	The return value is passed in D0 for an integer (or D0:D1 for a 64-bit value),
72	or A0 for a pointer.
73	
74	If the return value is a value larger than 64-bits, or is a structure or an
75	array, then a hidden first argument will be passed to the callee by the caller:
76	this will point to a piece of memory large enough to hold the result of the
77	function. In this case, the callee will return the value in that piece of
78	memory, and no value will be returned in D0 or A0.
79	
80	
81	===================
82	REGISTER CLOBBERING
83	===================
84	
85	The values in certain registers may be clobbered by the callee, and other
86	values must be saved:
87	
88		Clobber:	D0-D1, A0-A1, E0-E3
89		Save:		D2-D3, A2-A3, E4-E7, SP
90	
91	All other non-supervisor-only registers are clobberable (such as MDR, MCRL,
92	MCRH).
93	
94	
95	=================
96	SPECIAL REGISTERS
97	=================
98	
99	Certain ordinary registers may carry special usage for the compiler:
100	
101		A3:	Frame pointer
102		E2:	TLS pointer
103	
104	
105	==========
106	KERNEL ABI
107	==========
108	
109	The kernel may use a slightly different ABI internally.
110	
111	 (*) E2
112	
113	     If CONFIG_MN10300_CURRENT_IN_E2 is defined, then the current task pointer
114	     will be kept in the E2 register, and that register will be marked
115	     unavailable for the compiler to use as a scratch register.
116	
117	     Normally the kernel uses something like:
118	
119		MOV	SP,An
120		AND	0xFFFFE000,An
121		MOV	(An),Rm		// Rm holds current
122		MOV	(yyy,Rm)	// Access current->yyy
123	
124	     To find the address of current; but since this option permits current to
125	     be carried globally in an register, it can use:
126	
127		MOV	(yyy,E2)	// Access current->yyy
128	
129	     instead.
130	
131	
132	===============
133	SYSTEM CALL ABI
134	===============
135	
136	System calls are called with the following convention:
137	
138		REGISTER	ENTRY			EXIT
139		===============	=======================	=======================
140		D0		Syscall number		Return value
141		A0		1st syscall argument	Saved
142		D1		2nd syscall argument	Saved
143		A3		3rd syscall argument	Saved
144		A2		4th syscall argument	Saved
145		D3		5th syscall argument	Saved
146		D2		6th syscall argument	Saved
147	
148	All other registers are saved.  The layout is a consequence of the way the MOVM
149	instruction stores registers onto the stack.
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