[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / parisc / registers

Register Usage for Linux/PA-RISC

[ an asterisk is used for planned usage which is currently unimplemented ]

	General Registers as specified by ABI

	Control Registers

CR 0 (Recovery Counter)		used for ptrace
CR 1-CR 7(undefined)		unused
CR 8 (Protection ID)		per-process value*
CR 9, 12, 13 (PIDS)		unused
CR10 (CCR)			lazy FPU saving*
CR11				as specified by ABI (SAR)
CR14 (interruption vector)	initialized to fault_vector
CR15 (EIEM)			initialized to all ones*
CR16 (Interval Timer)		read for cycle count/write starts Interval Tmr
CR17-CR22			interruption parameters
CR19				Interrupt Instruction Register
CR20				Interrupt Space Register
CR21				Interrupt Offset Register
CR22				Interrupt PSW
CR23 (EIRR)			read for pending interrupts/write clears bits
CR24 (TR 0)			Kernel Space Page Directory Pointer
CR25 (TR 1)			User   Space Page Directory Pointer
CR26 (TR 2)			not used
CR27 (TR 3)			Thread descriptor pointer
CR28 (TR 4)			not used
CR29 (TR 5)			not used
CR30 (TR 6)			current / 0
CR31 (TR 7)			Temporary register, used in various places

	Space Registers (kernel mode)

SR0				temporary space register
SR4-SR7 			set to 0
SR1				temporary space register
SR2				kernel should not clobber this
SR3				used for userspace accesses (current process)

	Space Registers (user mode)

SR0				temporary space register
SR1                             temporary space register
SR2                             holds space of linux gateway page
SR3                             holds user address space value while in kernel
SR4-SR7                         Defines short address space for user/kernel


	Processor Status Word

W (64-bit addresses)		0
E (Little-endian)		0
S (Secure Interval Timer)	0
T (Taken Branch Trap)		0
H (Higher-privilege trap)	0
L (Lower-privilege trap)	0
N (Nullify next instruction)	used by C code
X (Data memory break disable)	0
B (Taken Branch)		used by C code
C (code address translation)	1, 0 while executing real-mode code
V (divide step correction)	used by C code
M (HPMC mask)			0, 1 while executing HPMC handler*
C/B (carry/borrow bits)		used by C code
O (ordered references)		1*
F (performance monitor)		0
R (Recovery Counter trap)	0
Q (collect interruption state)	1 (0 in code directly preceding an rfi)
P (Protection Identifiers)	1*
D (Data address translation)	1, 0 while executing real-mode code
I (external interrupt mask)	used by cli()/sti() macros

	"Invisible" Registers

PSW default W value		0
PSW default E value		0
Shadow Registers		used by interruption handler code
TOC enable bit			1

=========================================================================
Register usage notes, originally from John Marvin, with some additional
notes from Randolph Chung.

For the general registers:

r1,r2,r19-r26,r28,r29 & r31 can be used without saving them first. And of
course, you need to save them if you care about them, before calling
another procedure. Some of the above registers do have special meanings
that you should be aware of:

    r1: The addil instruction is hardwired to place its result in r1,
	so if you use that instruction be aware of that.

    r2: This is the return pointer. In general you don't want to
	use this, since you need the pointer to get back to your
	caller. However, it is grouped with this set of registers
	since the caller can't rely on the value being the same
	when you return, i.e. you can copy r2 to another register
	and return through that register after trashing r2, and
	that should not cause a problem for the calling routine.

    r19-r22: these are generally regarded as temporary registers.
	Note that in 64 bit they are arg7-arg4.

    r23-r26: these are arg3-arg0, i.e. you can use them if you
	don't care about the values that were passed in anymore.

    r28,r29: are ret0 and ret1. They are what you pass return values
	in. r28 is the primary return. When returning small structures
	r29 may also be used to pass data back to the caller.

    r30: stack pointer

    r31: the ble instruction puts the return pointer in here.


r3-r18,r27,r30 need to be saved and restored. r3-r18 are just
    general purpose registers. r27 is the data pointer, and is
    used to make references to global variables easier. r30 is
    the stack pointer.
Commit	Line	Data
1da177e4 LT	1	Register Usage for Linux/PA-RISC
	2
	3	[ an asterisk is used for planned usage which is currently unimplemented ]
	4
	5	General Registers as specified by ABI
	6
	7	Control Registers
	8
	9	CR 0 (Recovery Counter) used for ptrace
	10	CR 1-CR 7(undefined) unused
	11	CR 8 (Protection ID) per-process value*
	12	CR 9, 12, 13 (PIDS) unused
	13	CR10 (CCR) lazy FPU saving*
	14	CR11 as specified by ABI (SAR)
	15	CR14 (interruption vector) initialized to fault_vector
	16	CR15 (EIEM) initialized to all ones*
	17	CR16 (Interval Timer) read for cycle count/write starts Interval Tmr
	18	CR17-CR22 interruption parameters
	19	CR19 Interrupt Instruction Register
	20	CR20 Interrupt Space Register
	21	CR21 Interrupt Offset Register
	22	CR22 Interrupt PSW
	23	CR23 (EIRR) read for pending interrupts/write clears bits
	24	CR24 (TR 0) Kernel Space Page Directory Pointer
	25	CR25 (TR 1) User Space Page Directory Pointer
	26	CR26 (TR 2) not used
	27	CR27 (TR 3) Thread descriptor pointer
	28	CR28 (TR 4) not used
	29	CR29 (TR 5) not used
	30	CR30 (TR 6) current / 0
	31	CR31 (TR 7) Temporary register, used in various places
	32
	33	Space Registers (kernel mode)
	34
	35	SR0 temporary space register
	36	SR4-SR7 set to 0
	37	SR1 temporary space register
	38	SR2 kernel should not clobber this
	39	SR3 used for userspace accesses (current process)
	40
	41	Space Registers (user mode)
	42
	43	SR0 temporary space register
	44	SR1 temporary space register
	45	SR2 holds space of linux gateway page
	46	SR3 holds user address space value while in kernel
	47	SR4-SR7 Defines short address space for user/kernel
	48
	49
	50	Processor Status Word
	51
	52	W (64-bit addresses) 0
	53	E (Little-endian) 0
	54	S (Secure Interval Timer) 0
	55	T (Taken Branch Trap) 0
	56	H (Higher-privilege trap) 0
	57	L (Lower-privilege trap) 0
	58	N (Nullify next instruction) used by C code
	59	X (Data memory break disable) 0
	60	B (Taken Branch) used by C code
	61	C (code address translation) 1, 0 while executing real-mode code
	62	V (divide step correction) used by C code
	63	M (HPMC mask) 0, 1 while executing HPMC handler*
	64	C/B (carry/borrow bits) used by C code
65	O (ordered references) 1*
66	F (performance monitor) 0
67	R (Recovery Counter trap) 0
68	Q (collect interruption state) 1 (0 in code directly preceding an rfi)
69	P (Protection Identifiers) 1*
70	D (Data address translation) 1, 0 while executing real-mode code
71	I (external interrupt mask) used by cli()/sti() macros
72
73	"Invisible" Registers
74
75	PSW default W value 0
76	PSW default E value 0
77	Shadow Registers used by interruption handler code
78	TOC enable bit 1
79
80	=========================================================================
81	Register usage notes, originally from John Marvin, with some additional
82	notes from Randolph Chung.
83
84	For the general registers:
85
86	r1,r2,r19-r26,r28,r29 & r31 can be used without saving them first. And of
87	course, you need to save them if you care about them, before calling
88	another procedure. Some of the above registers do have special meanings
89	that you should be aware of:
90
91	r1: The addil instruction is hardwired to place its result in r1,
92	so if you use that instruction be aware of that.
93
94	r2: This is the return pointer. In general you don't want to
95	use this, since you need the pointer to get back to your
96	caller. However, it is grouped with this set of registers
97	since the caller can't rely on the value being the same
98	when you return, i.e. you can copy r2 to another register
99	and return through that register after trashing r2, and
100	that should not cause a problem for the calling routine.
101
102	r19-r22: these are generally regarded as temporary registers.
103	Note that in 64 bit they are arg7-arg4.
104
105	r23-r26: these are arg3-arg0, i.e. you can use them if you
106	don't care about the values that were passed in anymore.
107
108	r28,r29: are ret0 and ret1. They are what you pass return values
109	in. r28 is the primary return. When returning small structures
110	r29 may also be used to pass data back to the caller.
111
112	r30: stack pointer
113
114	r31: the ble instruction puts the return pointer in here.
115
116
117	r3-r18,r27,r30 need to be saved and restored. r3-r18 are just
118	general purpose registers. r27 is the data pointer, and is
119	used to make references to global variables easier. r30 is
120	the stack pointer.
121