1 ================================
2 Register Usage for Linux/PA-RISC
3 ================================
4
5 [ an asterisk is used for planned usage which
6
7 General Registers as specified by ABI
8 =====================================
9
10 Control Registers
11 -----------------
12
13 =============================== ==============
14 CR 0 (Recovery Counter) used for ptrac
15 CR 1-CR 7(undefined) unused
16 CR 8 (Protection ID) per-process va
17 CR 9, 12, 13 (PIDS) unused
18 CR10 (CCR) lazy FPU savin
19 CR11 as specified b
20 CR14 (interruption vector) initialized to
21 CR15 (EIEM) initialized to
22 CR16 (Interval Timer) read for cycle
23 CR17-CR22 interruption p
24 CR19 Interrupt Inst
25 CR20 Interrupt Spac
26 CR21 Interrupt Offs
27 CR22 Interrupt PSW
28 CR23 (EIRR) read for pendi
29 CR24 (TR 0) Kernel Space P
30 CR25 (TR 1) User Space P
31 CR26 (TR 2) not used
32 CR27 (TR 3) Thread descrip
33 CR28 (TR 4) not used
34 CR29 (TR 5) not used
35 CR30 (TR 6) current / 0
36 CR31 (TR 7) Temporary regi
37 =============================== ==============
38
39 Space Registers (kernel mode)
40 -----------------------------
41
42 =============================== ==============
43 SR0 temporary spac
44 SR4-SR7 set to 0
45 SR1 temporary spac
46 SR2 kernel should
47 SR3 used for users
48 =============================== ==============
49
50 Space Registers (user mode)
51 ---------------------------
52
53 =============================== ==============
54 SR0 temporary spac
55 SR1 temporary spac
56 SR2 holds space of
57 SR3 holds user add
58 SR4-SR7 Defines short
59 =============================== ==============
60
61
62 Processor Status Word
63 ---------------------
64
65 =============================== ==============
66 W (64-bit addresses) 0
67 E (Little-endian) 0
68 S (Secure Interval Timer) 0
69 T (Taken Branch Trap) 0
70 H (Higher-privilege trap) 0
71 L (Lower-privilege trap) 0
72 N (Nullify next instruction) used by C code
73 X (Data memory break disable) 0
74 B (Taken Branch) used by C code
75 C (code address translation) 1, 0 while exe
76 V (divide step correction) used by C code
77 M (HPMC mask) 0, 1 while exe
78 C/B (carry/borrow bits) used by C code
79 O (ordered references) 1*
80 F (performance monitor) 0
81 R (Recovery Counter trap) 0
82 Q (collect interruption state) 1 (0 in code d
83 P (Protection Identifiers) 1*
84 D (Data address translation) 1, 0 while exe
85 I (external interrupt mask) used by cli()/
86 =============================== ==============
87
88 "Invisible" Registers
89 ---------------------
90
91 =============================== ==============
92 PSW default W value 0
93 PSW default E value 0
94 Shadow Registers used by interr
95 TOC enable bit 1
96 =============================== ==============
97
98 ----------------------------------------------
99
100 The PA-RISC architecture defines 7 registers a
101 Those are used in RETURN FROM INTERRUPTION AND
102 the state save and restore time by eliminating
103 (GR) saves and restores in interruption handle
104 Shadow registers are the GRs 1, 8, 9, 16, 17,
105
106 ----------------------------------------------
107
108 Register usage notes, originally from John Mar
109 notes from Randolph Chung.
110
111 For the general registers:
112
113 r1,r2,r19-r26,r28,r29 & r31 can be used withou
114 course, you need to save them if you care abou
115 another procedure. Some of the above registers
116 that you should be aware of:
117
118 r1:
119 The addil instruction is hardwired to
120 so if you use that instruction be awar
121
122 r2:
123 This is the return pointer. In general
124 use this, since you need the pointer t
125 caller. However, it is grouped with th
126 since the caller can't rely on the val
127 when you return, i.e. you can copy r2
128 and return through that register after
129 that should not cause a problem for th
130
131 r19-r22:
132 these are generally regarded as tempor
133 Note that in 64 bit they are arg7-arg4
134
135 r23-r26:
136 these are arg3-arg0, i.e. you can use
137 don't care about the values that were
138
139 r28,r29:
140 are ret0 and ret1. They are what you p
141 in. r28 is the primary return. When re
142 r29 may also be used to pass data back
143
144 r30:
145 stack pointer
146
147 r31:
148 the ble instruction puts the return po
149
150
151 r3-r18,r27,r30 need to be saved and restor
152 general purpose registers. r27 is the data
153 used to make references to global variable
154 the stack pointer.
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