Contents of /alx-src/tags/kernel26-2.6.12-alx-r9/Documentation/parisc/registers
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Wed Mar 4 11:03:09 2009 UTC (15 years, 3 months ago) by niro
File size: 4235 byte(s)
Wed Mar 4 11:03:09 2009 UTC (15 years, 3 months ago) by niro
File size: 4235 byte(s)
Tag kernel26-2.6.12-alx-r9
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 |