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 |