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Based on kernel version 3.9. Page generated on 2013-05-02 23:12 EST.
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.
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