^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) ================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) Register Usage for Linux/PA-RISC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) ================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) [ an asterisk is used for planned usage which is currently unimplemented ]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) General Registers as specified by ABI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) =====================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) Control Registers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) -----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) CR 0 (Recovery Counter) used for ptrace
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) CR 1-CR 7(undefined) unused
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) CR 8 (Protection ID) per-process value*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) CR 9, 12, 13 (PIDS) unused
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) CR10 (CCR) lazy FPU saving*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) CR11 as specified by ABI (SAR)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) CR14 (interruption vector) initialized to fault_vector
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) CR15 (EIEM) initialized to all ones*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) CR16 (Interval Timer) read for cycle count/write starts Interval Tmr
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) CR17-CR22 interruption parameters
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) CR19 Interrupt Instruction Register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) CR20 Interrupt Space Register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) CR21 Interrupt Offset Register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) CR22 Interrupt PSW
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) CR23 (EIRR) read for pending interrupts/write clears bits
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) CR24 (TR 0) Kernel Space Page Directory Pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) CR25 (TR 1) User Space Page Directory Pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) CR26 (TR 2) not used
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) CR27 (TR 3) Thread descriptor pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) CR28 (TR 4) not used
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) CR29 (TR 5) not used
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) CR30 (TR 6) current / 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) CR31 (TR 7) Temporary register, used in various places
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) Space Registers (kernel mode)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) -----------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) SR0 temporary space register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) SR4-SR7 set to 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) SR1 temporary space register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) SR2 kernel should not clobber this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) SR3 used for userspace accesses (current process)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) Space Registers (user mode)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) ---------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) SR0 temporary space register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) SR1 temporary space register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) SR2 holds space of linux gateway page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) SR3 holds user address space value while in kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) SR4-SR7 Defines short address space for user/kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) Processor Status Word
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) ---------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) W (64-bit addresses) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) E (Little-endian) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) S (Secure Interval Timer) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) T (Taken Branch Trap) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) H (Higher-privilege trap) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) L (Lower-privilege trap) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) N (Nullify next instruction) used by C code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) X (Data memory break disable) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) B (Taken Branch) used by C code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) C (code address translation) 1, 0 while executing real-mode code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) V (divide step correction) used by C code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) M (HPMC mask) 0, 1 while executing HPMC handler*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) C/B (carry/borrow bits) used by C code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) O (ordered references) 1*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) F (performance monitor) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) R (Recovery Counter trap) 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) Q (collect interruption state) 1 (0 in code directly preceding an rfi)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) P (Protection Identifiers) 1*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) D (Data address translation) 1, 0 while executing real-mode code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) I (external interrupt mask) used by cli()/sti() macros
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) "Invisible" Registers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) ---------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) PSW default W value 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93) PSW default E value 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) Shadow Registers used by interruption handler code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) TOC enable bit 1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) =============================== ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) -------------------------------------------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) The PA-RISC architecture defines 7 registers as "shadow registers".
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) Those are used in RETURN FROM INTERRUPTION AND RESTORE instruction to reduce
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) the state save and restore time by eliminating the need for general register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) (GR) saves and restores in interruption handlers.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) Shadow registers are the GRs 1, 8, 9, 16, 17, 24, and 25.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) -------------------------------------------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) Register usage notes, originally from John Marvin, with some additional
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) notes from Randolph Chung.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) For the general registers:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) r1,r2,r19-r26,r28,r29 & r31 can be used without saving them first. And of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) course, you need to save them if you care about them, before calling
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) another procedure. Some of the above registers do have special meanings
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) that you should be aware of:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) r1:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) The addil instruction is hardwired to place its result in r1,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) so if you use that instruction be aware of that.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) r2:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) This is the return pointer. In general you don't want to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) use this, since you need the pointer to get back to your
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) caller. However, it is grouped with this set of registers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) since the caller can't rely on the value being the same
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) when you return, i.e. you can copy r2 to another register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) and return through that register after trashing r2, and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) that should not cause a problem for the calling routine.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) r19-r22:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) these are generally regarded as temporary registers.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) Note that in 64 bit they are arg7-arg4.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) r23-r26:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) these are arg3-arg0, i.e. you can use them if you
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) don't care about the values that were passed in anymore.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) r28,r29:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) are ret0 and ret1. They are what you pass return values
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) in. r28 is the primary return. When returning small structures
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) r29 may also be used to pass data back to the caller.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) r30:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) stack pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) r31:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) the ble instruction puts the return pointer in here.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) r3-r18,r27,r30 need to be saved and restored. r3-r18 are just
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) general purpose registers. r27 is the data pointer, and is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) used to make references to global variables easier. r30 is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) the stack pointer.
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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