mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-27 11:19:37 +00:00
122 lines
4.1 KiB
Text
122 lines
4.1 KiB
Text
![]() |
Register Usage for Linux/PA-RISC
|
||
|
|
||
|
[ an asterisk is used for planned usage which is currently unimplemented ]
|
||
|
|
||
|
General Registers as specified by ABI
|
||
|
|
||
|
Control Registers
|
||
|
|
||
|
CR 0 (Recovery Counter) used for ptrace
|
||
|
CR 1-CR 7(undefined) unused
|
||
|
CR 8 (Protection ID) per-process value*
|
||
|
CR 9, 12, 13 (PIDS) unused
|
||
|
CR10 (CCR) lazy FPU saving*
|
||
|
CR11 as specified by ABI (SAR)
|
||
|
CR14 (interruption vector) initialized to fault_vector
|
||
|
CR15 (EIEM) initialized to all ones*
|
||
|
CR16 (Interval Timer) read for cycle count/write starts Interval Tmr
|
||
|
CR17-CR22 interruption parameters
|
||
|
CR19 Interrupt Instruction Register
|
||
|
CR20 Interrupt Space Register
|
||
|
CR21 Interrupt Offset Register
|
||
|
CR22 Interrupt PSW
|
||
|
CR23 (EIRR) read for pending interrupts/write clears bits
|
||
|
CR24 (TR 0) Kernel Space Page Directory Pointer
|
||
|
CR25 (TR 1) User Space Page Directory Pointer
|
||
|
CR26 (TR 2) not used
|
||
|
CR27 (TR 3) Thread descriptor pointer
|
||
|
CR28 (TR 4) not used
|
||
|
CR29 (TR 5) not used
|
||
|
CR30 (TR 6) current / 0
|
||
|
CR31 (TR 7) Temporary register, used in various places
|
||
|
|
||
|
Space Registers (kernel mode)
|
||
|
|
||
|
SR0 temporary space register
|
||
|
SR4-SR7 set to 0
|
||
|
SR1 temporary space register
|
||
|
SR2 kernel should not clobber this
|
||
|
SR3 used for userspace accesses (current process)
|
||
|
|
||
|
Space Registers (user mode)
|
||
|
|
||
|
SR0 temporary space register
|
||
|
SR1 temporary space register
|
||
|
SR2 holds space of linux gateway page
|
||
|
SR3 holds user address space value while in kernel
|
||
|
SR4-SR7 Defines short address space for user/kernel
|
||
|
|
||
|
|
||
|
Processor Status Word
|
||
|
|
||
|
W (64-bit addresses) 0
|
||
|
E (Little-endian) 0
|
||
|
S (Secure Interval Timer) 0
|
||
|
T (Taken Branch Trap) 0
|
||
|
H (Higher-privilege trap) 0
|
||
|
L (Lower-privilege trap) 0
|
||
|
N (Nullify next instruction) used by C code
|
||
|
X (Data memory break disable) 0
|
||
|
B (Taken Branch) used by C code
|
||
|
C (code address translation) 1, 0 while executing real-mode code
|
||
|
V (divide step correction) used by C code
|
||
|
M (HPMC mask) 0, 1 while executing HPMC handler*
|
||
|
C/B (carry/borrow bits) used by C code
|
||
|
O (ordered references) 1*
|
||
|
F (performance monitor) 0
|
||
|
R (Recovery Counter trap) 0
|
||
|
Q (collect interruption state) 1 (0 in code directly preceding an rfi)
|
||
|
P (Protection Identifiers) 1*
|
||
|
D (Data address translation) 1, 0 while executing real-mode code
|
||
|
I (external interrupt mask) used by cli()/sti() macros
|
||
|
|
||
|
"Invisible" Registers
|
||
|
|
||
|
PSW default W value 0
|
||
|
PSW default E value 0
|
||
|
Shadow Registers used by interruption handler code
|
||
|
TOC enable bit 1
|
||
|
|
||
|
=========================================================================
|
||
|
Register usage notes, originally from John Marvin, with some additional
|
||
|
notes from Randolph Chung.
|
||
|
|
||
|
For the general registers:
|
||
|
|
||
|
r1,r2,r19-r26,r28,r29 & r31 can be used without saving them first. And of
|
||
|
course, you need to save them if you care about them, before calling
|
||
|
another procedure. Some of the above registers do have special meanings
|
||
|
that you should be aware of:
|
||
|
|
||
|
r1: The addil instruction is hardwired to place its result in r1,
|
||
|
so if you use that instruction be aware of that.
|
||
|
|
||
|
r2: This is the return pointer. In general you don't want to
|
||
|
use this, since you need the pointer to get back to your
|
||
|
caller. However, it is grouped with this set of registers
|
||
|
since the caller can't rely on the value being the same
|
||
|
when you return, i.e. you can copy r2 to another register
|
||
|
and return through that register after trashing r2, and
|
||
|
that should not cause a problem for the calling routine.
|
||
|
|
||
|
r19-r22: these are generally regarded as temporary registers.
|
||
|
Note that in 64 bit they are arg7-arg4.
|
||
|
|
||
|
r23-r26: these are arg3-arg0, i.e. you can use them if you
|
||
|
don't care about the values that were passed in anymore.
|
||
|
|
||
|
r28,r29: are ret0 and ret1. They are what you pass return values
|
||
|
in. r28 is the primary return. When returning small structures
|
||
|
r29 may also be used to pass data back to the caller.
|
||
|
|
||
|
r30: stack pointer
|
||
|
|
||
|
r31: the ble instruction puts the return pointer in here.
|
||
|
|
||
|
|
||
|
r3-r18,r27,r30 need to be saved and restored. r3-r18 are just
|
||
|
general purpose registers. r27 is the data pointer, and is
|
||
|
used to make references to global variables easier. r30 is
|
||
|
the stack pointer.
|
||
|
|