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! -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
!
! This Source Code Form is subject to the terms of the Mozilla Public
! License, v. 2.0. If a copy of the MPL was not distributed with this
! file, You can obtain one at http://mozilla.org/MPL/2.0/.
!
! atomic increment, decrement and swap routines for V8+ sparc (ultrasparc)
! using CAS (compare-and-swap) atomic instructions
!
! this MUST be compiled with an ultrasparc-aware assembler
!
! standard asm linkage macros; this module must be compiled
! with the -P option (use C preprocessor)
#include <sys/asm_linkage.h>
! ======================================================================
!
! Perform the sequence a = a + 1 atomically with respect to other
! fetch-and-adds to location a in a wait-free fashion.
!
! usage : val = PR_AtomicIncrement(address)
! return: current value (you'd think this would be old val)
!
! -----------------------
! Note on REGISTER USAGE:
! as this is a LEAF procedure, a new stack frame is not created;
! we use the caller's stack frame so what would normally be %i (input)
! registers are actually %o (output registers). Also, we must not
! overwrite the contents of %l (local) registers as they are not
! assumed to be volatile during calls.
!
! So, the registers used are:
! %o0 [input] - the address of the value to increment
! %o1 [local] - work register
! %o2 [local] - work register
! %o3 [local] - work register
! -----------------------
ENTRY(PR_AtomicIncrement) ! standard assembler/ELF prologue
retryAI:
ld [%o0], %o2 ! set o2 to the current value
add %o2, 0x1, %o3 ! calc the new value
mov %o3, %o1 ! save the return value
cas [%o0], %o2, %o3 ! atomically set if o0 hasn't changed
cmp %o2, %o3 ! see if we set the value
bne retryAI ! if not, try again
nop ! empty out the branch pipeline
retl ! return back to the caller
mov %o1, %o0 ! set the return code to the new value
SET_SIZE(PR_AtomicIncrement) ! standard assembler/ELF epilogue
!
! end
!
! ======================================================================
!
! ======================================================================
!
! Perform the sequence a = a - 1 atomically with respect to other
! fetch-and-decs to location a in a wait-free fashion.
!
! usage : val = PR_AtomicDecrement(address)
! return: current value (you'd think this would be old val)
!
! -----------------------
! Note on REGISTER USAGE:
! as this is a LEAF procedure, a new stack frame is not created;
! we use the caller's stack frame so what would normally be %i (input)
! registers are actually %o (output registers). Also, we must not
! overwrite the contents of %l (local) registers as they are not
! assumed to be volatile during calls.
!
! So, the registers used are:
! %o0 [input] - the address of the value to increment
! %o1 [local] - work register
! %o2 [local] - work register
! %o3 [local] - work register
! -----------------------
ENTRY(PR_AtomicDecrement) ! standard assembler/ELF prologue
retryAD:
ld [%o0], %o2 ! set o2 to the current value
sub %o2, 0x1, %o3 ! calc the new value
mov %o3, %o1 ! save the return value
cas [%o0], %o2, %o3 ! atomically set if o0 hasn't changed
cmp %o2, %o3 ! see if we set the value
bne retryAD ! if not, try again
nop ! empty out the branch pipeline
retl ! return back to the caller
mov %o1, %o0 ! set the return code to the new value
SET_SIZE(PR_AtomicDecrement) ! standard assembler/ELF epilogue
!
! end
!
! ======================================================================
!
! ======================================================================
!
! Perform the sequence a = b atomically with respect to other
! fetch-and-stores to location a in a wait-free fashion.
!
! usage : old_val = PR_AtomicSet(address, newval)
!
! -----------------------
! Note on REGISTER USAGE:
! as this is a LEAF procedure, a new stack frame is not created;
! we use the caller's stack frame so what would normally be %i (input)
! registers are actually %o (output registers). Also, we must not
! overwrite the contents of %l (local) registers as they are not
! assumed to be volatile during calls.
!
! So, the registers used are:
! %o0 [input] - the address of the value to increment
! %o1 [input] - the new value to set for [%o0]
! %o2 [local] - work register
! %o3 [local] - work register
! -----------------------
ENTRY(PR_AtomicSet) ! standard assembler/ELF prologue
retryAS:
ld [%o0], %o2 ! set o2 to the current value
mov %o1, %o3 ! set up the new value
cas [%o0], %o2, %o3 ! atomically set if o0 hasn't changed
cmp %o2, %o3 ! see if we set the value
bne retryAS ! if not, try again
nop ! empty out the branch pipeline
retl ! return back to the caller
mov %o3, %o0 ! set the return code to the prev value
SET_SIZE(PR_AtomicSet) ! standard assembler/ELF epilogue
!
! end
!
! ======================================================================
!
! ======================================================================
!
! Perform the sequence a = a + b atomically with respect to other
! fetch-and-adds to location a in a wait-free fashion.
!
! usage : newval = PR_AtomicAdd(address, val)
! return: the value after addition
!
ENTRY(PR_AtomicAdd) ! standard assembler/ELF prologue
retryAA:
ld [%o0], %o2 ! set o2 to the current value
add %o2, %o1, %o3 ! calc the new value
mov %o3, %o4 ! save the return value
cas [%o0], %o2, %o3 ! atomically set if o0 hasn't changed
cmp %o2, %o3 ! see if we set the value
bne retryAA ! if not, try again
nop ! empty out the branch pipeline
retl ! return back to the caller
mov %o4, %o0 ! set the return code to the new value
SET_SIZE(PR_AtomicAdd) ! standard assembler/ELF epilogue
!
! end
!
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