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