diff options
Diffstat (limited to 'pkg/safecopy/memcpy_arm64.s')
| -rw-r--r-- | pkg/safecopy/memcpy_arm64.s | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/pkg/safecopy/memcpy_arm64.s b/pkg/safecopy/memcpy_arm64.s new file mode 100644 index 000000000..e7e541565 --- /dev/null +++ b/pkg/safecopy/memcpy_arm64.s @@ -0,0 +1,78 @@ +// Copyright 2014 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +#include "textflag.h" + +// handleMemcpyFault returns (the value stored in R0, the value stored in R1). +// Control is transferred to it when memcpy below receives SIGSEGV or SIGBUS, +// with the faulting address stored in R0 and the signal number stored in R1. +// +// It must have the same frame configuration as memcpy so that it can undo any +// potential call frame set up by the assembler. +TEXT handleMemcpyFault(SB), NOSPLIT, $0-36 + MOVD R0, addr+24(FP) + MOVW R1, sig+32(FP) + RET + +// memcpy copies data from src to dst. If a SIGSEGV or SIGBUS signal is received +// during the copy, it returns the address that caused the fault and the number +// of the signal that was received. Otherwise, it returns an unspecified address +// and a signal number of 0. +// +// Data is copied in order, such that if a fault happens at address p, it is +// safe to assume that all data before p-maxRegisterSize has already been +// successfully copied. +// +// The code is derived from the Go source runtime.memmove. +// +// func memcpy(dst, src unsafe.Pointer, n uintptr) (fault unsafe.Pointer, sig int32) +TEXT ·memcpy(SB), NOSPLIT, $-8-36 + // Store 0 as the returned signal number. If we run to completion, + // this is the value the caller will see; if a signal is received, + // handleMemcpyFault will store a different value in this address. + MOVW $0, sig+32(FP) + + MOVD to+0(FP), R3 + MOVD from+8(FP), R4 + MOVD n+16(FP), R5 + CMP $0, R5 + BNE check + RET + +check: + AND $~7, R5, R7 // R7 is N&~7. + SUB R7, R5, R6 // R6 is N&7. + + // Copying forward proceeds by copying R7/8 words then copying R6 bytes. + // R3 and R4 are advanced as we copy. + + // (There may be implementations of armv8 where copying by bytes until + // at least one of source or dest is word aligned is a worthwhile + // optimization, but the on the one tested so far (xgene) it did not + // make a significance difference.) + + CMP $0, R7 // Do we need to do any word-by-word copying? + BEQ noforwardlarge + ADD R3, R7, R9 // R9 points just past where we copy by word. + +forwardlargeloop: + MOVD.P 8(R4), R8 // R8 is just a scratch register. + MOVD.P R8, 8(R3) + CMP R3, R9 + BNE forwardlargeloop + +noforwardlarge: + CMP $0, R6 // Do we need to do any byte-by-byte copying? + BNE forwardtail + RET + +forwardtail: + ADD R3, R6, R9 // R9 points just past the destination memory. + +forwardtailloop: + MOVBU.P 1(R4), R8 + MOVBU.P R8, 1(R3) + CMP R3, R9 + BNE forwardtailloop + RET |