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Source file src/runtime/lfstack_64bit.go

Documentation: runtime

     1  // Copyright 2014 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build amd64 arm64 mips64 mips64le ppc64 ppc64le s390x wasm
     6  
     7  package runtime
     8  
     9  import "unsafe"
    10  
    11  const (
    12  	// addrBits is the number of bits needed to represent a virtual address.
    13  	//
    14  	// See heapAddrBits for a table of address space sizes on
    15  	// various architectures. 48 bits is enough for all
    16  	// architectures except s390x.
    17  	//
    18  	// On AMD64, virtual addresses are 48-bit (or 57-bit) numbers sign extended to 64.
    19  	// We shift the address left 16 to eliminate the sign extended part and make
    20  	// room in the bottom for the count.
    21  	//
    22  	// On s390x, virtual addresses are 64-bit. There's not much we
    23  	// can do about this, so we just hope that the kernel doesn't
    24  	// get to really high addresses and panic if it does.
    25  	addrBits = 48
    26  
    27  	// In addition to the 16 bits taken from the top, we can take 3 from the
    28  	// bottom, because node must be pointer-aligned, giving a total of 19 bits
    29  	// of count.
    30  	cntBits = 64 - addrBits + 3
    31  
    32  	// On AIX, 64-bit addresses are split into 36-bit segment number and 28-bit
    33  	// offset in segment.  Segment numbers in the range 0x0A0000000-0x0AFFFFFFF(LSA)
    34  	// are available for mmap.
    35  	// We assume all lfnode addresses are from memory allocated with mmap.
    36  	// We use one bit to distinguish between the two ranges.
    37  	aixAddrBits = 57
    38  	aixCntBits  = 64 - aixAddrBits + 3
    39  )
    40  
    41  func lfstackPack(node *lfnode, cnt uintptr) uint64 {
    42  	if GOARCH == "ppc64" && GOOS == "aix" {
    43  		return uint64(uintptr(unsafe.Pointer(node)))<<(64-aixAddrBits) | uint64(cnt&(1<<aixCntBits-1))
    44  	}
    45  	return uint64(uintptr(unsafe.Pointer(node)))<<(64-addrBits) | uint64(cnt&(1<<cntBits-1))
    46  }
    47  
    48  func lfstackUnpack(val uint64) *lfnode {
    49  	if GOARCH == "amd64" {
    50  		// amd64 systems can place the stack above the VA hole, so we need to sign extend
    51  		// val before unpacking.
    52  		return (*lfnode)(unsafe.Pointer(uintptr(int64(val) >> cntBits << 3)))
    53  	}
    54  	if GOARCH == "ppc64" && GOOS == "aix" {
    55  		return (*lfnode)(unsafe.Pointer(uintptr((val >> aixCntBits << 3) | 0xa<<56)))
    56  	}
    57  	return (*lfnode)(unsafe.Pointer(uintptr(val >> cntBits << 3)))
    58  }
    59  

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