tagptr_64bit.go

     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  //go:build amd64 || arm64 || loong64 || mips64 || mips64le || ppc64 || ppc64le || riscv64 || s390x || wasm
     6  
     7  package runtime
     8  
     9  import (
    10  	"internal/goarch"
    11  	"internal/goos"
    12  	"unsafe"
    13  )
    14  
    15  const (
    16  	// addrBits is the number of bits needed to represent a virtual address.
    17  	//
    18  	// See heapAddrBits for a table of address space sizes on
    19  	// various architectures. 48 bits is enough for all
    20  	// architectures except s390x.
    21  	//
    22  	// On AMD64, virtual addresses are 48-bit (or 57-bit) numbers sign extended to 64.
    23  	// We shift the address left 16 to eliminate the sign extended part and make
    24  	// room in the bottom for the count.
    25  	//
    26  	// On s390x, virtual addresses are 64-bit. There's not much we
    27  	// can do about this, so we just hope that the kernel doesn't
    28  	// get to really high addresses and panic if it does.
    29  	addrBits = 48
    30  
    31  	// In addition to the 16 bits taken from the top, we can take 3 from the
    32  	// bottom, because node must be pointer-aligned, giving a total of 19 bits
    33  	// of count.
    34  	tagBits = 64 - addrBits + 3
    35  
    36  	// On AIX, 64-bit addresses are split into 36-bit segment number and 28-bit
    37  	// offset in segment.  Segment numbers in the range 0x0A0000000-0x0AFFFFFFF(LSA)
    38  	// are available for mmap.
    39  	// We assume all tagged addresses are from memory allocated with mmap.
    40  	// We use one bit to distinguish between the two ranges.
    41  	aixAddrBits = 57
    42  	aixTagBits  = 64 - aixAddrBits + 3
    43  
    44  	// riscv64 SV57 mode gives 56 bits of userspace VA.
    45  	// tagged pointer code supports it,
    46  	// but broader support for SV57 mode is incomplete,
    47  	// and there may be other issues (see #54104).
    48  	riscv64AddrBits = 56
    49  	riscv64TagBits  = 64 - riscv64AddrBits + 3
    50  )
    51  
    52  // The number of bits stored in the numeric tag of a taggedPointer
    53  const taggedPointerBits = (goos.IsAix * aixTagBits) + (goarch.IsRiscv64 * riscv64TagBits) + ((1 - goos.IsAix) * (1 - goarch.IsRiscv64) * tagBits)
    54  
    55  // taggedPointerPack created a taggedPointer from a pointer and a tag.
    56  // Tag bits that don't fit in the result are discarded.
    57  func taggedPointerPack(ptr unsafe.Pointer, tag uintptr) taggedPointer {
    58  	if GOOS == "aix" {
    59  		if GOARCH != "ppc64" {
    60  			throw("check this code for aix on non-ppc64")
    61  		}
    62  		return taggedPointer(uint64(uintptr(ptr))<<(64-aixAddrBits) | uint64(tag&(1<<aixTagBits-1)))
    63  	}
    64  	if GOARCH == "riscv64" {
    65  		return taggedPointer(uint64(uintptr(ptr))<<(64-riscv64AddrBits) | uint64(tag&(1<<riscv64TagBits-1)))
    66  	}
    67  	return taggedPointer(uint64(uintptr(ptr))<<(64-addrBits) | uint64(tag&(1<<tagBits-1)))
    68  }
    69  
    70  // Pointer returns the pointer from a taggedPointer.
    71  func (tp taggedPointer) pointer() unsafe.Pointer {
    72  	if GOARCH == "amd64" {
    73  		// amd64 systems can place the stack above the VA hole, so we need to sign extend
    74  		// val before unpacking.
    75  		return unsafe.Pointer(uintptr(int64(tp) >> tagBits << 3))
    76  	}
    77  	if GOOS == "aix" {
    78  		return unsafe.Pointer(uintptr((tp >> aixTagBits << 3) | 0xa<<56))
    79  	}
    80  	if GOARCH == "riscv64" {
    81  		return unsafe.Pointer(uintptr(tp >> riscv64TagBits << 3))
    82  	}
    83  	return unsafe.Pointer(uintptr(tp >> tagBits << 3))
    84  }
    85  
    86  // Tag returns the tag from a taggedPointer.
    87  func (tp taggedPointer) tag() uintptr {
    88  	return uintptr(tp & (1<<taggedPointerBits - 1))
    89  }
    90
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