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  	// arch/os combos except s390x, aix, and riscv64.
    21  	//
    22  	// On AMD64, virtual addresses are 48-bit (or 57-bit) sign-extended.
    23  	// Other archs are 48-bit zero-extended.
    24  	//
    25  	// We use one extra bit to placate systems which simulate amd64 binaries on
    26  	// an arm64 host. Allocated arm64 addresses could be as high as 1<<48-1,
    27  	// which would be invalid if we assumed 48-bit sign-extended addresses.
    28  	// See issue 69255.
    29  	// (Note that this does not help the other way around, simluating arm64
    30  	// on amd64, but we don't have that problem at the moment.)
    31  	//
    32  	// On s390x, virtual addresses are 64-bit. There's not much we
    33  	// can do about this, so we just hope that the kernel doesn't
    34  	// get to really high addresses and panic if it does.
    35  	defaultAddrBits = 48 + 1
    36  
    37  	// On AIX, 64-bit addresses are split into 36-bit segment number and 28-bit
    38  	// offset in segment.  Segment numbers in the range 0x0A0000000-0x0AFFFFFFF(LSA)
    39  	// are available for mmap.
    40  	// We assume all tagged addresses are from memory allocated with mmap.
    41  	// We use one bit to distinguish between the two ranges.
    42  	aixAddrBits = 57
    43  
    44  	// Later versions of FreeBSD enable amd64's la57 by default.
    45  	freebsdAmd64AddrBits = 57
    46  
    47  	// riscv64 SV57 mode gives 56 bits of userspace VA.
    48  	// tagged pointer code supports it,
    49  	// but broader support for SV57 mode is incomplete,
    50  	// and there may be other issues (see #54104).
    51  	riscv64AddrBits = 56
    52  
    53  	addrBits = goos.IsAix*aixAddrBits + goarch.IsRiscv64*riscv64AddrBits + goos.IsFreebsd*goarch.IsAmd64*freebsdAmd64AddrBits + (1-goos.IsAix)*(1-goarch.IsRiscv64)*(1-goos.IsFreebsd*goarch.IsAmd64)*defaultAddrBits
    54  
    55  	// In addition to the 16 bits (or other, depending on arch/os) taken from the top,
    56  	// we can take 9 from the bottom, because we require pointers to be well-aligned
    57  	// (see tagptr.go:tagAlignBits). That gives us a total of 25 bits for the tag.
    58  	tagBits = 64 - addrBits + tagAlignBits
    59  )
    60  
    61  // taggedPointerPack created a taggedPointer from a pointer and a tag.
    62  // Tag bits that don't fit in the result are discarded.
    63  func taggedPointerPack(ptr unsafe.Pointer, tag uintptr) taggedPointer {
    64  	t := taggedPointer(uint64(uintptr(ptr))<<(tagBits-tagAlignBits) | uint64(tag&(1<<tagBits-1)))
    65  	if t.pointer() != ptr || t.tag() != tag {
    66  		print("runtime: taggedPointerPack invalid packing: ptr=", ptr, " tag=", hex(tag), " packed=", hex(t), " -> ptr=", t.pointer(), " tag=", hex(t.tag()), "\n")
    67  		throw("taggedPointerPack")
    68  	}
    69  	return t
    70  }
    71  
    72  // Pointer returns the pointer from a taggedPointer.
    73  func (tp taggedPointer) pointer() unsafe.Pointer {
    74  	if GOARCH == "amd64" {
    75  		// amd64 systems can place the stack above the VA hole, so we need to sign extend
    76  		// val before unpacking.
    77  		return unsafe.Pointer(uintptr(int64(tp) >> tagBits << tagAlignBits))
    78  	}
    79  	if GOOS == "aix" {
    80  		return unsafe.Pointer(uintptr((tp >> tagBits << tagAlignBits) | 0xa<<56))
    81  	}
    82  	return unsafe.Pointer(uintptr(tp >> tagBits << tagAlignBits))
    83  }
    84  
    85  // Tag returns the tag from a taggedPointer.
    86  func (tp taggedPointer) tag() uintptr {
    87  	return uintptr(tp & (1<<tagBits - 1))
    88  }
    89
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