github.com/gagliardetto/golang-go@v0.0.0-20201020153340-53909ea70814/cmd/link/internal/sym/reloc.go (about)

     1  // Copyright 2017 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  package sym
     6  
     7  import (
     8  	"github.com/gagliardetto/golang-go/cmd/internal/objabi"
     9  	"github.com/gagliardetto/golang-go/cmd/internal/sys"
    10  	"debug/elf"
    11  )
    12  
    13  // Reloc is a relocation.
    14  //
    15  // The typical Reloc rewrites part of a symbol at offset Off to address Sym.
    16  // A Reloc is stored in a slice on the Symbol it rewrites.
    17  //
    18  // Relocations are generated by the compiler as the type
    19  // cmd/internal/obj.Reloc, which is encoded into the object file wire
    20  // format and decoded by the linker into this type. A separate type is
    21  // used to hold linker-specific state about the relocation.
    22  //
    23  // Some relocations are created by cmd/link.
    24  type Reloc struct {
    25  	Off       int32            // offset to rewrite
    26  	Siz       uint8            // number of bytes to rewrite, 1, 2, or 4
    27  	Done      bool             // set to true when relocation is complete
    28  	Type      objabi.RelocType // the relocation type
    29  	Add       int64            // addend
    30  	Sym       *Symbol          // symbol the relocation addresses
    31  	*relocExt                  // extra fields (see below), may be nil, call InitExt before use
    32  }
    33  
    34  // relocExt contains extra fields in Reloc that are used only in
    35  // certain cases.
    36  type relocExt struct {
    37  	Xadd    int64        // addend passed to external linker
    38  	Xsym    *Symbol      // symbol passed to external linker
    39  	Variant RelocVariant // variation on Type, currently used only on PPC64 and S390X
    40  }
    41  
    42  func (r *Reloc) InitExt() {
    43  	if r.relocExt == nil {
    44  		r.relocExt = new(relocExt)
    45  	}
    46  }
    47  
    48  // RelocVariant is a linker-internal variation on a relocation.
    49  type RelocVariant uint8
    50  
    51  const (
    52  	RV_NONE RelocVariant = iota
    53  	RV_POWER_LO
    54  	RV_POWER_HI
    55  	RV_POWER_HA
    56  	RV_POWER_DS
    57  
    58  	// RV_390_DBL is a s390x-specific relocation variant that indicates that
    59  	// the value to be placed into the relocatable field should first be
    60  	// divided by 2.
    61  	RV_390_DBL
    62  
    63  	RV_CHECK_OVERFLOW RelocVariant = 1 << 7
    64  	RV_TYPE_MASK      RelocVariant = RV_CHECK_OVERFLOW - 1
    65  )
    66  
    67  func RelocName(arch *sys.Arch, r objabi.RelocType) string {
    68  	// We didn't have some relocation types at Go1.4.
    69  	// Uncomment code when we include those in bootstrap code.
    70  
    71  	switch {
    72  	case r >= objabi.MachoRelocOffset: // Mach-O
    73  		// nr := (r - objabi.MachoRelocOffset)>>1
    74  		// switch ctxt.Arch.Family {
    75  		// case sys.AMD64:
    76  		// 	return macho.RelocTypeX86_64(nr).String()
    77  		// case sys.ARM:
    78  		// 	return macho.RelocTypeARM(nr).String()
    79  		// case sys.ARM64:
    80  		// 	return macho.RelocTypeARM64(nr).String()
    81  		// case sys.I386:
    82  		// 	return macho.RelocTypeGeneric(nr).String()
    83  		// default:
    84  		// 	panic("unreachable")
    85  		// }
    86  	case r >= objabi.ElfRelocOffset: // ELF
    87  		nr := r - objabi.ElfRelocOffset
    88  		switch arch.Family {
    89  		case sys.AMD64:
    90  			return elf.R_X86_64(nr).String()
    91  		case sys.ARM:
    92  			return elf.R_ARM(nr).String()
    93  		case sys.ARM64:
    94  			return elf.R_AARCH64(nr).String()
    95  		case sys.I386:
    96  			return elf.R_386(nr).String()
    97  		case sys.MIPS, sys.MIPS64:
    98  			return elf.R_MIPS(nr).String()
    99  		case sys.PPC64:
   100  			return elf.R_PPC64(nr).String()
   101  		case sys.S390X:
   102  			return elf.R_390(nr).String()
   103  		default:
   104  			panic("unreachable")
   105  		}
   106  	}
   107  
   108  	return r.String()
   109  }
   110  
   111  // RelocByOff implements sort.Interface for sorting relocations by offset.
   112  type RelocByOff []Reloc
   113  
   114  func (x RelocByOff) Len() int { return len(x) }
   115  
   116  func (x RelocByOff) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
   117  
   118  func (x RelocByOff) Less(i, j int) bool {
   119  	a := &x[i]
   120  	b := &x[j]
   121  	if a.Off < b.Off {
   122  		return true
   123  	}
   124  	if a.Off > b.Off {
   125  		return false
   126  	}
   127  	return false
   128  }