github.com/goproxy0/go@v0.0.0-20171111080102-49cc0c489d2c/src/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  	"cmd/internal/objabi"
     9  	"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  	Variant RelocVariant     // variation on Type
    29  	Type    objabi.RelocType // the relocation type
    30  	Add     int64            // addend
    31  	Xadd    int64            // addend passed to external linker
    32  	Sym     *Symbol          // symbol the relocation addresses
    33  	Xsym    *Symbol          // symbol passed to external linker
    34  }
    35  
    36  // RelocVariant is a linker-internal variation on a relocation.
    37  type RelocVariant uint8
    38  
    39  const (
    40  	RV_NONE RelocVariant = iota
    41  	RV_POWER_LO
    42  	RV_POWER_HI
    43  	RV_POWER_HA
    44  	RV_POWER_DS
    45  
    46  	// RV_390_DBL is a s390x-specific relocation variant that indicates that
    47  	// the value to be placed into the relocatable field should first be
    48  	// divided by 2.
    49  	RV_390_DBL
    50  
    51  	RV_CHECK_OVERFLOW RelocVariant = 1 << 7
    52  	RV_TYPE_MASK      RelocVariant = RV_CHECK_OVERFLOW - 1
    53  )
    54  
    55  func RelocName(arch *sys.Arch, r objabi.RelocType) string {
    56  	// We didn't have some relocation types at Go1.4.
    57  	// Uncomment code when we include those in bootstrap code.
    58  
    59  	switch {
    60  	case r >= 512: // Mach-O
    61  		// nr := (r - 512)>>1
    62  		// switch ctxt.Arch.Family {
    63  		// case sys.AMD64:
    64  		// 	return macho.RelocTypeX86_64(nr).String()
    65  		// case sys.ARM:
    66  		// 	return macho.RelocTypeARM(nr).String()
    67  		// case sys.ARM64:
    68  		// 	return macho.RelocTypeARM64(nr).String()
    69  		// case sys.I386:
    70  		// 	return macho.RelocTypeGeneric(nr).String()
    71  		// default:
    72  		// 	panic("unreachable")
    73  		// }
    74  	case r >= 256: // ELF
    75  		nr := r - 256
    76  		switch arch.Family {
    77  		case sys.AMD64:
    78  			return elf.R_X86_64(nr).String()
    79  		case sys.ARM:
    80  			return elf.R_ARM(nr).String()
    81  		case sys.ARM64:
    82  			return elf.R_AARCH64(nr).String()
    83  		case sys.I386:
    84  			return elf.R_386(nr).String()
    85  		case sys.MIPS, sys.MIPS64:
    86  			// return elf.R_MIPS(nr).String()
    87  		case sys.PPC64:
    88  			// return elf.R_PPC64(nr).String()
    89  		case sys.S390X:
    90  			// return elf.R_390(nr).String()
    91  		default:
    92  			panic("unreachable")
    93  		}
    94  	}
    95  
    96  	return r.String()
    97  }
    98  
    99  // RelocByOff implements sort.Interface for sorting relocations by offset.
   100  type RelocByOff []Reloc
   101  
   102  func (x RelocByOff) Len() int { return len(x) }
   103  
   104  func (x RelocByOff) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
   105  
   106  func (x RelocByOff) Less(i, j int) bool {
   107  	a := &x[i]
   108  	b := &x[j]
   109  	if a.Off < b.Off {
   110  		return true
   111  	}
   112  	if a.Off > b.Off {
   113  		return false
   114  	}
   115  	return false
   116  }