Source file src/pkg/cmd/link/internal/sym/reloc.go

     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		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	}
   129	

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