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
5package sym
6
7import (
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.
24type 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.
36type 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
42func (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.
49type RelocVariant uint8
50
51const (
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
67func 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.
112type RelocByOff []Reloc
113
114func (x RelocByOff) Len() int { return len(x) }
115
116func (x RelocByOff) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
117
118func (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