Golang Link.DynlinkingGo方法代码示例

func gentext(ctxt *ld.Link) {
	if ctxt.DynlinkingGo() {
		genaddmoduledata(ctxt)
	}

	if ld.Linkmode == ld.LinkInternal {
		genplt(ctxt)
	}
}

// Convert the direct jump relocation r to refer to a trampoline if the target is too far
func trampoline(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol) {
	switch r.Type {
	case obj.R_CALLARM:
		// r.Add is the instruction
		// low 24-bit encodes the target address
		t := (ld.Symaddr(r.Sym) + int64(signext24(r.Add&0xffffff)*4) - (s.Value + int64(r.Off))) / 4
		if t > 0x7fffff || t < -0x800000 || (*ld.FlagDebugTramp > 1 && s.File != r.Sym.File) {
			// direct call too far, need to insert trampoline.
			// look up existing trampolines first. if we found one within the range
			// of direct call, we can reuse it. otherwise create a new one.
			offset := (signext24(r.Add&0xffffff) + 2) * 4
			var tramp *ld.Symbol
			for i := 0; ; i++ {
				name := r.Sym.Name + fmt.Sprintf("%+d-tramp%d", offset, i)
				tramp = ctxt.Syms.Lookup(name, int(r.Sym.Version))
				if tramp.Type == obj.SDYNIMPORT {
					// don't reuse trampoline defined in other module
					continue
				}
				if tramp.Value == 0 {
					// either the trampoline does not exist -- we need to create one,
					// or found one the address which is not assigned -- this will be
					// laid down immediately after the current function. use this one.
					break
				}

				t = (ld.Symaddr(tramp) - 8 - (s.Value + int64(r.Off))) / 4
				if t >= -0x800000 && t < 0x7fffff {
					// found an existing trampoline that is not too far
					// we can just use it
					break
				}
			}
			if tramp.Type == 0 {
				// trampoline does not exist, create one
				ctxt.AddTramp(tramp)
				if ctxt.DynlinkingGo() {
					if immrot(uint32(offset)) == 0 {
						ld.Errorf(s, "odd offset in dynlink direct call: %v+%d", r.Sym, offset)
					}
					gentrampdyn(tramp, r.Sym, int64(offset))
				} else if ld.Buildmode == ld.BuildmodeCArchive || ld.Buildmode == ld.BuildmodeCShared || ld.Buildmode == ld.BuildmodePIE {
					gentramppic(tramp, r.Sym, int64(offset))
				} else {
					gentramp(tramp, r.Sym, int64(offset))
				}
			}
			// modify reloc to point to tramp, which will be resolved later
			r.Sym = tramp
			r.Add = r.Add&0xff000000 | 0xfffffe // clear the offset embedded in the instruction
			r.Done = 0
		}
	default:
		ld.Errorf(s, "trampoline called with non-jump reloc: %v", r.Type)
	}
}

// gentext generates assembly to append the local moduledata to the global
// moduledata linked list at initialization time. This is only done if the runtime
// is in a different module.
//
// <go.link.addmoduledata>:
// 	larl  %r2, <local.moduledata>
// 	jg    <[email protected]>
//	undef
//
// The job of appending the moduledata is delegated to runtime.addmoduledata.
func gentext(ctxt *ld.Link) {
	if !ctxt.DynlinkingGo() {
		return
	}
	addmoduledata := ctxt.Syms.Lookup("runtime.addmoduledata", 0)
	if addmoduledata.Type == obj.STEXT {
		// we're linking a module containing the runtime -> no need for
		// an init function
		return
	}
	addmoduledata.Attr |= ld.AttrReachable
	initfunc := ctxt.Syms.Lookup("go.link.addmoduledata", 0)
	initfunc.Type = obj.STEXT
	initfunc.Attr |= ld.AttrLocal
	initfunc.Attr |= ld.AttrReachable

	// larl %r2, <local.moduledata>
	ld.Adduint8(ctxt, initfunc, 0xc0)
	ld.Adduint8(ctxt, initfunc, 0x20)
	lmd := ld.Addrel(initfunc)
	lmd.Off = int32(initfunc.Size)
	lmd.Siz = 4
	lmd.Sym = ctxt.Moduledata
	lmd.Type = obj.R_PCREL
	lmd.Variant = ld.RV_390_DBL
	lmd.Add = 2 + int64(lmd.Siz)
	ld.Adduint32(ctxt, initfunc, 0)

	// jg <runtime.addmoduledata[@plt]>
	ld.Adduint8(ctxt, initfunc, 0xc0)
	ld.Adduint8(ctxt, initfunc, 0xf4)
	rel := ld.Addrel(initfunc)
	rel.Off = int32(initfunc.Size)
	rel.Siz = 4
	rel.Sym = ctxt.Syms.Lookup("runtime.addmoduledata", 0)
	rel.Type = obj.R_CALL
	rel.Variant = ld.RV_390_DBL
	rel.Add = 2 + int64(rel.Siz)
	ld.Adduint32(ctxt, initfunc, 0)

	// undef (for debugging)
	ld.Adduint32(ctxt, initfunc, 0)

	ctxt.Textp = append(ctxt.Textp, initfunc)
	initarray_entry := ctxt.Syms.Lookup("go.link.addmoduledatainit", 0)
	initarray_entry.Attr |= ld.AttrLocal
	initarray_entry.Attr |= ld.AttrReachable
	initarray_entry.Type = obj.SINITARR
	ld.Addaddr(ctxt, initarray_entry, initfunc)
}

func archreloc(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol, val *int64) int {
	if ld.Linkmode == ld.LinkExternal {
		switch r.Type {
		default:
			return -1

		case obj.R_ARM64_GOTPCREL:
			var o1, o2 uint32
			if ctxt.Arch.ByteOrder == binary.BigEndian {
				o1 = uint32(*val >> 32)
				o2 = uint32(*val)
			} else {
				o1 = uint32(*val)
				o2 = uint32(*val >> 32)
			}
			// Any relocation against a function symbol is redirected to
			// be against a local symbol instead (see putelfsym in
			// symtab.go) but unfortunately the system linker was buggy
			// when confronted with a R_AARCH64_ADR_GOT_PAGE relocation
			// against a local symbol until May 2015
			// (https://sourceware.org/bugzilla/show_bug.cgi?id=18270). So
			// we convert the adrp; ld64 + R_ARM64_GOTPCREL into adrp;
			// add + R_ADDRARM64.
			if !(r.Sym.Version != 0 || (r.Sym.Type&obj.SHIDDEN != 0) || r.Sym.Attr.Local()) && r.Sym.Type == obj.STEXT && ctxt.DynlinkingGo() {
				if o2&0xffc00000 != 0xf9400000 {
					ld.Errorf(s, "R_ARM64_GOTPCREL against unexpected instruction %x", o2)
				}
				o2 = 0x91000000 | (o2 & 0x000003ff)
				r.Type = obj.R_ADDRARM64
			}
			if ctxt.Arch.ByteOrder == binary.BigEndian {
				*val = int64(o1)<<32 | int64(o2)
			} else {
				*val = int64(o2)<<32 | int64(o1)
			}
			fallthrough

		case obj.R_ADDRARM64:
			r.Done = 0

			// set up addend for eventual relocation via outer symbol.
			rs := r.Sym
			r.Xadd = r.Add
			for rs.Outer != nil {
				r.Xadd += ld.Symaddr(rs) - ld.Symaddr(rs.Outer)
				rs = rs.Outer
			}

			if rs.Type != obj.SHOSTOBJ && rs.Type != obj.SDYNIMPORT && rs.Sect == nil {
				ld.Errorf(s, "missing section for %s", rs.Name)
			}
			r.Xsym = rs

			// Note: ld64 currently has a bug that any non-zero addend for BR26 relocation
			// will make the linking fail because it thinks the code is not PIC even though
			// the BR26 relocation should be fully resolved at link time.
			// That is the reason why the next if block is disabled. When the bug in ld64
			// is fixed, we can enable this block and also enable duff's device in cmd/7g.
			if false && ld.Headtype == obj.Hdarwin {
				var o0, o1 uint32

				if ctxt.Arch.ByteOrder == binary.BigEndian {
					o0 = uint32(*val >> 32)
					o1 = uint32(*val)
				} else {
					o0 = uint32(*val)
					o1 = uint32(*val >> 32)
				}
				// Mach-O wants the addend to be encoded in the instruction
				// Note that although Mach-O supports ARM64_RELOC_ADDEND, it
				// can only encode 24-bit of signed addend, but the instructions
				// supports 33-bit of signed addend, so we always encode the
				// addend in place.
				o0 |= (uint32((r.Xadd>>12)&3) << 29) | (uint32((r.Xadd>>12>>2)&0x7ffff) << 5)
				o1 |= uint32(r.Xadd&0xfff) << 10
				r.Xadd = 0

				// when laid out, the instruction order must always be o1, o2.
				if ctxt.Arch.ByteOrder == binary.BigEndian {
					*val = int64(o0)<<32 | int64(o1)
				} else {
					*val = int64(o1)<<32 | int64(o0)
				}
			}

			return 0

		case obj.R_CALLARM64,
			obj.R_ARM64_TLS_LE,
			obj.R_ARM64_TLS_IE:
			r.Done = 0
			r.Xsym = r.Sym
			r.Xadd = r.Add
			return 0
		}
	}

	switch r.Type {
	case obj.R_CONST:
		*val = r.Add
//.........这里部分代码省略.........

func elfreloc1(ctxt *ld.Link, r *ld.Reloc, sectoff int64) int {
	ld.Thearch.Vput(uint64(sectoff))

	elfsym := r.Xsym.ElfsymForReloc()
	switch r.Type {
	default:
		return -1

	case obj.R_ADDR:
		if r.Siz == 4 {
			ld.Thearch.Vput(ld.R_X86_64_32 | uint64(elfsym)<<32)
		} else if r.Siz == 8 {
			ld.Thearch.Vput(ld.R_X86_64_64 | uint64(elfsym)<<32)
		} else {
			return -1
		}

	case obj.R_TLS_LE:
		if r.Siz == 4 {
			ld.Thearch.Vput(ld.R_X86_64_TPOFF32 | uint64(elfsym)<<32)
		} else {
			return -1
		}

	case obj.R_TLS_IE:
		if r.Siz == 4 {
			ld.Thearch.Vput(ld.R_X86_64_GOTTPOFF | uint64(elfsym)<<32)
		} else {
			return -1
		}

	case obj.R_CALL:
		if r.Siz == 4 {
			if r.Xsym.Type == obj.SDYNIMPORT {
				if ctxt.DynlinkingGo() {
					ld.Thearch.Vput(ld.R_X86_64_PLT32 | uint64(elfsym)<<32)
				} else {
					ld.Thearch.Vput(ld.R_X86_64_GOTPCREL | uint64(elfsym)<<32)
				}
			} else {
				ld.Thearch.Vput(ld.R_X86_64_PC32 | uint64(elfsym)<<32)
			}
		} else {
			return -1
		}

	case obj.R_PCREL:
		if r.Siz == 4 {
			if r.Xsym.Type == obj.SDYNIMPORT && r.Xsym.ElfType == elf.STT_FUNC {
				ld.Thearch.Vput(ld.R_X86_64_PLT32 | uint64(elfsym)<<32)
			} else {
				ld.Thearch.Vput(ld.R_X86_64_PC32 | uint64(elfsym)<<32)
			}
		} else {
			return -1
		}

	case obj.R_GOTPCREL:
		if r.Siz == 4 {
			ld.Thearch.Vput(ld.R_X86_64_GOTPCREL | uint64(elfsym)<<32)
		} else {
			return -1
		}
	}

	ld.Thearch.Vput(uint64(r.Xadd))
	return 0
}