cmd/link: support windows/arm

Enable the Go linker to generate executables for windows/arm.

Generates PE relocation tables, which are used by Windows to
dynamically relocate the Go binary in memory. Windows on ARM
requires all modules to be relocatable, unlike x86/amd64 which are
permitted to have fixed base addresses.

Updates #26148

Change-Id: Ie63964ff52c2377e121b2885e9d05ec3ed8dc1cd
Reviewed-on: https://go-review.googlesource.com/125648
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/objfile/pe.go

@@ -190,6 +190,9 @@ func (f *peFile) goarch() string {
 	if _, err := findPESymbol(f.pe, "_rt0_amd64_windows"); err == nil {
 		return "amd64"
 	}
+	if _, err := findPESymbol(f.pe, "_rt0_arm_windows"); err == nil {
+		return "arm"
+	}
 	return ""
 }
 

src/cmd/link/internal/arm/asm.go

@@ -411,6 +411,35 @@ func machoreloc1(arch *sys.Arch, out *ld.OutBuf, s *sym.Symbol, r *sym.Reloc, se
 	return true
 }
 
+func pereloc1(arch *sys.Arch, out *ld.OutBuf, s *sym.Symbol, r *sym.Reloc, sectoff int64) bool {
+	rs := r.Xsym
+
+	if rs.Dynid < 0 {
+		ld.Errorf(s, "reloc %d (%s) to non-coff symbol %s type=%d (%s)", r.Type, sym.RelocName(arch, r.Type), rs.Name, rs.Type, rs.Type)
+		return false
+	}
+
+	out.Write32(uint32(sectoff))
+	out.Write32(uint32(rs.Dynid))
+
+	var v uint32
+	switch r.Type {
+	default:
+		// unsupported relocation type
+		return false
+
+	case objabi.R_DWARFSECREF:
+		v = ld.IMAGE_REL_ARM_SECREL
+
+	case objabi.R_ADDR:
+		v = ld.IMAGE_REL_ARM_ADDR32
+	}
+
+	out.Write16(uint16(v))
+
+	return true
+}
+
 // sign extend a 24-bit integer
 func signext24(x int64) int32 {
 	return (int32(x) << 8) >> 8
@@ -799,6 +828,10 @@ func asmb(ctxt *ld.Link) {
 
 		case objabi.Hdarwin:
 			symo = uint32(ld.Segdwarf.Fileoff + uint64(ld.Rnd(int64(ld.Segdwarf.Filelen), int64(*ld.FlagRound))) + uint64(machlink))
+
+		case objabi.Hwindows:
+			symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
+			symo = uint32(ld.Rnd(int64(symo), ld.PEFILEALIGN))
 		}
 
 		ctxt.Out.SeekSet(int64(symo))
@@ -828,6 +861,11 @@ func asmb(ctxt *ld.Link) {
 				ctxt.Out.Flush()
 			}
 
+		case objabi.Hwindows:
+			if ctxt.Debugvlog != 0 {
+				ctxt.Logf("%5.2f dwarf\n", ld.Cputime())
+			}
+
 		case objabi.Hdarwin:
 			if ctxt.LinkMode == ld.LinkExternal {
 				ld.Machoemitreloc(ctxt)
@@ -860,6 +898,9 @@ func asmb(ctxt *ld.Link) {
 
 	case objabi.Hdarwin:
 		ld.Asmbmacho(ctxt)
+
+	case objabi.Hwindows:
+		ld.Asmbpe(ctxt)
 	}
 
 	ctxt.Out.Flush()

src/cmd/link/internal/arm/obj.go

@@ -57,6 +57,7 @@ func Init() (*sys.Arch, ld.Arch) {
 		Elfsetupplt:      elfsetupplt,
 		Gentext:          gentext,
 		Machoreloc1:      machoreloc1,
+		PEreloc1:         pereloc1,
 
 		Linuxdynld:     "/lib/ld-linux.so.3", // 2 for OABI, 3 for EABI
 		Freebsddynld:   "/usr/libexec/ld-elf.so.1",
@@ -130,6 +131,10 @@ func archinit(ctxt *ld.Link) {
 		if *ld.FlagRound == -1 {
 			*ld.FlagRound = 4096
 		}
+
+	case objabi.Hwindows: /* PE executable */
+		// ld.HEADR, ld.FlagTextAddr, ld.FlagDataAddr and ld.FlagRound are set in ld.Peinit
+		return
 	}
 
 	if *ld.FlagDataAddr != 0 && *ld.FlagRound != 0 {

src/cmd/link/internal/ld/config.go

@@ -60,7 +60,7 @@ func (mode *BuildMode) Set(s string) error {
 			}
 		case "windows":
 			switch objabi.GOARCH {
-			case "amd64", "386":
+			case "amd64", "386", "arm":
 			default:
 				return badmode()
 			}

src/cmd/link/internal/ld/data.go

@@ -539,13 +539,17 @@ func windynrelocsym(ctxt *Link, s *sym.Symbol) {
 			r.Add = int64(targ.Plt)
 
 			// jmp *addr
-			if ctxt.Arch.Family == sys.I386 {
+			switch ctxt.Arch.Family {
+			default:
+				Errorf(s, "unsupported arch %v", ctxt.Arch.Family)
+				return
+			case sys.I386:
 				rel.AddUint8(0xff)
 				rel.AddUint8(0x25)
 				rel.AddAddr(ctxt.Arch, targ)
 				rel.AddUint8(0x90)
 				rel.AddUint8(0x90)
-			} else {
+			case sys.AMD64:
 				rel.AddUint8(0xff)
 				rel.AddUint8(0x24)
 				rel.AddUint8(0x25)

src/cmd/link/internal/loadpe/ldpe.go

@@ -101,6 +101,19 @@ const (
 	IMAGE_REL_AMD64_SREL32           = 0x000E
 	IMAGE_REL_AMD64_PAIR             = 0x000F
 	IMAGE_REL_AMD64_SSPAN32          = 0x0010
+	IMAGE_REL_ARM_ABSOLUTE           = 0x0000
+	IMAGE_REL_ARM_ADDR32             = 0x0001
+	IMAGE_REL_ARM_ADDR32NB           = 0x0002
+	IMAGE_REL_ARM_BRANCH24           = 0x0003
+	IMAGE_REL_ARM_BRANCH11           = 0x0004
+	IMAGE_REL_ARM_SECTION            = 0x000E
+	IMAGE_REL_ARM_SECREL             = 0x000F
+	IMAGE_REL_ARM_MOV32              = 0x0010
+	IMAGE_REL_THUMB_MOV32            = 0x0011
+	IMAGE_REL_THUMB_BRANCH20         = 0x0012
+	IMAGE_REL_THUMB_BRANCH24         = 0x0014
+	IMAGE_REL_THUMB_BLX23            = 0x0015
+	IMAGE_REL_ARM_PAIR               = 0x0016
 )
 
 // TODO(crawshaw): de-duplicate these symbols with cmd/internal/ld, ideally in debug/pe.
@@ -241,30 +254,56 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng
 			rp.Sym = gosym
 			rp.Siz = 4
 			rp.Off = int32(r.VirtualAddress)
-			switch r.Type {
+			switch arch.Family {
 			default:
-				return nil, nil, fmt.Errorf("%s: %v: unknown relocation type %v", pn, sectsyms[rsect], r.Type)
+				return nil, nil, fmt.Errorf("%s: unsupported arch %v", pn, arch.Family)
+			case sys.I386, sys.AMD64:
+				switch r.Type {
+				default:
+					return nil, nil, fmt.Errorf("%s: %v: unknown relocation type %v", pn, sectsyms[rsect], r.Type)
 
-			case IMAGE_REL_I386_REL32, IMAGE_REL_AMD64_REL32,
-				IMAGE_REL_AMD64_ADDR32, // R_X86_64_PC32
-				IMAGE_REL_AMD64_ADDR32NB:
-				rp.Type = objabi.R_PCREL
+				case IMAGE_REL_I386_REL32, IMAGE_REL_AMD64_REL32,
+					IMAGE_REL_AMD64_ADDR32, // R_X86_64_PC32
+					IMAGE_REL_AMD64_ADDR32NB:
+					rp.Type = objabi.R_PCREL
 
-				rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
+					rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
 
-			case IMAGE_REL_I386_DIR32NB, IMAGE_REL_I386_DIR32:
-				rp.Type = objabi.R_ADDR
+				case IMAGE_REL_I386_DIR32NB, IMAGE_REL_I386_DIR32:
+					rp.Type = objabi.R_ADDR
 
-				// load addend from image
-				rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
+					// load addend from image
+					rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
 
-			case IMAGE_REL_AMD64_ADDR64: // R_X86_64_64
-				rp.Siz = 8
+				case IMAGE_REL_AMD64_ADDR64: // R_X86_64_64
+					rp.Siz = 8
 
-				rp.Type = objabi.R_ADDR
+					rp.Type = objabi.R_ADDR
 
-				// load addend from image
-				rp.Add = int64(binary.LittleEndian.Uint64(sectdata[rsect][rp.Off:]))
+					// load addend from image
+					rp.Add = int64(binary.LittleEndian.Uint64(sectdata[rsect][rp.Off:]))
+				}
+
+			case sys.ARM:
+				switch r.Type {
+				default:
+					return nil, nil, fmt.Errorf("%s: %v: unknown ARM relocation type %v", pn, sectsyms[rsect], r.Type)
+
+				case IMAGE_REL_ARM_SECREL:
+					rp.Type = objabi.R_PCREL
+
+					rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
+
+				case IMAGE_REL_ARM_ADDR32:
+					rp.Type = objabi.R_ADDR
+
+					rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
+
+				case IMAGE_REL_ARM_BRANCH24:
+					rp.Type = objabi.R_CALLARM
+
+					rp.Add = int64(int32(binary.LittleEndian.Uint32(sectdata[rsect][rp.Off:])))
+				}
 			}
 
 			// ld -r could generate multiple section symbols for the