src/cmd/link/internal/x86/asm.go

// Inferno utils/8l/asm.c
// https://bitbucket.org/inferno-os/inferno-os/src/master/utils/8l/asm.c
//
//	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
//	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
//	Portions Copyright © 1997-1999 Vita Nuova Limited
//	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
//	Portions Copyright © 2004,2006 Bruce Ellis
//	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
//	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
//	Portions Copyright © 2009 The Go Authors. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package x86

import (
	"cmd/internal/objabi"
	"cmd/internal/sys"
	"cmd/link/internal/ld"
	"cmd/link/internal/loader"
	"cmd/link/internal/sym"
	"debug/elf"
	"log"
)

func gentext(ctxt *ld.Link, ldr *loader.Loader) {
	if ctxt.DynlinkingGo() {
		// We need get_pc_thunk.
	} else {
		switch ctxt.BuildMode {
		case ld.BuildModeCArchive:
			if !ctxt.IsELF {
				return
			}
		case ld.BuildModePIE, ld.BuildModeCShared, ld.BuildModePlugin:
			// We need get_pc_thunk.
		default:
			return
		}
	}

	// Generate little thunks that load the PC of the next instruction into a register.
	thunks := make([]loader.Sym, 0, 7+len(ctxt.Textp))
	for _, r := range [...]struct {
		name string
		num  uint8
	}{
		{"ax", 0},
		{"cx", 1},
		{"dx", 2},
		{"bx", 3},
		// sp
		{"bp", 5},
		{"si", 6},
		{"di", 7},
	} {
		thunkfunc := ldr.CreateSymForUpdate("__x86.get_pc_thunk."+r.name, 0)
		thunkfunc.SetType(sym.STEXT)
		ldr.SetAttrLocal(thunkfunc.Sym(), true)
		o := func(op ...uint8) {
			for _, op1 := range op {
				thunkfunc.AddUint8(op1)
			}
		}
		// 8b 04 24	mov    (%esp),%eax
		// Destination register is in bits 3-5 of the middle byte, so add that in.
		o(0x8b, 0x04+r.num<<3, 0x24)
		// c3		ret
		o(0xc3)

		thunks = append(thunks, thunkfunc.Sym())
	}
	ctxt.Textp = append(thunks, ctxt.Textp...) // keep Textp in dependency order

	initfunc, addmoduledata := ld.PrepareAddmoduledata(ctxt)
	if initfunc == nil {
		return
	}

	o := func(op ...uint8) {
		for _, op1 := range op {
			initfunc.AddUint8(op1)
		}
	}

	// go.link.addmoduledata:
	//      53                      push %ebx
	//      e8 00 00 00 00          call __x86.get_pc_thunk.cx + R_CALL __x86.get_pc_thunk.cx
	//      8d 81 00 00 00 00       lea 0x0(%ecx), %eax + R_PCREL ctxt.Moduledata
	//      8d 99 00 00 00 00       lea 0x0(%ecx), %ebx + R_GOTPC _GLOBAL_OFFSET_TABLE_
	//      e8 00 00 00 00          call runtime.addmoduledata@plt + R_CALL runtime.addmoduledata
	//      5b                      pop %ebx
	//      c3                      ret

	o(0x53)

	o(0xe8)
	initfunc.AddSymRef(ctxt.Arch, ldr.Lookup("__x86.get_pc_thunk.cx", 0), 0, objabi.R_CALL, 4)

	o(0x8d, 0x81)
	initfunc.AddPCRelPlus(ctxt.Arch, ctxt.Moduledata, 6)

	o(0x8d, 0x99)
	gotsym := ldr.LookupOrCreateSym("_GLOBAL_OFFSET_TABLE_", 0)
	initfunc.AddSymRef(ctxt.Arch, gotsym, 12, objabi.R_PCREL, 4)
	o(0xe8)
	initfunc.AddSymRef(ctxt.Arch, addmoduledata, 0, objabi.R_CALL, 4)

	o(0x5b)

	o(0xc3)
}

func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym, r loader.Reloc, rIdx int) bool {
	targ := r.Sym()
	var targType sym.SymKind
	if targ != 0 {
		targType = ldr.SymType(targ)
	}

	switch r.Type() {
	default:
		if r.Type() >= objabi.ElfRelocOffset {
			ldr.Errorf(s, "unexpected relocation type %d (%s)", r.Type(), sym.RelocName(target.Arch, r.Type()))
			return false
		}

		// Handle relocations found in ELF object files.
	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_386_PC32):
		if targType == sym.SDYNIMPORT {
			ldr.Errorf(s, "unexpected R_386_PC32 relocation for dynamic symbol %s", ldr.SymName(targ))
		}
		if targType == 0 || targType == sym.SXREF {
			ldr.Errorf(s, "unknown symbol %s in pcrel", ldr.SymName(targ))
		}
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		su.SetRelocAdd(rIdx, r.Add()+4)
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_386_PLT32):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		su.SetRelocAdd(rIdx, r.Add()+4)
		if targType == sym.SDYNIMPORT {
			addpltsym(target, ldr, syms, targ)
			su.SetRelocSym(rIdx, syms.PLT)
			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
		}

		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_386_GOT32),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_386_GOT32X):
		su := ldr.MakeSymbolUpdater(s)
		if targType != sym.SDYNIMPORT {
			// have symbol
			sData := ldr.Data(s)

			if r.Off() >= 2 && sData[r.Off()-2] == 0x8b {
				su.MakeWritable()

				// turn MOVL of GOT entry into LEAL of symbol address, relative to GOT.
				writeableData := su.Data()
				writeableData[r.Off()-2] = 0x8d
				su.SetRelocType(rIdx, objabi.R_GOTOFF)
				return true
			}

			if r.Off() >= 2 && sData[r.Off()-2] == 0xff && sData[r.Off()-1] == 0xb3 {
				su.MakeWritable()
				// turn PUSHL of GOT entry into PUSHL of symbol itself.
				// use unnecessary SS prefix to keep instruction same length.
				writeableData := su.Data()
				writeableData[r.Off()-2] = 0x36
				writeableData[r.Off()-1] = 0x68
				su.SetRelocType(rIdx, objabi.R_ADDR)
				return true
			}

			ldr.Errorf(s, "unexpected GOT reloc for non-dynamic symbol %s", ldr.SymName(targ))
			return false
		}

		ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_386_GLOB_DAT))
		su.SetRelocType(rIdx, objabi.R_CONST) // write r->add during relocsym
		su.SetRelocSym(rIdx, 0)
		su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_386_GOTOFF):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_GOTOFF)
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_386_GOTPC):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		su.SetRelocSym(rIdx, syms.GOT)
		su.SetRelocAdd(rIdx, r.Add()+4)
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_386_32):
		if targType == sym.SDYNIMPORT {
			ldr.Errorf(s, "unexpected R_386_32 relocation for dynamic symbol %s", ldr.SymName(targ))
		}
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_ADDR)
		return true

	case objabi.MachoRelocOffset + ld.MACHO_GENERIC_RELOC_VANILLA*2 + 0:
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_ADDR)
		if targType == sym.SDYNIMPORT {
			ldr.Errorf(s, "unexpected reloc for dynamic symbol %s", ldr.SymName(targ))
		}
		return true

	case objabi.MachoRelocOffset + ld.MACHO_GENERIC_RELOC_VANILLA*2 + 1:
		su := ldr.MakeSymbolUpdater(s)
		if targType == sym.SDYNIMPORT {
			addpltsym(target, ldr, syms, targ)
			su.SetRelocSym(rIdx, syms.PLT)
			su.SetRelocAdd(rIdx, int64(ldr.SymPlt(targ)))
			su.SetRelocType(rIdx, objabi.R_PCREL)
			return true
		}

		su.SetRelocType(rIdx, objabi.R_PCREL)
		return true

	case objabi.MachoRelocOffset + ld.MACHO_FAKE_GOTPCREL:
		su := ldr.MakeSymbolUpdater(s)
		if targType != sym.SDYNIMPORT {
			// have symbol
			// turn MOVL of GOT entry into LEAL of symbol itself
			sData := ldr.Data(s)
			if r.Off() < 2 || sData[r.Off()-2] != 0x8b {
				ldr.Errorf(s, "unexpected GOT reloc for non-dynamic symbol %s", ldr.SymName(targ))
				return false
			}

			su.MakeWritable()
			writeableData := su.Data()
			writeableData[r.Off()-2] = 0x8d
			su.SetRelocType(rIdx, objabi.R_PCREL)
			return true
		}

		ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_386_GLOB_DAT))
		su.SetRelocSym(rIdx, syms.GOT)
		su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
		su.SetRelocType(rIdx, objabi.R_PCREL)
		return true
	}

	// Handle references to ELF symbols from our own object files.
	if targType != sym.SDYNIMPORT {
		return true
	}

	// Reread the reloc to incorporate any changes in type above.
	relocs := ldr.Relocs(s)
	r = relocs.At(rIdx)

	switch r.Type() {
	case objabi.R_CALL,
		objabi.R_PCREL:
		if target.IsExternal() {
			// External linker will do this relocation.
			return true
		}
		addpltsym(target, ldr, syms, targ)
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocSym(rIdx, syms.PLT)
		su.SetRelocAdd(rIdx, int64(ldr.SymPlt(targ)))
		return true

	case objabi.R_ADDR:
		if !ldr.SymType(s).IsDATA() {
			break
		}
		if target.IsElf() {
			ld.Adddynsym(ldr, target, syms, targ)
			rel := ldr.MakeSymbolUpdater(syms.Rel)
			rel.AddAddrPlus(target.Arch, s, int64(r.Off()))
			rel.AddUint32(target.Arch, elf.R_INFO32(uint32(ldr.SymDynid(targ)), uint32(elf.R_386_32)))
			su := ldr.MakeSymbolUpdater(s)
			su.SetRelocType(rIdx, objabi.R_CONST) // write r->add during relocsym
			su.SetRelocSym(rIdx, 0)
			return true
		}
	}

	return false
}

func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, ri int, sectoff int64) bool {
	out.Write32(uint32(sectoff))

	elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
	siz := r.Size
	switch r.Type {
	default:
		return false
	case objabi.R_ADDR, objabi.R_DWARFSECREF:
		if siz == 4 {
			out.Write32(uint32(elf.R_386_32) | uint32(elfsym)<<8)
		} else {
			return false
		}
	case objabi.R_GOTPCREL:
		if siz == 4 {
			out.Write32(uint32(elf.R_386_GOTPC))
			if ldr.SymName(r.Xsym) != "_GLOBAL_OFFSET_TABLE_" {
				out.Write32(uint32(sectoff))
				out.Write32(uint32(elf.R_386_GOT32) | uint32(elfsym)<<8)
			}
		} else {
			return false
		}
	case objabi.R_CALL:
		if siz == 4 {
			if ldr.SymType(r.Xsym) == sym.SDYNIMPORT {
				out.Write32(uint32(elf.R_386_PLT32) | uint32(elfsym)<<8)
			} else {
				out.Write32(uint32(elf.R_386_PC32) | uint32(elfsym)<<8)
			}
		} else {
			return false
		}
	case objabi.R_PCREL:
		if siz == 4 {
			out.Write32(uint32(elf.R_386_PC32) | uint32(elfsym)<<8)
		} else {
			return false
		}
	case objabi.R_TLS_LE:
		if siz == 4 {
			out.Write32(uint32(elf.R_386_TLS_LE) | uint32(elfsym)<<8)
		} else {
			return false
		}
	case objabi.R_TLS_IE:
		if siz == 4 {
			out.Write32(uint32(elf.R_386_GOTPC))
			out.Write32(uint32(sectoff))
			out.Write32(uint32(elf.R_386_TLS_GOTIE) | uint32(elfsym)<<8)
		} else {
			return false
		}
	}

	return true
}

func machoreloc1(*sys.Arch, *ld.OutBuf, *loader.Loader, loader.Sym, loader.ExtReloc, int64) bool {
	return false
}

func pereloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, sectoff int64) bool {
	var v uint32

	rs := r.Xsym
	rt := r.Type

	if ldr.SymDynid(rs) < 0 {
		ldr.Errorf(s, "reloc %d (%s) to non-coff symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
		return false
	}

	out.Write32(uint32(sectoff))
	out.Write32(uint32(ldr.SymDynid(rs)))

	switch rt {
	default:
		return false

	case objabi.R_DWARFSECREF:
		v = ld.IMAGE_REL_I386_SECREL

	case objabi.R_ADDR:
		v = ld.IMAGE_REL_I386_DIR32

	case objabi.R_PEIMAGEOFF:
		v = ld.IMAGE_REL_I386_DIR32NB

	case objabi.R_CALL,
		objabi.R_PCREL:
		v = ld.IMAGE_REL_I386_REL32
	}

	out.Write16(uint16(v))

	return true
}

func archreloc(*ld.Target, *loader.Loader, *ld.ArchSyms, loader.Reloc, loader.Sym, int64) (int64, int, bool) {
	return -1, 0, false
}

func archrelocvariant(*ld.Target, *loader.Loader, loader.Reloc, sym.RelocVariant, loader.Sym, int64, []byte) int64 {
	log.Fatalf("unexpected relocation variant")
	return -1
}

func elfsetupplt(ctxt *ld.Link, ldr *loader.Loader, plt, got *loader.SymbolBuilder, dynamic loader.Sym) {
	if plt.Size() == 0 {
		// pushl got+4
		plt.AddUint8(0xff)

		plt.AddUint8(0x35)
		plt.AddAddrPlus(ctxt.Arch, got.Sym(), 4)

		// jmp *got+8
		plt.AddUint8(0xff)

		plt.AddUint8(0x25)
		plt.AddAddrPlus(ctxt.Arch, got.Sym(), 8)

		// zero pad
		plt.AddUint32(ctxt.Arch, 0)

		// assume got->size == 0 too
		got.AddAddrPlus(ctxt.Arch, dynamic, 0)

		got.AddUint32(ctxt.Arch, 0)
		got.AddUint32(ctxt.Arch, 0)
	}
}

func addpltsym(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym) {
	if ldr.SymPlt(s) >= 0 {
		return
	}

	ld.Adddynsym(ldr, target, syms, s)

	if target.IsElf() {
		plt := ldr.MakeSymbolUpdater(syms.PLT)
		got := ldr.MakeSymbolUpdater(syms.GOTPLT)
		rel := ldr.MakeSymbolUpdater(syms.RelPLT)
		if plt.Size() == 0 {
			panic("plt is not set up")
		}

		// jmpq *got+size
		plt.AddUint8(0xff)

		plt.AddUint8(0x25)
		plt.AddAddrPlus(target.Arch, got.Sym(), got.Size())

		// add to got: pointer to current pos in plt
		got.AddAddrPlus(target.Arch, plt.Sym(), plt.Size())

		// pushl $x
		plt.AddUint8(0x68)

		plt.AddUint32(target.Arch, uint32(rel.Size()))

		// jmp .plt
		plt.AddUint8(0xe9)

		plt.AddUint32(target.Arch, uint32(-(plt.Size() + 4)))

		// rel
		rel.AddAddrPlus(target.Arch, got.Sym(), got.Size()-4)

		sDynid := ldr.SymDynid(s)
		rel.AddUint32(target.Arch, elf.R_INFO32(uint32(sDynid), uint32(elf.R_386_JMP_SLOT)))

		ldr.SetPlt(s, int32(plt.Size()-16))
	} else {
		ldr.Errorf(s, "addpltsym: unsupported binary format")
	}
}