// Inferno utils/5l/asm.c
// https://bitbucket.org/inferno-os/inferno-os/src/master/utils/5l/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 s390x

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

// 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    <runtime.addmoduledata@plt>
//		undef
//
// The job of appending the moduledata is delegated to runtime.addmoduledata.
func gentext(ctxt *ld.Link, ldr *loader.Loader) {
	initfunc, addmoduledata := ld.PrepareAddmoduledata(ctxt)
	if initfunc == nil {
		return
	}

	// larl %r2, <local.moduledata>
	initfunc.AddUint8(0xc0)
	initfunc.AddUint8(0x20)
	initfunc.AddSymRef(ctxt.Arch, ctxt.Moduledata, 6, objabi.R_PCREL, 4)
	r1 := initfunc.Relocs()
	ldr.SetRelocVariant(initfunc.Sym(), r1.Count()-1, sym.RV_390_DBL)

	// jg <runtime.addmoduledata[@plt]>
	initfunc.AddUint8(0xc0)
	initfunc.AddUint8(0xf4)
	initfunc.AddSymRef(ctxt.Arch, addmoduledata, 6, objabi.R_CALL, 4)
	r2 := initfunc.Relocs()
	ldr.SetRelocVariant(initfunc.Sym(), r2.Count()-1, sym.RV_390_DBL)

	// undef (for debugging)
	initfunc.AddUint32(ctxt.Arch, 0)
}

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", r.Type())
			return false
		}

	// Handle relocations found in ELF object files.
	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_12),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOT12):
		ldr.Errorf(s, "s390x 12-bit relocations have not been implemented (relocation type %d)", r.Type()-objabi.ElfRelocOffset)
		return false

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_8),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_16),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_32),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_64):
		if targType == sym.SDYNIMPORT {
			ldr.Errorf(s, "unexpected R_390_nn relocation for dynamic symbol %s", ldr.SymName(targ))
		}
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_ADDR)
		if target.IsPIE() && target.IsInternal() {
			// For internal linking PIE, this R_ADDR relocation cannot
			// be resolved statically. We need to generate a dynamic
			// relocation. Let the code below handle it.
			break
		}
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PC16),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PC32),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PC64):
		if targType == sym.SDYNIMPORT {
			ldr.Errorf(s, "unexpected R_390_PCnn 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()+int64(r.Siz()))
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOT16),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOT32),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOT64):
		ldr.Errorf(s, "unimplemented S390x relocation: %v", r.Type()-objabi.ElfRelocOffset)
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PLT16DBL),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PLT32DBL):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		ldr.SetRelocVariant(s, rIdx, sym.RV_390_DBL)
		su.SetRelocAdd(rIdx, r.Add()+int64(r.Siz()))
		if targType == sym.SDYNIMPORT {
			addpltsym(target, ldr, syms, targ)
			r.SetSym(syms.PLT)
			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
		}
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PLT32),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PLT64):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		su.SetRelocAdd(rIdx, r.Add()+int64(r.Siz()))
		if targType == sym.SDYNIMPORT {
			addpltsym(target, ldr, syms, targ)
			r.SetSym(syms.PLT)
			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
		}
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_COPY):
		ldr.Errorf(s, "unimplemented S390x relocation: %v", r.Type()-objabi.ElfRelocOffset)
		return false

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GLOB_DAT):
		ldr.Errorf(s, "unimplemented S390x relocation: %v", r.Type()-objabi.ElfRelocOffset)
		return false

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_JMP_SLOT):
		ldr.Errorf(s, "unimplemented S390x relocation: %v", r.Type()-objabi.ElfRelocOffset)
		return false

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_RELATIVE):
		ldr.Errorf(s, "unimplemented S390x relocation: %v", r.Type()-objabi.ElfRelocOffset)
		return false

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOTOFF):
		if targType == sym.SDYNIMPORT {
			ldr.Errorf(s, "unexpected R_390_GOTOFF relocation for dynamic symbol %s", ldr.SymName(targ))
		}
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_GOTOFF)
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOTPC):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		r.SetSym(syms.GOT)
		su.SetRelocAdd(rIdx, r.Add()+int64(r.Siz()))
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PC16DBL),
		objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_PC32DBL):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		ldr.SetRelocVariant(s, rIdx, sym.RV_390_DBL)
		su.SetRelocAdd(rIdx, r.Add()+int64(r.Siz()))
		if targType == sym.SDYNIMPORT {
			ldr.Errorf(s, "unexpected R_390_PCnnDBL relocation for dynamic symbol %s", ldr.SymName(targ))
		}
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOTPCDBL):
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		ldr.SetRelocVariant(s, rIdx, sym.RV_390_DBL)
		r.SetSym(syms.GOT)
		su.SetRelocAdd(rIdx, r.Add()+int64(r.Siz()))
		return true

	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_390_GOTENT):
		ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_390_GLOB_DAT))
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocType(rIdx, objabi.R_PCREL)
		ldr.SetRelocVariant(s, rIdx, sym.RV_390_DBL)
		r.SetSym(syms.GOT)
		su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ))+int64(r.Siz()))
		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_PCRELDBL:
		if targType != sym.SDYNIMPORT {
			// nothing to do, the relocation will be laid out in reloc
			return true
		}
		if target.IsExternal() {
			// External linker will do this relocation.
			return true
		}
		// Internal linking: build a PLT entry and redirect to it.
		addpltsym(target, ldr, syms, targ)
		su := ldr.MakeSymbolUpdater(s)
		su.SetRelocSym(rIdx, syms.PLT)
		su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
		return true

	case objabi.R_ADDR:
		if ldr.SymType(s).IsText() && target.IsElf() {
			// The code is asking for the address of an external
			// function. We provide it with the address of the
			// correspondent GOT symbol.
			ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_390_GLOB_DAT))
			su := ldr.MakeSymbolUpdater(s)
			su.SetRelocSym(rIdx, syms.GOT)
			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
			return true
		}

		// Process dynamic relocations for the data sections.
		if target.IsPIE() && target.IsInternal() {
			// When internally linking, generate dynamic relocations
			// for all typical R_ADDR relocations. The exception
			// are those R_ADDR that are created as part of generating
			// the dynamic relocations and must be resolved statically.
			//
			// These synthetic static R_ADDR relocs must be skipped
			// now, or else we will be caught in an infinite loop
			// of generating synthetic relocs for our synthetic
			// relocs.
			switch ldr.SymName(s) {
			case ".dynsym", ".rela", ".rela.plt", ".got.plt", ".dynamic":
				return false
			}
		} else {
			// Either internally linking a static executable,
			// in which case we can resolve these relocations
			// statically in the 'reloc' phase, or externally
			// linking, in which case the relocation will be
			// prepared in the 'reloc' phase and passed to the
			// external linker in the 'asmb' phase.
			if t := ldr.SymType(s); !t.IsDATA() && !t.IsRODATA() {
				break
			}
		}

		if target.IsElf() {
			// Generate R_390_RELATIVE relocations for best
			// efficiency in the dynamic linker.
			//
			// As noted above, symbol addresses have not been
			// assigned yet, so we can't generate the final reloc
			// entry yet. We ultimately want:
			//
			// r_offset = s + r.Off
			// r_info = R_390_RELATIVE
			// r_addend = targ + r.Add
			//
			// The dynamic linker will set *offset = base address +
			// addend.
			//
			// AddAddrPlus is used for r_offset and r_addend to
			// generate new R_ADDR relocations that will update
			// these fields in the 'reloc' phase.
			rela := ldr.MakeSymbolUpdater(syms.Rela)
			rela.AddAddrPlus(target.Arch, s, int64(r.Off()))
			if r.Siz() == 8 {
				rela.AddUint64(target.Arch, elf.R_INFO(0, uint32(elf.R_390_RELATIVE)))
			} else {
				ldr.Errorf(s, "unexpected relocation for dynamic symbol %s", ldr.SymName(targ))
			}
			rela.AddAddrPlus(target.Arch, targ, r.Add())
			// Not mark r done here. So we still apply it statically,
			// so in the file content we'll also have the right offset
			// to the relocation target. So it can be examined statically
			// (e.g. go version).
			return true
		}
	}

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

func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, ri int, sectoff int64) bool {
	out.Write64(uint64(sectoff))

	elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
	siz := r.Size
	switch r.Type {
	default:
		return false
	case objabi.R_TLS_LE:
		switch siz {
		default:
			return false
		case 4:
			// WARNING - silently ignored by linker in ELF64
			out.Write64(uint64(elf.R_390_TLS_LE32) | uint64(elfsym)<<32)
		case 8:
			// WARNING - silently ignored by linker in ELF32
			out.Write64(uint64(elf.R_390_TLS_LE64) | uint64(elfsym)<<32)
		}
	case objabi.R_TLS_IE:
		switch siz {
		default:
			return false
		case 4:
			out.Write64(uint64(elf.R_390_TLS_IEENT) | uint64(elfsym)<<32)
		}
	case objabi.R_ADDR, objabi.R_DWARFSECREF:
		switch siz {
		default:
			return false
		case 4:
			out.Write64(uint64(elf.R_390_32) | uint64(elfsym)<<32)
		case 8:
			out.Write64(uint64(elf.R_390_64) | uint64(elfsym)<<32)
		}
	case objabi.R_GOTPCREL:
		if siz == 4 {
			out.Write64(uint64(elf.R_390_GOTENT) | uint64(elfsym)<<32)
		} else {
			return false
		}
	case objabi.R_PCREL, objabi.R_PCRELDBL, objabi.R_CALL:
		elfrel := elf.R_390_NONE
		rVariant := ldr.RelocVariant(s, ri)
		isdbl := rVariant&sym.RV_TYPE_MASK == sym.RV_390_DBL
		// TODO(mundaym): all DBL style relocations should be
		// signalled using the variant - see issue 14218.
		switch r.Type {
		case objabi.R_PCRELDBL, objabi.R_CALL:
			isdbl = true
		}
		if ldr.SymType(r.Xsym) == sym.SDYNIMPORT && (ldr.SymElfType(r.Xsym) == elf.STT_FUNC || r.Type == objabi.R_CALL) {
			if isdbl {
				switch siz {
				case 2:
					elfrel = elf.R_390_PLT16DBL
				case 4:
					elfrel = elf.R_390_PLT32DBL
				}
			} else {
				switch siz {
				case 4:
					elfrel = elf.R_390_PLT32
				case 8:
					elfrel = elf.R_390_PLT64
				}
			}
		} else {
			if isdbl {
				switch siz {
				case 2:
					elfrel = elf.R_390_PC16DBL
				case 4:
					elfrel = elf.R_390_PC32DBL
				}
			} else {
				switch siz {
				case 2:
					elfrel = elf.R_390_PC16
				case 4:
					elfrel = elf.R_390_PC32
				case 8:
					elfrel = elf.R_390_PC64
				}
			}
		}
		if elfrel == elf.R_390_NONE {
			return false // unsupported size/dbl combination
		}
		out.Write64(uint64(elfrel) | uint64(elfsym)<<32)
	}

	out.Write64(uint64(r.Xadd))
	return true
}

func elfsetupplt(ctxt *ld.Link, ldr *loader.Loader, plt, gotplt *loader.SymbolBuilder, dynamic loader.Sym) {
	if plt.Size() == 0 {
		// stg     %r1,56(%r15)
		plt.AddUint8(0xe3)
		plt.AddUint8(0x10)
		plt.AddUint8(0xf0)
		plt.AddUint8(0x38)
		plt.AddUint8(0x00)
		plt.AddUint8(0x24)
		// larl    %r1,_GLOBAL_OFFSET_TABLE_
		plt.AddUint8(0xc0)
		plt.AddUint8(0x10)
		plt.AddSymRef(ctxt.Arch, gotplt.Sym(), 6, objabi.R_PCRELDBL, 4)
		// mvc     48(8,%r15),8(%r1)
		plt.AddUint8(0xd2)
		plt.AddUint8(0x07)
		plt.AddUint8(0xf0)
		plt.AddUint8(0x30)
		plt.AddUint8(0x10)
		plt.AddUint8(0x08)
		// lg      %r1,16(%r1)
		plt.AddUint8(0xe3)
		plt.AddUint8(0x10)
		plt.AddUint8(0x10)
		plt.AddUint8(0x10)
		plt.AddUint8(0x00)
		plt.AddUint8(0x04)
		// br      %r1
		plt.AddUint8(0x07)
		plt.AddUint8(0xf1)
		// nopr    %r0
		plt.AddUint8(0x07)
		plt.AddUint8(0x00)
		// nopr    %r0
		plt.AddUint8(0x07)
		plt.AddUint8(0x00)
		// nopr    %r0
		plt.AddUint8(0x07)
		plt.AddUint8(0x00)

		// assume gotplt.size == 0 too
		gotplt.AddAddrPlus(ctxt.Arch, dynamic, 0)

		gotplt.AddUint64(ctxt.Arch, 0)
		gotplt.AddUint64(ctxt.Arch, 0)
	}
}

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

func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loader.Reloc, s loader.Sym, val int64) (o int64, nExtReloc int, ok bool) {
	return val, 0, false
}

func archrelocvariant(target *ld.Target, ldr *loader.Loader, r loader.Reloc, rv sym.RelocVariant, s loader.Sym, t int64, p []byte) int64 {
	switch rv & sym.RV_TYPE_MASK {
	default:
		ldr.Errorf(s, "unexpected relocation variant %d", rv)
		return t

	case sym.RV_NONE:
		return t

	case sym.RV_390_DBL:
		if t&1 != 0 {
			ldr.Errorf(s, "%s+%v is not 2-byte aligned", ldr.SymName(r.Sym()), ldr.SymValue(r.Sym()))
		}
		return t >> 1
	}
}

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)
		gotplt := ldr.MakeSymbolUpdater(syms.GOTPLT)
		rela := ldr.MakeSymbolUpdater(syms.RelaPLT)
		if plt.Size() == 0 {
			panic("plt is not set up")
		}
		// larl    %r1,_GLOBAL_OFFSET_TABLE_+index

		plt.AddUint8(0xc0)
		plt.AddUint8(0x10)
		plt.AddPCRelPlus(target.Arch, gotplt.Sym(), gotplt.Size()+6)
		pltrelocs := plt.Relocs()
		ldr.SetRelocVariant(plt.Sym(), pltrelocs.Count()-1, sym.RV_390_DBL)

		// add to gotplt: pointer to current pos in plt
		gotplt.AddAddrPlus(target.Arch, plt.Sym(), plt.Size()+8) // weird but correct
		// lg      %r1,0(%r1)
		plt.AddUint8(0xe3)
		plt.AddUint8(0x10)
		plt.AddUint8(0x10)
		plt.AddUint8(0x00)
		plt.AddUint8(0x00)
		plt.AddUint8(0x04)
		// br      %r1
		plt.AddUint8(0x07)
		plt.AddUint8(0xf1)
		// basr    %r1,%r0
		plt.AddUint8(0x0d)
		plt.AddUint8(0x10)
		// lgf     %r1,12(%r1)
		plt.AddUint8(0xe3)
		plt.AddUint8(0x10)
		plt.AddUint8(0x10)
		plt.AddUint8(0x0c)
		plt.AddUint8(0x00)
		plt.AddUint8(0x14)
		// jg .plt
		plt.AddUint8(0xc0)
		plt.AddUint8(0xf4)

		plt.AddUint32(target.Arch, uint32(-((plt.Size() - 2) >> 1))) // roll-your-own relocation
		//.plt index
		plt.AddUint32(target.Arch, uint32(rela.Size())) // rela size before current entry

		// rela
		rela.AddAddrPlus(target.Arch, gotplt.Sym(), gotplt.Size()-8)

		sDynid := ldr.SymDynid(s)
		rela.AddUint64(target.Arch, elf.R_INFO(uint32(sDynid), uint32(elf.R_390_JMP_SLOT)))
		rela.AddUint64(target.Arch, 0)

		ldr.SetPlt(s, int32(plt.Size()-32))

	} else {
		ldr.Errorf(s, "addpltsym: unsupported binary format")
	}
}

// tlsIEtoLE converts TLS Initial Exec (IE) relocation to TLS Local Exec (LE).
//
// On s390x, the TLS IE sequence is:
//
//	LARL %rN, <var>@INDNTPOFF   ; 6 bytes - load address of GOT entry
//	LG   %rN, 0(%rN)            ; 6 bytes - load offset from GOT
//
// We convert this to TLS LE by replacing it with:
//
//	LGFI %rN, <offset>          ; 6 bytes - load 32-bit sign-extended immediate
//	BCR  0,0                    ; 2 bytes - NOP
//	BCR  0,0                    ; 2 bytes - NOP
//	BCR  0,0                    ; 2 bytes - NOP
//
// The relocation offset points to byte 2 of the LARL instruction (the immediate field).
func tlsIEtoLE(P []byte, off, size int) {
	// off is the offset of the relocation within the instruction sequence,
	// which is at byte 2 of the LARL instruction (the 4-byte immediate).
	// We need to work with the beginning of LARL (off-2) through LG (off+10).

	if off < 2 {
		log.Fatalf("R_390_TLS_IEENT relocation at offset %d is too small", off)
	}

	// Verify we have a LARL instruction (opcode 0xC0, second nibble 0x0)
	// LARL format: C0 R0 I2 I2 I2 I2 (where R is register, I2 is 32-bit immediate)
	if P[off-2] != 0xc0 || P[off-1]&0x0f != 0x00 {
		log.Fatalf("R_390_TLS_IEENT relocation not preceded by LARL instruction: %02x %02x", P[off-2], P[off-1])
	}

	// Extract the register from LARL (upper nibble of second byte)
	reg := P[off-1] >> 4

	// Convert LARL to LGFI: change opcode from C0x0 to C0x1
	// LGFI format: C0 R1 I2 I2 I2 I2
	P[off-1] = (reg << 4) | 0x01

	// The immediate field (bytes off to off+3) will be filled in by the linker
	// with the TLS offset value.

	// Replace the LG instruction (6 bytes starting at off+4) with NOPs
	// BCR 0,0 = 0x07 0x00 (2 bytes each, need 3 of them)
	P[off+4] = 0x07
	P[off+5] = 0x00
	P[off+6] = 0x07
	P[off+7] = 0x00
	P[off+8] = 0x07
	P[off+9] = 0x00
}