Source file src/cmd/link/internal/ppc64/asm.go

     1  // Inferno utils/5l/asm.c
     2  // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/5l/asm.c
     3  //
     4  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     5  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     6  //	Portions Copyright © 1997-1999 Vita Nuova Limited
     7  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     8  //	Portions Copyright © 2004,2006 Bruce Ellis
     9  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    10  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    11  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
    12  //
    13  // Permission is hereby granted, free of charge, to any person obtaining a copy
    14  // of this software and associated documentation files (the "Software"), to deal
    15  // in the Software without restriction, including without limitation the rights
    16  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    17  // copies of the Software, and to permit persons to whom the Software is
    18  // furnished to do so, subject to the following conditions:
    19  //
    20  // The above copyright notice and this permission notice shall be included in
    21  // all copies or substantial portions of the Software.
    22  //
    23  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    24  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    25  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    26  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    27  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    28  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    29  // THE SOFTWARE.
    30  
    31  package ppc64
    32  
    33  import (
    34  	"cmd/internal/objabi"
    35  	"cmd/internal/sys"
    36  	"cmd/link/internal/ld"
    37  	"cmd/link/internal/loader"
    38  	"cmd/link/internal/sym"
    39  	"debug/elf"
    40  	"encoding/binary"
    41  	"fmt"
    42  	"internal/buildcfg"
    43  	"log"
    44  	"strconv"
    45  	"strings"
    46  )
    47  
    48  // The build configuration supports PC-relative instructions and relocations (limited to tested targets).
    49  var hasPCrel = buildcfg.GOPPC64 >= 10 && buildcfg.GOOS == "linux"
    50  
    51  const (
    52  	// For genstub, the type of stub required by the caller.
    53  	STUB_TOC = iota
    54  	STUB_PCREL
    55  )
    56  
    57  var stubStrs = []string{
    58  	STUB_TOC:   "_callstub_toc",
    59  	STUB_PCREL: "_callstub_pcrel",
    60  }
    61  
    62  const (
    63  	OP_TOCRESTORE    = 0xe8410018 // ld r2,24(r1)
    64  	OP_TOCSAVE       = 0xf8410018 // std r2,24(r1)
    65  	OP_NOP           = 0x60000000 // nop
    66  	OP_BL            = 0x48000001 // bl 0
    67  	OP_BCTR          = 0x4e800420 // bctr
    68  	OP_BCTRL         = 0x4e800421 // bctrl
    69  	OP_BCL           = 0x40000001 // bcl
    70  	OP_ADDI          = 0x38000000 // addi
    71  	OP_ADDIS         = 0x3c000000 // addis
    72  	OP_LD            = 0xe8000000 // ld
    73  	OP_PLA_PFX       = 0x06100000 // pla (prefix instruction word)
    74  	OP_PLA_SFX       = 0x38000000 // pla (suffix instruction word)
    75  	OP_PLD_PFX_PCREL = 0x04100000 // pld (prefix instruction word, R=1)
    76  	OP_PLD_SFX       = 0xe4000000 // pld (suffix instruction word)
    77  	OP_MFLR          = 0x7c0802a6 // mflr
    78  	OP_MTLR          = 0x7c0803a6 // mtlr
    79  	OP_MFCTR         = 0x7c0902a6 // mfctr
    80  	OP_MTCTR         = 0x7c0903a6 // mtctr
    81  
    82  	OP_ADDIS_R12_R2  = OP_ADDIS | 12<<21 | 2<<16  // addis r12,r2,0
    83  	OP_ADDIS_R12_R12 = OP_ADDIS | 12<<21 | 12<<16 // addis  r12,r12,0
    84  	OP_ADDI_R12_R12  = OP_ADDI | 12<<21 | 12<<16  // addi  r12,r12,0
    85  	OP_PLD_SFX_R12   = OP_PLD_SFX | 12<<21        // pld   r12,0 (suffix instruction word)
    86  	OP_PLA_SFX_R12   = OP_PLA_SFX | 12<<21        // pla   r12,0 (suffix instruction word)
    87  	OP_LIS_R12       = OP_ADDIS | 12<<21          // lis r12,0
    88  	OP_LD_R12_R12    = OP_LD | 12<<21 | 12<<16    // ld r12,0(r12)
    89  	OP_MTCTR_R12     = OP_MTCTR | 12<<21          // mtctr r12
    90  	OP_MFLR_R12      = OP_MFLR | 12<<21           // mflr r12
    91  	OP_MFLR_R0       = OP_MFLR | 0<<21            // mflr r0
    92  	OP_MTLR_R0       = OP_MTLR | 0<<21            // mtlr r0
    93  
    94  	// This is a special, preferred form of bcl to obtain the next
    95  	// instruction address (NIA, aka PC+4) in LR.
    96  	OP_BCL_NIA = OP_BCL | 20<<21 | 31<<16 | 1<<2 // bcl 20,31,$+4
    97  
    98  	// Masks to match opcodes
    99  	MASK_PLD_PFX  = 0xfff70000
   100  	MASK_PLD_SFX  = 0xfc1f0000 // Also checks RA = 0 if check value is OP_PLD_SFX.
   101  	MASK_PLD_RT   = 0x03e00000 // Extract RT from the pld suffix.
   102  	MASK_OP_LD    = 0xfc000003
   103  	MASK_OP_ADDIS = 0xfc000000
   104  )
   105  
   106  // Generate a stub to call between TOC and NOTOC functions. See genpltstub for more details about calling stubs.
   107  // This is almost identical to genpltstub, except the location of the target symbol is known at link time.
   108  func genstub(ctxt *ld.Link, ldr *loader.Loader, r loader.Reloc, ri int, s loader.Sym, stubType int) (ssym loader.Sym, firstUse bool) {
   109  	addendStr := ""
   110  	if r.Add() != 0 {
   111  		addendStr = fmt.Sprintf("%+d", r.Add())
   112  	}
   113  
   114  	stubName := fmt.Sprintf("%s%s.%s", stubStrs[stubType], addendStr, ldr.SymName(r.Sym()))
   115  	stub := ldr.CreateSymForUpdate(stubName, 0)
   116  	firstUse = stub.Size() == 0
   117  	if firstUse {
   118  		switch stubType {
   119  		// A call from a function using a TOC pointer.
   120  		case STUB_TOC:
   121  			stub.AddUint32(ctxt.Arch, OP_TOCSAVE) // std r2,24(r1)
   122  			stub.AddSymRef(ctxt.Arch, r.Sym(), r.Add(), objabi.R_ADDRPOWER_TOCREL_DS, 8)
   123  			stub.SetUint32(ctxt.Arch, stub.Size()-8, OP_ADDIS_R12_R2) // addis r12,r2,targ@toc@ha
   124  			stub.SetUint32(ctxt.Arch, stub.Size()-4, OP_ADDI_R12_R12) // addi  r12,targ@toc@l(r12)
   125  
   126  		// A call from PC relative function.
   127  		case STUB_PCREL:
   128  			if buildcfg.GOPPC64 >= 10 {
   129  				// Set up address of targ in r12, PCrel
   130  				stub.AddSymRef(ctxt.Arch, r.Sym(), r.Add(), objabi.R_ADDRPOWER_PCREL34, 8)
   131  				stub.SetUint32(ctxt.Arch, stub.Size()-8, OP_PLA_PFX)
   132  				stub.SetUint32(ctxt.Arch, stub.Size()-4, OP_PLA_SFX_R12) // pla r12, r
   133  			} else {
   134  				// The target may not be a P10. Generate a P8 compatible stub.
   135  				stub.AddUint32(ctxt.Arch, OP_MFLR_R0)  // mflr r0
   136  				stub.AddUint32(ctxt.Arch, OP_BCL_NIA)  // bcl 20,31,1f
   137  				stub.AddUint32(ctxt.Arch, OP_MFLR_R12) // 1: mflr r12  (r12 is the address of this instruction)
   138  				stub.AddUint32(ctxt.Arch, OP_MTLR_R0)  // mtlr r0
   139  				stub.AddSymRef(ctxt.Arch, r.Sym(), r.Add()+8, objabi.R_ADDRPOWER_PCREL, 8)
   140  				stub.SetUint32(ctxt.Arch, stub.Size()-8, OP_ADDIS_R12_R12) // addis r12,(r - 1b) + 8
   141  				stub.SetUint32(ctxt.Arch, stub.Size()-4, OP_ADDI_R12_R12)  // addi  r12,(r - 1b) + 12
   142  			}
   143  		}
   144  		// Jump to the loaded pointer
   145  		stub.AddUint32(ctxt.Arch, OP_MTCTR_R12) // mtctr r12
   146  		stub.AddUint32(ctxt.Arch, OP_BCTR)      // bctr
   147  		stub.SetType(sym.STEXT)
   148  	}
   149  
   150  	// Update the relocation to use the call stub
   151  	su := ldr.MakeSymbolUpdater(s)
   152  	su.SetRelocSym(ri, stub.Sym())
   153  
   154  	// Rewrite the TOC restore slot (a nop) if the caller uses a TOC pointer.
   155  	switch stubType {
   156  	case STUB_TOC:
   157  		rewritetoinsn(&ctxt.Target, ldr, su, int64(r.Off()+4), 0xFFFFFFFF, OP_NOP, OP_TOCRESTORE)
   158  	}
   159  
   160  	return stub.Sym(), firstUse
   161  }
   162  
   163  func genpltstub(ctxt *ld.Link, ldr *loader.Loader, r loader.Reloc, ri int, s loader.Sym) (sym loader.Sym, firstUse bool) {
   164  	// The ppc64 ABI PLT has similar concepts to other
   165  	// architectures, but is laid out quite differently. When we
   166  	// see a relocation to a dynamic symbol (indicating that the
   167  	// call needs to go through the PLT), we generate up to three
   168  	// stubs and reserve a PLT slot.
   169  	//
   170  	// 1) The call site is a "bl x" where genpltstub rewrites it to
   171  	//    "bl x_stub". Depending on the properties of the caller
   172  	//    (see ELFv2 1.5 4.2.5.3), a nop may be expected immediately
   173  	//    after the bl. This nop is rewritten to ld r2,24(r1) to
   174  	//    restore the toc pointer saved by x_stub.
   175  	//
   176  	// 2) We reserve space for a pointer in the .plt section (once
   177  	//    per referenced dynamic function).  .plt is a data
   178  	//    section filled solely by the dynamic linker (more like
   179  	//    .plt.got on other architectures).  Initially, the
   180  	//    dynamic linker will fill each slot with a pointer to the
   181  	//    corresponding x@plt entry point.
   182  	//
   183  	// 3) We generate a "call stub" x_stub based on the properties
   184  	//    of the caller.
   185  	//
   186  	// 4) We generate the "symbol resolver stub" x@plt (once per
   187  	//    dynamic function).  This is solely a branch to the glink
   188  	//    resolver stub.
   189  	//
   190  	// 5) We generate the glink resolver stub (only once).  This
   191  	//    computes which symbol resolver stub we came through and
   192  	//    invokes the dynamic resolver via a pointer provided by
   193  	//    the dynamic linker. This will patch up the .plt slot to
   194  	//    point directly at the function so future calls go
   195  	//    straight from the call stub to the real function, and
   196  	//    then call the function.
   197  
   198  	// NOTE: It's possible we could make ppc64 closer to other
   199  	// architectures: ppc64's .plt is like .plt.got on other
   200  	// platforms and ppc64's .glink is like .plt on other
   201  	// platforms.
   202  
   203  	// Find all relocations that reference dynamic imports.
   204  	// Reserve PLT entries for these symbols and generate call
   205  	// stubs. The call stubs need to live in .text, which is why we
   206  	// need to do this pass this early.
   207  
   208  	// Reserve PLT entry and generate symbol resolver
   209  	addpltsym(ctxt, ldr, r.Sym())
   210  
   211  	// The stub types are described in gencallstub.
   212  	stubType := 0
   213  	stubTypeStr := ""
   214  
   215  	// For now, the choice of call stub type is determined by whether
   216  	// the caller maintains a TOC pointer in R2. A TOC pointer implies
   217  	// we can always generate a position independent stub.
   218  	//
   219  	// For dynamic calls made from an external object, a caller maintains
   220  	// a TOC pointer only when an R_PPC64_REL24 relocation is used.
   221  	// An R_PPC64_REL24_NOTOC relocation does not use or maintain
   222  	// a TOC pointer, and almost always implies a Power10 target.
   223  	//
   224  	// For dynamic calls made from a Go caller, a TOC relative stub is
   225  	// always needed when a TOC pointer is maintained (specifically, if
   226  	// the Go caller is PIC, and cannot use PCrel instructions).
   227  	if (r.Type() == objabi.ElfRelocOffset+objabi.RelocType(elf.R_PPC64_REL24)) || (!ldr.AttrExternal(s) && ldr.AttrShared(s) && !hasPCrel) {
   228  		stubTypeStr = "_tocrel"
   229  		stubType = 1
   230  	} else {
   231  		stubTypeStr = "_notoc"
   232  		stubType = 3
   233  	}
   234  	n := fmt.Sprintf("_pltstub%s.%s", stubTypeStr, ldr.SymName(r.Sym()))
   235  
   236  	// When internal linking, all text symbols share the same toc pointer.
   237  	stub := ldr.CreateSymForUpdate(n, 0)
   238  	firstUse = stub.Size() == 0
   239  	if firstUse {
   240  		gencallstub(ctxt, ldr, stubType, stub, r.Sym())
   241  	}
   242  
   243  	// Update the relocation to use the call stub
   244  	su := ldr.MakeSymbolUpdater(s)
   245  	su.SetRelocSym(ri, stub.Sym())
   246  
   247  	// A type 1 call must restore the toc pointer after the call.
   248  	if stubType == 1 {
   249  		su.MakeWritable()
   250  		p := su.Data()
   251  
   252  		// Check for a toc pointer restore slot (a nop), and rewrite to restore the toc pointer.
   253  		var nop uint32
   254  		if len(p) >= int(r.Off()+8) {
   255  			nop = ctxt.Arch.ByteOrder.Uint32(p[r.Off()+4:])
   256  		}
   257  		if nop != OP_NOP {
   258  			ldr.Errorf(s, "Symbol %s is missing toc restoration slot at offset %d", ldr.SymName(s), r.Off()+4)
   259  		}
   260  		ctxt.Arch.ByteOrder.PutUint32(p[r.Off()+4:], OP_TOCRESTORE)
   261  	}
   262  
   263  	return stub.Sym(), firstUse
   264  }
   265  
   266  // Scan relocs and generate PLT stubs and generate/fixup ABI defined functions created by the linker.
   267  func genstubs(ctxt *ld.Link, ldr *loader.Loader) {
   268  	var stubs []loader.Sym
   269  	var abifuncs []loader.Sym
   270  	for _, s := range ctxt.Textp {
   271  		relocs := ldr.Relocs(s)
   272  		for i := 0; i < relocs.Count(); i++ {
   273  			switch r := relocs.At(i); r.Type() {
   274  			case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL24), objabi.R_CALLPOWER:
   275  				switch t := ldr.SymType(r.Sym()); {
   276  				case t == sym.SDYNIMPORT:
   277  					// This call goes through the PLT, generate and call through a PLT stub.
   278  					if sym, firstUse := genpltstub(ctxt, ldr, r, i, s); firstUse {
   279  						stubs = append(stubs, sym)
   280  					}
   281  
   282  				case t == sym.SXREF:
   283  					// Is this an ELF ABI defined function which is (in practice)
   284  					// generated by the linker to save/restore callee save registers?
   285  					// These are defined similarly for both PPC64 ELF and ELFv2.
   286  					targName := ldr.SymName(r.Sym())
   287  					if strings.HasPrefix(targName, "_save") || strings.HasPrefix(targName, "_rest") {
   288  						if sym, firstUse := rewriteABIFuncReloc(ctxt, ldr, targName, r); firstUse {
   289  							abifuncs = append(abifuncs, sym)
   290  						}
   291  					}
   292  				case t.IsText():
   293  					targ := r.Sym()
   294  					if (ldr.AttrExternal(targ) && ldr.SymLocalentry(targ) != 1) || !ldr.AttrExternal(targ) {
   295  						// All local symbols share the same TOC pointer. This caller has a valid TOC
   296  						// pointer in R2. Calls into a Go symbol preserve R2. No call stub is needed.
   297  					} else {
   298  						// This caller has a TOC pointer. The callee might clobber it. R2 needs to be saved
   299  						// and restored.
   300  						if sym, firstUse := genstub(ctxt, ldr, r, i, s, STUB_TOC); firstUse {
   301  							stubs = append(stubs, sym)
   302  						}
   303  					}
   304  				}
   305  
   306  			case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL24_P9NOTOC):
   307  				// This can be treated identically to R_PPC64_REL24_NOTOC, as stubs are determined by
   308  				// GOPPC64 and -buildmode.
   309  				fallthrough
   310  			case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL24_NOTOC):
   311  				switch rt := ldr.SymType(r.Sym()); {
   312  				case rt == sym.SDYNIMPORT:
   313  					// This call goes through the PLT, generate and call through a PLT stub.
   314  					if sym, firstUse := genpltstub(ctxt, ldr, r, i, s); firstUse {
   315  						stubs = append(stubs, sym)
   316  					}
   317  
   318  				case rt == sym.SXREF:
   319  					// TODO: This is not supported yet.
   320  					ldr.Errorf(s, "Unsupported NOTOC external reference call into %s", ldr.SymName(r.Sym()))
   321  
   322  				case rt.IsText():
   323  					targ := r.Sym()
   324  					if (ldr.AttrExternal(targ) && ldr.SymLocalentry(targ) <= 1) || (!ldr.AttrExternal(targ) && (!ldr.AttrShared(targ) || hasPCrel)) {
   325  						// This is NOTOC to NOTOC call (st_other is 0 or 1). No call stub is needed.
   326  					} else {
   327  						// This is a NOTOC to TOC function. Generate a calling stub.
   328  						if sym, firstUse := genstub(ctxt, ldr, r, i, s, STUB_PCREL); firstUse {
   329  							stubs = append(stubs, sym)
   330  						}
   331  					}
   332  				}
   333  
   334  			// Handle objects compiled with -fno-plt. Rewrite local calls to avoid indirect calling.
   335  			// These are 0 sized relocs. They mark the mtctr r12, or bctrl + ld r2,24(r1).
   336  			case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_PLTSEQ):
   337  				if ldr.SymType(r.Sym()).IsText() {
   338  					// This should be an mtctr instruction. Turn it into a nop.
   339  					su := ldr.MakeSymbolUpdater(s)
   340  					const MASK_OP_MTCTR = 63<<26 | 0x3FF<<11 | 0x1FF<<1
   341  					rewritetonop(&ctxt.Target, ldr, su, int64(r.Off()), MASK_OP_MTCTR, OP_MTCTR)
   342  				}
   343  			case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_PLTCALL):
   344  				if ldr.SymType(r.Sym()).IsText() {
   345  					// This relocation should point to a bctrl followed by a ld r2, 24(41)
   346  					// Convert the bctrl into a bl.
   347  					su := ldr.MakeSymbolUpdater(s)
   348  					rewritetoinsn(&ctxt.Target, ldr, su, int64(r.Off()), 0xFFFFFFFF, OP_BCTRL, OP_BL)
   349  
   350  					// Turn this reloc into an R_CALLPOWER, and convert the TOC restore into a nop.
   351  					su.SetRelocType(i, objabi.R_CALLPOWER)
   352  					localEoffset := int64(ldr.SymLocalentry(r.Sym()))
   353  					if localEoffset == 1 {
   354  						ldr.Errorf(s, "Unsupported NOTOC call to %s", ldr.SymName(r.Sym()))
   355  					}
   356  					su.SetRelocAdd(i, r.Add()+localEoffset)
   357  					r.SetSiz(4)
   358  					rewritetonop(&ctxt.Target, ldr, su, int64(r.Off()+4), 0xFFFFFFFF, OP_TOCRESTORE)
   359  				}
   360  			}
   361  		}
   362  	}
   363  
   364  	// Append any usage of the go versions of ELF save/restore
   365  	// functions to the end of the callstub list to minimize
   366  	// chances a trampoline might be needed.
   367  	stubs = append(stubs, abifuncs...)
   368  
   369  	// Put stubs at the beginning (instead of the end).
   370  	// So when resolving the relocations to calls to the stubs,
   371  	// the addresses are known and trampolines can be inserted
   372  	// when necessary.
   373  	ctxt.Textp = append(stubs, ctxt.Textp...)
   374  }
   375  
   376  func genaddmoduledata(ctxt *ld.Link, ldr *loader.Loader) {
   377  	initfunc, addmoduledata := ld.PrepareAddmoduledata(ctxt)
   378  	if initfunc == nil {
   379  		return
   380  	}
   381  
   382  	o := func(op uint32) {
   383  		initfunc.AddUint32(ctxt.Arch, op)
   384  	}
   385  
   386  	// Write a function to load this module's local.moduledata. This is shared code.
   387  	//
   388  	// package link
   389  	// void addmoduledata() {
   390  	//	runtime.addmoduledata(local.moduledata)
   391  	// }
   392  
   393  	if !hasPCrel {
   394  		// Regenerate TOC from R12 (the address of this function).
   395  		sz := initfunc.AddSymRef(ctxt.Arch, ctxt.DotTOC[0], 0, objabi.R_ADDRPOWER_PCREL, 8)
   396  		initfunc.SetUint32(ctxt.Arch, sz-8, 0x3c4c0000) // addis r2, r12, .TOC.-func@ha
   397  		initfunc.SetUint32(ctxt.Arch, sz-4, 0x38420000) // addi r2, r2, .TOC.-func@l
   398  	}
   399  
   400  	// This is Go ABI. Stack a frame and save LR.
   401  	o(OP_MFLR_R0) // mflr r0
   402  	o(0xf801ffe1) // stdu r0, -32(r1)
   403  
   404  	// Get the moduledata pointer from GOT and put into R3.
   405  	var tgt loader.Sym
   406  	if s := ldr.Lookup("local.moduledata", 0); s != 0 {
   407  		tgt = s
   408  	} else if s := ldr.Lookup("local.pluginmoduledata", 0); s != 0 {
   409  		tgt = s
   410  	} else {
   411  		tgt = ldr.LookupOrCreateSym("runtime.firstmoduledata", 0)
   412  	}
   413  
   414  	if !hasPCrel {
   415  		sz := initfunc.AddSymRef(ctxt.Arch, tgt, 0, objabi.R_ADDRPOWER_GOT, 8)
   416  		initfunc.SetUint32(ctxt.Arch, sz-8, 0x3c620000) // addis r3, r2, local.moduledata@got@ha
   417  		initfunc.SetUint32(ctxt.Arch, sz-4, 0xe8630000) // ld r3, local.moduledata@got@l(r3)
   418  	} else {
   419  		sz := initfunc.AddSymRef(ctxt.Arch, tgt, 0, objabi.R_ADDRPOWER_GOT_PCREL34, 8)
   420  		// Note, this is prefixed instruction. It must not cross a 64B boundary.
   421  		// It is doubleworld aligned here, so it will never cross (this function is 16B aligned, minimum).
   422  		initfunc.SetUint32(ctxt.Arch, sz-8, OP_PLD_PFX_PCREL)
   423  		initfunc.SetUint32(ctxt.Arch, sz-4, OP_PLD_SFX|(3<<21)) // pld r3, local.moduledata@got@pcrel
   424  	}
   425  
   426  	// Call runtime.addmoduledata
   427  	sz := initfunc.AddSymRef(ctxt.Arch, addmoduledata, 0, objabi.R_CALLPOWER, 4)
   428  	initfunc.SetUint32(ctxt.Arch, sz-4, OP_BL) // bl runtime.addmoduledata
   429  	o(OP_NOP)                                  // nop (for TOC restore)
   430  
   431  	// Pop stack frame and return.
   432  	o(0xe8010000) // ld r0, 0(r1)
   433  	o(OP_MTLR_R0) // mtlr r0
   434  	o(0x38210020) // addi r1,r1,32
   435  	o(0x4e800020) // blr
   436  }
   437  
   438  // Rewrite ELF (v1 or v2) calls to _savegpr0_n, _savegpr1_n, _savefpr_n, _restfpr_n, _savevr_m, or
   439  // _restvr_m (14<=n<=31, 20<=m<=31). Redirect them to runtime.elf_restgpr0+(n-14)*4,
   440  // runtime.elf_restvr+(m-20)*8, and similar.
   441  //
   442  // These functions are defined in the ELFv2 ABI (generated when using gcc -Os option) to save and
   443  // restore callee-saved registers (as defined in the PPC64 ELF ABIs) from registers n or m to 31 of
   444  // the named type. R12 and R0 are sometimes used in exceptional ways described in the ABI.
   445  //
   446  // Final note, this is only needed when linking internally. The external linker will generate these
   447  // functions if they are used.
   448  func rewriteABIFuncReloc(ctxt *ld.Link, ldr *loader.Loader, tname string, r loader.Reloc) (sym loader.Sym, firstUse bool) {
   449  	s := strings.Split(tname, "_")
   450  	// A valid call will split like {"", "savegpr0", "20"}
   451  	if len(s) != 3 {
   452  		return 0, false // Not an abi func.
   453  	}
   454  	minReg := 14 // _savegpr0_{n}, _savegpr1_{n}, _savefpr_{n}, 14 <= n <= 31
   455  	offMul := 4  // 1 instruction per register op.
   456  	switch s[1] {
   457  	case "savegpr0", "savegpr1", "savefpr":
   458  	case "restgpr0", "restgpr1", "restfpr":
   459  	case "savevr", "restvr":
   460  		minReg = 20 // _savevr_{n} or _restvr_{n}, 20 <= n <= 31
   461  		offMul = 8  // 2 instructions per register op.
   462  	default:
   463  		return 0, false // Not an abi func
   464  	}
   465  	n, e := strconv.Atoi(s[2])
   466  	if e != nil || n < minReg || n > 31 || r.Add() != 0 {
   467  		return 0, false // Invalid register number, or non-zero addend. Not an abi func.
   468  	}
   469  
   470  	// tname is a valid relocation to an ABI defined register save/restore function. Re-relocate
   471  	// them to a go version of these functions in runtime/asm_ppc64x.s
   472  	ts := ldr.LookupOrCreateSym("runtime.elf_"+s[1], 0)
   473  	r.SetSym(ts)
   474  	r.SetAdd(int64((n - minReg) * offMul))
   475  	firstUse = !ldr.AttrReachable(ts)
   476  	if firstUse {
   477  		// This function only becomes reachable now. It has been dropped from
   478  		// the text section (it was unreachable until now), it needs included.
   479  		ldr.SetAttrReachable(ts, true)
   480  	}
   481  	return ts, firstUse
   482  }
   483  
   484  func gentext(ctxt *ld.Link, ldr *loader.Loader) {
   485  	if ctxt.DynlinkingGo() {
   486  		genaddmoduledata(ctxt, ldr)
   487  	}
   488  
   489  	if ctxt.LinkMode == ld.LinkInternal {
   490  		genstubs(ctxt, ldr)
   491  	}
   492  }
   493  
   494  // Create a calling stub. The stubType maps directly to the properties listed in the ELFv2 1.5
   495  // section 4.2.5.3.
   496  //
   497  // There are 3 cases today (as paraphrased from the ELFv2 document):
   498  //
   499  //  1. R2 holds the TOC pointer on entry. The call stub must save R2 into the ELFv2 TOC stack save slot.
   500  //
   501  //  2. R2 holds the TOC pointer on entry. The caller has already saved R2 to the TOC stack save slot.
   502  //
   503  //  3. R2 does not hold the TOC pointer on entry. The caller has no expectations of R2.
   504  //
   505  // Go only needs case 1 and 3 today. Go symbols which have AttrShare set could use case 2, but case 1 always
   506  // works in those cases too.
   507  func gencallstub(ctxt *ld.Link, ldr *loader.Loader, stubType int, stub *loader.SymbolBuilder, targ loader.Sym) {
   508  	plt := ctxt.PLT
   509  	stub.SetType(sym.STEXT)
   510  
   511  	switch stubType {
   512  	case 1:
   513  		// Save TOC, then load targ address from PLT using TOC.
   514  		stub.AddUint32(ctxt.Arch, OP_TOCSAVE) // std r2,24(r1)
   515  		stub.AddSymRef(ctxt.Arch, plt, int64(ldr.SymPlt(targ)), objabi.R_ADDRPOWER_TOCREL_DS, 8)
   516  		stub.SetUint32(ctxt.Arch, stub.Size()-8, OP_ADDIS_R12_R2) // addis r12,r2,targ@plt@toc@ha
   517  		stub.SetUint32(ctxt.Arch, stub.Size()-4, OP_LD_R12_R12)   // ld r12,targ@plt@toc@l(r12)
   518  	case 3:
   519  		// No TOC needs to be saved, but the stub may need to position-independent.
   520  		if buildcfg.GOPPC64 >= 10 {
   521  			// Power10 is supported, load targ address into r12 using PCrel load.
   522  			stub.AddSymRef(ctxt.Arch, plt, int64(ldr.SymPlt(targ)), objabi.R_ADDRPOWER_PCREL34, 8)
   523  			stub.SetUint32(ctxt.Arch, stub.Size()-8, OP_PLD_PFX_PCREL)
   524  			stub.SetUint32(ctxt.Arch, stub.Size()-4, OP_PLD_SFX_R12) // pld r12, targ@plt
   525  		} else if !isLinkingPIC(ctxt) {
   526  			// This stub doesn't need to be PIC. Load targ address from the PLT via its absolute address.
   527  			stub.AddSymRef(ctxt.Arch, plt, int64(ldr.SymPlt(targ)), objabi.R_ADDRPOWER_DS, 8)
   528  			stub.SetUint32(ctxt.Arch, stub.Size()-8, OP_LIS_R12)    // lis r12,targ@plt@ha
   529  			stub.SetUint32(ctxt.Arch, stub.Size()-4, OP_LD_R12_R12) // ld r12,targ@plt@l(r12)
   530  		} else {
   531  			// Generate a PIC stub. This is ugly as the stub must determine its location using
   532  			// POWER8 or older instruction. These stubs are likely the combination of using
   533  			// GOPPC64 < 8 and linking external objects built with CFLAGS="... -mcpu=power10 ..."
   534  			stub.AddUint32(ctxt.Arch, OP_MFLR_R0)  // mflr r0
   535  			stub.AddUint32(ctxt.Arch, OP_BCL_NIA)  // bcl 20,31,1f
   536  			stub.AddUint32(ctxt.Arch, OP_MFLR_R12) // 1: mflr r12  (r12 is the address of this instruction)
   537  			stub.AddUint32(ctxt.Arch, OP_MTLR_R0)  // mtlr r0
   538  			stub.AddSymRef(ctxt.Arch, plt, int64(ldr.SymPlt(targ))+8, objabi.R_ADDRPOWER_PCREL, 8)
   539  			stub.SetUint32(ctxt.Arch, stub.Size()-8, OP_ADDIS_R12_R12) // addis r12,(targ@plt - 1b) + 8
   540  			stub.SetUint32(ctxt.Arch, stub.Size()-4, OP_ADDI_R12_R12)  // addi  r12,(targ@plt - 1b) + 12
   541  			stub.AddUint32(ctxt.Arch, OP_LD_R12_R12)                   // ld r12, 0(r12)
   542  		}
   543  	default:
   544  		log.Fatalf("gencallstub does not support ELFv2 ABI property %d", stubType)
   545  	}
   546  
   547  	// Jump to the loaded pointer
   548  	stub.AddUint32(ctxt.Arch, OP_MTCTR_R12) // mtctr r12
   549  	stub.AddUint32(ctxt.Arch, OP_BCTR)      // bctr
   550  }
   551  
   552  // Rewrite the instruction at offset into newinsn. Also, verify the
   553  // existing instruction under mask matches the check value.
   554  func rewritetoinsn(target *ld.Target, ldr *loader.Loader, su *loader.SymbolBuilder, offset int64, mask, check, newinsn uint32) {
   555  	su.MakeWritable()
   556  	op := target.Arch.ByteOrder.Uint32(su.Data()[offset:])
   557  	if op&mask != check {
   558  		ldr.Errorf(su.Sym(), "Rewrite offset 0x%x to 0x%08X failed check (0x%08X&0x%08X != 0x%08X)", offset, newinsn, op, mask, check)
   559  	}
   560  	su.SetUint32(target.Arch, offset, newinsn)
   561  }
   562  
   563  // Rewrite the instruction at offset into a hardware nop instruction. Also, verify the
   564  // existing instruction under mask matches the check value.
   565  func rewritetonop(target *ld.Target, ldr *loader.Loader, su *loader.SymbolBuilder, offset int64, mask, check uint32) {
   566  	rewritetoinsn(target, ldr, su, offset, mask, check, OP_NOP)
   567  }
   568  
   569  func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym, r loader.Reloc, rIdx int) bool {
   570  	if target.IsElf() {
   571  		return addelfdynrel(target, ldr, syms, s, r, rIdx)
   572  	} else if target.IsAIX() {
   573  		return ld.Xcoffadddynrel(target, ldr, syms, s, r, rIdx)
   574  	}
   575  	return false
   576  }
   577  
   578  func addelfdynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym, r loader.Reloc, rIdx int) bool {
   579  	targ := r.Sym()
   580  	var targType sym.SymKind
   581  	if targ != 0 {
   582  		targType = ldr.SymType(targ)
   583  	}
   584  
   585  	switch r.Type() {
   586  	default:
   587  		if r.Type() >= objabi.ElfRelocOffset {
   588  			ldr.Errorf(s, "unexpected relocation type %d (%s)", r.Type(), sym.RelocName(target.Arch, r.Type()))
   589  			return false
   590  		}
   591  
   592  		// Handle relocations found in ELF object files.
   593  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL24_NOTOC),
   594  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL24_P9NOTOC):
   595  		su := ldr.MakeSymbolUpdater(s)
   596  		su.SetRelocType(rIdx, objabi.R_CALLPOWER)
   597  
   598  		if targType == sym.SDYNIMPORT {
   599  			// Should have been handled in elfsetupplt
   600  			ldr.Errorf(s, "unexpected R_PPC64_REL24_NOTOC/R_PPC64_REL24_P9NOTOC for dyn import")
   601  		}
   602  		return true
   603  
   604  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL24):
   605  		su := ldr.MakeSymbolUpdater(s)
   606  		su.SetRelocType(rIdx, objabi.R_CALLPOWER)
   607  
   608  		// This is a local call, so the caller isn't setting
   609  		// up r12 and r2 is the same for the caller and
   610  		// callee. Hence, we need to go to the local entry
   611  		// point.  (If we don't do this, the callee will try
   612  		// to use r12 to compute r2.)
   613  		localEoffset := int64(ldr.SymLocalentry(targ))
   614  		if localEoffset == 1 {
   615  			ldr.Errorf(s, "Unsupported NOTOC call to %s", targ)
   616  		}
   617  		su.SetRelocAdd(rIdx, r.Add()+localEoffset)
   618  
   619  		if targType == sym.SDYNIMPORT {
   620  			// Should have been handled in genstubs
   621  			ldr.Errorf(s, "unexpected R_PPC64_REL24 for dyn import")
   622  		}
   623  
   624  		return true
   625  
   626  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_PCREL34):
   627  		su := ldr.MakeSymbolUpdater(s)
   628  		su.SetRelocType(rIdx, objabi.R_ADDRPOWER_PCREL34)
   629  		return true
   630  
   631  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_GOT_PCREL34):
   632  		su := ldr.MakeSymbolUpdater(s)
   633  		su.SetRelocType(rIdx, objabi.R_ADDRPOWER_PCREL34)
   634  		if !targType.IsText() {
   635  			ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_PPC64_GLOB_DAT))
   636  			su.SetRelocSym(rIdx, syms.GOT)
   637  			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
   638  		} else {
   639  			// The address of targ is known at link time. Rewrite to "pla rt,targ" from "pld rt,targ@got"
   640  			rewritetoinsn(target, ldr, su, int64(r.Off()), MASK_PLD_PFX, OP_PLD_PFX_PCREL, OP_PLA_PFX)
   641  			pla_sfx := target.Arch.ByteOrder.Uint32(su.Data()[r.Off()+4:])&MASK_PLD_RT | OP_PLA_SFX
   642  			rewritetoinsn(target, ldr, su, int64(r.Off()+4), MASK_PLD_SFX, OP_PLD_SFX, pla_sfx)
   643  		}
   644  		return true
   645  
   646  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC_REL32):
   647  		su := ldr.MakeSymbolUpdater(s)
   648  		su.SetRelocType(rIdx, objabi.R_PCREL)
   649  		su.SetRelocAdd(rIdx, r.Add()+4)
   650  
   651  		if targType == sym.SDYNIMPORT {
   652  			ldr.Errorf(s, "unexpected R_PPC_REL32 for dyn import")
   653  		}
   654  
   655  		return true
   656  
   657  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_ADDR64):
   658  		su := ldr.MakeSymbolUpdater(s)
   659  		su.SetRelocType(rIdx, objabi.R_ADDR)
   660  		if targType == sym.SDYNIMPORT {
   661  			// These happen in .toc sections
   662  			ld.Adddynsym(ldr, target, syms, targ)
   663  
   664  			rela := ldr.MakeSymbolUpdater(syms.Rela)
   665  			rela.AddAddrPlus(target.Arch, s, int64(r.Off()))
   666  			rela.AddUint64(target.Arch, elf.R_INFO(uint32(ldr.SymDynid(targ)), uint32(elf.R_PPC64_ADDR64)))
   667  			rela.AddUint64(target.Arch, uint64(r.Add()))
   668  			su.SetRelocType(rIdx, objabi.ElfRelocOffset) // ignore during relocsym
   669  		} else if target.IsPIE() && target.IsInternal() {
   670  			// For internal linking PIE, this R_ADDR relocation cannot
   671  			// be resolved statically. We need to generate a dynamic
   672  			// relocation. Let the code below handle it.
   673  			break
   674  		}
   675  		return true
   676  
   677  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_TOC16):
   678  		su := ldr.MakeSymbolUpdater(s)
   679  		su.SetRelocType(rIdx, objabi.R_POWER_TOC)
   680  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_LO|sym.RV_CHECK_OVERFLOW)
   681  		return true
   682  
   683  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_TOC16_LO):
   684  		su := ldr.MakeSymbolUpdater(s)
   685  		su.SetRelocType(rIdx, objabi.R_POWER_TOC)
   686  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_LO)
   687  		return true
   688  
   689  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_TOC16_HA):
   690  		su := ldr.MakeSymbolUpdater(s)
   691  		su.SetRelocType(rIdx, objabi.R_POWER_TOC)
   692  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_HA|sym.RV_CHECK_OVERFLOW)
   693  		return true
   694  
   695  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_TOC16_HI):
   696  		su := ldr.MakeSymbolUpdater(s)
   697  		su.SetRelocType(rIdx, objabi.R_POWER_TOC)
   698  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_HI|sym.RV_CHECK_OVERFLOW)
   699  		return true
   700  
   701  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_TOC16_DS):
   702  		su := ldr.MakeSymbolUpdater(s)
   703  		su.SetRelocType(rIdx, objabi.R_POWER_TOC)
   704  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_DS|sym.RV_CHECK_OVERFLOW)
   705  		return true
   706  
   707  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_TOC16_LO_DS):
   708  		su := ldr.MakeSymbolUpdater(s)
   709  		su.SetRelocType(rIdx, objabi.R_POWER_TOC)
   710  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_DS)
   711  		return true
   712  
   713  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL16_LO):
   714  		su := ldr.MakeSymbolUpdater(s)
   715  		su.SetRelocType(rIdx, objabi.R_PCREL)
   716  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_LO)
   717  		su.SetRelocAdd(rIdx, r.Add()+2) // Compensate for relocation size of 2
   718  		return true
   719  
   720  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL16_HI):
   721  		su := ldr.MakeSymbolUpdater(s)
   722  		su.SetRelocType(rIdx, objabi.R_PCREL)
   723  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_HI|sym.RV_CHECK_OVERFLOW)
   724  		su.SetRelocAdd(rIdx, r.Add()+2)
   725  		return true
   726  
   727  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_REL16_HA):
   728  		su := ldr.MakeSymbolUpdater(s)
   729  		su.SetRelocType(rIdx, objabi.R_PCREL)
   730  		ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_HA|sym.RV_CHECK_OVERFLOW)
   731  		su.SetRelocAdd(rIdx, r.Add()+2)
   732  		return true
   733  
   734  	// When compiling with gcc's -fno-plt option (no PLT), the following code and relocation
   735  	// sequences may be present to call an external function:
   736  	//
   737  	//   1. addis Rx,foo@R_PPC64_PLT16_HA
   738  	//   2. ld 12,foo@R_PPC64_PLT16_LO_DS(Rx)
   739  	//   3. mtctr 12 ; foo@R_PPC64_PLTSEQ
   740  	//   4. bctrl ; foo@R_PPC64_PLTCALL
   741  	//   5. ld r2,24(r1)
   742  	//
   743  	// Note, 5 is required to follow the R_PPC64_PLTCALL. Similarly, relocations targeting
   744  	// instructions 3 and 4 are zero sized informational relocations.
   745  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_PLT16_HA),
   746  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_PPC64_PLT16_LO_DS):
   747  		su := ldr.MakeSymbolUpdater(s)
   748  		isPLT16_LO_DS := r.Type() == objabi.ElfRelocOffset+objabi.RelocType(elf.R_PPC64_PLT16_LO_DS)
   749  		if isPLT16_LO_DS {
   750  			ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_DS)
   751  		} else {
   752  			ldr.SetRelocVariant(s, rIdx, sym.RV_POWER_HA|sym.RV_CHECK_OVERFLOW)
   753  		}
   754  		su.SetRelocType(rIdx, objabi.R_POWER_TOC)
   755  		if targType == sym.SDYNIMPORT {
   756  			// This is an external symbol, make space in the GOT and retarget the reloc.
   757  			ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_PPC64_GLOB_DAT))
   758  			su.SetRelocSym(rIdx, syms.GOT)
   759  			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
   760  		} else if targType.IsText() {
   761  			if isPLT16_LO_DS {
   762  				// Expect an ld opcode to nop
   763  				rewritetonop(target, ldr, su, int64(r.Off()), MASK_OP_LD, OP_LD)
   764  			} else {
   765  				// Expect an addis opcode to nop
   766  				rewritetonop(target, ldr, su, int64(r.Off()), MASK_OP_ADDIS, OP_ADDIS)
   767  			}
   768  			// And we can ignore this reloc now.
   769  			su.SetRelocType(rIdx, objabi.ElfRelocOffset)
   770  		} else {
   771  			ldr.Errorf(s, "unexpected PLT relocation target symbol type %s", targType.String())
   772  		}
   773  		return true
   774  	}
   775  
   776  	// Handle references to ELF symbols from our own object files.
   777  	relocs := ldr.Relocs(s)
   778  	r = relocs.At(rIdx)
   779  
   780  	switch r.Type() {
   781  	case objabi.R_ADDR:
   782  		if ldr.SymType(s).IsText() {
   783  			log.Fatalf("R_ADDR relocation in text symbol %s is unsupported\n", ldr.SymName(s))
   784  		}
   785  		if target.IsPIE() && target.IsInternal() {
   786  			// When internally linking, generate dynamic relocations
   787  			// for all typical R_ADDR relocations. The exception
   788  			// are those R_ADDR that are created as part of generating
   789  			// the dynamic relocations and must be resolved statically.
   790  			//
   791  			// There are three phases relevant to understanding this:
   792  			//
   793  			//	dodata()  // we are here
   794  			//	address() // symbol address assignment
   795  			//	reloc()   // resolution of static R_ADDR relocs
   796  			//
   797  			// At this point symbol addresses have not been
   798  			// assigned yet (as the final size of the .rela section
   799  			// will affect the addresses), and so we cannot write
   800  			// the Elf64_Rela.r_offset now. Instead we delay it
   801  			// until after the 'address' phase of the linker is
   802  			// complete. We do this via Addaddrplus, which creates
   803  			// a new R_ADDR relocation which will be resolved in
   804  			// the 'reloc' phase.
   805  			//
   806  			// These synthetic static R_ADDR relocs must be skipped
   807  			// now, or else we will be caught in an infinite loop
   808  			// of generating synthetic relocs for our synthetic
   809  			// relocs.
   810  			//
   811  			// Furthermore, the rela sections contain dynamic
   812  			// relocations with R_ADDR relocations on
   813  			// Elf64_Rela.r_offset. This field should contain the
   814  			// symbol offset as determined by reloc(), not the
   815  			// final dynamically linked address as a dynamic
   816  			// relocation would provide.
   817  			switch ldr.SymName(s) {
   818  			case ".dynsym", ".rela", ".rela.plt", ".got.plt", ".dynamic":
   819  				return false
   820  			}
   821  		} else {
   822  			// Either internally linking a static executable,
   823  			// in which case we can resolve these relocations
   824  			// statically in the 'reloc' phase, or externally
   825  			// linking, in which case the relocation will be
   826  			// prepared in the 'reloc' phase and passed to the
   827  			// external linker in the 'asmb' phase.
   828  			if t := ldr.SymType(s); !t.IsDATA() && !t.IsRODATA() {
   829  				break
   830  			}
   831  		}
   832  		// Generate R_PPC64_RELATIVE relocations for best
   833  		// efficiency in the dynamic linker.
   834  		//
   835  		// As noted above, symbol addresses have not been
   836  		// assigned yet, so we can't generate the final reloc
   837  		// entry yet. We ultimately want:
   838  		//
   839  		// r_offset = s + r.Off
   840  		// r_info = R_PPC64_RELATIVE
   841  		// r_addend = targ + r.Add
   842  		//
   843  		// The dynamic linker will set *offset = base address +
   844  		// addend.
   845  		//
   846  		// AddAddrPlus is used for r_offset and r_addend to
   847  		// generate new R_ADDR relocations that will update
   848  		// these fields in the 'reloc' phase.
   849  		rela := ldr.MakeSymbolUpdater(syms.Rela)
   850  		rela.AddAddrPlus(target.Arch, s, int64(r.Off()))
   851  		if r.Siz() == 8 {
   852  			rela.AddUint64(target.Arch, elf.R_INFO(0, uint32(elf.R_PPC64_RELATIVE)))
   853  		} else {
   854  			ldr.Errorf(s, "unexpected relocation for dynamic symbol %s", ldr.SymName(targ))
   855  		}
   856  		rela.AddAddrPlus(target.Arch, targ, int64(r.Add()))
   857  
   858  		// Not mark r done here. So we still apply it statically,
   859  		// so in the file content we'll also have the right offset
   860  		// to the relocation target. So it can be examined statically
   861  		// (e.g. go version).
   862  		return true
   863  	}
   864  
   865  	return false
   866  }
   867  
   868  func xcoffreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, sectoff int64) bool {
   869  	rs := r.Xsym
   870  
   871  	emitReloc := func(v uint16, off uint64) {
   872  		out.Write64(uint64(sectoff) + off)
   873  		out.Write32(uint32(ldr.SymDynid(rs)))
   874  		out.Write16(v)
   875  	}
   876  
   877  	var v uint16
   878  	switch r.Type {
   879  	default:
   880  		return false
   881  	case objabi.R_ADDR, objabi.R_DWARFSECREF:
   882  		v = ld.XCOFF_R_POS
   883  		if r.Size == 4 {
   884  			v |= 0x1F << 8
   885  		} else {
   886  			v |= 0x3F << 8
   887  		}
   888  		emitReloc(v, 0)
   889  	case objabi.R_ADDRPOWER_TOCREL:
   890  	case objabi.R_ADDRPOWER_TOCREL_DS:
   891  		emitReloc(ld.XCOFF_R_TOCU|(0x0F<<8), 2)
   892  		emitReloc(ld.XCOFF_R_TOCL|(0x0F<<8), 6)
   893  	case objabi.R_POWER_TLS_LE:
   894  		// This only supports 16b relocations.  It is fixed up in archreloc.
   895  		emitReloc(ld.XCOFF_R_TLS_LE|0x0F<<8, 2)
   896  	case objabi.R_CALLPOWER:
   897  		if r.Size != 4 {
   898  			return false
   899  		}
   900  		emitReloc(ld.XCOFF_R_RBR|0x19<<8, 0)
   901  	case objabi.R_XCOFFREF:
   902  		emitReloc(ld.XCOFF_R_REF|0x3F<<8, 0)
   903  	}
   904  	return true
   905  }
   906  
   907  func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, ri int, sectoff int64) bool {
   908  	// Beware that bit0~bit15 start from the third byte of an instruction in Big-Endian machines.
   909  	rt := r.Type
   910  	if rt == objabi.R_ADDR || rt == objabi.R_POWER_TLS || rt == objabi.R_CALLPOWER || rt == objabi.R_DWARFSECREF {
   911  	} else {
   912  		if ctxt.Arch.ByteOrder == binary.BigEndian {
   913  			sectoff += 2
   914  		}
   915  	}
   916  	out.Write64(uint64(sectoff))
   917  
   918  	elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
   919  	switch rt {
   920  	default:
   921  		return false
   922  	case objabi.R_ADDR, objabi.R_DWARFSECREF:
   923  		switch r.Size {
   924  		case 4:
   925  			out.Write64(uint64(elf.R_PPC64_ADDR32) | uint64(elfsym)<<32)
   926  		case 8:
   927  			out.Write64(uint64(elf.R_PPC64_ADDR64) | uint64(elfsym)<<32)
   928  		default:
   929  			return false
   930  		}
   931  	case objabi.R_ADDRPOWER_D34:
   932  		out.Write64(uint64(elf.R_PPC64_D34) | uint64(elfsym)<<32)
   933  	case objabi.R_ADDRPOWER_PCREL34:
   934  		out.Write64(uint64(elf.R_PPC64_PCREL34) | uint64(elfsym)<<32)
   935  	case objabi.R_POWER_TLS:
   936  		out.Write64(uint64(elf.R_PPC64_TLS) | uint64(elfsym)<<32)
   937  	case objabi.R_POWER_TLS_LE:
   938  		out.Write64(uint64(elf.R_PPC64_TPREL16_HA) | uint64(elfsym)<<32)
   939  		out.Write64(uint64(r.Xadd))
   940  		out.Write64(uint64(sectoff + 4))
   941  		out.Write64(uint64(elf.R_PPC64_TPREL16_LO) | uint64(elfsym)<<32)
   942  	case objabi.R_POWER_TLS_LE_TPREL34:
   943  		out.Write64(uint64(elf.R_PPC64_TPREL34) | uint64(elfsym)<<32)
   944  	case objabi.R_POWER_TLS_IE_PCREL34:
   945  		out.Write64(uint64(elf.R_PPC64_GOT_TPREL_PCREL34) | uint64(elfsym)<<32)
   946  	case objabi.R_POWER_TLS_IE:
   947  		out.Write64(uint64(elf.R_PPC64_GOT_TPREL16_HA) | uint64(elfsym)<<32)
   948  		out.Write64(uint64(r.Xadd))
   949  		out.Write64(uint64(sectoff + 4))
   950  		out.Write64(uint64(elf.R_PPC64_GOT_TPREL16_LO_DS) | uint64(elfsym)<<32)
   951  	case objabi.R_ADDRPOWER:
   952  		out.Write64(uint64(elf.R_PPC64_ADDR16_HA) | uint64(elfsym)<<32)
   953  		out.Write64(uint64(r.Xadd))
   954  		out.Write64(uint64(sectoff + 4))
   955  		out.Write64(uint64(elf.R_PPC64_ADDR16_LO) | uint64(elfsym)<<32)
   956  	case objabi.R_ADDRPOWER_DS:
   957  		out.Write64(uint64(elf.R_PPC64_ADDR16_HA) | uint64(elfsym)<<32)
   958  		out.Write64(uint64(r.Xadd))
   959  		out.Write64(uint64(sectoff + 4))
   960  		out.Write64(uint64(elf.R_PPC64_ADDR16_LO_DS) | uint64(elfsym)<<32)
   961  	case objabi.R_ADDRPOWER_GOT:
   962  		out.Write64(uint64(elf.R_PPC64_GOT16_HA) | uint64(elfsym)<<32)
   963  		out.Write64(uint64(r.Xadd))
   964  		out.Write64(uint64(sectoff + 4))
   965  		out.Write64(uint64(elf.R_PPC64_GOT16_LO_DS) | uint64(elfsym)<<32)
   966  	case objabi.R_ADDRPOWER_GOT_PCREL34:
   967  		out.Write64(uint64(elf.R_PPC64_GOT_PCREL34) | uint64(elfsym)<<32)
   968  	case objabi.R_ADDRPOWER_PCREL:
   969  		out.Write64(uint64(elf.R_PPC64_REL16_HA) | uint64(elfsym)<<32)
   970  		out.Write64(uint64(r.Xadd))
   971  		out.Write64(uint64(sectoff + 4))
   972  		out.Write64(uint64(elf.R_PPC64_REL16_LO) | uint64(elfsym)<<32)
   973  		r.Xadd += 4
   974  	case objabi.R_ADDRPOWER_TOCREL:
   975  		out.Write64(uint64(elf.R_PPC64_TOC16_HA) | uint64(elfsym)<<32)
   976  		out.Write64(uint64(r.Xadd))
   977  		out.Write64(uint64(sectoff + 4))
   978  		out.Write64(uint64(elf.R_PPC64_TOC16_LO) | uint64(elfsym)<<32)
   979  	case objabi.R_ADDRPOWER_TOCREL_DS:
   980  		out.Write64(uint64(elf.R_PPC64_TOC16_HA) | uint64(elfsym)<<32)
   981  		out.Write64(uint64(r.Xadd))
   982  		out.Write64(uint64(sectoff + 4))
   983  		out.Write64(uint64(elf.R_PPC64_TOC16_LO_DS) | uint64(elfsym)<<32)
   984  	case objabi.R_CALLPOWER:
   985  		if r.Size != 4 {
   986  			return false
   987  		}
   988  		if !hasPCrel {
   989  			out.Write64(uint64(elf.R_PPC64_REL24) | uint64(elfsym)<<32)
   990  		} else {
   991  			// TOC is not used in PCrel compiled Go code.
   992  			out.Write64(uint64(elf.R_PPC64_REL24_NOTOC) | uint64(elfsym)<<32)
   993  		}
   994  
   995  	}
   996  	out.Write64(uint64(r.Xadd))
   997  
   998  	return true
   999  }
  1000  
  1001  func elfsetupplt(ctxt *ld.Link, ldr *loader.Loader, plt, got *loader.SymbolBuilder, dynamic loader.Sym) {
  1002  	if plt.Size() == 0 {
  1003  		// The dynamic linker stores the address of the
  1004  		// dynamic resolver and the DSO identifier in the two
  1005  		// doublewords at the beginning of the .plt section
  1006  		// before the PLT array. Reserve space for these.
  1007  		plt.SetSize(16)
  1008  	}
  1009  }
  1010  
  1011  func machoreloc1(*sys.Arch, *ld.OutBuf, *loader.Loader, loader.Sym, loader.ExtReloc, int64) bool {
  1012  	return false
  1013  }
  1014  
  1015  // Return the value of .TOC. for symbol s
  1016  func symtoc(ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym) int64 {
  1017  	v := ldr.SymVersion(s)
  1018  	if out := ldr.OuterSym(s); out != 0 {
  1019  		v = ldr.SymVersion(out)
  1020  	}
  1021  
  1022  	toc := syms.DotTOC[v]
  1023  	if toc == 0 {
  1024  		ldr.Errorf(s, "TOC-relative relocation in object without .TOC.")
  1025  		return 0
  1026  	}
  1027  
  1028  	return ldr.SymValue(toc)
  1029  }
  1030  
  1031  // archreloctoc relocates a TOC relative symbol.
  1032  func archreloctoc(ldr *loader.Loader, target *ld.Target, syms *ld.ArchSyms, r loader.Reloc, s loader.Sym, val int64) int64 {
  1033  	rs := r.Sym()
  1034  	var o1, o2 uint32
  1035  	var t int64
  1036  	useAddi := false
  1037  
  1038  	if target.IsBigEndian() {
  1039  		o1 = uint32(val >> 32)
  1040  		o2 = uint32(val)
  1041  	} else {
  1042  		o1 = uint32(val)
  1043  		o2 = uint32(val >> 32)
  1044  	}
  1045  
  1046  	// On AIX, TOC data accesses are always made indirectly against R2 (a sequence of addis+ld+load/store). If the
  1047  	// The target of the load is known, the sequence can be written into addis+addi+load/store. On Linux,
  1048  	// TOC data accesses are always made directly against R2 (e.g addis+load/store).
  1049  	if target.IsAIX() {
  1050  		if !strings.HasPrefix(ldr.SymName(rs), "TOC.") {
  1051  			ldr.Errorf(s, "archreloctoc called for a symbol without TOC anchor")
  1052  		}
  1053  		relocs := ldr.Relocs(rs)
  1054  		tarSym := relocs.At(0).Sym()
  1055  
  1056  		if target.IsInternal() && tarSym != 0 && ldr.AttrReachable(tarSym) && ldr.SymSect(tarSym).Seg == &ld.Segdata {
  1057  			t = ldr.SymValue(tarSym) + r.Add() - ldr.SymValue(syms.TOC)
  1058  			// change ld to addi in the second instruction
  1059  			o2 = (o2 & 0x03FF0000) | 0xE<<26
  1060  			useAddi = true
  1061  		} else {
  1062  			t = ldr.SymValue(rs) + r.Add() - ldr.SymValue(syms.TOC)
  1063  		}
  1064  	} else {
  1065  		t = ldr.SymValue(rs) + r.Add() - symtoc(ldr, syms, s)
  1066  	}
  1067  
  1068  	if t != int64(int32(t)) {
  1069  		ldr.Errorf(s, "TOC relocation for %s is too big to relocate %s: 0x%x", ldr.SymName(s), rs, t)
  1070  	}
  1071  
  1072  	if t&0x8000 != 0 {
  1073  		t += 0x10000
  1074  	}
  1075  
  1076  	o1 |= uint32((t >> 16) & 0xFFFF)
  1077  
  1078  	switch r.Type() {
  1079  	case objabi.R_ADDRPOWER_TOCREL_DS:
  1080  		if useAddi {
  1081  			o2 |= uint32(t) & 0xFFFF
  1082  		} else {
  1083  			if t&3 != 0 {
  1084  				ldr.Errorf(s, "bad DS reloc for %s: %d", ldr.SymName(s), ldr.SymValue(rs))
  1085  			}
  1086  			o2 |= uint32(t) & 0xFFFC
  1087  		}
  1088  	case objabi.R_ADDRPOWER_TOCREL:
  1089  		o2 |= uint32(t) & 0xffff
  1090  	default:
  1091  		return -1
  1092  	}
  1093  
  1094  	if target.IsBigEndian() {
  1095  		return int64(o1)<<32 | int64(o2)
  1096  	}
  1097  	return int64(o2)<<32 | int64(o1)
  1098  }
  1099  
  1100  // archrelocaddr relocates a symbol address.
  1101  // This code is for linux only.
  1102  func archrelocaddr(ldr *loader.Loader, target *ld.Target, syms *ld.ArchSyms, r loader.Reloc, s loader.Sym, val int64) int64 {
  1103  	rs := r.Sym()
  1104  	if target.IsAIX() {
  1105  		ldr.Errorf(s, "archrelocaddr called for %s relocation\n", ldr.SymName(rs))
  1106  	}
  1107  	o1, o2 := unpackInstPair(target, val)
  1108  
  1109  	// Verify resulting address fits within a 31 bit (2GB) address space.
  1110  	// This is a restriction arising  from the usage of lis (HA) + d-form
  1111  	// (LO) instruction sequences used to implement absolute relocations
  1112  	// on PPC64 prior to ISA 3.1 (P10). For consistency, maintain this
  1113  	// restriction for ISA 3.1 unless it becomes problematic.
  1114  	t := ldr.SymAddr(rs) + r.Add()
  1115  	if t < 0 || t >= 1<<31 {
  1116  		ldr.Errorf(s, "relocation for %s is too big (>=2G): 0x%x", ldr.SymName(s), ldr.SymValue(rs))
  1117  	}
  1118  
  1119  	// Note, relocations imported from external objects may not have cleared bits
  1120  	// within a relocatable field. They need cleared before applying the relocation.
  1121  	switch r.Type() {
  1122  	case objabi.R_ADDRPOWER_PCREL34:
  1123  		// S + A - P
  1124  		t -= (ldr.SymValue(s) + int64(r.Off()))
  1125  		o1 &^= 0x3ffff
  1126  		o2 &^= 0x0ffff
  1127  		o1 |= computePrefix34HI(t)
  1128  		o2 |= computeLO(int32(t))
  1129  	case objabi.R_ADDRPOWER_D34:
  1130  		o1 &^= 0x3ffff
  1131  		o2 &^= 0x0ffff
  1132  		o1 |= computePrefix34HI(t)
  1133  		o2 |= computeLO(int32(t))
  1134  	case objabi.R_ADDRPOWER:
  1135  		o1 &^= 0xffff
  1136  		o2 &^= 0xffff
  1137  		o1 |= computeHA(int32(t))
  1138  		o2 |= computeLO(int32(t))
  1139  	case objabi.R_ADDRPOWER_DS:
  1140  		o1 &^= 0xffff
  1141  		o2 &^= 0xfffc
  1142  		o1 |= computeHA(int32(t))
  1143  		o2 |= computeLO(int32(t))
  1144  		if t&3 != 0 {
  1145  			ldr.Errorf(s, "bad DS reloc for %s: %d", ldr.SymName(s), ldr.SymValue(rs))
  1146  		}
  1147  	default:
  1148  		return -1
  1149  	}
  1150  
  1151  	return packInstPair(target, o1, o2)
  1152  }
  1153  
  1154  // Determine if the code was compiled so that the TOC register R2 is initialized and maintained.
  1155  func r2Valid(ctxt *ld.Link) bool {
  1156  	return isLinkingPIC(ctxt)
  1157  }
  1158  
  1159  // Determine if this is linking a position-independent binary.
  1160  func isLinkingPIC(ctxt *ld.Link) bool {
  1161  	switch ctxt.BuildMode {
  1162  	case ld.BuildModeCArchive, ld.BuildModeCShared, ld.BuildModePIE, ld.BuildModeShared, ld.BuildModePlugin:
  1163  		return true
  1164  	}
  1165  	// -linkshared option
  1166  	return ctxt.IsSharedGoLink()
  1167  }
  1168  
  1169  // resolve direct jump relocation r in s, and add trampoline if necessary.
  1170  func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
  1171  
  1172  	// Trampolines are created if the branch offset is too large and the linker cannot insert a call stub to handle it.
  1173  	// For internal linking, trampolines are always created for long calls.
  1174  	// For external linking, the linker can insert a call stub to handle a long call, but depends on having the TOC address in
  1175  	// r2.  For those build modes with external linking where the TOC address is not maintained in r2, trampolines must be created.
  1176  	if ctxt.IsExternal() && r2Valid(ctxt) {
  1177  		// The TOC pointer is valid. The external linker will insert trampolines.
  1178  		return
  1179  	}
  1180  
  1181  	relocs := ldr.Relocs(s)
  1182  	r := relocs.At(ri)
  1183  	var t int64
  1184  	// ldr.SymValue(rs) == 0 indicates a cross-package jump to a function that is not yet
  1185  	// laid out. Conservatively use a trampoline. This should be rare, as we lay out packages
  1186  	// in dependency order.
  1187  	if ldr.SymValue(rs) != 0 {
  1188  		t = ldr.SymValue(rs) + r.Add() - (ldr.SymValue(s) + int64(r.Off()))
  1189  	}
  1190  	switch r.Type() {
  1191  	case objabi.R_CALLPOWER:
  1192  		// If branch offset is too far then create a trampoline.
  1193  		if (ctxt.IsExternal() && ldr.SymSect(s) != ldr.SymSect(rs)) || (ctxt.IsInternal() && int64(int32(t<<6)>>6) != t) || ldr.SymValue(rs) == 0 || (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {
  1194  			var tramp loader.Sym
  1195  			for i := 0; ; i++ {
  1196  
  1197  				// Using r.Add as part of the name is significant in functions like duffzero where the call
  1198  				// target is at some offset within the function.  Calls to duff+8 and duff+256 must appear as
  1199  				// distinct trampolines.
  1200  
  1201  				oName := ldr.SymName(rs)
  1202  				name := oName
  1203  				if r.Add() == 0 {
  1204  					name += fmt.Sprintf("-tramp%d", i)
  1205  				} else {
  1206  					name += fmt.Sprintf("%+x-tramp%d", r.Add(), i)
  1207  				}
  1208  
  1209  				// Look up the trampoline in case it already exists
  1210  
  1211  				tramp = ldr.LookupOrCreateSym(name, int(ldr.SymVersion(rs)))
  1212  				if oName == "runtime.deferreturn" {
  1213  					ldr.SetIsDeferReturnTramp(tramp, true)
  1214  				}
  1215  				if ldr.SymValue(tramp) == 0 {
  1216  					break
  1217  				}
  1218  				// Note, the trampoline is always called directly. The addend of the original relocation is accounted for in the
  1219  				// trampoline itself.
  1220  				t = ldr.SymValue(tramp) - (ldr.SymValue(s) + int64(r.Off()))
  1221  
  1222  				// With internal linking, the trampoline can be used if it is not too far.
  1223  				// With external linking, the trampoline must be in this section for it to be reused.
  1224  				if (ctxt.IsInternal() && int64(int32(t<<6)>>6) == t) || (ctxt.IsExternal() && ldr.SymSect(s) == ldr.SymSect(tramp)) {
  1225  					break
  1226  				}
  1227  			}
  1228  			if ldr.SymType(tramp) == 0 {
  1229  				trampb := ldr.MakeSymbolUpdater(tramp)
  1230  				ctxt.AddTramp(trampb, ldr.SymType(s))
  1231  				gentramp(ctxt, ldr, trampb, rs, r.Add())
  1232  			}
  1233  			sb := ldr.MakeSymbolUpdater(s)
  1234  			relocs := sb.Relocs()
  1235  			r := relocs.At(ri)
  1236  			r.SetSym(tramp)
  1237  			r.SetAdd(0) // This was folded into the trampoline target address
  1238  		}
  1239  	default:
  1240  		ctxt.Errorf(s, "trampoline called with non-jump reloc: %d (%s)", r.Type(), sym.RelocName(ctxt.Arch, r.Type()))
  1241  	}
  1242  }
  1243  
  1244  func gentramp(ctxt *ld.Link, ldr *loader.Loader, tramp *loader.SymbolBuilder, target loader.Sym, offset int64) {
  1245  	tramp.SetSize(16) // 4 instructions
  1246  	P := make([]byte, tramp.Size())
  1247  	var o1, o2 uint32
  1248  
  1249  	// ELFv2 save/restore functions use R0/R12 in special ways, therefore trampolines
  1250  	// as generated here will not always work correctly.
  1251  	if strings.HasPrefix(ldr.SymName(target), "runtime.elf_") {
  1252  		log.Fatalf("Internal linker does not support trampolines to ELFv2 ABI"+
  1253  			" register save/restore function %s", ldr.SymName(target))
  1254  	}
  1255  
  1256  	if ctxt.IsAIX() {
  1257  		// On AIX, the address is retrieved with a TOC symbol.
  1258  		// For internal linking, the "Linux" way might still be used.
  1259  		// However, all text symbols are accessed with a TOC symbol as
  1260  		// text relocations aren't supposed to be possible.
  1261  		// So, keep using the external linking way to be more AIX friendly.
  1262  		o1 = uint32(OP_ADDIS_R12_R2) // addis r12,  r2, toctargetaddr hi
  1263  		o2 = uint32(OP_LD_R12_R12)   // ld    r12, r12, toctargetaddr lo
  1264  
  1265  		toctramp := ldr.CreateSymForUpdate("TOC."+ldr.SymName(tramp.Sym()), 0)
  1266  		toctramp.SetType(sym.SXCOFFTOC)
  1267  		toctramp.AddAddrPlus(ctxt.Arch, target, offset)
  1268  
  1269  		r, _ := tramp.AddRel(objabi.R_ADDRPOWER_TOCREL_DS)
  1270  		r.SetOff(0)
  1271  		r.SetSiz(8) // generates 2 relocations: HA + LO
  1272  		r.SetSym(toctramp.Sym())
  1273  	} else if hasPCrel {
  1274  		// pla r12, addr (PCrel). This works for static or PIC, with or without a valid TOC pointer.
  1275  		o1 = uint32(OP_PLA_PFX)
  1276  		o2 = uint32(OP_PLA_SFX_R12) // pla r12, addr
  1277  
  1278  		// The trampoline's position is not known yet, insert a relocation.
  1279  		r, _ := tramp.AddRel(objabi.R_ADDRPOWER_PCREL34)
  1280  		r.SetOff(0)
  1281  		r.SetSiz(8) // This spans 2 words.
  1282  		r.SetSym(target)
  1283  		r.SetAdd(offset)
  1284  	} else {
  1285  		// Used for default build mode for an executable
  1286  		// Address of the call target is generated using
  1287  		// relocation and doesn't depend on r2 (TOC).
  1288  		o1 = uint32(OP_LIS_R12)      // lis  r12,targetaddr hi
  1289  		o2 = uint32(OP_ADDI_R12_R12) // addi r12,r12,targetaddr lo
  1290  
  1291  		t := ldr.SymValue(target)
  1292  		if t == 0 || r2Valid(ctxt) || ctxt.IsExternal() {
  1293  			// Target address is unknown, generate relocations
  1294  			r, _ := tramp.AddRel(objabi.R_ADDRPOWER)
  1295  			if r2Valid(ctxt) {
  1296  				// Use a TOC relative address if R2 holds the TOC pointer
  1297  				o1 |= uint32(2 << 16) // Transform lis r31,ha into addis r31,r2,ha
  1298  				r.SetType(objabi.R_ADDRPOWER_TOCREL)
  1299  			}
  1300  			r.SetOff(0)
  1301  			r.SetSiz(8) // generates 2 relocations: HA + LO
  1302  			r.SetSym(target)
  1303  			r.SetAdd(offset)
  1304  		} else {
  1305  			// The target address is known, resolve it
  1306  			t += offset
  1307  			o1 |= (uint32(t) + 0x8000) >> 16 // HA
  1308  			o2 |= uint32(t) & 0xFFFF         // LO
  1309  		}
  1310  	}
  1311  
  1312  	o3 := uint32(OP_MTCTR_R12) // mtctr r12
  1313  	o4 := uint32(OP_BCTR)      // bctr
  1314  	ctxt.Arch.ByteOrder.PutUint32(P, o1)
  1315  	ctxt.Arch.ByteOrder.PutUint32(P[4:], o2)
  1316  	ctxt.Arch.ByteOrder.PutUint32(P[8:], o3)
  1317  	ctxt.Arch.ByteOrder.PutUint32(P[12:], o4)
  1318  	tramp.SetData(P)
  1319  }
  1320  
  1321  // Unpack a pair of 32 bit instruction words from
  1322  // a 64 bit relocation into instN and instN+1 in endian order.
  1323  func unpackInstPair(target *ld.Target, r int64) (uint32, uint32) {
  1324  	if target.IsBigEndian() {
  1325  		return uint32(r >> 32), uint32(r)
  1326  	}
  1327  	return uint32(r), uint32(r >> 32)
  1328  }
  1329  
  1330  // Pack a pair of 32 bit instruction words o1, o2 into 64 bit relocation
  1331  // in endian order.
  1332  func packInstPair(target *ld.Target, o1, o2 uint32) int64 {
  1333  	if target.IsBigEndian() {
  1334  		return (int64(o1) << 32) | int64(o2)
  1335  	}
  1336  	return int64(o1) | (int64(o2) << 32)
  1337  }
  1338  
  1339  // Compute the high-adjusted value (always a signed 32b value) per the ELF ABI.
  1340  // The returned value is always 0 <= x <= 0xFFFF.
  1341  func computeHA(val int32) uint32 {
  1342  	return uint32(uint16((val + 0x8000) >> 16))
  1343  }
  1344  
  1345  // Compute the low value (the lower 16 bits of any 32b value) per the ELF ABI.
  1346  // The returned value is always 0 <= x <= 0xFFFF.
  1347  func computeLO(val int32) uint32 {
  1348  	return uint32(uint16(val))
  1349  }
  1350  
  1351  // Compute the high 18 bits of a signed 34b constant. Used to pack the high 18 bits
  1352  // of a prefix34 relocation field. This assumes the input is already restricted to
  1353  // 34 bits.
  1354  func computePrefix34HI(val int64) uint32 {
  1355  	return uint32((val >> 16) & 0x3FFFF)
  1356  }
  1357  
  1358  func computeTLSLEReloc(target *ld.Target, ldr *loader.Loader, rs, s loader.Sym) int64 {
  1359  	// The thread pointer points 0x7000 bytes after the start of the
  1360  	// thread local storage area as documented in section "3.7.2 TLS
  1361  	// Runtime Handling" of "Power Architecture 64-Bit ELF V2 ABI
  1362  	// Specification".
  1363  	v := ldr.SymValue(rs) - 0x7000
  1364  	if target.IsAIX() {
  1365  		// On AIX, the thread pointer points 0x7800 bytes after
  1366  		// the TLS.
  1367  		v -= 0x800
  1368  	}
  1369  
  1370  	if int64(int32(v)) != v {
  1371  		ldr.Errorf(s, "TLS offset out of range %d", v)
  1372  	}
  1373  	return v
  1374  }
  1375  
  1376  func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loader.Reloc, s loader.Sym, val int64) (relocatedOffset int64, nExtReloc int, ok bool) {
  1377  	rs := r.Sym()
  1378  	if target.IsExternal() {
  1379  		// On AIX, relocations (except TLS ones) must be also done to the
  1380  		// value with the current addresses.
  1381  		switch rt := r.Type(); rt {
  1382  		default:
  1383  			if !target.IsAIX() {
  1384  				return val, nExtReloc, false
  1385  			}
  1386  		case objabi.R_POWER_TLS, objabi.R_POWER_TLS_IE_PCREL34, objabi.R_POWER_TLS_LE_TPREL34, objabi.R_ADDRPOWER_GOT_PCREL34:
  1387  			nExtReloc = 1
  1388  			return val, nExtReloc, true
  1389  		case objabi.R_POWER_TLS_LE, objabi.R_POWER_TLS_IE:
  1390  			if target.IsAIX() && rt == objabi.R_POWER_TLS_LE {
  1391  				// Fixup val, an addis/addi pair of instructions, which generate a 32b displacement
  1392  				// from the threadpointer (R13), into a 16b relocation. XCOFF only supports 16b
  1393  				// TLS LE relocations. Likewise, verify this is an addis/addi sequence.
  1394  				const expectedOpcodes = 0x3C00000038000000
  1395  				const expectedOpmasks = 0xFC000000FC000000
  1396  				if uint64(val)&expectedOpmasks != expectedOpcodes {
  1397  					ldr.Errorf(s, "relocation for %s+%d is not an addis/addi pair: %16x", ldr.SymName(rs), r.Off(), uint64(val))
  1398  				}
  1399  				nval := (int64(uint32(0x380d0000)) | val&0x03e00000) << 32 // addi rX, r13, $0
  1400  				nval |= int64(OP_NOP)                                      // nop
  1401  				val = nval
  1402  				nExtReloc = 1
  1403  			} else {
  1404  				nExtReloc = 2
  1405  			}
  1406  			return val, nExtReloc, true
  1407  		case objabi.R_ADDRPOWER,
  1408  			objabi.R_ADDRPOWER_DS,
  1409  			objabi.R_ADDRPOWER_TOCREL,
  1410  			objabi.R_ADDRPOWER_TOCREL_DS,
  1411  			objabi.R_ADDRPOWER_GOT,
  1412  			objabi.R_ADDRPOWER_PCREL:
  1413  			nExtReloc = 2 // need two ELF relocations, see elfreloc1
  1414  			if !target.IsAIX() {
  1415  				return val, nExtReloc, true
  1416  			}
  1417  		case objabi.R_CALLPOWER, objabi.R_ADDRPOWER_D34, objabi.R_ADDRPOWER_PCREL34:
  1418  			nExtReloc = 1
  1419  			if !target.IsAIX() {
  1420  				return val, nExtReloc, true
  1421  			}
  1422  		}
  1423  	}
  1424  
  1425  	switch r.Type() {
  1426  	case objabi.R_ADDRPOWER_TOCREL, objabi.R_ADDRPOWER_TOCREL_DS:
  1427  		return archreloctoc(ldr, target, syms, r, s, val), nExtReloc, true
  1428  	case objabi.R_ADDRPOWER, objabi.R_ADDRPOWER_DS, objabi.R_ADDRPOWER_D34, objabi.R_ADDRPOWER_PCREL34:
  1429  		return archrelocaddr(ldr, target, syms, r, s, val), nExtReloc, true
  1430  	case objabi.R_CALLPOWER:
  1431  		// Bits 6 through 29 = (S + A - P) >> 2
  1432  
  1433  		t := ldr.SymValue(rs) + r.Add() - (ldr.SymValue(s) + int64(r.Off()))
  1434  
  1435  		tgtName := ldr.SymName(rs)
  1436  
  1437  		// If we are linking PIE or shared code, non-PCrel golang generated object files have an extra 2 instruction prologue
  1438  		// to regenerate the TOC pointer from R12.  The exception are two special case functions tested below.  Note,
  1439  		// local call offsets for externally generated objects are accounted for when converting into golang relocs.
  1440  		if !hasPCrel && !ldr.AttrExternal(rs) && ldr.AttrShared(rs) && tgtName != "runtime.duffzero" && tgtName != "runtime.duffcopy" {
  1441  			// Furthermore, only apply the offset if the target looks like the start of a function call.
  1442  			if r.Add() == 0 && ldr.SymType(rs).IsText() {
  1443  				t += 8
  1444  			}
  1445  		}
  1446  
  1447  		if t&3 != 0 {
  1448  			ldr.Errorf(s, "relocation for %s+%d is not aligned: %d", ldr.SymName(rs), r.Off(), t)
  1449  		}
  1450  		// If branch offset is too far then create a trampoline.
  1451  
  1452  		if int64(int32(t<<6)>>6) != t {
  1453  			ldr.Errorf(s, "direct call too far: %s %x", ldr.SymName(rs), t)
  1454  		}
  1455  		return val | int64(uint32(t)&^0xfc000003), nExtReloc, true
  1456  	case objabi.R_POWER_TOC: // S + A - .TOC.
  1457  		return ldr.SymValue(rs) + r.Add() - symtoc(ldr, syms, s), nExtReloc, true
  1458  
  1459  	case objabi.R_ADDRPOWER_PCREL: // S + A - P
  1460  		t := ldr.SymValue(rs) + r.Add() - (ldr.SymValue(s) + int64(r.Off()))
  1461  		ha, l := unpackInstPair(target, val)
  1462  		l |= computeLO(int32(t))
  1463  		ha |= computeHA(int32(t))
  1464  		return packInstPair(target, ha, l), nExtReloc, true
  1465  
  1466  	case objabi.R_POWER_TLS:
  1467  		const OP_ADD = 31<<26 | 266<<1
  1468  		const MASK_OP_ADD = 0x3F<<26 | 0x1FF<<1
  1469  		if val&MASK_OP_ADD != OP_ADD {
  1470  			ldr.Errorf(s, "R_POWER_TLS reloc only supports XO form ADD, not %08X", val)
  1471  		}
  1472  		// Verify RB is R13 in ADD RA,RB,RT.
  1473  		if (val>>11)&0x1F != 13 {
  1474  			// If external linking is made to support this, it may expect the linker to rewrite RB.
  1475  			ldr.Errorf(s, "R_POWER_TLS reloc requires R13 in RB (%08X).", uint32(val))
  1476  		}
  1477  		return val, nExtReloc, true
  1478  
  1479  	case objabi.R_POWER_TLS_IE:
  1480  		// Convert TLS_IE relocation to TLS_LE if supported.
  1481  		if !(target.IsPIE() && target.IsElf()) {
  1482  			log.Fatalf("cannot handle R_POWER_TLS_IE (sym %s) when linking non-PIE, non-ELF binaries internally", ldr.SymName(s))
  1483  		}
  1484  
  1485  		// We are an ELF binary, we can safely convert to TLS_LE from:
  1486  		// addis to, r2, x@got@tprel@ha
  1487  		// ld to, to, x@got@tprel@l(to)
  1488  		//
  1489  		// to TLS_LE by converting to:
  1490  		// addis to, r0, x@tprel@ha
  1491  		// addi to, to, x@tprel@l(to)
  1492  
  1493  		const OP_MASK = 0x3F << 26
  1494  		const OP_RA_MASK = 0x1F << 16
  1495  		// convert r2 to r0, and ld to addi
  1496  		mask := packInstPair(target, OP_RA_MASK, OP_MASK)
  1497  		addi_op := packInstPair(target, 0, OP_ADDI)
  1498  		val &^= mask
  1499  		val |= addi_op
  1500  		fallthrough
  1501  
  1502  	case objabi.R_POWER_TLS_LE:
  1503  		v := computeTLSLEReloc(target, ldr, rs, s)
  1504  		o1, o2 := unpackInstPair(target, val)
  1505  		o1 |= computeHA(int32(v))
  1506  		o2 |= computeLO(int32(v))
  1507  		return packInstPair(target, o1, o2), nExtReloc, true
  1508  
  1509  	case objabi.R_POWER_TLS_IE_PCREL34:
  1510  		// Convert TLS_IE relocation to TLS_LE if supported.
  1511  		if !(target.IsPIE() && target.IsElf()) {
  1512  			log.Fatalf("cannot handle R_POWER_TLS_IE (sym %s) when linking non-PIE, non-ELF binaries internally", ldr.SymName(s))
  1513  		}
  1514  
  1515  		// We are an ELF binary, we can safely convert to TLS_LE_TPREL34 from:
  1516  		// pld rX, x@got@tprel@pcrel
  1517  		//
  1518  		// to TLS_LE_TPREL32 by converting to:
  1519  		// pla rX, x@tprel
  1520  
  1521  		const OP_MASK_PFX = 0xFFFFFFFF        // Discard prefix word
  1522  		const OP_MASK = (0x3F << 26) | 0xFFFF // Preserve RT, RA
  1523  		const OP_PFX = 1<<26 | 2<<24
  1524  		const OP_PLA = 14 << 26
  1525  		mask := packInstPair(target, OP_MASK_PFX, OP_MASK)
  1526  		pla_op := packInstPair(target, OP_PFX, OP_PLA)
  1527  		val &^= mask
  1528  		val |= pla_op
  1529  		fallthrough
  1530  
  1531  	case objabi.R_POWER_TLS_LE_TPREL34:
  1532  		v := computeTLSLEReloc(target, ldr, rs, s)
  1533  		o1, o2 := unpackInstPair(target, val)
  1534  		o1 |= computePrefix34HI(v)
  1535  		o2 |= computeLO(int32(v))
  1536  		return packInstPair(target, o1, o2), nExtReloc, true
  1537  	}
  1538  
  1539  	return val, nExtReloc, false
  1540  }
  1541  
  1542  func archrelocvariant(target *ld.Target, ldr *loader.Loader, r loader.Reloc, rv sym.RelocVariant, s loader.Sym, t int64, p []byte) (relocatedOffset int64) {
  1543  	rs := r.Sym()
  1544  	switch rv & sym.RV_TYPE_MASK {
  1545  	default:
  1546  		ldr.Errorf(s, "unexpected relocation variant %d", rv)
  1547  		fallthrough
  1548  
  1549  	case sym.RV_NONE:
  1550  		return t
  1551  
  1552  	case sym.RV_POWER_LO:
  1553  		if rv&sym.RV_CHECK_OVERFLOW != 0 {
  1554  			// Whether to check for signed or unsigned
  1555  			// overflow depends on the instruction
  1556  			var o1 uint32
  1557  			if target.IsBigEndian() {
  1558  				o1 = binary.BigEndian.Uint32(p[r.Off()-2:])
  1559  			} else {
  1560  				o1 = binary.LittleEndian.Uint32(p[r.Off():])
  1561  			}
  1562  			switch o1 >> 26 {
  1563  			case 24, // ori
  1564  				26, // xori
  1565  				28: // andi
  1566  				if t>>16 != 0 {
  1567  					goto overflow
  1568  				}
  1569  
  1570  			default:
  1571  				if int64(int16(t)) != t {
  1572  					goto overflow
  1573  				}
  1574  			}
  1575  		}
  1576  
  1577  		return int64(int16(t))
  1578  
  1579  	case sym.RV_POWER_HA:
  1580  		t += 0x8000
  1581  		fallthrough
  1582  
  1583  		// Fallthrough
  1584  	case sym.RV_POWER_HI:
  1585  		t >>= 16
  1586  
  1587  		if rv&sym.RV_CHECK_OVERFLOW != 0 {
  1588  			// Whether to check for signed or unsigned
  1589  			// overflow depends on the instruction
  1590  			var o1 uint32
  1591  			if target.IsBigEndian() {
  1592  				o1 = binary.BigEndian.Uint32(p[r.Off()-2:])
  1593  			} else {
  1594  				o1 = binary.LittleEndian.Uint32(p[r.Off():])
  1595  			}
  1596  			switch o1 >> 26 {
  1597  			case 25, // oris
  1598  				27, // xoris
  1599  				29: // andis
  1600  				if t>>16 != 0 {
  1601  					goto overflow
  1602  				}
  1603  
  1604  			default:
  1605  				if int64(int16(t)) != t {
  1606  					goto overflow
  1607  				}
  1608  			}
  1609  		}
  1610  
  1611  		return int64(int16(t))
  1612  
  1613  	case sym.RV_POWER_DS:
  1614  		var o1 uint32
  1615  		if target.IsBigEndian() {
  1616  			o1 = uint32(binary.BigEndian.Uint16(p[r.Off():]))
  1617  		} else {
  1618  			o1 = uint32(binary.LittleEndian.Uint16(p[r.Off():]))
  1619  		}
  1620  		if t&3 != 0 {
  1621  			ldr.Errorf(s, "relocation for %s+%d is not aligned: %d", ldr.SymName(rs), r.Off(), t)
  1622  		}
  1623  		if (rv&sym.RV_CHECK_OVERFLOW != 0) && int64(int16(t)) != t {
  1624  			goto overflow
  1625  		}
  1626  		return int64(o1)&0x3 | int64(int16(t))
  1627  	}
  1628  
  1629  overflow:
  1630  	ldr.Errorf(s, "relocation for %s+%d is too big: %d", ldr.SymName(rs), r.Off(), t)
  1631  	return t
  1632  }
  1633  
  1634  func extreloc(target *ld.Target, ldr *loader.Loader, r loader.Reloc, s loader.Sym) (loader.ExtReloc, bool) {
  1635  	switch r.Type() {
  1636  	case objabi.R_POWER_TLS, objabi.R_POWER_TLS_LE, objabi.R_POWER_TLS_IE, objabi.R_POWER_TLS_IE_PCREL34, objabi.R_POWER_TLS_LE_TPREL34, objabi.R_CALLPOWER:
  1637  		return ld.ExtrelocSimple(ldr, r), true
  1638  	case objabi.R_ADDRPOWER,
  1639  		objabi.R_ADDRPOWER_DS,
  1640  		objabi.R_ADDRPOWER_TOCREL,
  1641  		objabi.R_ADDRPOWER_TOCREL_DS,
  1642  		objabi.R_ADDRPOWER_GOT,
  1643  		objabi.R_ADDRPOWER_GOT_PCREL34,
  1644  		objabi.R_ADDRPOWER_PCREL,
  1645  		objabi.R_ADDRPOWER_D34,
  1646  		objabi.R_ADDRPOWER_PCREL34:
  1647  		return ld.ExtrelocViaOuterSym(ldr, r, s), true
  1648  	}
  1649  	return loader.ExtReloc{}, false
  1650  }
  1651  
  1652  func addpltsym(ctxt *ld.Link, ldr *loader.Loader, s loader.Sym) {
  1653  	if ldr.SymPlt(s) >= 0 {
  1654  		return
  1655  	}
  1656  
  1657  	ld.Adddynsym(ldr, &ctxt.Target, &ctxt.ArchSyms, s)
  1658  
  1659  	if ctxt.IsELF {
  1660  		plt := ldr.MakeSymbolUpdater(ctxt.PLT)
  1661  		rela := ldr.MakeSymbolUpdater(ctxt.RelaPLT)
  1662  		if plt.Size() == 0 {
  1663  			panic("plt is not set up")
  1664  		}
  1665  
  1666  		// Create the glink resolver if necessary
  1667  		glink := ensureglinkresolver(ctxt, ldr)
  1668  
  1669  		// Write symbol resolver stub (just a branch to the
  1670  		// glink resolver stub)
  1671  		rel, _ := glink.AddRel(objabi.R_CALLPOWER)
  1672  		rel.SetOff(int32(glink.Size()))
  1673  		rel.SetSiz(4)
  1674  		rel.SetSym(glink.Sym())
  1675  		glink.AddUint32(ctxt.Arch, 0x48000000) // b .glink
  1676  
  1677  		// In the ppc64 ABI, the dynamic linker is responsible
  1678  		// for writing the entire PLT.  We just need to
  1679  		// reserve 8 bytes for each PLT entry and generate a
  1680  		// JMP_SLOT dynamic relocation for it.
  1681  		//
  1682  		// TODO(austin): ABI v1 is different
  1683  		ldr.SetPlt(s, int32(plt.Size()))
  1684  
  1685  		plt.Grow(plt.Size() + 8)
  1686  		plt.SetSize(plt.Size() + 8)
  1687  
  1688  		rela.AddAddrPlus(ctxt.Arch, plt.Sym(), int64(ldr.SymPlt(s)))
  1689  		rela.AddUint64(ctxt.Arch, elf.R_INFO(uint32(ldr.SymDynid(s)), uint32(elf.R_PPC64_JMP_SLOT)))
  1690  		rela.AddUint64(ctxt.Arch, 0)
  1691  	} else {
  1692  		ctxt.Errorf(s, "addpltsym: unsupported binary format")
  1693  	}
  1694  }
  1695  
  1696  // Generate the glink resolver stub if necessary and return the .glink section.
  1697  func ensureglinkresolver(ctxt *ld.Link, ldr *loader.Loader) *loader.SymbolBuilder {
  1698  	glink := ldr.CreateSymForUpdate(".glink", 0)
  1699  	if glink.Size() != 0 {
  1700  		return glink
  1701  	}
  1702  
  1703  	// This is essentially the resolver from the ppc64 ELFv2 ABI.
  1704  	// At entry, r12 holds the address of the symbol resolver stub
  1705  	// for the target routine and the argument registers hold the
  1706  	// arguments for the target routine.
  1707  	//
  1708  	// PC-rel offsets are computed once the final codesize of the
  1709  	// resolver is known.
  1710  	//
  1711  	// This stub is PIC, so first get the PC of label 1 into r11.
  1712  	glink.AddUint32(ctxt.Arch, OP_MFLR_R0) // mflr r0
  1713  	glink.AddUint32(ctxt.Arch, OP_BCL_NIA) // bcl 20,31,1f
  1714  	glink.AddUint32(ctxt.Arch, 0x7d6802a6) // 1: mflr r11
  1715  	glink.AddUint32(ctxt.Arch, OP_MTLR_R0) // mtlr r0
  1716  
  1717  	// Compute the .plt array index from the entry point address
  1718  	// into r0. This is computed relative to label 1 above.
  1719  	glink.AddUint32(ctxt.Arch, 0x38000000) // li r0,-(res_0-1b)
  1720  	glink.AddUint32(ctxt.Arch, 0x7c006214) // add r0,r0,r12
  1721  	glink.AddUint32(ctxt.Arch, 0x7c0b0050) // sub r0,r0,r11
  1722  	glink.AddUint32(ctxt.Arch, 0x7800f082) // srdi r0,r0,2
  1723  
  1724  	// Load the PC-rel offset of ".plt - 1b", and add it to 1b.
  1725  	// This is stored after this stub and before the resolvers.
  1726  	glink.AddUint32(ctxt.Arch, 0xe98b0000) // ld r12,res_0-1b-8(r11)
  1727  	glink.AddUint32(ctxt.Arch, 0x7d6b6214) // add r11,r11,r12
  1728  
  1729  	// Load r12 = dynamic resolver address and r11 = DSO
  1730  	// identifier from the first two doublewords of the PLT.
  1731  	glink.AddUint32(ctxt.Arch, 0xe98b0000) // ld r12,0(r11)
  1732  	glink.AddUint32(ctxt.Arch, 0xe96b0008) // ld r11,8(r11)
  1733  
  1734  	// Jump to the dynamic resolver
  1735  	glink.AddUint32(ctxt.Arch, OP_MTCTR_R12) // mtctr r12
  1736  	glink.AddUint32(ctxt.Arch, OP_BCTR)      // bctr
  1737  
  1738  	// Store the PC-rel offset to the PLT
  1739  	r, _ := glink.AddRel(objabi.R_PCREL)
  1740  	r.SetSym(ctxt.PLT)
  1741  	r.SetSiz(8)
  1742  	r.SetOff(int32(glink.Size()))
  1743  	r.SetAdd(glink.Size())        // Adjust the offset to be relative to label 1 above.
  1744  	glink.AddUint64(ctxt.Arch, 0) // The offset to the PLT.
  1745  
  1746  	// Resolve PC-rel offsets above now the final size of the stub is known.
  1747  	res0m1b := glink.Size() - 8 // res_0 - 1b
  1748  	glink.SetUint32(ctxt.Arch, 16, 0x38000000|uint32(uint16(-res0m1b)))
  1749  	glink.SetUint32(ctxt.Arch, 32, 0xe98b0000|uint32(uint16(res0m1b-8)))
  1750  
  1751  	// The symbol resolvers must immediately follow.
  1752  	//   res_0:
  1753  
  1754  	// Add DT_PPC64_GLINK .dynamic entry, which points to 32 bytes
  1755  	// before the first symbol resolver stub.
  1756  	du := ldr.MakeSymbolUpdater(ctxt.Dynamic)
  1757  	ld.Elfwritedynentsymplus(ctxt, du, elf.DT_PPC64_GLINK, glink.Sym(), glink.Size()-32)
  1758  
  1759  	return glink
  1760  }
  1761  

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