asm.go

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package riscv64
     6  
     7  import (
     8  	"cmd/internal/obj/riscv"
     9  	"cmd/internal/objabi"
    10  	"cmd/internal/sys"
    11  	"cmd/link/internal/ld"
    12  	"cmd/link/internal/loader"
    13  	"cmd/link/internal/sym"
    14  	"debug/elf"
    15  	"fmt"
    16  	"log"
    17  	"sort"
    18  )
    19  
    20  // fakeLabelName matches the RISCV_FAKE_LABEL_NAME from binutils.
    21  const fakeLabelName = ".L0 "
    22  
    23  func gentext(ctxt *ld.Link, ldr *loader.Loader) {
    24  	initfunc, addmoduledata := ld.PrepareAddmoduledata(ctxt)
    25  	if initfunc == nil {
    26  		return
    27  	}
    28  
    29  	// Emit the following function:
    30  	//
    31  	// go.link.addmoduledatainit:
    32  	//      auipc a0, %pcrel_hi(local.moduledata)
    33  	//      addi  a0, %pcrel_lo(local.moduledata)
    34  	//      j     runtime.addmoduledata
    35  
    36  	sz := initfunc.AddSymRef(ctxt.Arch, ctxt.Moduledata, 0, objabi.R_RISCV_PCREL_ITYPE, 8)
    37  	initfunc.SetUint32(ctxt.Arch, sz-8, 0x00000517) // auipc a0, %pcrel_hi(local.moduledata)
    38  	initfunc.SetUint32(ctxt.Arch, sz-4, 0x00050513) // addi  a0, %pcrel_lo(local.moduledata)
    39  
    40  	sz = initfunc.AddSymRef(ctxt.Arch, addmoduledata, 0, objabi.R_RISCV_JAL, 4)
    41  	initfunc.SetUint32(ctxt.Arch, sz-4, 0x0000006f) // j runtime.addmoduledata
    42  }
    43  
    44  func findHI20Reloc(ldr *loader.Loader, s loader.Sym, val int64) *loader.Reloc {
    45  	outer := ldr.OuterSym(s)
    46  	if outer == 0 {
    47  		return nil
    48  	}
    49  	relocs := ldr.Relocs(outer)
    50  	start := sort.Search(relocs.Count(), func(i int) bool { return ldr.SymValue(outer)+int64(relocs.At(i).Off()) >= val })
    51  	for idx := start; idx < relocs.Count(); idx++ {
    52  		r := relocs.At(idx)
    53  		if ldr.SymValue(outer)+int64(r.Off()) != val {
    54  			break
    55  		}
    56  		if r.Type() == objabi.R_RISCV_GOT_HI20 || r.Type() == objabi.R_RISCV_PCREL_HI20 {
    57  			return &r
    58  		}
    59  	}
    60  	return nil
    61  }
    62  
    63  func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym, r loader.Reloc, rIdx int) bool {
    64  	targ := r.Sym()
    65  
    66  	var targType sym.SymKind
    67  	if targ != 0 {
    68  		targType = ldr.SymType(targ)
    69  	}
    70  
    71  	switch r.Type() {
    72  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_CALL),
    73  		objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_CALL_PLT):
    74  
    75  		if targType == sym.SDYNIMPORT {
    76  			addpltsym(target, ldr, syms, targ)
    77  			su := ldr.MakeSymbolUpdater(s)
    78  			su.SetRelocSym(rIdx, syms.PLT)
    79  			su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymPlt(targ)))
    80  		}
    81  		if targType == 0 || targType == sym.SXREF {
    82  			ldr.Errorf(s, "unknown symbol %s in RISCV call", ldr.SymName(targ))
    83  		}
    84  		su := ldr.MakeSymbolUpdater(s)
    85  		su.SetRelocType(rIdx, objabi.R_RISCV_CALL)
    86  		return true
    87  
    88  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_GOT_HI20):
    89  		if targType != sym.SDYNIMPORT {
    90  			// TODO(jsing): Could convert to non-GOT reference.
    91  		}
    92  
    93  		ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_RISCV_64))
    94  		su := ldr.MakeSymbolUpdater(s)
    95  		su.SetRelocType(rIdx, objabi.R_RISCV_GOT_HI20)
    96  		su.SetRelocSym(rIdx, syms.GOT)
    97  		su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymGot(targ)))
    98  		return true
    99  
   100  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_PCREL_HI20):
   101  		su := ldr.MakeSymbolUpdater(s)
   102  		su.SetRelocType(rIdx, objabi.R_RISCV_PCREL_HI20)
   103  		return true
   104  
   105  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_PCREL_LO12_I):
   106  		if r.Add() != 0 {
   107  			ldr.Errorf(s, "R_RISCV_PCREL_LO12_I with non-zero addend")
   108  		}
   109  		su := ldr.MakeSymbolUpdater(s)
   110  		su.SetRelocType(rIdx, objabi.R_RISCV_PCREL_LO12_I)
   111  		return true
   112  
   113  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_PCREL_LO12_S):
   114  		if r.Add() != 0 {
   115  			ldr.Errorf(s, "R_RISCV_PCREL_LO12_S with non-zero addend")
   116  		}
   117  		su := ldr.MakeSymbolUpdater(s)
   118  		su.SetRelocType(rIdx, objabi.R_RISCV_PCREL_LO12_S)
   119  		return true
   120  
   121  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_RVC_BRANCH):
   122  		su := ldr.MakeSymbolUpdater(s)
   123  		su.SetRelocType(rIdx, objabi.R_RISCV_RVC_BRANCH)
   124  		return true
   125  
   126  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_RVC_JUMP):
   127  		su := ldr.MakeSymbolUpdater(s)
   128  		su.SetRelocType(rIdx, objabi.R_RISCV_RVC_JUMP)
   129  		return true
   130  
   131  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_BRANCH):
   132  		su := ldr.MakeSymbolUpdater(s)
   133  		su.SetRelocType(rIdx, objabi.R_RISCV_BRANCH)
   134  		return true
   135  
   136  	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_RISCV_RELAX):
   137  		// Ignore relaxations, at least for now.
   138  		return true
   139  
   140  	default:
   141  		if r.Type() >= objabi.ElfRelocOffset {
   142  			ldr.Errorf(s, "unexpected relocation type %d (%s)", r.Type(), sym.RelocName(target.Arch, r.Type()))
   143  			return false
   144  		}
   145  	}
   146  
   147  	// Reread the reloc to incorporate any changes in type above.
   148  	relocs := ldr.Relocs(s)
   149  	r = relocs.At(rIdx)
   150  
   151  	switch r.Type() {
   152  	case objabi.R_RISCV_CALL:
   153  		if targType != sym.SDYNIMPORT {
   154  			// nothing to do, the relocation will be laid out in reloc
   155  			return true
   156  		}
   157  		if target.IsExternal() {
   158  			// External linker will do this relocation.
   159  			return true
   160  		}
   161  		// Internal linking.
   162  		if r.Add() != 0 {
   163  			ldr.Errorf(s, "PLT reference with non-zero addend (%v)", r.Add())
   164  		}
   165  		// Build a PLT entry and change the relocation target to that entry.
   166  		addpltsym(target, ldr, syms, targ)
   167  		su := ldr.MakeSymbolUpdater(s)
   168  		su.SetRelocSym(rIdx, syms.PLT)
   169  		su.SetRelocAdd(rIdx, int64(ldr.SymPlt(targ)))
   170  
   171  		return true
   172  	}
   173  
   174  	return false
   175  }
   176  
   177  func genSymsLate(ctxt *ld.Link, ldr *loader.Loader) {
   178  	if ctxt.LinkMode != ld.LinkExternal {
   179  		return
   180  	}
   181  
   182  	// Generate a local text symbol for each relocation target, as the
   183  	// R_RISCV_PCREL_LO12_* relocations generated by elfreloc1 need it.
   184  	if ctxt.Textp == nil {
   185  		log.Fatal("genSymsLate called before Textp has been assigned")
   186  	}
   187  	var hi20Syms []loader.Sym
   188  	for _, s := range ctxt.Textp {
   189  		relocs := ldr.Relocs(s)
   190  		for ri := 0; ri < relocs.Count(); ri++ {
   191  			r := relocs.At(ri)
   192  			if r.Type() != objabi.R_RISCV_CALL &&
   193  				r.Type() != objabi.R_RISCV_PCREL_ITYPE &&
   194  				r.Type() != objabi.R_RISCV_PCREL_STYPE &&
   195  				r.Type() != objabi.R_RISCV_TLS_IE &&
   196  				r.Type() != objabi.R_RISCV_GOT_PCREL_ITYPE {
   197  				continue
   198  			}
   199  			if r.Off() == 0 && ldr.SymType(s).IsText() {
   200  				// Use the symbol for the function instead of creating
   201  				// an overlapping symbol.
   202  				continue
   203  			}
   204  
   205  			// TODO(jsing): Consider generating ELF symbols without needing
   206  			// loader symbols, in order to reduce memory consumption. This
   207  			// would require changes to genelfsym so that it called
   208  			// putelfsym and putelfsyment as appropriate.
   209  			sb := ldr.MakeSymbolBuilder(fakeLabelName)
   210  			sb.SetType(sym.STEXT)
   211  			sb.SetValue(ldr.SymValue(s) + int64(r.Off()))
   212  			sb.SetLocal(true)
   213  			sb.SetReachable(true)
   214  			sb.SetVisibilityHidden(true)
   215  			sb.SetSect(ldr.SymSect(s))
   216  			if outer := ldr.OuterSym(s); outer != 0 {
   217  				ldr.AddInteriorSym(outer, sb.Sym())
   218  			}
   219  			hi20Syms = append(hi20Syms, sb.Sym())
   220  		}
   221  	}
   222  	ctxt.Textp = append(ctxt.Textp, hi20Syms...)
   223  	ldr.SortSyms(ctxt.Textp)
   224  }
   225  
   226  func findHI20Symbol(ctxt *ld.Link, ldr *loader.Loader, val int64) loader.Sym {
   227  	idx := sort.Search(len(ctxt.Textp), func(i int) bool { return ldr.SymValue(ctxt.Textp[i]) >= val })
   228  	if idx >= len(ctxt.Textp) {
   229  		return 0
   230  	}
   231  	if s := ctxt.Textp[idx]; ldr.SymValue(s) == val && ldr.SymType(s).IsText() {
   232  		return s
   233  	}
   234  	return 0
   235  }
   236  
   237  func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, ri int, sectoff int64) bool {
   238  	elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
   239  	switch r.Type {
   240  	case objabi.R_ADDR, objabi.R_DWARFSECREF:
   241  		out.Write64(uint64(sectoff))
   242  		switch r.Size {
   243  		case 4:
   244  			out.Write64(uint64(elf.R_RISCV_32) | uint64(elfsym)<<32)
   245  		case 8:
   246  			out.Write64(uint64(elf.R_RISCV_64) | uint64(elfsym)<<32)
   247  		default:
   248  			ld.Errorf("unknown size %d for %v relocation", r.Size, r.Type)
   249  			return false
   250  		}
   251  		out.Write64(uint64(r.Xadd))
   252  
   253  	case objabi.R_RISCV_JAL, objabi.R_RISCV_JAL_TRAMP:
   254  		out.Write64(uint64(sectoff))
   255  		out.Write64(uint64(elf.R_RISCV_JAL) | uint64(elfsym)<<32)
   256  		out.Write64(uint64(r.Xadd))
   257  
   258  	case objabi.R_RISCV_CALL,
   259  		objabi.R_RISCV_PCREL_ITYPE,
   260  		objabi.R_RISCV_PCREL_STYPE,
   261  		objabi.R_RISCV_TLS_IE,
   262  		objabi.R_RISCV_GOT_PCREL_ITYPE:
   263  		// Find the text symbol for the AUIPC instruction targeted
   264  		// by this relocation.
   265  		relocs := ldr.Relocs(s)
   266  		offset := int64(relocs.At(ri).Off())
   267  		hi20Sym := findHI20Symbol(ctxt, ldr, ldr.SymValue(s)+offset)
   268  		if hi20Sym == 0 {
   269  			ld.Errorf("failed to find text symbol for HI20 relocation at %d (%x)", sectoff, ldr.SymValue(s)+offset)
   270  			return false
   271  		}
   272  		hi20ElfSym := ld.ElfSymForReloc(ctxt, hi20Sym)
   273  
   274  		// Emit two relocations - a R_RISCV_PCREL_HI20 relocation and a
   275  		// corresponding R_RISCV_PCREL_LO12_I or R_RISCV_PCREL_LO12_S relocation.
   276  		// Note that the LO12 relocation must point to a target that has a valid
   277  		// HI20 PC-relative relocation text symbol, which in turn points to the
   278  		// given symbol. For further details see section 8.4.9 of the RISC-V ABIs
   279  		// Specification:
   280  		//
   281  		//  https://github.com/riscv-non-isa/riscv-elf-psabi-doc/releases/download/v1.0/riscv-abi.pdf
   282  		//
   283  		var hiRel, loRel elf.R_RISCV
   284  		switch r.Type {
   285  		case objabi.R_RISCV_CALL, objabi.R_RISCV_PCREL_ITYPE:
   286  			hiRel, loRel = elf.R_RISCV_PCREL_HI20, elf.R_RISCV_PCREL_LO12_I
   287  		case objabi.R_RISCV_PCREL_STYPE:
   288  			hiRel, loRel = elf.R_RISCV_PCREL_HI20, elf.R_RISCV_PCREL_LO12_S
   289  		case objabi.R_RISCV_TLS_IE:
   290  			hiRel, loRel = elf.R_RISCV_TLS_GOT_HI20, elf.R_RISCV_PCREL_LO12_I
   291  		case objabi.R_RISCV_GOT_PCREL_ITYPE:
   292  			hiRel, loRel = elf.R_RISCV_GOT_HI20, elf.R_RISCV_PCREL_LO12_I
   293  		}
   294  		out.Write64(uint64(sectoff))
   295  		out.Write64(uint64(hiRel) | uint64(elfsym)<<32)
   296  		out.Write64(uint64(r.Xadd))
   297  		out.Write64(uint64(sectoff + 4))
   298  		out.Write64(uint64(loRel) | uint64(hi20ElfSym)<<32)
   299  		out.Write64(uint64(0))
   300  
   301  	case objabi.R_RISCV_TLS_LE:
   302  		out.Write64(uint64(sectoff))
   303  		out.Write64(uint64(elf.R_RISCV_TPREL_HI20) | uint64(elfsym)<<32)
   304  		out.Write64(uint64(r.Xadd))
   305  		out.Write64(uint64(sectoff + 4))
   306  		out.Write64(uint64(elf.R_RISCV_TPREL_LO12_I) | uint64(elfsym)<<32)
   307  		out.Write64(uint64(r.Xadd))
   308  
   309  	default:
   310  		return false
   311  	}
   312  
   313  	return true
   314  }
   315  
   316  func elfsetupplt(ctxt *ld.Link, ldr *loader.Loader, plt, gotplt *loader.SymbolBuilder, dynamic loader.Sym) {
   317  	if plt.Size() != 0 {
   318  		return
   319  	}
   320  	if gotplt.Size() != 0 {
   321  		ctxt.Errorf(gotplt.Sym(), "got.plt is not empty")
   322  	}
   323  
   324  	// See section 8.4.6 of the RISC-V ABIs Specification:
   325  	//
   326  	//  https://github.com/riscv-non-isa/riscv-elf-psabi-doc/releases/download/v1.0/riscv-abi.pdf
   327  	//
   328  	// 1:   auipc  t2, %pcrel_hi(.got.plt)
   329  	//      sub    t1, t1, t3               # shifted .got.plt offset + hdr size + 12
   330  	//      l[w|d] t3, %pcrel_lo(1b)(t2)    # _dl_runtime_resolve
   331  	//      addi   t1, t1, -(hdr size + 12) # shifted .got.plt offset
   332  	//      addi   t0, t2, %pcrel_lo(1b)    # &.got.plt
   333  	//      srli   t1, t1, log2(16/PTRSIZE) # .got.plt offset
   334  	//      l[w|d] t0, PTRSIZE(t0)          # link map
   335  	//      jr     t3
   336  
   337  	plt.AddSymRef(ctxt.Arch, gotplt.Sym(), 0, objabi.R_RISCV_PCREL_HI20, 4)
   338  	plt.SetUint32(ctxt.Arch, plt.Size()-4, 0x00000397) // auipc   t2,0x0
   339  
   340  	sb := ldr.MakeSymbolBuilder(fakeLabelName)
   341  	sb.SetType(sym.STEXT)
   342  	sb.SetValue(ldr.SymValue(plt.Sym()) + plt.Size() - 4)
   343  	sb.SetLocal(true)
   344  	sb.SetReachable(true)
   345  	sb.SetVisibilityHidden(true)
   346  	plt.AddInteriorSym(sb.Sym())
   347  
   348  	plt.AddUint32(ctxt.Arch, 0x41c30333) // sub     t1,t1,t3
   349  
   350  	plt.AddSymRef(ctxt.Arch, sb.Sym(), 0, objabi.R_RISCV_PCREL_LO12_I, 4)
   351  	plt.SetUint32(ctxt.Arch, plt.Size()-4, 0x0003be03) // ld      t3,0(t2)
   352  
   353  	plt.AddUint32(ctxt.Arch, 0xfd430313) // addi    t1,t1,-44
   354  
   355  	plt.AddSymRef(ctxt.Arch, sb.Sym(), 0, objabi.R_RISCV_PCREL_LO12_I, 4)
   356  	plt.SetUint32(ctxt.Arch, plt.Size()-4, 0x00038293) // addi    t0,t2,0
   357  
   358  	plt.AddUint32(ctxt.Arch, 0x00135313) // srli    t1,t1,0x1
   359  	plt.AddUint32(ctxt.Arch, 0x0082b283) // ld      t0,8(t0)
   360  	plt.AddUint32(ctxt.Arch, 0x00008e02) // jr      t3
   361  
   362  	gotplt.AddAddrPlus(ctxt.Arch, dynamic, 0) // got.plt[0] = _dl_runtime_resolve
   363  	gotplt.AddUint64(ctxt.Arch, 0)            // got.plt[1] = link map
   364  }
   365  
   366  func addpltsym(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loader.Sym) {
   367  	if ldr.SymPlt(s) >= 0 {
   368  		return
   369  	}
   370  
   371  	ld.Adddynsym(ldr, target, syms, s)
   372  
   373  	plt := ldr.MakeSymbolUpdater(syms.PLT)
   374  	gotplt := ldr.MakeSymbolUpdater(syms.GOTPLT)
   375  	rela := ldr.MakeSymbolUpdater(syms.RelaPLT)
   376  	if plt.Size() == 0 {
   377  		panic("plt is not set up")
   378  	}
   379  
   380  	// See section 8.4.6 of the RISC-V ABIs Specification:
   381  	//
   382  	//  https://github.com/riscv-non-isa/riscv-elf-psabi-doc/releases/download/v1.0/riscv-abi.pdf
   383  	//
   384  	// 1:  auipc   t3, %pcrel_hi(function@.got.plt)
   385  	//     l[w|d]  t3, %pcrel_lo(1b)(t3)
   386  	//     jalr    t1, t3
   387  	//     nop
   388  
   389  	plt.AddSymRef(target.Arch, gotplt.Sym(), gotplt.Size(), objabi.R_RISCV_PCREL_HI20, 4)
   390  	plt.SetUint32(target.Arch, plt.Size()-4, 0x00000e17) // auipc   t3,0x0
   391  
   392  	sb := ldr.MakeSymbolBuilder(fakeLabelName)
   393  	sb.SetType(sym.STEXT)
   394  	sb.SetValue(ldr.SymValue(plt.Sym()) + plt.Size() - 4)
   395  	sb.SetLocal(true)
   396  	sb.SetReachable(true)
   397  	sb.SetVisibilityHidden(true)
   398  	plt.AddInteriorSym(sb.Sym())
   399  
   400  	plt.AddSymRef(target.Arch, sb.Sym(), 0, objabi.R_RISCV_PCREL_LO12_I, 4)
   401  	plt.SetUint32(target.Arch, plt.Size()-4, 0x000e3e03) // ld      t3,0(t3)
   402  	plt.AddUint32(target.Arch, 0x000e0367)               // jalr    t1,t3
   403  	plt.AddUint32(target.Arch, 0x00000001)               // nop
   404  
   405  	ldr.SetPlt(s, int32(plt.Size()-16))
   406  
   407  	// add to got.plt: pointer to plt[0]
   408  	gotplt.AddAddrPlus(target.Arch, plt.Sym(), 0)
   409  
   410  	// rela
   411  	rela.AddAddrPlus(target.Arch, gotplt.Sym(), gotplt.Size()-8)
   412  	sDynid := ldr.SymDynid(s)
   413  
   414  	rela.AddUint64(target.Arch, elf.R_INFO(uint32(sDynid), uint32(elf.R_RISCV_JUMP_SLOT)))
   415  	rela.AddUint64(target.Arch, 0)
   416  }
   417  
   418  func machoreloc1(*sys.Arch, *ld.OutBuf, *loader.Loader, loader.Sym, loader.ExtReloc, int64) bool {
   419  	log.Fatalf("machoreloc1 not implemented")
   420  	return false
   421  }
   422  
   423  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) {
   424  	rs := r.Sym()
   425  	pc := ldr.SymValue(s) + int64(r.Off())
   426  
   427  	// If the call points to a trampoline, see if we can reach the symbol
   428  	// directly. This situation can occur when the relocation symbol is
   429  	// not assigned an address until after the trampolines are generated.
   430  	if r.Type() == objabi.R_RISCV_JAL_TRAMP {
   431  		relocs := ldr.Relocs(rs)
   432  		if relocs.Count() != 1 {
   433  			ldr.Errorf(s, "trampoline %v has %d relocations", ldr.SymName(rs), relocs.Count())
   434  		}
   435  		tr := relocs.At(0)
   436  		if tr.Type() != objabi.R_RISCV_CALL {
   437  			ldr.Errorf(s, "trampoline %v has unexpected relocation %v", ldr.SymName(rs), tr.Type())
   438  		}
   439  		trs := tr.Sym()
   440  		if ldr.SymValue(trs) != 0 && ldr.SymType(trs) != sym.SDYNIMPORT && ldr.SymType(trs) != sym.SUNDEFEXT {
   441  			trsOff := ldr.SymValue(trs) + tr.Add() - pc
   442  			if trsOff >= -(1<<20) && trsOff < (1<<20) {
   443  				r.SetType(objabi.R_RISCV_JAL)
   444  				r.SetSym(trs)
   445  				r.SetAdd(tr.Add())
   446  				rs = trs
   447  			}
   448  		}
   449  
   450  	}
   451  
   452  	if target.IsExternal() {
   453  		switch r.Type() {
   454  		case objabi.R_RISCV_JAL, objabi.R_RISCV_JAL_TRAMP:
   455  			return val, 1, true
   456  
   457  		case objabi.R_RISCV_CALL, objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE, objabi.R_RISCV_TLS_LE, objabi.R_RISCV_GOT_PCREL_ITYPE:
   458  			return val, 2, true
   459  		}
   460  
   461  		return val, 0, false
   462  	}
   463  
   464  	off := ldr.SymValue(rs) + r.Add() - pc
   465  
   466  	switch r.Type() {
   467  	case objabi.R_RISCV_JAL, objabi.R_RISCV_JAL_TRAMP:
   468  		// Generate instruction immediates.
   469  		imm, err := riscv.EncodeJImmediate(off)
   470  		if err != nil {
   471  			ldr.Errorf(s, "cannot encode J-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   472  		}
   473  		immMask := int64(riscv.JTypeImmMask)
   474  
   475  		val = (val &^ immMask) | int64(imm)
   476  
   477  		return val, 0, true
   478  
   479  	case objabi.R_RISCV_TLS_IE:
   480  		log.Fatalf("cannot handle R_RISCV_TLS_IE (sym %s) when linking internally", ldr.SymName(s))
   481  		return val, 0, false
   482  
   483  	case objabi.R_RISCV_TLS_LE:
   484  		// Generate LUI and ADDIW instruction immediates.
   485  		off := r.Add()
   486  
   487  		low, high, err := riscv.Split32BitImmediate(off)
   488  		if err != nil {
   489  			ldr.Errorf(s, "relocation does not fit in 32-bits: %d", off)
   490  		}
   491  
   492  		luiImm, err := riscv.EncodeUImmediate(high)
   493  		if err != nil {
   494  			ldr.Errorf(s, "cannot encode R_RISCV_TLS_LE LUI relocation offset for %s: %v", ldr.SymName(rs), err)
   495  		}
   496  
   497  		addiwImm, err := riscv.EncodeIImmediate(low)
   498  		if err != nil {
   499  			ldr.Errorf(s, "cannot encode R_RISCV_TLS_LE I-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   500  		}
   501  
   502  		lui := int64(uint32(val))
   503  		addiw := int64(uint32(val >> 32))
   504  
   505  		lui = (lui &^ riscv.UTypeImmMask) | int64(uint32(luiImm))
   506  		addiw = (addiw &^ riscv.ITypeImmMask) | int64(uint32(addiwImm))
   507  
   508  		return addiw<<32 | lui, 0, true
   509  
   510  	case objabi.R_RISCV_BRANCH:
   511  		pc := ldr.SymValue(s) + int64(r.Off())
   512  		off := ldr.SymValue(rs) + r.Add() - pc
   513  
   514  		imm, err := riscv.EncodeBImmediate(off)
   515  		if err != nil {
   516  			ldr.Errorf(s, "cannot encode B-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   517  		}
   518  		ins := (int64(uint32(val)) &^ riscv.BTypeImmMask) | int64(uint32(imm))
   519  
   520  		return ins, 0, true
   521  
   522  	case objabi.R_RISCV_RVC_BRANCH, objabi.R_RISCV_RVC_JUMP:
   523  		pc := ldr.SymValue(s) + int64(r.Off())
   524  		off := ldr.SymValue(rs) + r.Add() - pc
   525  
   526  		var err error
   527  		var imm, immMask int64
   528  		switch r.Type() {
   529  		case objabi.R_RISCV_RVC_BRANCH:
   530  			immMask = riscv.CBTypeImmMask
   531  			imm, err = riscv.EncodeCBImmediate(off)
   532  			if err != nil {
   533  				ldr.Errorf(s, "cannot encode CB-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   534  			}
   535  		case objabi.R_RISCV_RVC_JUMP:
   536  			immMask = riscv.CJTypeImmMask
   537  			imm, err = riscv.EncodeCJImmediate(off)
   538  			if err != nil {
   539  				ldr.Errorf(s, "cannot encode CJ-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   540  			}
   541  		default:
   542  			panic(fmt.Sprintf("unknown relocation type: %v", r.Type()))
   543  		}
   544  
   545  		ins := (int64(uint16(val)) &^ immMask) | int64(uint16(imm))
   546  
   547  		return ins, 0, true
   548  
   549  	case objabi.R_RISCV_GOT_HI20, objabi.R_RISCV_PCREL_HI20:
   550  		pc := ldr.SymValue(s) + int64(r.Off())
   551  		off := ldr.SymValue(rs) + r.Add() - pc
   552  
   553  		// Generate AUIPC immediates.
   554  		_, high, err := riscv.Split32BitImmediate(off)
   555  		if err != nil {
   556  			ldr.Errorf(s, "relocation does not fit in 32-bits: %d", off)
   557  		}
   558  
   559  		auipcImm, err := riscv.EncodeUImmediate(high)
   560  		if err != nil {
   561  			ldr.Errorf(s, "cannot encode R_RISCV_PCREL_ AUIPC relocation offset for %s: %v", ldr.SymName(rs), err)
   562  		}
   563  
   564  		auipc := int64(uint32(val))
   565  		auipc = (auipc &^ riscv.UTypeImmMask) | int64(uint32(auipcImm))
   566  
   567  		return auipc, 0, true
   568  
   569  	case objabi.R_RISCV_PCREL_LO12_I, objabi.R_RISCV_PCREL_LO12_S:
   570  		hi20Reloc := findHI20Reloc(ldr, rs, ldr.SymValue(rs))
   571  		if hi20Reloc == nil {
   572  			ldr.Errorf(s, "missing HI20 relocation for LO12 relocation with %s (%d)", ldr.SymName(rs), rs)
   573  		}
   574  
   575  		pc := ldr.SymValue(s) + int64(hi20Reloc.Off())
   576  		off := ldr.SymValue(hi20Reloc.Sym()) + hi20Reloc.Add() - pc
   577  
   578  		low, _, err := riscv.Split32BitImmediate(off)
   579  		if err != nil {
   580  			ldr.Errorf(s, "relocation does not fit in 32-bits: %d", off)
   581  		}
   582  
   583  		var imm, immMask int64
   584  		switch r.Type() {
   585  		case objabi.R_RISCV_PCREL_LO12_I:
   586  			immMask = riscv.ITypeImmMask
   587  			imm, err = riscv.EncodeIImmediate(low)
   588  			if err != nil {
   589  				ldr.Errorf(s, "cannot encode objabi.R_RISCV_PCREL_LO12_I I-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   590  			}
   591  		case objabi.R_RISCV_PCREL_LO12_S:
   592  			immMask = riscv.STypeImmMask
   593  			imm, err = riscv.EncodeSImmediate(low)
   594  			if err != nil {
   595  				ldr.Errorf(s, "cannot encode R_RISCV_PCREL_LO12_S S-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   596  			}
   597  		default:
   598  			panic(fmt.Sprintf("unknown relocation type: %v", r.Type()))
   599  		}
   600  
   601  		ins := int64(uint32(val))
   602  		ins = (ins &^ immMask) | int64(uint32(imm))
   603  		return ins, 0, true
   604  
   605  	case objabi.R_RISCV_CALL, objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE:
   606  		// Generate AUIPC and second instruction immediates.
   607  		low, high, err := riscv.Split32BitImmediate(off)
   608  		if err != nil {
   609  			ldr.Errorf(s, "pc-relative relocation does not fit in 32 bits: %d", off)
   610  		}
   611  
   612  		auipcImm, err := riscv.EncodeUImmediate(high)
   613  		if err != nil {
   614  			ldr.Errorf(s, "cannot encode AUIPC relocation offset for %s: %v", ldr.SymName(rs), err)
   615  		}
   616  
   617  		var secondImm, secondImmMask int64
   618  		switch r.Type() {
   619  		case objabi.R_RISCV_CALL, objabi.R_RISCV_PCREL_ITYPE:
   620  			secondImmMask = riscv.ITypeImmMask
   621  			secondImm, err = riscv.EncodeIImmediate(low)
   622  			if err != nil {
   623  				ldr.Errorf(s, "cannot encode I-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   624  			}
   625  		case objabi.R_RISCV_PCREL_STYPE:
   626  			secondImmMask = riscv.STypeImmMask
   627  			secondImm, err = riscv.EncodeSImmediate(low)
   628  			if err != nil {
   629  				ldr.Errorf(s, "cannot encode S-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
   630  			}
   631  		default:
   632  			panic(fmt.Sprintf("unknown relocation type: %v", r.Type()))
   633  		}
   634  
   635  		auipc := int64(uint32(val))
   636  		second := int64(uint32(val >> 32))
   637  
   638  		auipc = (auipc &^ riscv.UTypeImmMask) | int64(uint32(auipcImm))
   639  		second = (second &^ secondImmMask) | int64(uint32(secondImm))
   640  
   641  		return second<<32 | auipc, 0, true
   642  	}
   643  
   644  	return val, 0, false
   645  }
   646  
   647  func archrelocvariant(*ld.Target, *loader.Loader, loader.Reloc, sym.RelocVariant, loader.Sym, int64, []byte) int64 {
   648  	log.Fatalf("archrelocvariant")
   649  	return -1
   650  }
   651  
   652  func extreloc(target *ld.Target, ldr *loader.Loader, r loader.Reloc, s loader.Sym) (loader.ExtReloc, bool) {
   653  	switch r.Type() {
   654  	case objabi.R_RISCV_JAL, objabi.R_RISCV_JAL_TRAMP:
   655  		return ld.ExtrelocSimple(ldr, r), true
   656  
   657  	case objabi.R_RISCV_CALL, objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE, objabi.R_RISCV_TLS_LE, objabi.R_RISCV_GOT_PCREL_ITYPE:
   658  		return ld.ExtrelocViaOuterSym(ldr, r, s), true
   659  	}
   660  	return loader.ExtReloc{}, false
   661  }
   662  
   663  func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
   664  	relocs := ldr.Relocs(s)
   665  	r := relocs.At(ri)
   666  
   667  	switch r.Type() {
   668  	case objabi.R_RISCV_JAL:
   669  		pc := ldr.SymValue(s) + int64(r.Off())
   670  		off := ldr.SymValue(rs) + r.Add() - pc
   671  
   672  		// Relocation symbol has an address and is directly reachable,
   673  		// therefore there is no need for a trampoline.
   674  		if ldr.SymValue(rs) != 0 && off >= -(1<<20) && off < (1<<20) && (*ld.FlagDebugTramp <= 1 || ldr.SymPkg(s) == ldr.SymPkg(rs)) {
   675  			break
   676  		}
   677  
   678  		// Relocation symbol is too far for a direct call or has not
   679  		// yet been given an address. See if an existing trampoline is
   680  		// reachable and if so, reuse it. Otherwise we need to create
   681  		// a new trampoline.
   682  		var tramp loader.Sym
   683  		for i := 0; ; i++ {
   684  			oName := ldr.SymName(rs)
   685  			name := fmt.Sprintf("%s-tramp%d", oName, i)
   686  			if r.Add() != 0 {
   687  				name = fmt.Sprintf("%s%+x-tramp%d", oName, r.Add(), i)
   688  			}
   689  			tramp = ldr.LookupOrCreateSym(name, int(ldr.SymVersion(rs)))
   690  			ldr.SetAttrReachable(tramp, true)
   691  			if ldr.SymType(tramp) == sym.SDYNIMPORT {
   692  				// Do not reuse trampoline defined in other module.
   693  				continue
   694  			}
   695  			if oName == "runtime.deferreturn" {
   696  				ldr.SetIsDeferReturnTramp(tramp, true)
   697  			}
   698  			if ldr.SymValue(tramp) == 0 {
   699  				// Either trampoline does not exist or we found one
   700  				// that does not have an address assigned and will be
   701  				// laid down immediately after the current function.
   702  				break
   703  			}
   704  
   705  			trampOff := ldr.SymValue(tramp) - (ldr.SymValue(s) + int64(r.Off()))
   706  			if trampOff >= -(1<<20) && trampOff < (1<<20) {
   707  				// An existing trampoline that is reachable.
   708  				break
   709  			}
   710  		}
   711  		if ldr.SymType(tramp) == 0 {
   712  			trampb := ldr.MakeSymbolUpdater(tramp)
   713  			ctxt.AddTramp(trampb, ldr.SymType(s))
   714  			genCallTramp(ctxt.Arch, ctxt.LinkMode, ldr, trampb, rs, int64(r.Add()))
   715  		}
   716  		sb := ldr.MakeSymbolUpdater(s)
   717  		if ldr.SymValue(rs) == 0 {
   718  			// In this case the target symbol has not yet been assigned an
   719  			// address, so we have to assume a trampoline is required. Mark
   720  			// this as a call via a trampoline so that we can potentially
   721  			// switch to a direct call during relocation.
   722  			sb.SetRelocType(ri, objabi.R_RISCV_JAL_TRAMP)
   723  		}
   724  		relocs := sb.Relocs()
   725  		r := relocs.At(ri)
   726  		r.SetSym(tramp)
   727  		r.SetAdd(0)
   728  
   729  	case objabi.R_RISCV_CALL:
   730  		// Nothing to do, already using AUIPC+JALR.
   731  
   732  	default:
   733  		ctxt.Errorf(s, "trampoline called with non-jump reloc: %d (%s)", r.Type(), sym.RelocName(ctxt.Arch, r.Type()))
   734  	}
   735  }
   736  
   737  func genCallTramp(arch *sys.Arch, linkmode ld.LinkMode, ldr *loader.Loader, tramp *loader.SymbolBuilder, target loader.Sym, offset int64) {
   738  	tramp.AddUint32(arch, 0x00000f97) // AUIPC	$0, X31
   739  	tramp.AddUint32(arch, 0x000f8067) // JALR	X0, (X31)
   740  
   741  	r, _ := tramp.AddRel(objabi.R_RISCV_CALL)
   742  	r.SetSiz(8)
   743  	r.SetSym(target)
   744  	r.SetAdd(offset)
   745  }
   746
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