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