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// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package riscv64
import (
"cmd/internal/obj/riscv"
"cmd/internal/objabi"
"cmd/internal/sys"
"cmd/link/internal/ld"
"cmd/link/internal/loader"
"cmd/link/internal/sym"
"debug/elf"
"fmt"
"log"
"sort"
)
// fakeLabelName matches the RISCV_FAKE_LABEL_NAME from binutils.
const fakeLabelName = ".L0 "
func gentext(ctxt *ld.Link, ldr *loader.Loader) {
}
func genSymsLate(ctxt *ld.Link, ldr *loader.Loader) {
if ctxt.LinkMode != ld.LinkExternal {
return
}
// Generate a local text symbol for each relocation target, as the
// R_RISCV_PCREL_LO12_* relocations generated by elfreloc1 need it.
if ctxt.Textp == nil {
log.Fatal("genSymsLate called before Textp has been assigned")
}
var hi20Syms []loader.Sym
for _, s := range ctxt.Textp {
relocs := ldr.Relocs(s)
for ri := 0; ri < relocs.Count(); ri++ {
r := relocs.At(ri)
if r.Type() != objabi.R_RISCV_PCREL_ITYPE && r.Type() != objabi.R_RISCV_PCREL_STYPE &&
r.Type() != objabi.R_RISCV_TLS_IE_ITYPE && r.Type() != objabi.R_RISCV_TLS_IE_STYPE {
continue
}
if r.Off() == 0 && ldr.SymType(s) == sym.STEXT {
// Use the symbol for the function instead of creating
// an overlapping symbol.
continue
}
// TODO(jsing): Consider generating ELF symbols without needing
// loader symbols, in order to reduce memory consumption. This
// would require changes to genelfsym so that it called
// putelfsym and putelfsyment as appropriate.
sb := ldr.MakeSymbolBuilder(fakeLabelName)
sb.SetType(sym.STEXT)
sb.SetValue(ldr.SymValue(s) + int64(r.Off()))
sb.SetLocal(true)
sb.SetReachable(true)
sb.SetVisibilityHidden(true)
sb.SetSect(ldr.SymSect(s))
if outer := ldr.OuterSym(s); outer != 0 {
ldr.AddInteriorSym(outer, sb.Sym())
}
hi20Syms = append(hi20Syms, sb.Sym())
}
}
ctxt.Textp = append(ctxt.Textp, hi20Syms...)
ldr.SortSyms(ctxt.Textp)
}
func findHI20Symbol(ctxt *ld.Link, ldr *loader.Loader, val int64) loader.Sym {
idx := sort.Search(len(ctxt.Textp), func(i int) bool { return ldr.SymValue(ctxt.Textp[i]) >= val })
if idx >= len(ctxt.Textp) {
return 0
}
if s := ctxt.Textp[idx]; ldr.SymValue(s) == val && ldr.SymType(s) == sym.STEXT {
return s
}
return 0
}
func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym, r loader.ExtReloc, ri int, sectoff int64) bool {
elfsym := ld.ElfSymForReloc(ctxt, r.Xsym)
switch r.Type {
case objabi.R_ADDR, objabi.R_DWARFSECREF:
out.Write64(uint64(sectoff))
switch r.Size {
case 4:
out.Write64(uint64(elf.R_RISCV_32) | uint64(elfsym)<<32)
case 8:
out.Write64(uint64(elf.R_RISCV_64) | uint64(elfsym)<<32)
default:
ld.Errorf(nil, "unknown size %d for %v relocation", r.Size, r.Type)
return false
}
out.Write64(uint64(r.Xadd))
case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
out.Write64(uint64(sectoff))
out.Write64(uint64(elf.R_RISCV_JAL) | uint64(elfsym)<<32)
out.Write64(uint64(r.Xadd))
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
// Find the text symbol for the AUIPC instruction targeted
// by this relocation.
relocs := ldr.Relocs(s)
offset := int64(relocs.At(ri).Off())
hi20Sym := findHI20Symbol(ctxt, ldr, ldr.SymValue(s)+offset)
if hi20Sym == 0 {
ld.Errorf(nil, "failed to find text symbol for HI20 relocation at %d (%x)", sectoff, ldr.SymValue(s)+offset)
return false
}
hi20ElfSym := ld.ElfSymForReloc(ctxt, hi20Sym)
// Emit two relocations - a R_RISCV_PCREL_HI20 relocation and a
// corresponding R_RISCV_PCREL_LO12_I or R_RISCV_PCREL_LO12_S relocation.
// Note that the LO12 relocation must point to a target that has a valid
// HI20 PC-relative relocation text symbol, which in turn points to the
// given symbol. For further details see the ELF specification for RISC-V:
//
// https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md#pc-relative-symbol-addresses
//
var hiRel, loRel elf.R_RISCV
switch r.Type {
case objabi.R_RISCV_PCREL_ITYPE:
hiRel, loRel = elf.R_RISCV_PCREL_HI20, elf.R_RISCV_PCREL_LO12_I
case objabi.R_RISCV_PCREL_STYPE:
hiRel, loRel = elf.R_RISCV_PCREL_HI20, elf.R_RISCV_PCREL_LO12_S
case objabi.R_RISCV_TLS_IE_ITYPE:
hiRel, loRel = elf.R_RISCV_TLS_GOT_HI20, elf.R_RISCV_PCREL_LO12_I
case objabi.R_RISCV_TLS_IE_STYPE:
hiRel, loRel = elf.R_RISCV_TLS_GOT_HI20, elf.R_RISCV_PCREL_LO12_S
}
out.Write64(uint64(sectoff))
out.Write64(uint64(hiRel) | uint64(elfsym)<<32)
out.Write64(uint64(r.Xadd))
out.Write64(uint64(sectoff + 4))
out.Write64(uint64(loRel) | uint64(hi20ElfSym)<<32)
out.Write64(uint64(0))
default:
return false
}
return true
}
func elfsetupplt(ctxt *ld.Link, plt, gotplt *loader.SymbolBuilder, dynamic loader.Sym) {
log.Fatalf("elfsetupplt")
}
func machoreloc1(*sys.Arch, *ld.OutBuf, *loader.Loader, loader.Sym, loader.ExtReloc, int64) bool {
log.Fatalf("machoreloc1 not implemented")
return false
}
func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loader.Reloc, s loader.Sym, val int64) (o int64, nExtReloc int, ok bool) {
rs := r.Sym()
pc := ldr.SymValue(s) + int64(r.Off())
// If the call points to a trampoline, see if we can reach the symbol
// directly. This situation can occur when the relocation symbol is
// not assigned an address until after the trampolines are generated.
if r.Type() == objabi.R_RISCV_CALL_TRAMP {
relocs := ldr.Relocs(rs)
if relocs.Count() != 1 {
ldr.Errorf(s, "trampoline %v has %d relocations", ldr.SymName(rs), relocs.Count())
}
tr := relocs.At(0)
if tr.Type() != objabi.R_RISCV_PCREL_ITYPE {
ldr.Errorf(s, "trampoline %v has unexpected relocation %v", ldr.SymName(rs), tr.Type())
}
trs := tr.Sym()
if ldr.SymValue(trs) != 0 && ldr.SymType(trs) != sym.SDYNIMPORT && ldr.SymType(trs) != sym.SUNDEFEXT {
trsOff := ldr.SymValue(trs) + tr.Add() - pc
if trsOff >= -(1<<20) && trsOff < (1<<20) {
r.SetType(objabi.R_RISCV_CALL)
r.SetSym(trs)
r.SetAdd(tr.Add())
rs = trs
}
}
}
if target.IsExternal() {
switch r.Type() {
case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
return val, 1, true
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
return val, 2, true
}
return val, 0, false
}
off := ldr.SymValue(rs) + r.Add() - pc
switch r.Type() {
case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
// Generate instruction immediates.
imm, err := riscv.EncodeJImmediate(off)
if err != nil {
ldr.Errorf(s, "cannot encode R_RISCV_CALL relocation offset for %s: %v", ldr.SymName(rs), err)
}
immMask := int64(riscv.JTypeImmMask)
val = (val &^ immMask) | int64(imm)
return val, 0, true
case objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
// TLS relocations are not currently handled for internal linking.
// For now, TLS is only used when cgo is in use and cgo currently
// requires external linking. However, we need to accept these
// relocations so that code containing TLS variables will link,
// even when they're not being used. For now, replace these
// instructions with EBREAK to detect accidental use.
const ebreakIns = 0x00100073
return ebreakIns<<32 | ebreakIns, 0, true
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE:
// Generate AUIPC and second instruction immediates.
low, high, err := riscv.Split32BitImmediate(off)
if err != nil {
ldr.Errorf(s, "R_RISCV_PCREL_ relocation does not fit in 32 bits: %d", off)
}
auipcImm, err := riscv.EncodeUImmediate(high)
if err != nil {
ldr.Errorf(s, "cannot encode R_RISCV_PCREL_ AUIPC relocation offset for %s: %v", ldr.SymName(rs), err)
}
var secondImm, secondImmMask int64
switch r.Type() {
case objabi.R_RISCV_PCREL_ITYPE:
secondImmMask = riscv.ITypeImmMask
secondImm, err = riscv.EncodeIImmediate(low)
if err != nil {
ldr.Errorf(s, "cannot encode R_RISCV_PCREL_ITYPE I-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
}
case objabi.R_RISCV_PCREL_STYPE:
secondImmMask = riscv.STypeImmMask
secondImm, err = riscv.EncodeSImmediate(low)
if err != nil {
ldr.Errorf(s, "cannot encode R_RISCV_PCREL_STYPE S-type instruction relocation offset for %s: %v", ldr.SymName(rs), err)
}
default:
panic(fmt.Sprintf("Unknown relocation type: %v", r.Type()))
}
auipc := int64(uint32(val))
second := int64(uint32(val >> 32))
auipc = (auipc &^ riscv.UTypeImmMask) | int64(uint32(auipcImm))
second = (second &^ secondImmMask) | int64(uint32(secondImm))
return second<<32 | auipc, 0, true
}
return val, 0, false
}
func archrelocvariant(*ld.Target, *loader.Loader, loader.Reloc, sym.RelocVariant, loader.Sym, int64, []byte) int64 {
log.Fatalf("archrelocvariant")
return -1
}
func extreloc(target *ld.Target, ldr *loader.Loader, r loader.Reloc, s loader.Sym) (loader.ExtReloc, bool) {
switch r.Type() {
case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
return ld.ExtrelocSimple(ldr, r), true
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
return ld.ExtrelocViaOuterSym(ldr, r, s), true
}
return loader.ExtReloc{}, false
}
func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
relocs := ldr.Relocs(s)
r := relocs.At(ri)
switch r.Type() {
case objabi.R_RISCV_CALL:
pc := ldr.SymValue(s) + int64(r.Off())
off := ldr.SymValue(rs) + r.Add() - pc
// Relocation symbol has an address and is directly reachable,
// therefore there is no need for a trampoline.
if ldr.SymValue(rs) != 0 && off >= -(1<<20) && off < (1<<20) && (*ld.FlagDebugTramp <= 1 || ldr.SymPkg(s) == ldr.SymPkg(rs)) {
break
}
// Relocation symbol is too far for a direct call or has not
// yet been given an address. See if an existing trampoline is
// reachable and if so, reuse it. Otherwise we need to create
// a new trampoline.
var tramp loader.Sym
for i := 0; ; i++ {
oName := ldr.SymName(rs)
name := fmt.Sprintf("%s-tramp%d", oName, i)
if r.Add() != 0 {
name = fmt.Sprintf("%s%+x-tramp%d", oName, r.Add(), i)
}
tramp = ldr.LookupOrCreateSym(name, int(ldr.SymVersion(rs)))
ldr.SetAttrReachable(tramp, true)
if ldr.SymType(tramp) == sym.SDYNIMPORT {
// Do not reuse trampoline defined in other module.
continue
}
if oName == "runtime.deferreturn" {
ldr.SetIsDeferReturnTramp(tramp, true)
}
if ldr.SymValue(tramp) == 0 {
// Either trampoline does not exist or we found one
// that does not have an address assigned and will be
// laid down immediately after the current function.
break
}
trampOff := ldr.SymValue(tramp) - (ldr.SymValue(s) + int64(r.Off()))
if trampOff >= -(1<<20) && trampOff < (1<<20) {
// An existing trampoline that is reachable.
break
}
}
if ldr.SymType(tramp) == 0 {
trampb := ldr.MakeSymbolUpdater(tramp)
ctxt.AddTramp(trampb)
genCallTramp(ctxt.Arch, ctxt.LinkMode, ldr, trampb, rs, int64(r.Add()))
}
sb := ldr.MakeSymbolUpdater(s)
if ldr.SymValue(rs) == 0 {
// In this case the target symbol has not yet been assigned an
// address, so we have to assume a trampoline is required. Mark
// this as a call via a trampoline so that we can potentially
// switch to a direct call during relocation.
sb.SetRelocType(ri, objabi.R_RISCV_CALL_TRAMP)
}
relocs := sb.Relocs()
r := relocs.At(ri)
r.SetSym(tramp)
r.SetAdd(0)
default:
ctxt.Errorf(s, "trampoline called with non-jump reloc: %d (%s)", r.Type(), sym.RelocName(ctxt.Arch, r.Type()))
}
}
func genCallTramp(arch *sys.Arch, linkmode ld.LinkMode, ldr *loader.Loader, tramp *loader.SymbolBuilder, target loader.Sym, offset int64) {
tramp.AddUint32(arch, 0x00000f97) // AUIPC $0, X31
tramp.AddUint32(arch, 0x000f8067) // JALR X0, (X31)
r, _ := tramp.AddRel(objabi.R_RISCV_PCREL_ITYPE)
r.SetSiz(8)
r.SetSym(target)
r.SetAdd(offset)
}