Current File : //usr/local/go/src/cmd/link/internal/riscv64/asm.go
// 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_CALLRISCV:
// Call relocations are currently handled via R_RISCV_PCREL_ITYPE.
// TODO(jsing): Consider generating elf.R_RISCV_CALL instead of a
// HI20/LO12_I pair.
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) {
if target.IsExternal() {
switch r.Type() {
case objabi.R_CALLRISCV:
return val, 0, 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
}
rs := ldr.ResolveABIAlias(r.Sym())
switch r.Type() {
case objabi.R_CALLRISCV:
// Nothing to do.
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:
pc := ldr.SymValue(s) + int64(r.Off())
off := ldr.SymValue(rs) + r.Add() - pc
// 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_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
}
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