[lld] r270606 - Create Relocations.cpp and move scanRelocs there.
Rui Ueyama via llvm-commits
llvm-commits at lists.llvm.org
Tue May 24 13:24:43 PDT 2016
Author: ruiu
Date: Tue May 24 15:24:43 2016
New Revision: 270606
URL: http://llvm.org/viewvc/llvm-project?rev=270606&view=rev
Log:
Create Relocations.cpp and move scanRelocs there.
scanReloc and the functions on which scanReloc depends is in total
more than 600 lines of code. Since scanReloc does not depend on Writer,
it is better to move it into a separate file.
Differential Revision: http://reviews.llvm.org/D20554
Added:
lld/trunk/ELF/Relocations.cpp
lld/trunk/ELF/Relocations.h
Modified:
lld/trunk/ELF/CMakeLists.txt
lld/trunk/ELF/InputSection.h
lld/trunk/ELF/Writer.cpp
Modified: lld/trunk/ELF/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/CMakeLists.txt?rev=270606&r1=270605&r2=270606&view=diff
==============================================================================
--- lld/trunk/ELF/CMakeLists.txt (original)
+++ lld/trunk/ELF/CMakeLists.txt Tue May 24 15:24:43 2016
@@ -14,6 +14,7 @@ add_lld_library(lldELF
LinkerScript.cpp
MarkLive.cpp
OutputSections.cpp
+ Relocations.cpp
ScriptParser.cpp
SymbolListFile.cpp
SymbolTable.cpp
Modified: lld/trunk/ELF/InputSection.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.h?rev=270606&r1=270605&r2=270606&view=diff
==============================================================================
--- lld/trunk/ELF/InputSection.h (original)
+++ lld/trunk/ELF/InputSection.h Tue May 24 15:24:43 2016
@@ -11,6 +11,7 @@
#define LLD_ELF_INPUT_SECTION_H
#include "Config.h"
+#include "Relocations.h"
#include "lld/Core/LLVM.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/TinyPtrVector.h"
@@ -27,54 +28,6 @@ template <class ELFT> class ObjectFile;
template <class ELFT> class OutputSection;
template <class ELFT> class OutputSectionBase;
-enum RelExpr {
- R_ABS,
- R_GOT,
- R_GOTONLY_PC,
- R_GOTREL,
- R_GOT_FROM_END,
- R_GOT_OFF,
- R_GOT_PAGE_PC,
- R_GOT_PC,
- R_HINT,
- R_MIPS_GOT_LOCAL,
- R_MIPS_GOT_LOCAL_PAGE,
- R_NEG_TLS,
- R_PAGE_PC,
- R_PC,
- R_PLT,
- R_PLT_PC,
- R_PPC_OPD,
- R_PPC_PLT_OPD,
- R_PPC_TOC,
- R_RELAX_TLS_GD_TO_IE,
- R_RELAX_TLS_GD_TO_LE,
- R_RELAX_TLS_IE_TO_LE,
- R_RELAX_TLS_LD_TO_LE,
- R_SIZE,
- R_THUNK,
- R_TLS,
- R_TLSGD,
- R_TLSGD_PC,
- R_TLSLD,
- R_TLSLD_PC
-};
-
-inline bool refersToGotEntry(RelExpr Expr) {
- return Expr == R_GOT || Expr == R_GOT_OFF || Expr == R_MIPS_GOT_LOCAL ||
- Expr == R_MIPS_GOT_LOCAL_PAGE || Expr == R_GOT_PAGE_PC ||
- Expr == R_GOT_PC || Expr == R_GOT_FROM_END || Expr == R_TLSGD ||
- Expr == R_TLSGD_PC;
-}
-
-struct Relocation {
- RelExpr Expr;
- uint32_t Type;
- uint64_t Offset;
- uint64_t Addend;
- SymbolBody *Sym;
-};
-
// This corresponds to a section of an input file.
template <class ELFT> class InputSectionBase {
protected:
Added: lld/trunk/ELF/Relocations.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Relocations.cpp?rev=270606&view=auto
==============================================================================
--- lld/trunk/ELF/Relocations.cpp (added)
+++ lld/trunk/ELF/Relocations.cpp Tue May 24 15:24:43 2016
@@ -0,0 +1,637 @@
+//===- Relocations.cpp ----------------------------------------------------===//
+//
+// The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains platform-independent functions to processe relocations.
+// I'll describe the overview of this file here.
+//
+// Simple relocations are easy to handle for the linker. For example,
+// for R_X86_64_PC64 relocs, the linker just has to fix up locations
+// with the relative offsets to the target symbols. It would just be
+// reading records from relocation sections and applying them to output.
+//
+// But not all relocations are that easy to handle. For example, for
+// R_386_GOTOFF relocs, the linker has to create new GOT entries for
+// symbols if they don't exist, and fix up locations with GOT entry
+// offsets from the beginning of GOT section. So there is more than
+// fixing addresses in relocation processing.
+//
+// ELF defines a large number of complex relocations.
+//
+// The functions in this file analyze relocations and do whatever needs
+// to be done. It includes, but not limited to, the following.
+//
+// - create GOT/PLT entries
+// - create new relocations in .dynsym to let the dynamic linker resolve
+// them at runtime (since ELF supports dynamic linking, not all
+// relocations can be resolved at link-time)
+// - create COPY relocs and reserve space in .bss
+// - replace expensive relocs (in terms of runtime cost) with cheap ones
+// - error out infeasible combinations such as PIC and non-relative relocs
+//
+// Note that the functions in this file don't actually apply relocations
+// because it doesn't know about the output file nor the output file buffer.
+// It instead stores Relocation objects to InputSection's Relocations
+// vector to let it apply later in InputSection::writeTo.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Relocations.h"
+#include "Config.h"
+#include "OutputSections.h"
+#include "SymbolTable.h"
+#include "Target.h"
+
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+using namespace llvm::ELF;
+using namespace llvm::object;
+using namespace llvm::support::endian;
+
+namespace lld {
+namespace elf {
+
+static bool refersToGotEntry(RelExpr Expr) {
+ return Expr == R_GOT || Expr == R_GOT_OFF || Expr == R_MIPS_GOT_LOCAL ||
+ Expr == R_MIPS_GOT_LOCAL_PAGE || Expr == R_GOT_PAGE_PC ||
+ Expr == R_GOT_PC || Expr == R_GOT_FROM_END || Expr == R_TLSGD ||
+ Expr == R_TLSGD_PC;
+}
+
+// Returns the number of relocations processed.
+template <class ELFT>
+static unsigned handleTlsRelocation(uint32_t Type, SymbolBody &Body,
+ InputSectionBase<ELFT> &C,
+ typename ELFT::uint Offset,
+ typename ELFT::uint Addend, RelExpr Expr) {
+ if (!(C.getSectionHdr()->sh_flags & SHF_ALLOC))
+ return 0;
+
+ if (!Body.isTls())
+ return 0;
+
+ typedef typename ELFT::uint uintX_t;
+ if (Expr == R_TLSLD_PC || Expr == R_TLSLD) {
+ // Local-Dynamic relocs can be relaxed to Local-Exec.
+ if (!Config->Shared) {
+ C.Relocations.push_back(
+ {R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
+ return 2;
+ }
+ if (Out<ELFT>::Got->addTlsIndex())
+ Out<ELFT>::RelaDyn->addReloc({Target->TlsModuleIndexRel, Out<ELFT>::Got,
+ Out<ELFT>::Got->getTlsIndexOff(), false,
+ nullptr, 0});
+ C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
+ return 1;
+ }
+
+ // Local-Dynamic relocs can be relaxed to Local-Exec.
+ if (Target->isTlsLocalDynamicRel(Type) && !Config->Shared) {
+ C.Relocations.push_back(
+ {R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
+ return 1;
+ }
+
+ if (Target->isTlsGlobalDynamicRel(Type)) {
+ if (Config->Shared) {
+ if (Out<ELFT>::Got->addDynTlsEntry(Body)) {
+ uintX_t Off = Out<ELFT>::Got->getGlobalDynOffset(Body);
+ Out<ELFT>::RelaDyn->addReloc(
+ {Target->TlsModuleIndexRel, Out<ELFT>::Got, Off, false, &Body, 0});
+ Out<ELFT>::RelaDyn->addReloc({Target->TlsOffsetRel, Out<ELFT>::Got,
+ Off + (uintX_t)sizeof(uintX_t), false,
+ &Body, 0});
+ }
+ C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
+ return 1;
+ }
+
+ // Global-Dynamic relocs can be relaxed to Initial-Exec or Local-Exec
+ // depending on the symbol being locally defined or not.
+ if (Body.isPreemptible()) {
+ C.Relocations.push_back(
+ {R_RELAX_TLS_GD_TO_IE, Type, Offset, Addend, &Body});
+ if (!Body.isInGot()) {
+ Out<ELFT>::Got->addEntry(Body);
+ Out<ELFT>::RelaDyn->addReloc({Target->TlsGotRel, Out<ELFT>::Got,
+ Body.getGotOffset<ELFT>(), false, &Body,
+ 0});
+ }
+ return 2;
+ }
+ C.Relocations.push_back(
+ {R_RELAX_TLS_GD_TO_LE, Type, Offset, Addend, &Body});
+ return Target->TlsGdToLeSkip;
+ }
+
+ // Initial-Exec relocs can be relaxed to Local-Exec if the symbol is locally
+ // defined.
+ if (Target->isTlsInitialExecRel(Type) && !Config->Shared &&
+ !Body.isPreemptible()) {
+ C.Relocations.push_back(
+ {R_RELAX_TLS_IE_TO_LE, Type, Offset, Addend, &Body});
+ return 1;
+ }
+ return 0;
+}
+
+// Some targets might require creation of thunks for relocations. Now we
+// support only MIPS which requires LA25 thunk to call PIC code from non-PIC
+// one. Scan relocations to find each one requires thunk.
+template <class ELFT, class RelTy>
+static void scanRelocsForThunks(const elf::ObjectFile<ELFT> &File,
+ ArrayRef<RelTy> Rels) {
+ for (const RelTy &RI : Rels) {
+ uint32_t Type = RI.getType(Config->Mips64EL);
+ SymbolBody &Body = File.getRelocTargetSym(RI);
+ if (Body.hasThunk() || !Target->needsThunk(Type, File, Body))
+ continue;
+ auto *D = cast<DefinedRegular<ELFT>>(&Body);
+ auto *S = cast<InputSection<ELFT>>(D->Section);
+ S->addThunk(Body);
+ }
+}
+
+template <endianness E> static int16_t readSignedLo16(const uint8_t *Loc) {
+ return read32<E>(Loc) & 0xffff;
+}
+
+template <class RelTy>
+static uint32_t getMipsPairType(const RelTy *Rel, const SymbolBody &Sym) {
+ switch (Rel->getType(Config->Mips64EL)) {
+ case R_MIPS_HI16:
+ return R_MIPS_LO16;
+ case R_MIPS_GOT16:
+ return Sym.isLocal() ? R_MIPS_LO16 : R_MIPS_NONE;
+ case R_MIPS_PCHI16:
+ return R_MIPS_PCLO16;
+ case R_MICROMIPS_HI16:
+ return R_MICROMIPS_LO16;
+ default:
+ return R_MIPS_NONE;
+ }
+}
+
+template <class ELFT, class RelTy>
+static int32_t findMipsPairedAddend(const uint8_t *Buf, const uint8_t *BufLoc,
+ SymbolBody &Sym, const RelTy *Rel,
+ const RelTy *End) {
+ uint32_t SymIndex = Rel->getSymbol(Config->Mips64EL);
+ uint32_t Type = getMipsPairType(Rel, Sym);
+
+ // Some MIPS relocations use addend calculated from addend of the relocation
+ // itself and addend of paired relocation. ABI requires to compute such
+ // combined addend in case of REL relocation record format only.
+ // See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+ if (RelTy::IsRela || Type == R_MIPS_NONE)
+ return 0;
+
+ for (const RelTy *RI = Rel; RI != End; ++RI) {
+ if (RI->getType(Config->Mips64EL) != Type)
+ continue;
+ if (RI->getSymbol(Config->Mips64EL) != SymIndex)
+ continue;
+ const endianness E = ELFT::TargetEndianness;
+ return ((read32<E>(BufLoc) & 0xffff) << 16) +
+ readSignedLo16<E>(Buf + RI->r_offset);
+ }
+ unsigned OldType = Rel->getType(Config->Mips64EL);
+ StringRef OldName = getELFRelocationTypeName(Config->EMachine, OldType);
+ StringRef NewName = getELFRelocationTypeName(Config->EMachine, Type);
+ warning("can't find matching " + NewName + " relocation for " + OldName);
+ return 0;
+}
+
+// True if non-preemptable symbol always has the same value regardless of where
+// the DSO is loaded.
+template <class ELFT> static bool isAbsolute(const SymbolBody &Body) {
+ if (Body.isUndefined())
+ return !Body.isLocal() && Body.symbol()->isWeak();
+ if (const auto *DR = dyn_cast<DefinedRegular<ELFT>>(&Body))
+ return DR->Section == nullptr; // Absolute symbol.
+ return false;
+}
+
+static bool needsPlt(RelExpr Expr) {
+ return Expr == R_PLT_PC || Expr == R_PPC_PLT_OPD || Expr == R_PLT;
+}
+
+// True if this expression is of the form Sym - X, where X is a position in the
+// file (PC, or GOT for example).
+static bool isRelExpr(RelExpr Expr) {
+ return Expr == R_PC || Expr == R_GOTREL || Expr == R_PAGE_PC;
+}
+
+template <class ELFT>
+static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
+ const SymbolBody &Body) {
+ // These expressions always compute a constant
+ if (E == R_SIZE || E == R_GOT_FROM_END || E == R_GOT_OFF ||
+ E == R_MIPS_GOT_LOCAL || E == R_MIPS_GOT_LOCAL_PAGE ||
+ E == R_GOT_PAGE_PC || E == R_GOT_PC || E == R_PLT_PC || E == R_TLSGD_PC ||
+ E == R_TLSGD || E == R_PPC_PLT_OPD)
+ return true;
+
+ // These never do, except if the entire file is position dependent or if
+ // only the low bits are used.
+ if (E == R_GOT || E == R_PLT)
+ return Target->usesOnlyLowPageBits(Type) || !Config->Pic;
+
+ if (Body.isPreemptible())
+ return false;
+
+ if (!Config->Pic)
+ return true;
+
+ bool AbsVal = isAbsolute<ELFT>(Body) || Body.isTls();
+ bool RelE = isRelExpr(E);
+ if (AbsVal && !RelE)
+ return true;
+ if (!AbsVal && RelE)
+ return true;
+
+ // Relative relocation to an absolute value. This is normally unrepresentable,
+ // but if the relocation refers to a weak undefined symbol, we allow it to
+ // resolve to the image base. This is a little strange, but it allows us to
+ // link function calls to such symbols. Normally such a call will be guarded
+ // with a comparison, which will load a zero from the GOT.
+ if (AbsVal && RelE) {
+ if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak())
+ return true;
+ StringRef S = getELFRelocationTypeName(Config->EMachine, Type);
+ error("relocation " + S + " cannot refer to absolute symbol " +
+ Body.getName());
+ return true;
+ }
+
+ return Target->usesOnlyLowPageBits(Type);
+}
+
+static RelExpr toPlt(RelExpr Expr) {
+ if (Expr == R_PPC_OPD)
+ return R_PPC_PLT_OPD;
+ if (Expr == R_PC)
+ return R_PLT_PC;
+ if (Expr == R_ABS)
+ return R_PLT;
+ return Expr;
+}
+
+static RelExpr fromPlt(RelExpr Expr) {
+ // We decided not to use a plt. Optimize a reference to the plt to a
+ // reference to the symbol itself.
+ if (Expr == R_PLT_PC)
+ return R_PC;
+ if (Expr == R_PPC_PLT_OPD)
+ return R_PPC_OPD;
+ if (Expr == R_PLT)
+ return R_ABS;
+ return Expr;
+}
+
+template <class ELFT> static uint32_t getAlignment(SharedSymbol<ELFT> *SS) {
+ typedef typename ELFT::uint uintX_t;
+
+ uintX_t SecAlign = SS->File->getSection(SS->Sym)->sh_addralign;
+ uintX_t SymValue = SS->Sym.st_value;
+ int TrailingZeros =
+ std::min(countTrailingZeros(SecAlign), countTrailingZeros(SymValue));
+ return 1 << TrailingZeros;
+}
+
+// Reserve space in .bss for copy relocation.
+template <class ELFT> static void addCopyRelSymbol(SharedSymbol<ELFT> *SS) {
+ typedef typename ELFT::uint uintX_t;
+ typedef typename ELFT::Sym Elf_Sym;
+
+ // Copy relocation against zero-sized symbol doesn't make sense.
+ uintX_t SymSize = SS->template getSize<ELFT>();
+ if (SymSize == 0)
+ fatal("cannot create a copy relocation for " + SS->getName());
+
+ uintX_t Align = getAlignment(SS);
+ uintX_t Off = alignTo(Out<ELFT>::Bss->getSize(), Align);
+ Out<ELFT>::Bss->setSize(Off + SymSize);
+ Out<ELFT>::Bss->updateAlign(Align);
+ uintX_t Shndx = SS->Sym.st_shndx;
+ uintX_t Value = SS->Sym.st_value;
+ // Look through the DSO's dynamic symbol table for aliases and create a
+ // dynamic symbol for each one. This causes the copy relocation to correctly
+ // interpose any aliases.
+ for (const Elf_Sym &S : SS->File->getElfSymbols(true)) {
+ if (S.st_shndx != Shndx || S.st_value != Value)
+ continue;
+ auto *Alias = dyn_cast_or_null<SharedSymbol<ELFT>>(
+ Symtab<ELFT>::X->find(check(S.getName(SS->File->getStringTable()))));
+ if (!Alias)
+ continue;
+ Alias->OffsetInBss = Off;
+ Alias->NeedsCopyOrPltAddr = true;
+ Alias->symbol()->IsUsedInRegularObj = true;
+ }
+ Out<ELFT>::RelaDyn->addReloc(
+ {Target->CopyRel, Out<ELFT>::Bss, SS->OffsetInBss, false, SS, 0});
+}
+
+template <class ELFT>
+static RelExpr adjustExpr(const elf::ObjectFile<ELFT> &File, SymbolBody &Body,
+ bool IsWrite, RelExpr Expr, uint32_t Type) {
+ if (Target->needsThunk(Type, File, Body))
+ return R_THUNK;
+ bool Preemptible = Body.isPreemptible();
+ if (Body.isGnuIFunc())
+ Expr = toPlt(Expr);
+ else if (needsPlt(Expr) && !Preemptible)
+ Expr = fromPlt(Expr);
+
+ if (IsWrite || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body))
+ return Expr;
+
+ // This relocation would require the dynamic linker to write a value to read
+ // only memory. We can hack around it if we are producing an executable and
+ // the refered symbol can be preemepted to refer to the executable.
+ if (Config->Shared || (Config->Pic && !isRelExpr(Expr))) {
+ StringRef S = getELFRelocationTypeName(Config->EMachine, Type);
+ error("relocation " + S + " cannot be used when making a shared "
+ "object; recompile with -fPIC.");
+ return Expr;
+ }
+ if (Body.getVisibility() != STV_DEFAULT) {
+ error("Cannot preempt symbol");
+ return Expr;
+ }
+ if (Body.isObject()) {
+ // Produce a copy relocation.
+ auto *B = cast<SharedSymbol<ELFT>>(&Body);
+ if (!B->needsCopy())
+ addCopyRelSymbol(B);
+ return Expr;
+ }
+ if (Body.isFunc()) {
+ // This handles a non PIC program call to function in a shared library. In
+ // an ideal world, we could just report an error saying the relocation can
+ // overflow at runtime. In the real world with glibc, crt1.o has a
+ // R_X86_64_PC32 pointing to libc.so.
+ //
+ // The general idea on how to handle such cases is to create a PLT entry and
+ // use that as the function value.
+ //
+ // For the static linking part, we just return a plt expr and everything
+ // else will use the the PLT entry as the address.
+ //
+ // The remaining problem is making sure pointer equality still works. We
+ // need the help of the dynamic linker for that. We let it know that we have
+ // a direct reference to a so symbol by creating an undefined symbol with a
+ // non zero st_value. Seeing that, the dynamic linker resolves the symbol to
+ // the value of the symbol we created. This is true even for got entries, so
+ // pointer equality is maintained. To avoid an infinite loop, the only entry
+ // that points to the real function is a dedicated got entry used by the
+ // plt. That is identified by special relocation types (R_X86_64_JUMP_SLOT,
+ // R_386_JMP_SLOT, etc).
+ Body.NeedsCopyOrPltAddr = true;
+ return toPlt(Expr);
+ }
+ error("Symbol is missing type");
+
+ return Expr;
+}
+
+template <class ELFT, class RelTy>
+static typename ELFT::uint computeAddend(const elf::ObjectFile<ELFT> &File,
+ const uint8_t *SectionData,
+ const RelTy *End, const RelTy &RI,
+ RelExpr Expr, SymbolBody &Body) {
+ typedef typename ELFT::uint uintX_t;
+
+ uint32_t Type = RI.getType(Config->Mips64EL);
+ uintX_t Addend = getAddend<ELFT>(RI);
+ const uint8_t *BufLoc = SectionData + RI.r_offset;
+ if (!RelTy::IsRela)
+ Addend += Target->getImplicitAddend(BufLoc, Type);
+ if (Config->EMachine == EM_MIPS) {
+ Addend += findMipsPairedAddend<ELFT>(SectionData, BufLoc, Body, &RI, End);
+ if (Type == R_MIPS_LO16 && Expr == R_PC)
+ // R_MIPS_LO16 expression has R_PC type iif the target is _gp_disp
+ // symbol. In that case we should use the following formula for
+ // calculation "AHL + GP - P + 4". Let's add 4 right here.
+ // For details see p. 4-19 at
+ // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+ Addend += 4;
+ if (Expr == R_GOT_OFF)
+ Addend -= MipsGPOffset;
+ if (Expr == R_GOTREL) {
+ Addend -= MipsGPOffset;
+ if (Body.isLocal())
+ Addend += File.getMipsGp0();
+ }
+ }
+ if (Config->Pic && Config->EMachine == EM_PPC64 && Type == R_PPC64_TOC)
+ Addend += getPPC64TocBase();
+ return Addend;
+}
+
+// The reason we have to do this early scan is as follows
+// * To mmap the output file, we need to know the size
+// * For that, we need to know how many dynamic relocs we will have.
+// It might be possible to avoid this by outputting the file with write:
+// * Write the allocated output sections, computing addresses.
+// * Apply relocations, recording which ones require a dynamic reloc.
+// * Write the dynamic relocations.
+// * Write the rest of the file.
+// This would have some drawbacks. For example, we would only know if .rela.dyn
+// is needed after applying relocations. If it is, it will go after rw and rx
+// sections. Given that it is ro, we will need an extra PT_LOAD. This
+// complicates things for the dynamic linker and means we would have to reserve
+// space for the extra PT_LOAD even if we end up not using it.
+template <class ELFT, class RelTy>
+void scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
+ typedef typename ELFT::uint uintX_t;
+
+ uintX_t Flags = C.getSectionHdr()->sh_flags;
+ bool IsWrite = Flags & SHF_WRITE;
+
+ auto AddDyn = [=](const DynamicReloc<ELFT> &Reloc) {
+ Out<ELFT>::RelaDyn->addReloc(Reloc);
+ };
+
+ const elf::ObjectFile<ELFT> &File = *C.getFile();
+ ArrayRef<uint8_t> SectionData = C.getSectionData();
+ const uint8_t *Buf = SectionData.begin();
+ for (auto I = Rels.begin(), E = Rels.end(); I != E; ++I) {
+ const RelTy &RI = *I;
+ SymbolBody &Body = File.getRelocTargetSym(RI);
+ uint32_t Type = RI.getType(Config->Mips64EL);
+
+ RelExpr Expr = Target->getRelExpr(Type, Body);
+ // Ignore "hint" relocation because it is for optional code optimization.
+ if (Expr == R_HINT)
+ continue;
+
+ uintX_t Offset = C.getOffset(RI.r_offset);
+ if (Offset == (uintX_t)-1)
+ continue;
+
+ bool Preemptible = Body.isPreemptible();
+ Expr = adjustExpr(File, Body, IsWrite, Expr, Type);
+ if (HasError)
+ continue;
+
+ // This relocation does not require got entry, but it is relative to got and
+ // needs it to be created. Here we request for that.
+ if (Expr == R_GOTONLY_PC || Expr == R_GOTREL || Expr == R_PPC_TOC)
+ Out<ELFT>::Got->HasGotOffRel = true;
+
+ uintX_t Addend = computeAddend(File, Buf, E, RI, Expr, Body);
+
+ if (unsigned Processed =
+ handleTlsRelocation<ELFT>(Type, Body, C, Offset, Addend, Expr)) {
+ I += (Processed - 1);
+ continue;
+ }
+
+ if (needsPlt(Expr) || Expr == R_THUNK || refersToGotEntry(Expr) ||
+ !Body.isPreemptible()) {
+ // If the relocation points to something in the file, we can process it.
+ bool Constant = isStaticLinkTimeConstant<ELFT>(Expr, Type, Body);
+
+ // If the output being produced is position independent, the final value
+ // is still not known. In that case we still need some help from the
+ // dynamic linker. We can however do better than just copying the incoming
+ // relocation. We can process some of it and and just ask the dynamic
+ // linker to add the load address.
+ if (!Constant)
+ AddDyn({Target->RelativeRel, C.OutSec, Offset, true, &Body, Addend});
+
+ // If the produced value is a constant, we just remember to write it
+ // when outputting this section. We also have to do it if the format
+ // uses Elf_Rel, since in that case the written value is the addend.
+ if (Constant || !RelTy::IsRela)
+ C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
+ } else {
+ // We don't know anything about the finaly symbol. Just ask the dynamic
+ // linker to handle the relocation for us.
+ AddDyn({Target->getDynRel(Type), C.OutSec, Offset, false, &Body, Addend});
+ // MIPS ABI turns using of GOT and dynamic relocations inside out.
+ // While regular ABI uses dynamic relocations to fill up GOT entries
+ // MIPS ABI requires dynamic linker to fills up GOT entries using
+ // specially sorted dynamic symbol table. This affects even dynamic
+ // relocations against symbols which do not require GOT entries
+ // creation explicitly, i.e. do not have any GOT-relocations. So if
+ // a preemptible symbol has a dynamic relocation we anyway have
+ // to create a GOT entry for it.
+ // If a non-preemptible symbol has a dynamic relocation against it,
+ // dynamic linker takes it st_value, adds offset and writes down
+ // result of the dynamic relocation. In case of preemptible symbol
+ // dynamic linker performs symbol resolution, writes the symbol value
+ // to the GOT entry and reads the GOT entry when it needs to perform
+ // a dynamic relocation.
+ // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf p.4-19
+ if (Config->EMachine == EM_MIPS && !Body.isInGot())
+ Out<ELFT>::Got->addEntry(Body);
+ continue;
+ }
+
+ if (Expr == R_THUNK)
+ continue;
+
+ // At this point we are done with the relocated position. Some relocations
+ // also require us to create a got or plt entry.
+
+ // If a relocation needs PLT, we create a PLT and a GOT slot for the symbol.
+ if (needsPlt(Expr)) {
+ if (Body.isInPlt())
+ continue;
+ Out<ELFT>::Plt->addEntry(Body);
+
+ uint32_t Rel;
+ if (Body.isGnuIFunc() && !Preemptible)
+ Rel = Target->IRelativeRel;
+ else
+ Rel = Target->PltRel;
+
+ Out<ELFT>::GotPlt->addEntry(Body);
+ Out<ELFT>::RelaPlt->addReloc({Rel, Out<ELFT>::GotPlt,
+ Body.getGotPltOffset<ELFT>(), !Preemptible,
+ &Body, 0});
+ continue;
+ }
+
+ if (refersToGotEntry(Expr)) {
+ if (Body.isInGot())
+ continue;
+ Out<ELFT>::Got->addEntry(Body);
+
+ if (Config->EMachine == EM_MIPS)
+ // MIPS ABI has special rules to process GOT entries
+ // and doesn't require relocation entries for them.
+ // See "Global Offset Table" in Chapter 5 in the following document
+ // for detailed description:
+ // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+ continue;
+
+ if (Preemptible || (Config->Pic && !isAbsolute<ELFT>(Body))) {
+ uint32_t DynType;
+ if (Body.isTls())
+ DynType = Target->TlsGotRel;
+ else if (Preemptible)
+ DynType = Target->GotRel;
+ else
+ DynType = Target->RelativeRel;
+ AddDyn({DynType, Out<ELFT>::Got, Body.getGotOffset<ELFT>(),
+ !Preemptible, &Body, 0});
+ }
+ continue;
+ }
+ }
+
+ // Scan relocations for necessary thunks.
+ if (Config->EMachine == EM_MIPS)
+ scanRelocsForThunks<ELFT>(File, Rels);
+}
+
+template <class ELFT> void scanRelocations(InputSection<ELFT> &C) {
+ typedef typename ELFT::Shdr Elf_Shdr;
+
+ // Scan all relocations. Each relocation goes through a series
+ // of tests to determine if it needs special treatment, such as
+ // creating GOT, PLT, copy relocations, etc.
+ // Note that relocations for non-alloc sections are directly
+ // processed by InputSection::relocateNative.
+ if (C.getSectionHdr()->sh_flags & SHF_ALLOC)
+ for (const Elf_Shdr *RelSec : C.RelocSections)
+ scanRelocations(C, *RelSec);
+}
+
+template <class ELFT>
+void scanRelocations(InputSectionBase<ELFT> &S,
+ const typename ELFT::Shdr &RelSec) {
+ ELFFile<ELFT> &EObj = S.getFile()->getObj();
+ if (RelSec.sh_type == SHT_RELA)
+ scanRelocs(S, EObj.relas(&RelSec));
+ else
+ scanRelocs(S, EObj.rels(&RelSec));
+}
+
+template void scanRelocations<ELF32LE>(InputSection<ELF32LE> &);
+template void scanRelocations<ELF32BE>(InputSection<ELF32BE> &);
+template void scanRelocations<ELF64LE>(InputSection<ELF64LE> &);
+template void scanRelocations<ELF64BE>(InputSection<ELF64BE> &);
+
+template void scanRelocations<ELF32LE>(InputSectionBase<ELF32LE> &,
+ const ELF32LE::Shdr &);
+template void scanRelocations<ELF32BE>(InputSectionBase<ELF32BE> &,
+ const ELF32BE::Shdr &);
+template void scanRelocations<ELF64LE>(InputSectionBase<ELF64LE> &,
+ const ELF64LE::Shdr &);
+template void scanRelocations<ELF64BE>(InputSectionBase<ELF64BE> &,
+ const ELF64BE::Shdr &);
+}
+}
Added: lld/trunk/ELF/Relocations.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Relocations.h?rev=270606&view=auto
==============================================================================
--- lld/trunk/ELF/Relocations.h (added)
+++ lld/trunk/ELF/Relocations.h Tue May 24 15:24:43 2016
@@ -0,0 +1,69 @@
+//===- Relocations.h -------------------------------------------*- C++ -*-===//
+//
+// The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_ELF_RELOCATIONS_H
+#define LLD_ELF_RELOCATIONS_H
+
+#include "lld/Core/LLVM.h"
+
+namespace lld {
+namespace elf {
+class SymbolBody;
+template <class ELFT> class InputSection;
+template <class ELFT> class InputSectionBase;
+
+enum RelExpr {
+ R_ABS,
+ R_GOT,
+ R_GOTONLY_PC,
+ R_GOTREL,
+ R_GOT_FROM_END,
+ R_GOT_OFF,
+ R_GOT_PAGE_PC,
+ R_GOT_PC,
+ R_HINT,
+ R_MIPS_GOT_LOCAL,
+ R_MIPS_GOT_LOCAL_PAGE,
+ R_NEG_TLS,
+ R_PAGE_PC,
+ R_PC,
+ R_PLT,
+ R_PLT_PC,
+ R_PPC_OPD,
+ R_PPC_PLT_OPD,
+ R_PPC_TOC,
+ R_RELAX_TLS_GD_TO_IE,
+ R_RELAX_TLS_GD_TO_LE,
+ R_RELAX_TLS_IE_TO_LE,
+ R_RELAX_TLS_LD_TO_LE,
+ R_SIZE,
+ R_THUNK,
+ R_TLS,
+ R_TLSGD,
+ R_TLSGD_PC,
+ R_TLSLD,
+ R_TLSLD_PC
+};
+
+struct Relocation {
+ RelExpr Expr;
+ uint32_t Type;
+ uint64_t Offset;
+ uint64_t Addend;
+ SymbolBody *Sym;
+};
+
+template <class ELFT> void scanRelocations(InputSection<ELFT> &);
+
+template <class ELFT>
+void scanRelocations(InputSectionBase<ELFT> &, const typename ELFT::Shdr &);
+}
+}
+
+#endif
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=270606&r1=270605&r2=270606&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Tue May 24 15:24:43 2016
@@ -11,13 +11,12 @@
#include "Config.h"
#include "LinkerScript.h"
#include "OutputSections.h"
+#include "Relocations.h"
#include "SymbolTable.h"
#include "Target.h"
-#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringSwitch.h"
-#include "llvm/Support/Endian.h"
#include "llvm/Support/FileOutputBuffer.h"
#include "llvm/Support/StringSaver.h"
#include "llvm/Support/raw_ostream.h"
@@ -25,7 +24,6 @@
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
-using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
@@ -270,523 +268,6 @@ template <bool Is64Bits> struct DenseMap
};
}
-// Returns the number of relocations processed.
-template <class ELFT>
-static unsigned handleTlsRelocation(uint32_t Type, SymbolBody &Body,
- InputSectionBase<ELFT> &C,
- typename ELFT::uint Offset,
- typename ELFT::uint Addend, RelExpr Expr) {
- if (!(C.getSectionHdr()->sh_flags & SHF_ALLOC))
- return 0;
-
- if (!Body.isTls())
- return 0;
-
- typedef typename ELFT::uint uintX_t;
- if (Expr == R_TLSLD_PC || Expr == R_TLSLD) {
- // Local-Dynamic relocs can be relaxed to Local-Exec.
- if (!Config->Shared) {
- C.Relocations.push_back(
- {R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
- return 2;
- }
- if (Out<ELFT>::Got->addTlsIndex())
- Out<ELFT>::RelaDyn->addReloc({Target->TlsModuleIndexRel, Out<ELFT>::Got,
- Out<ELFT>::Got->getTlsIndexOff(), false,
- nullptr, 0});
- C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
- return 1;
- }
-
- // Local-Dynamic relocs can be relaxed to Local-Exec.
- if (Target->isTlsLocalDynamicRel(Type) && !Config->Shared) {
- C.Relocations.push_back(
- {R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
- return 1;
- }
-
- if (Target->isTlsGlobalDynamicRel(Type)) {
- if (Config->Shared) {
- if (Out<ELFT>::Got->addDynTlsEntry(Body)) {
- uintX_t Off = Out<ELFT>::Got->getGlobalDynOffset(Body);
- Out<ELFT>::RelaDyn->addReloc(
- {Target->TlsModuleIndexRel, Out<ELFT>::Got, Off, false, &Body, 0});
- Out<ELFT>::RelaDyn->addReloc({Target->TlsOffsetRel, Out<ELFT>::Got,
- Off + (uintX_t)sizeof(uintX_t), false,
- &Body, 0});
- }
- C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
- return 1;
- }
-
- // Global-Dynamic relocs can be relaxed to Initial-Exec or Local-Exec
- // depending on the symbol being locally defined or not.
- if (Body.isPreemptible()) {
- C.Relocations.push_back(
- {R_RELAX_TLS_GD_TO_IE, Type, Offset, Addend, &Body});
- if (!Body.isInGot()) {
- Out<ELFT>::Got->addEntry(Body);
- Out<ELFT>::RelaDyn->addReloc({Target->TlsGotRel, Out<ELFT>::Got,
- Body.getGotOffset<ELFT>(), false, &Body,
- 0});
- }
- return 2;
- }
- C.Relocations.push_back(
- {R_RELAX_TLS_GD_TO_LE, Type, Offset, Addend, &Body});
- return Target->TlsGdToLeSkip;
- }
-
- // Initial-Exec relocs can be relaxed to Local-Exec if the symbol is locally
- // defined.
- if (Target->isTlsInitialExecRel(Type) && !Config->Shared &&
- !Body.isPreemptible()) {
- C.Relocations.push_back(
- {R_RELAX_TLS_IE_TO_LE, Type, Offset, Addend, &Body});
- return 1;
- }
- return 0;
-}
-
-// Some targets might require creation of thunks for relocations. Now we
-// support only MIPS which requires LA25 thunk to call PIC code from non-PIC
-// one. Scan relocations to find each one requires thunk.
-template <class ELFT, class RelTy>
-static void scanRelocsForThunks(const elf::ObjectFile<ELFT> &File,
- ArrayRef<RelTy> Rels) {
- for (const RelTy &RI : Rels) {
- uint32_t Type = RI.getType(Config->Mips64EL);
- SymbolBody &Body = File.getRelocTargetSym(RI);
- if (Body.hasThunk() || !Target->needsThunk(Type, File, Body))
- continue;
- auto *D = cast<DefinedRegular<ELFT>>(&Body);
- auto *S = cast<InputSection<ELFT>>(D->Section);
- S->addThunk(Body);
- }
-}
-
-template <endianness E> static int16_t readSignedLo16(const uint8_t *Loc) {
- return read32<E>(Loc) & 0xffff;
-}
-
-template <class RelTy>
-static uint32_t getMipsPairType(const RelTy *Rel, const SymbolBody &Sym) {
- switch (Rel->getType(Config->Mips64EL)) {
- case R_MIPS_HI16:
- return R_MIPS_LO16;
- case R_MIPS_GOT16:
- return Sym.isLocal() ? R_MIPS_LO16 : R_MIPS_NONE;
- case R_MIPS_PCHI16:
- return R_MIPS_PCLO16;
- case R_MICROMIPS_HI16:
- return R_MICROMIPS_LO16;
- default:
- return R_MIPS_NONE;
- }
-}
-
-template <class ELFT, class RelTy>
-static int32_t findMipsPairedAddend(const uint8_t *Buf, const uint8_t *BufLoc,
- SymbolBody &Sym, const RelTy *Rel,
- const RelTy *End) {
- uint32_t SymIndex = Rel->getSymbol(Config->Mips64EL);
- uint32_t Type = getMipsPairType(Rel, Sym);
-
- // Some MIPS relocations use addend calculated from addend of the relocation
- // itself and addend of paired relocation. ABI requires to compute such
- // combined addend in case of REL relocation record format only.
- // See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
- if (RelTy::IsRela || Type == R_MIPS_NONE)
- return 0;
-
- for (const RelTy *RI = Rel; RI != End; ++RI) {
- if (RI->getType(Config->Mips64EL) != Type)
- continue;
- if (RI->getSymbol(Config->Mips64EL) != SymIndex)
- continue;
- const endianness E = ELFT::TargetEndianness;
- return ((read32<E>(BufLoc) & 0xffff) << 16) +
- readSignedLo16<E>(Buf + RI->r_offset);
- }
- unsigned OldType = Rel->getType(Config->Mips64EL);
- StringRef OldName = getELFRelocationTypeName(Config->EMachine, OldType);
- StringRef NewName = getELFRelocationTypeName(Config->EMachine, Type);
- warning("can't find matching " + NewName + " relocation for " + OldName);
- return 0;
-}
-
-// True if non-preemptable symbol always has the same value regardless of where
-// the DSO is loaded.
-template <class ELFT> static bool isAbsolute(const SymbolBody &Body) {
- if (Body.isUndefined())
- return !Body.isLocal() && Body.symbol()->isWeak();
- if (const auto *DR = dyn_cast<DefinedRegular<ELFT>>(&Body))
- return DR->Section == nullptr; // Absolute symbol.
- return false;
-}
-
-static bool needsPlt(RelExpr Expr) {
- return Expr == R_PLT_PC || Expr == R_PPC_PLT_OPD || Expr == R_PLT;
-}
-
-// True if this expression is of the form Sym - X, where X is a position in the
-// file (PC, or GOT for example).
-static bool isRelExpr(RelExpr Expr) {
- return Expr == R_PC || Expr == R_GOTREL || Expr == R_PAGE_PC;
-}
-
-template <class ELFT>
-static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
- const SymbolBody &Body) {
- // These expressions always compute a constant
- if (E == R_SIZE || E == R_GOT_FROM_END || E == R_GOT_OFF ||
- E == R_MIPS_GOT_LOCAL || E == R_MIPS_GOT_LOCAL_PAGE ||
- E == R_GOT_PAGE_PC || E == R_GOT_PC || E == R_PLT_PC || E == R_TLSGD_PC ||
- E == R_TLSGD || E == R_PPC_PLT_OPD)
- return true;
-
- // These never do, except if the entire file is position dependent or if
- // only the low bits are used.
- if (E == R_GOT || E == R_PLT)
- return Target->usesOnlyLowPageBits(Type) || !Config->Pic;
-
- if (Body.isPreemptible())
- return false;
-
- if (!Config->Pic)
- return true;
-
- bool AbsVal = isAbsolute<ELFT>(Body) || Body.isTls();
- bool RelE = isRelExpr(E);
- if (AbsVal && !RelE)
- return true;
- if (!AbsVal && RelE)
- return true;
-
- // Relative relocation to an absolute value. This is normally unrepresentable,
- // but if the relocation refers to a weak undefined symbol, we allow it to
- // resolve to the image base. This is a little strange, but it allows us to
- // link function calls to such symbols. Normally such a call will be guarded
- // with a comparison, which will load a zero from the GOT.
- if (AbsVal && RelE) {
- if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak())
- return true;
- StringRef S = getELFRelocationTypeName(Config->EMachine, Type);
- error("relocation " + S + " cannot refer to absolute symbol " +
- Body.getName());
- return true;
- }
-
- return Target->usesOnlyLowPageBits(Type);
-}
-
-static RelExpr toPlt(RelExpr Expr) {
- if (Expr == R_PPC_OPD)
- return R_PPC_PLT_OPD;
- if (Expr == R_PC)
- return R_PLT_PC;
- if (Expr == R_ABS)
- return R_PLT;
- return Expr;
-}
-
-static RelExpr fromPlt(RelExpr Expr) {
- // We decided not to use a plt. Optimize a reference to the plt to a
- // reference to the symbol itself.
- if (Expr == R_PLT_PC)
- return R_PC;
- if (Expr == R_PPC_PLT_OPD)
- return R_PPC_OPD;
- if (Expr == R_PLT)
- return R_ABS;
- return Expr;
-}
-
-template <class ELFT> static void addCopyRelSymbol(SharedSymbol<ELFT> *SS);
-
-template <class ELFT>
-static RelExpr adjustExpr(const elf::ObjectFile<ELFT> &File, SymbolBody &Body,
- bool IsWrite, RelExpr Expr, uint32_t Type) {
- if (Target->needsThunk(Type, File, Body))
- return R_THUNK;
- bool Preemptible = Body.isPreemptible();
- if (Body.isGnuIFunc())
- Expr = toPlt(Expr);
- else if (needsPlt(Expr) && !Preemptible)
- Expr = fromPlt(Expr);
-
- if (IsWrite || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body))
- return Expr;
-
- // This relocation would require the dynamic linker to write a value to read
- // only memory. We can hack around it if we are producing an executable and
- // the refered symbol can be preemepted to refer to the executable.
- if (Config->Shared || (Config->Pic && !isRelExpr(Expr))) {
- StringRef S = getELFRelocationTypeName(Config->EMachine, Type);
- error("relocation " + S + " cannot be used when making a shared "
- "object; recompile with -fPIC.");
- return Expr;
- }
- if (Body.getVisibility() != STV_DEFAULT) {
- error("Cannot preempt symbol");
- return Expr;
- }
- if (Body.isObject()) {
- // Produce a copy relocation.
- auto *B = cast<SharedSymbol<ELFT>>(&Body);
- if (!B->needsCopy())
- addCopyRelSymbol(B);
- return Expr;
- }
- if (Body.isFunc()) {
- // This handles a non PIC program call to function in a shared library. In
- // an ideal world, we could just report an error saying the relocation can
- // overflow at runtime. In the real world with glibc, crt1.o has a
- // R_X86_64_PC32 pointing to libc.so.
- //
- // The general idea on how to handle such cases is to create a PLT entry and
- // use that as the function value.
- //
- // For the static linking part, we just return a plt expr and everything
- // else will use the the PLT entry as the address.
- //
- // The remaining problem is making sure pointer equality still works. We
- // need the help of the dynamic linker for that. We let it know that we have
- // a direct reference to a so symbol by creating an undefined symbol with a
- // non zero st_value. Seeing that, the dynamic linker resolves the symbol to
- // the value of the symbol we created. This is true even for got entries, so
- // pointer equality is maintained. To avoid an infinite loop, the only entry
- // that points to the real function is a dedicated got entry used by the
- // plt. That is identified by special relocation types (R_X86_64_JUMP_SLOT,
- // R_386_JMP_SLOT, etc).
- Body.NeedsCopyOrPltAddr = true;
- return toPlt(Expr);
- }
- error("Symbol is missing type");
-
- return Expr;
-}
-
-template <class ELFT, class RelTy>
-static typename ELFT::uint computeAddend(const elf::ObjectFile<ELFT> &File,
- const uint8_t *SectionData,
- const RelTy *End, const RelTy &RI,
- RelExpr Expr, SymbolBody &Body) {
- typedef typename ELFT::uint uintX_t;
-
- uint32_t Type = RI.getType(Config->Mips64EL);
- uintX_t Addend = getAddend<ELFT>(RI);
- const uint8_t *BufLoc = SectionData + RI.r_offset;
- if (!RelTy::IsRela)
- Addend += Target->getImplicitAddend(BufLoc, Type);
- if (Config->EMachine == EM_MIPS) {
- Addend += findMipsPairedAddend<ELFT>(SectionData, BufLoc, Body, &RI, End);
- if (Type == R_MIPS_LO16 && Expr == R_PC)
- // R_MIPS_LO16 expression has R_PC type iif the target is _gp_disp
- // symbol. In that case we should use the following formula for
- // calculation "AHL + GP - P + 4". Let's add 4 right here.
- // For details see p. 4-19 at
- // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
- Addend += 4;
- if (Expr == R_GOT_OFF)
- Addend -= MipsGPOffset;
- if (Expr == R_GOTREL) {
- Addend -= MipsGPOffset;
- if (Body.isLocal())
- Addend += File.getMipsGp0();
- }
- }
- if (Config->Pic && Config->EMachine == EM_PPC64 && Type == R_PPC64_TOC)
- Addend += getPPC64TocBase();
- return Addend;
-}
-
-// The reason we have to do this early scan is as follows
-// * To mmap the output file, we need to know the size
-// * For that, we need to know how many dynamic relocs we will have.
-// It might be possible to avoid this by outputting the file with write:
-// * Write the allocated output sections, computing addresses.
-// * Apply relocations, recording which ones require a dynamic reloc.
-// * Write the dynamic relocations.
-// * Write the rest of the file.
-// This would have some drawbacks. For example, we would only know if .rela.dyn
-// is needed after applying relocations. If it is, it will go after rw and rx
-// sections. Given that it is ro, we will need an extra PT_LOAD. This
-// complicates things for the dynamic linker and means we would have to reserve
-// space for the extra PT_LOAD even if we end up not using it.
-template <class ELFT, class RelTy>
-void scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
- typedef typename ELFT::uint uintX_t;
-
- uintX_t Flags = C.getSectionHdr()->sh_flags;
- bool IsWrite = Flags & SHF_WRITE;
-
- auto AddDyn = [=](const DynamicReloc<ELFT> &Reloc) {
- Out<ELFT>::RelaDyn->addReloc(Reloc);
- };
-
- const elf::ObjectFile<ELFT> &File = *C.getFile();
- ArrayRef<uint8_t> SectionData = C.getSectionData();
- const uint8_t *Buf = SectionData.begin();
- for (auto I = Rels.begin(), E = Rels.end(); I != E; ++I) {
- const RelTy &RI = *I;
- SymbolBody &Body = File.getRelocTargetSym(RI);
- uint32_t Type = RI.getType(Config->Mips64EL);
-
- RelExpr Expr = Target->getRelExpr(Type, Body);
- // Ignore "hint" relocation because it is for optional code optimization.
- if (Expr == R_HINT)
- continue;
-
- uintX_t Offset = C.getOffset(RI.r_offset);
- if (Offset == (uintX_t)-1)
- continue;
-
- bool Preemptible = Body.isPreemptible();
- Expr = adjustExpr(File, Body, IsWrite, Expr, Type);
- if (HasError)
- continue;
-
- // This relocation does not require got entry, but it is relative to got and
- // needs it to be created. Here we request for that.
- if (Expr == R_GOTONLY_PC || Expr == R_GOTREL || Expr == R_PPC_TOC)
- Out<ELFT>::Got->HasGotOffRel = true;
-
- uintX_t Addend = computeAddend(File, Buf, E, RI, Expr, Body);
-
- if (unsigned Processed =
- handleTlsRelocation<ELFT>(Type, Body, C, Offset, Addend, Expr)) {
- I += (Processed - 1);
- continue;
- }
-
- if (needsPlt(Expr) || Expr == R_THUNK || refersToGotEntry(Expr) ||
- !Body.isPreemptible()) {
- // If the relocation points to something in the file, we can process it.
- bool Constant = isStaticLinkTimeConstant<ELFT>(Expr, Type, Body);
-
- // If the output being produced is position independent, the final value
- // is still not known. In that case we still need some help from the
- // dynamic linker. We can however do better than just copying the incoming
- // relocation. We can process some of it and and just ask the dynamic
- // linker to add the load address.
- if (!Constant)
- AddDyn({Target->RelativeRel, C.OutSec, Offset, true, &Body, Addend});
-
- // If the produced value is a constant, we just remember to write it
- // when outputting this section. We also have to do it if the format
- // uses Elf_Rel, since in that case the written value is the addend.
- if (Constant || !RelTy::IsRela)
- C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
- } else {
- // We don't know anything about the finaly symbol. Just ask the dynamic
- // linker to handle the relocation for us.
- AddDyn({Target->getDynRel(Type), C.OutSec, Offset, false, &Body, Addend});
- // MIPS ABI turns using of GOT and dynamic relocations inside out.
- // While regular ABI uses dynamic relocations to fill up GOT entries
- // MIPS ABI requires dynamic linker to fills up GOT entries using
- // specially sorted dynamic symbol table. This affects even dynamic
- // relocations against symbols which do not require GOT entries
- // creation explicitly, i.e. do not have any GOT-relocations. So if
- // a preemptible symbol has a dynamic relocation we anyway have
- // to create a GOT entry for it.
- // If a non-preemptible symbol has a dynamic relocation against it,
- // dynamic linker takes it st_value, adds offset and writes down
- // result of the dynamic relocation. In case of preemptible symbol
- // dynamic linker performs symbol resolution, writes the symbol value
- // to the GOT entry and reads the GOT entry when it needs to perform
- // a dynamic relocation.
- // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf p.4-19
- if (Config->EMachine == EM_MIPS && !Body.isInGot())
- Out<ELFT>::Got->addEntry(Body);
- continue;
- }
-
- if (Expr == R_THUNK)
- continue;
-
- // At this point we are done with the relocated position. Some relocations
- // also require us to create a got or plt entry.
-
- // If a relocation needs PLT, we create a PLT and a GOT slot for the symbol.
- if (needsPlt(Expr)) {
- if (Body.isInPlt())
- continue;
- Out<ELFT>::Plt->addEntry(Body);
-
- uint32_t Rel;
- if (Body.isGnuIFunc() && !Preemptible)
- Rel = Target->IRelativeRel;
- else
- Rel = Target->PltRel;
-
- Out<ELFT>::GotPlt->addEntry(Body);
- Out<ELFT>::RelaPlt->addReloc({Rel, Out<ELFT>::GotPlt,
- Body.getGotPltOffset<ELFT>(), !Preemptible,
- &Body, 0});
- continue;
- }
-
- if (refersToGotEntry(Expr)) {
- if (Body.isInGot())
- continue;
- Out<ELFT>::Got->addEntry(Body);
-
- if (Config->EMachine == EM_MIPS)
- // MIPS ABI has special rules to process GOT entries
- // and doesn't require relocation entries for them.
- // See "Global Offset Table" in Chapter 5 in the following document
- // for detailed description:
- // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
- continue;
-
- if (Preemptible || (Config->Pic && !isAbsolute<ELFT>(Body))) {
- uint32_t DynType;
- if (Body.isTls())
- DynType = Target->TlsGotRel;
- else if (Preemptible)
- DynType = Target->GotRel;
- else
- DynType = Target->RelativeRel;
- AddDyn({DynType, Out<ELFT>::Got, Body.getGotOffset<ELFT>(),
- !Preemptible, &Body, 0});
- }
- continue;
- }
- }
-
- // Scan relocations for necessary thunks.
- if (Config->EMachine == EM_MIPS)
- scanRelocsForThunks<ELFT>(File, Rels);
-}
-
-template <class ELFT>
-static void scanRelocs(InputSectionBase<ELFT> &S,
- const typename ELFT::Shdr &RelSec);
-
-template <class ELFT> static void scanRelocs(InputSection<ELFT> &C) {
- typedef typename ELFT::Shdr Elf_Shdr;
-
- // Scan all relocations. Each relocation goes through a series
- // of tests to determine if it needs special treatment, such as
- // creating GOT, PLT, copy relocations, etc.
- // Note that relocations for non-alloc sections are directly
- // processed by InputSection::relocateNative.
- if (C.getSectionHdr()->sh_flags & SHF_ALLOC)
- for (const Elf_Shdr *RelSec : C.RelocSections)
- scanRelocs(C, *RelSec);
-}
-
-template <class ELFT>
-static void scanRelocs(InputSectionBase<ELFT> &S,
- const typename ELFT::Shdr &RelSec) {
- ELFFile<ELFT> &EObj = S.getFile()->getObj();
- if (RelSec.sh_type == SHT_RELA)
- scanRelocs(S, EObj.relas(&RelSec));
- else
- scanRelocs(S, EObj.rels(&RelSec));
-}
-
template <class ELFT>
static void reportUndefined(SymbolTable<ELFT> &Symtab, SymbolBody *Sym) {
if (!Config->NoUndefined) {
@@ -1019,50 +500,6 @@ void Writer<ELFT>::addCommonSymbols(std:
Out<ELFT>::Bss->setSize(Off);
}
-template <class ELFT> static uint32_t getAlignment(SharedSymbol<ELFT> *SS) {
- typedef typename ELFT::uint uintX_t;
-
- uintX_t SecAlign = SS->File->getSection(SS->Sym)->sh_addralign;
- uintX_t SymValue = SS->Sym.st_value;
- int TrailingZeros =
- std::min(countTrailingZeros(SecAlign), countTrailingZeros(SymValue));
- return 1 << TrailingZeros;
-}
-
-// Reserve space in .bss for copy relocation.
-template <class ELFT> static void addCopyRelSymbol(SharedSymbol<ELFT> *SS) {
- typedef typename ELFT::uint uintX_t;
- typedef typename ELFT::Sym Elf_Sym;
-
- // Copy relocation against zero-sized symbol doesn't make sense.
- uintX_t SymSize = SS->template getSize<ELFT>();
- if (SymSize == 0)
- fatal("cannot create a copy relocation for " + SS->getName());
-
- uintX_t Align = getAlignment(SS);
- uintX_t Off = alignTo(Out<ELFT>::Bss->getSize(), Align);
- Out<ELFT>::Bss->setSize(Off + SymSize);
- Out<ELFT>::Bss->updateAlign(Align);
- uintX_t Shndx = SS->Sym.st_shndx;
- uintX_t Value = SS->Sym.st_value;
- // Look through the DSO's dynamic symbol table for aliases and create a
- // dynamic symbol for each one. This causes the copy relocation to correctly
- // interpose any aliases.
- for (const Elf_Sym &S : SS->File->getElfSymbols(true)) {
- if (S.st_shndx != Shndx || S.st_value != Value)
- continue;
- auto *Alias = dyn_cast_or_null<SharedSymbol<ELFT>>(
- Symtab<ELFT>::X->find(check(S.getName(SS->File->getStringTable()))));
- if (!Alias)
- continue;
- Alias->OffsetInBss = Off;
- Alias->NeedsCopyOrPltAddr = true;
- Alias->symbol()->IsUsedInRegularObj = true;
- }
- Out<ELFT>::RelaDyn->addReloc(
- {Target->CopyRel, Out<ELFT>::Bss, SS->OffsetInBss, false, SS, 0});
-}
-
template <class ELFT>
StringRef Writer<ELFT>::getOutputSectionName(InputSectionBase<ELFT> *S) const {
StringRef Dest = Script<ELFT>::X->getOutputSection(S);
@@ -1355,17 +792,17 @@ template <class ELFT> void Writer<ELFT>:
for (OutputSectionBase<ELFT> *Sec : OutputSections) {
Sec->forEachInputSection([&](InputSectionBase<ELFT> *S) {
if (auto *IS = dyn_cast<InputSection<ELFT>>(S)) {
- // Set OutSecOff so that scanRelocs can use it.
+ // Set OutSecOff so that scanRelocations can use it.
uintX_t Off = alignTo(Sec->getSize(), S->Align);
IS->OutSecOff = Off;
- scanRelocs(*IS);
+ scanRelocations(*IS);
// Now that scan relocs possibly changed the size, update the offset.
Sec->setSize(Off + S->getSize());
} else if (auto *EH = dyn_cast<EhInputSection<ELFT>>(S)) {
if (EH->RelocSection)
- scanRelocs(*EH, *EH->RelocSection);
+ scanRelocations(*EH, *EH->RelocSection);
}
});
}
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