Move all sources from the llvm project into contrib/llvm-project.

This uses the new layout of the upstream repository, which was recently
migrated to GitHub, and converted into a "monorepo".  That is, most of
the earlier separate sub-projects with their own branches and tags were
consolidated into one top-level directory, and are now branched and
tagged together.

Updating the vendor area to match this layout is next.

1 files changed, 1819 insertions, 0 deletions

diff --git a/contrib/llvm-project/lld/ELF/Relocations.cpp b/contrib/llvm-project/lld/ELF/Relocations.cpp
new file mode 100644
index 000000000000..ee48f4808136
--- /dev/null
+++ b/contrib/llvm-project/lld/ELF/Relocations.cpp
@@ -0,0 +1,1819 @@
+//===- Relocations.cpp ----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains platform-independent functions to process 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 "LinkerScript.h"
+#include "OutputSections.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "SyntheticSections.h"
+#include "Target.h"
+#include "Thunks.h"
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Memory.h"
+#include "lld/Common/Strings.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+
+using namespace llvm;
+using namespace llvm::ELF;
+using namespace llvm::object;
+using namespace llvm::support::endian;
+
+using namespace lld;
+using namespace lld::elf;
+
+static Optional<std::string> getLinkerScriptLocation(const Symbol &sym) {
+  for (BaseCommand *base : script->sectionCommands)
+    if (auto *cmd = dyn_cast<SymbolAssignment>(base))
+      if (cmd->sym == &sym)
+        return cmd->location;
+  return None;
+}
+
+// Construct a message in the following format.
+//
+// >>> defined in /home/alice/src/foo.o
+// >>> referenced by bar.c:12 (/home/alice/src/bar.c:12)
+// >>>               /home/alice/src/bar.o:(.text+0x1)
+static std::string getLocation(InputSectionBase &s, const Symbol &sym,
+                               uint64_t off) {
+  std::string msg = "\n>>> defined in ";
+  if (sym.file)
+    msg += toString(sym.file);
+  else if (Optional<std::string> loc = getLinkerScriptLocation(sym))
+    msg += *loc;
+
+  msg += "\n>>> referenced by ";
+  std::string src = s.getSrcMsg(sym, off);
+  if (!src.empty())
+    msg += src + "\n>>>               ";
+  return msg + s.getObjMsg(off);
+}
+
+namespace {
+// Build a bitmask with one bit set for each RelExpr.
+//
+// Constexpr function arguments can't be used in static asserts, so we
+// use template arguments to build the mask.
+// But function template partial specializations don't exist (needed
+// for base case of the recursion), so we need a dummy struct.
+template <RelExpr... Exprs> struct RelExprMaskBuilder {
+  static inline uint64_t build() { return 0; }
+};
+
+// Specialization for recursive case.
+template <RelExpr Head, RelExpr... Tail>
+struct RelExprMaskBuilder<Head, Tail...> {
+  static inline uint64_t build() {
+    static_assert(0 <= Head && Head < 64,
+                  "RelExpr is too large for 64-bit mask!");
+    return (uint64_t(1) << Head) | RelExprMaskBuilder<Tail...>::build();
+  }
+};
+} // namespace
+
+// Return true if `Expr` is one of `Exprs`.
+// There are fewer than 64 RelExpr's, so we can represent any set of
+// RelExpr's as a constant bit mask and test for membership with a
+// couple cheap bitwise operations.
+template <RelExpr... Exprs> bool oneof(RelExpr expr) {
+  assert(0 <= expr && (int)expr < 64 &&
+         "RelExpr is too large for 64-bit mask!");
+  return (uint64_t(1) << expr) & RelExprMaskBuilder<Exprs...>::build();
+}
+
+// This function is similar to the `handleTlsRelocation`. MIPS does not
+// support any relaxations for TLS relocations so by factoring out MIPS
+// handling in to the separate function we can simplify the code and do not
+// pollute other `handleTlsRelocation` by MIPS `ifs` statements.
+// Mips has a custom MipsGotSection that handles the writing of GOT entries
+// without dynamic relocations.
+static unsigned handleMipsTlsRelocation(RelType type, Symbol &sym,
+                                        InputSectionBase &c, uint64_t offset,
+                                        int64_t addend, RelExpr expr) {
+  if (expr == R_MIPS_TLSLD) {
+    in.mipsGot->addTlsIndex(*c.file);
+    c.relocations.push_back({expr, type, offset, addend, &sym});
+    return 1;
+  }
+  if (expr == R_MIPS_TLSGD) {
+    in.mipsGot->addDynTlsEntry(*c.file, sym);
+    c.relocations.push_back({expr, type, offset, addend, &sym});
+    return 1;
+  }
+  return 0;
+}
+
+// Notes about General Dynamic and Local Dynamic TLS models below. They may
+// require the generation of a pair of GOT entries that have associated dynamic
+// relocations. The pair of GOT entries created are of the form GOT[e0] Module
+// Index (Used to find pointer to TLS block at run-time) GOT[e1] Offset of
+// symbol in TLS block.
+//
+// Returns the number of relocations processed.
+template <class ELFT>
+static unsigned
+handleTlsRelocation(RelType type, Symbol &sym, InputSectionBase &c,
+                    typename ELFT::uint offset, int64_t addend, RelExpr expr) {
+  if (!sym.isTls())
+    return 0;
+
+  if (config->emachine == EM_MIPS)
+    return handleMipsTlsRelocation(type, sym, c, offset, addend, expr);
+
+  if (oneof<R_AARCH64_TLSDESC_PAGE, R_TLSDESC, R_TLSDESC_CALL, R_TLSDESC_PC>(
+          expr) &&
+      config->shared) {
+    if (in.got->addDynTlsEntry(sym)) {
+      uint64_t off = in.got->getGlobalDynOffset(sym);
+      mainPart->relaDyn->addReloc(
+          {target->tlsDescRel, in.got, off, !sym.isPreemptible, &sym, 0});
+    }
+    if (expr != R_TLSDESC_CALL)
+      c.relocations.push_back({expr, type, offset, addend, &sym});
+    return 1;
+  }
+
+  bool canRelax = config->emachine != EM_ARM && config->emachine != EM_RISCV;
+
+  // If we are producing an executable and the symbol is non-preemptable, it
+  // must be defined and the code sequence can be relaxed to use Local-Exec.
+  //
+  // ARM and RISC-V do not support any relaxations for TLS relocations, however,
+  // we can omit the DTPMOD dynamic relocations and resolve them at link time
+  // because them are always 1. This may be necessary for static linking as
+  // DTPMOD may not be expected at load time.
+  bool isLocalInExecutable = !sym.isPreemptible && !config->shared;
+
+  // Local Dynamic is for access to module local TLS variables, while still
+  // being suitable for being dynamically loaded via dlopen. GOT[e0] is the
+  // module index, with a special value of 0 for the current module. GOT[e1] is
+  // unused. There only needs to be one module index entry.
+  if (oneof<R_TLSLD_GOT, R_TLSLD_GOTPLT, R_TLSLD_PC, R_TLSLD_HINT>(
+          expr)) {
+    // Local-Dynamic relocs can be relaxed to Local-Exec.
+    if (canRelax && !config->shared) {
+      c.relocations.push_back(
+          {target->adjustRelaxExpr(type, nullptr, R_RELAX_TLS_LD_TO_LE), type,
+           offset, addend, &sym});
+      return target->getTlsGdRelaxSkip(type);
+    }
+    if (expr == R_TLSLD_HINT)
+      return 1;
+    if (in.got->addTlsIndex()) {
+      if (isLocalInExecutable)
+        in.got->relocations.push_back(
+            {R_ADDEND, target->symbolicRel, in.got->getTlsIndexOff(), 1, &sym});
+      else
+        mainPart->relaDyn->addReloc(target->tlsModuleIndexRel, in.got,
+                                in.got->getTlsIndexOff(), nullptr);
+    }
+    c.relocations.push_back({expr, type, offset, addend, &sym});
+    return 1;
+  }
+
+  // Local-Dynamic relocs can be relaxed to Local-Exec.
+  if (expr == R_DTPREL && !config->shared) {
+    c.relocations.push_back(
+        {target->adjustRelaxExpr(type, nullptr, R_RELAX_TLS_LD_TO_LE), type,
+         offset, addend, &sym});
+    return 1;
+  }
+
+  // Local-Dynamic sequence where offset of tls variable relative to dynamic
+  // thread pointer is stored in the got. This cannot be relaxed to Local-Exec.
+  if (expr == R_TLSLD_GOT_OFF) {
+    if (!sym.isInGot()) {
+      in.got->addEntry(sym);
+      uint64_t off = sym.getGotOffset();
+      in.got->relocations.push_back(
+          {R_ABS, target->tlsOffsetRel, off, 0, &sym});
+    }
+    c.relocations.push_back({expr, type, offset, addend, &sym});
+    return 1;
+  }
+
+  if (oneof<R_AARCH64_TLSDESC_PAGE, R_TLSDESC, R_TLSDESC_CALL, R_TLSDESC_PC,
+            R_TLSGD_GOT, R_TLSGD_GOTPLT, R_TLSGD_PC>(expr)) {
+    if (!canRelax || config->shared) {
+      if (in.got->addDynTlsEntry(sym)) {
+        uint64_t off = in.got->getGlobalDynOffset(sym);
+
+        if (isLocalInExecutable)
+          // Write one to the GOT slot.
+          in.got->relocations.push_back(
+              {R_ADDEND, target->symbolicRel, off, 1, &sym});
+        else
+          mainPart->relaDyn->addReloc(target->tlsModuleIndexRel, in.got, off, &sym);
+
+        // If the symbol is preemptible we need the dynamic linker to write
+        // the offset too.
+        uint64_t offsetOff = off + config->wordsize;
+        if (sym.isPreemptible)
+          mainPart->relaDyn->addReloc(target->tlsOffsetRel, in.got, offsetOff,
+                                  &sym);
+        else
+          in.got->relocations.push_back(
+              {R_ABS, target->tlsOffsetRel, offsetOff, 0, &sym});
+      }
+      c.relocations.push_back({expr, type, offset, addend, &sym});
+      return 1;
+    }
+
+    // Global-Dynamic relocs can be relaxed to Initial-Exec or Local-Exec
+    // depending on the symbol being locally defined or not.
+    if (sym.isPreemptible) {
+      c.relocations.push_back(
+          {target->adjustRelaxExpr(type, nullptr, R_RELAX_TLS_GD_TO_IE), type,
+           offset, addend, &sym});
+      if (!sym.isInGot()) {
+        in.got->addEntry(sym);
+        mainPart->relaDyn->addReloc(target->tlsGotRel, in.got, sym.getGotOffset(),
+                                &sym);
+      }
+    } else {
+      c.relocations.push_back(
+          {target->adjustRelaxExpr(type, nullptr, R_RELAX_TLS_GD_TO_LE), type,
+           offset, addend, &sym});
+    }
+    return target->getTlsGdRelaxSkip(type);
+  }
+
+  // Initial-Exec relocs can be relaxed to Local-Exec if the symbol is locally
+  // defined.
+  if (oneof<R_GOT, R_GOTPLT, R_GOT_PC, R_AARCH64_GOT_PAGE_PC, R_GOT_OFF,
+            R_TLSIE_HINT>(expr) &&
+      canRelax && isLocalInExecutable) {
+    c.relocations.push_back({R_RELAX_TLS_IE_TO_LE, type, offset, addend, &sym});
+    return 1;
+  }
+
+  if (expr == R_TLSIE_HINT)
+    return 1;
+  return 0;
+}
+
+static RelType getMipsPairType(RelType type, bool isLocal) {
+  switch (type) {
+  case R_MIPS_HI16:
+    return R_MIPS_LO16;
+  case R_MIPS_GOT16:
+    // In case of global symbol, the R_MIPS_GOT16 relocation does not
+    // have a pair. Each global symbol has a unique entry in the GOT
+    // and a corresponding instruction with help of the R_MIPS_GOT16
+    // relocation loads an address of the symbol. In case of local
+    // symbol, the R_MIPS_GOT16 relocation creates a GOT entry to hold
+    // the high 16 bits of the symbol's value. A paired R_MIPS_LO16
+    // relocations handle low 16 bits of the address. That allows
+    // to allocate only one GOT entry for every 64 KBytes of local data.
+    return isLocal ? R_MIPS_LO16 : R_MIPS_NONE;
+  case R_MICROMIPS_GOT16:
+    return isLocal ? R_MICROMIPS_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;
+  }
+}
+
+// True if non-preemptable symbol always has the same value regardless of where
+// the DSO is loaded.
+static bool isAbsolute(const Symbol &sym) {
+  if (sym.isUndefWeak())
+    return true;
+  if (const auto *dr = dyn_cast<Defined>(&sym))
+    return dr->section == nullptr; // Absolute symbol.
+  return false;
+}
+
+static bool isAbsoluteValue(const Symbol &sym) {
+  return isAbsolute(sym) || sym.isTls();
+}
+
+// Returns true if Expr refers a PLT entry.
+static bool needsPlt(RelExpr expr) {
+  return oneof<R_PLT_PC, R_PPC32_PLTREL, R_PPC64_CALL_PLT, R_PLT>(expr);
+}
+
+// Returns true if Expr refers a GOT entry. Note that this function
+// returns false for TLS variables even though they need GOT, because
+// TLS variables uses GOT differently than the regular variables.
+static bool needsGot(RelExpr expr) {
+  return oneof<R_GOT, R_GOT_OFF, R_HEXAGON_GOT, R_MIPS_GOT_LOCAL_PAGE,
+               R_MIPS_GOT_OFF, R_MIPS_GOT_OFF32, R_AARCH64_GOT_PAGE_PC,
+               R_GOT_PC, R_GOTPLT>(expr);
+}
+
+// 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 oneof<R_PC, R_GOTREL, R_GOTPLTREL, R_MIPS_GOTREL, R_PPC64_CALL,
+               R_PPC64_RELAX_TOC, R_AARCH64_PAGE_PC, R_RELAX_GOT_PC,
+               R_RISCV_PC_INDIRECT>(expr);
+}
+
+// Returns true if a given relocation can be computed at link-time.
+//
+// For instance, we know the offset from a relocation to its target at
+// link-time if the relocation is PC-relative and refers a
+// non-interposable function in the same executable. This function
+// will return true for such relocation.
+//
+// If this function returns false, that means we need to emit a
+// dynamic relocation so that the relocation will be fixed at load-time.
+static bool isStaticLinkTimeConstant(RelExpr e, RelType type, const Symbol &sym,
+                                     InputSectionBase &s, uint64_t relOff) {
+  // These expressions always compute a constant
+  if (oneof<R_DTPREL, R_GOTPLT, R_GOT_OFF, R_HEXAGON_GOT, R_TLSLD_GOT_OFF,
+            R_MIPS_GOT_LOCAL_PAGE, R_MIPS_GOTREL, R_MIPS_GOT_OFF,
+            R_MIPS_GOT_OFF32, R_MIPS_GOT_GP_PC, R_MIPS_TLSGD,
+            R_AARCH64_GOT_PAGE_PC, R_GOT_PC, R_GOTONLY_PC, R_GOTPLTONLY_PC,
+            R_PLT_PC, R_TLSGD_GOT, R_TLSGD_GOTPLT, R_TLSGD_PC, R_PPC32_PLTREL,
+            R_PPC64_CALL_PLT, R_PPC64_RELAX_TOC, R_RISCV_ADD, R_TLSDESC_CALL,
+            R_TLSDESC_PC, R_AARCH64_TLSDESC_PAGE, R_HINT, R_TLSLD_HINT,
+            R_TLSIE_HINT>(e))
+    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 || e == R_TLSDESC)
+    return target->usesOnlyLowPageBits(type) || !config->isPic;
+
+  if (sym.isPreemptible)
+    return false;
+  if (!config->isPic)
+    return true;
+
+  // The size of a non preemptible symbol is a constant.
+  if (e == R_SIZE)
+    return true;
+
+  // For the target and the relocation, we want to know if they are
+  // absolute or relative.
+  bool absVal = isAbsoluteValue(sym);
+  bool relE = isRelExpr(e);
+  if (absVal && !relE)
+    return true;
+  if (!absVal && relE)
+    return true;
+  if (!absVal && !relE)
+    return target->usesOnlyLowPageBits(type);
+
+  // 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.
+  // Another special case is MIPS _gp_disp symbol which represents offset
+  // between start of a function and '_gp' value and defined as absolute just
+  // to simplify the code.
+  assert(absVal && relE);
+  if (sym.isUndefWeak())
+    return true;
+
+  // We set the final symbols values for linker script defined symbols later.
+  // They always can be computed as a link time constant.
+  if (sym.scriptDefined)
+      return true;
+
+  error("relocation " + toString(type) + " cannot refer to absolute symbol: " +
+        toString(sym) + getLocation(s, sym, relOff));
+  return true;
+}
+
+static RelExpr toPlt(RelExpr expr) {
+  switch (expr) {
+  case R_PPC64_CALL:
+    return R_PPC64_CALL_PLT;
+  case R_PC:
+    return R_PLT_PC;
+  case R_ABS:
+    return R_PLT;
+  default:
+    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.
+  switch (expr) {
+  case R_PLT_PC:
+  case R_PPC32_PLTREL:
+    return R_PC;
+  case R_PPC64_CALL_PLT:
+    return R_PPC64_CALL;
+  case R_PLT:
+    return R_ABS;
+  default:
+    return expr;
+  }
+}
+
+// Returns true if a given shared symbol is in a read-only segment in a DSO.
+template <class ELFT> static bool isReadOnly(SharedSymbol &ss) {
+  using Elf_Phdr = typename ELFT::Phdr;
+
+  // Determine if the symbol is read-only by scanning the DSO's program headers.
+  const SharedFile &file = ss.getFile();
+  for (const Elf_Phdr &phdr :
+       check(file.template getObj<ELFT>().program_headers()))
+    if ((phdr.p_type == ELF::PT_LOAD || phdr.p_type == ELF::PT_GNU_RELRO) &&
+        !(phdr.p_flags & ELF::PF_W) && ss.value >= phdr.p_vaddr &&
+        ss.value < phdr.p_vaddr + phdr.p_memsz)
+      return true;
+  return false;
+}
+
+// Returns symbols at the same offset as a given symbol, including SS itself.
+//
+// If two or more symbols are at the same offset, and at least one of
+// them are copied by a copy relocation, all of them need to be copied.
+// Otherwise, they would refer to different places at runtime.
+template <class ELFT>
+static SmallSet<SharedSymbol *, 4> getSymbolsAt(SharedSymbol &ss) {
+  using Elf_Sym = typename ELFT::Sym;
+
+  SharedFile &file = ss.getFile();
+
+  SmallSet<SharedSymbol *, 4> ret;
+  for (const Elf_Sym &s : file.template getGlobalELFSyms<ELFT>()) {
+    if (s.st_shndx == SHN_UNDEF || s.st_shndx == SHN_ABS ||
+        s.getType() == STT_TLS || s.st_value != ss.value)
+      continue;
+    StringRef name = check(s.getName(file.getStringTable()));
+    Symbol *sym = symtab->find(name);
+    if (auto *alias = dyn_cast_or_null<SharedSymbol>(sym))
+      ret.insert(alias);
+  }
+  return ret;
+}
+
+// When a symbol is copy relocated or we create a canonical plt entry, it is
+// effectively a defined symbol. In the case of copy relocation the symbol is
+// in .bss and in the case of a canonical plt entry it is in .plt. This function
+// replaces the existing symbol with a Defined pointing to the appropriate
+// location.
+static void replaceWithDefined(Symbol &sym, SectionBase *sec, uint64_t value,
+                               uint64_t size) {
+  Symbol old = sym;
+
+  sym.replace(Defined{sym.file, sym.getName(), sym.binding, sym.stOther,
+                      sym.type, value, size, sec});
+
+  sym.pltIndex = old.pltIndex;
+  sym.gotIndex = old.gotIndex;
+  sym.verdefIndex = old.verdefIndex;
+  sym.ppc64BranchltIndex = old.ppc64BranchltIndex;
+  sym.isPreemptible = true;
+  sym.exportDynamic = true;
+  sym.isUsedInRegularObj = true;
+  sym.used = true;
+}
+
+// Reserve space in .bss or .bss.rel.ro for copy relocation.
+//
+// The copy relocation is pretty much a hack. If you use a copy relocation
+// in your program, not only the symbol name but the symbol's size, RW/RO
+// bit and alignment become part of the ABI. In addition to that, if the
+// symbol has aliases, the aliases become part of the ABI. That's subtle,
+// but if you violate that implicit ABI, that can cause very counter-
+// intuitive consequences.
+//
+// So, what is the copy relocation? It's for linking non-position
+// independent code to DSOs. In an ideal world, all references to data
+// exported by DSOs should go indirectly through GOT. But if object files
+// are compiled as non-PIC, all data references are direct. There is no
+// way for the linker to transform the code to use GOT, as machine
+// instructions are already set in stone in object files. This is where
+// the copy relocation takes a role.
+//
+// A copy relocation instructs the dynamic linker to copy data from a DSO
+// to a specified address (which is usually in .bss) at load-time. If the
+// static linker (that's us) finds a direct data reference to a DSO
+// symbol, it creates a copy relocation, so that the symbol can be
+// resolved as if it were in .bss rather than in a DSO.
+//
+// As you can see in this function, we create a copy relocation for the
+// dynamic linker, and the relocation contains not only symbol name but
+// various other informtion about the symbol. So, such attributes become a
+// part of the ABI.
+//
+// Note for application developers: I can give you a piece of advice if
+// you are writing a shared library. You probably should export only
+// functions from your library. You shouldn't export variables.
+//
+// As an example what can happen when you export variables without knowing
+// the semantics of copy relocations, assume that you have an exported
+// variable of type T. It is an ABI-breaking change to add new members at
+// end of T even though doing that doesn't change the layout of the
+// existing members. That's because the space for the new members are not
+// reserved in .bss unless you recompile the main program. That means they
+// are likely to overlap with other data that happens to be laid out next
+// to the variable in .bss. This kind of issue is sometimes very hard to
+// debug. What's a solution? Instead of exporting a varaible V from a DSO,
+// define an accessor getV().
+template <class ELFT> static void addCopyRelSymbol(SharedSymbol &ss) {
+  // Copy relocation against zero-sized symbol doesn't make sense.
+  uint64_t symSize = ss.getSize();
+  if (symSize == 0 || ss.alignment == 0)
+    fatal("cannot create a copy relocation for symbol " + toString(ss));
+
+  // See if this symbol is in a read-only segment. If so, preserve the symbol's
+  // memory protection by reserving space in the .bss.rel.ro section.
+  bool isRO = isReadOnly<ELFT>(ss);
+  BssSection *sec =
+      make<BssSection>(isRO ? ".bss.rel.ro" : ".bss", symSize, ss.alignment);
+  if (isRO)
+    in.bssRelRo->getParent()->addSection(sec);
+  else
+    in.bss->getParent()->addSection(sec);
+
+  // 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 (SharedSymbol *sym : getSymbolsAt<ELFT>(ss))
+    replaceWithDefined(*sym, sec, 0, sym->size);
+
+  mainPart->relaDyn->addReloc(target->copyRel, sec, 0, &ss);
+}
+
+// MIPS has an odd notion of "paired" relocations to calculate addends.
+// For example, if a relocation is of R_MIPS_HI16, there must be a
+// R_MIPS_LO16 relocation after that, and an addend is calculated using
+// the two relocations.
+template <class ELFT, class RelTy>
+static int64_t computeMipsAddend(const RelTy &rel, const RelTy *end,
+                                 InputSectionBase &sec, RelExpr expr,
+                                 bool isLocal) {
+  if (expr == R_MIPS_GOTREL && isLocal)
+    return sec.getFile<ELFT>()->mipsGp0;
+
+  // The ABI says that the paired relocation is used only for REL.
+  // See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+  if (RelTy::IsRela)
+    return 0;
+
+  RelType type = rel.getType(config->isMips64EL);
+  uint32_t pairTy = getMipsPairType(type, isLocal);
+  if (pairTy == R_MIPS_NONE)
+    return 0;
+
+  const uint8_t *buf = sec.data().data();
+  uint32_t symIndex = rel.getSymbol(config->isMips64EL);
+
+  // To make things worse, paired relocations might not be contiguous in
+  // the relocation table, so we need to do linear search. *sigh*
+  for (const RelTy *ri = &rel; ri != end; ++ri)
+    if (ri->getType(config->isMips64EL) == pairTy &&
+        ri->getSymbol(config->isMips64EL) == symIndex)
+      return target->getImplicitAddend(buf + ri->r_offset, pairTy);
+
+  warn("can't find matching " + toString(pairTy) + " relocation for " +
+       toString(type));
+  return 0;
+}
+
+// Returns an addend of a given relocation. If it is RELA, an addend
+// is in a relocation itself. If it is REL, we need to read it from an
+// input section.
+template <class ELFT, class RelTy>
+static int64_t computeAddend(const RelTy &rel, const RelTy *end,
+                             InputSectionBase &sec, RelExpr expr,
+                             bool isLocal) {
+  int64_t addend;
+  RelType type = rel.getType(config->isMips64EL);
+
+  if (RelTy::IsRela) {
+    addend = getAddend<ELFT>(rel);
+  } else {
+    const uint8_t *buf = sec.data().data();
+    addend = target->getImplicitAddend(buf + rel.r_offset, type);
+  }
+
+  if (config->emachine == EM_PPC64 && config->isPic && type == R_PPC64_TOC)
+    addend += getPPC64TocBase();
+  if (config->emachine == EM_MIPS)
+    addend += computeMipsAddend<ELFT>(rel, end, sec, expr, isLocal);
+
+  return addend;
+}
+
+// Custom error message if Sym is defined in a discarded section.
+template <class ELFT>
+static std::string maybeReportDiscarded(Undefined &sym) {
+  auto *file = dyn_cast_or_null<ObjFile<ELFT>>(sym.file);
+  if (!file || !sym.discardedSecIdx ||
+      file->getSections()[sym.discardedSecIdx] != &InputSection::discarded)
+    return "";
+  ArrayRef<Elf_Shdr_Impl<ELFT>> objSections =
+      CHECK(file->getObj().sections(), file);
+
+  std::string msg;
+  if (sym.type == ELF::STT_SECTION) {
+    msg = "relocation refers to a discarded section: ";
+    msg += CHECK(
+        file->getObj().getSectionName(&objSections[sym.discardedSecIdx]), file);
+  } else {
+    msg = "relocation refers to a symbol in a discarded section: " +
+          toString(sym);
+  }
+  msg += "\n>>> defined in " + toString(file);
+
+  Elf_Shdr_Impl<ELFT> elfSec = objSections[sym.discardedSecIdx - 1];
+  if (elfSec.sh_type != SHT_GROUP)
+    return msg;
+
+  // If the discarded section is a COMDAT.
+  StringRef signature = file->getShtGroupSignature(objSections, elfSec);
+  if (const InputFile *prevailing =
+          symtab->comdatGroups.lookup(CachedHashStringRef(signature)))
+    msg += "\n>>> section group signature: " + signature.str() +
+           "\n>>> prevailing definition is in " + toString(prevailing);
+  return msg;
+}
+
+// Undefined diagnostics are collected in a vector and emitted once all of
+// them are known, so that some postprocessing on the list of undefined symbols
+// can happen before lld emits diagnostics.
+struct UndefinedDiag {
+  Symbol *sym;
+  struct Loc {
+    InputSectionBase *sec;
+    uint64_t offset;
+  };
+  std::vector<Loc> locs;
+  bool isWarning;
+};
+
+static std::vector<UndefinedDiag> undefs;
+
+template <class ELFT>
+static void reportUndefinedSymbol(const UndefinedDiag &undef) {
+  Symbol &sym = *undef.sym;
+
+  auto visibility = [&]() -> std::string {
+    switch (sym.visibility) {
+    case STV_INTERNAL:
+      return "internal ";
+    case STV_HIDDEN:
+      return "hidden ";
+    case STV_PROTECTED:
+      return "protected ";
+    default:
+      return "";
+    }
+  };
+
+  std::string msg = maybeReportDiscarded<ELFT>(cast<Undefined>(sym));
+  if (msg.empty())
+    msg = "undefined " + visibility() + "symbol: " + toString(sym);
+
+  const size_t maxUndefReferences = 10;
+  size_t i = 0;
+  for (UndefinedDiag::Loc l : undef.locs) {
+    if (i >= maxUndefReferences)
+      break;
+    InputSectionBase &sec = *l.sec;
+    uint64_t offset = l.offset;
+
+    msg += "\n>>> referenced by ";
+    std::string src = sec.getSrcMsg(sym, offset);
+    if (!src.empty())
+      msg += src + "\n>>>               ";
+    msg += sec.getObjMsg(offset);
+    i++;
+  }
+
+  if (i < undef.locs.size())
+    msg += ("\n>>> referenced " + Twine(undef.locs.size() - i) + " more times")
+               .str();
+
+  if (sym.getName().startswith("_ZTV"))
+    msg += "\nthe vtable symbol may be undefined because the class is missing "
+           "its key function (see https://lld.llvm.org/missingkeyfunction)";
+
+  if (undef.isWarning)
+    warn(msg);
+  else
+    error(msg);
+}
+
+template <class ELFT> void elf::reportUndefinedSymbols() {
+  // Find the first "undefined symbol" diagnostic for each diagnostic, and
+  // collect all "referenced from" lines at the first diagnostic.
+  DenseMap<Symbol *, UndefinedDiag *> firstRef;
+  for (UndefinedDiag &undef : undefs) {
+    assert(undef.locs.size() == 1);
+    if (UndefinedDiag *canon = firstRef.lookup(undef.sym)) {
+      canon->locs.push_back(undef.locs[0]);
+      undef.locs.clear();
+    } else
+      firstRef[undef.sym] = &undef;
+  }
+
+  for (const UndefinedDiag &undef : undefs) {
+    if (!undef.locs.empty())
+      reportUndefinedSymbol<ELFT>(undef);
+  }
+  undefs.clear();
+}
+
+// Report an undefined symbol if necessary.
+// Returns true if the undefined symbol will produce an error message.
+template <class ELFT>
+static bool maybeReportUndefined(Symbol &sym, InputSectionBase &sec,
+                                 uint64_t offset) {
+  if (!sym.isUndefined() || sym.isWeak())
+    return false;
+
+  bool canBeExternal = !sym.isLocal() && sym.computeBinding() != STB_LOCAL &&
+                       sym.visibility == STV_DEFAULT;
+  if (config->unresolvedSymbols == UnresolvedPolicy::Ignore && canBeExternal)
+    return false;
+
+  // clang (as of 2019-06-12) / gcc (as of 8.2.1) PPC64 may emit a .rela.toc
+  // which references a switch table in a discarded .rodata/.text section. The
+  // .toc and the .rela.toc are incorrectly not placed in the comdat. The ELF
+  // spec says references from outside the group to a STB_LOCAL symbol are not
+  // allowed. Work around the bug.
+  if (config->emachine == EM_PPC64 &&
+      cast<Undefined>(sym).discardedSecIdx != 0 && sec.name == ".toc")
+    return false;
+
+  bool isWarning =
+      (config->unresolvedSymbols == UnresolvedPolicy::Warn && canBeExternal) ||
+      config->noinhibitExec;
+  undefs.push_back({&sym, {{&sec, offset}}, isWarning});
+  return !isWarning;
+}
+
+// MIPS N32 ABI treats series of successive relocations with the same offset
+// as a single relocation. The similar approach used by N64 ABI, but this ABI
+// packs all relocations into the single relocation record. Here we emulate
+// this for the N32 ABI. Iterate over relocation with the same offset and put
+// theirs types into the single bit-set.
+template <class RelTy> static RelType getMipsN32RelType(RelTy *&rel, RelTy *end) {
+  RelType type = 0;
+  uint64_t offset = rel->r_offset;
+
+  int n = 0;
+  while (rel != end && rel->r_offset == offset)
+    type |= (rel++)->getType(config->isMips64EL) << (8 * n++);
+  return type;
+}
+
+// .eh_frame sections are mergeable input sections, so their input
+// offsets are not linearly mapped to output section. For each input
+// offset, we need to find a section piece containing the offset and
+// add the piece's base address to the input offset to compute the
+// output offset. That isn't cheap.
+//
+// This class is to speed up the offset computation. When we process
+// relocations, we access offsets in the monotonically increasing
+// order. So we can optimize for that access pattern.
+//
+// For sections other than .eh_frame, this class doesn't do anything.
+namespace {
+class OffsetGetter {
+public:
+  explicit OffsetGetter(InputSectionBase &sec) {
+    if (auto *eh = dyn_cast<EhInputSection>(&sec))
+      pieces = eh->pieces;
+  }
+
+  // Translates offsets in input sections to offsets in output sections.
+  // Given offset must increase monotonically. We assume that Piece is
+  // sorted by inputOff.
+  uint64_t get(uint64_t off) {
+    if (pieces.empty())
+      return off;
+
+    while (i != pieces.size() && pieces[i].inputOff + pieces[i].size <= off)
+      ++i;
+    if (i == pieces.size())
+      fatal(".eh_frame: relocation is not in any piece");
+
+    // Pieces must be contiguous, so there must be no holes in between.
+    assert(pieces[i].inputOff <= off && "Relocation not in any piece");
+
+    // Offset -1 means that the piece is dead (i.e. garbage collected).
+    if (pieces[i].outputOff == -1)
+      return -1;
+    return pieces[i].outputOff + off - pieces[i].inputOff;
+  }
+
+private:
+  ArrayRef<EhSectionPiece> pieces;
+  size_t i = 0;
+};
+} // namespace
+
+static void addRelativeReloc(InputSectionBase *isec, uint64_t offsetInSec,
+                             Symbol *sym, int64_t addend, RelExpr expr,
+                             RelType type) {
+  Partition &part = isec->getPartition();
+
+  // Add a relative relocation. If relrDyn section is enabled, and the
+  // relocation offset is guaranteed to be even, add the relocation to
+  // the relrDyn section, otherwise add it to the relaDyn section.
+  // relrDyn sections don't support odd offsets. Also, relrDyn sections
+  // don't store the addend values, so we must write it to the relocated
+  // address.
+  if (part.relrDyn && isec->alignment >= 2 && offsetInSec % 2 == 0) {
+    isec->relocations.push_back({expr, type, offsetInSec, addend, sym});
+    part.relrDyn->relocs.push_back({isec, offsetInSec});
+    return;
+  }
+  part.relaDyn->addReloc(target->relativeRel, isec, offsetInSec, sym, addend,
+                         expr, type);
+}
+
+template <class ELFT, class GotPltSection>
+static void addPltEntry(PltSection *plt, GotPltSection *gotPlt,
+                        RelocationBaseSection *rel, RelType type, Symbol &sym) {
+  plt->addEntry<ELFT>(sym);
+  gotPlt->addEntry(sym);
+  rel->addReloc(
+      {type, gotPlt, sym.getGotPltOffset(), !sym.isPreemptible, &sym, 0});
+}
+
+static void addGotEntry(Symbol &sym) {
+  in.got->addEntry(sym);
+
+  RelExpr expr = sym.isTls() ? R_TLS : R_ABS;
+  uint64_t off = sym.getGotOffset();
+
+  // If a GOT slot value can be calculated at link-time, which is now,
+  // we can just fill that out.
+  //
+  // (We don't actually write a value to a GOT slot right now, but we
+  // add a static relocation to a Relocations vector so that
+  // InputSection::relocate will do the work for us. We may be able
+  // to just write a value now, but it is a TODO.)
+  bool isLinkTimeConstant =
+      !sym.isPreemptible && (!config->isPic || isAbsolute(sym));
+  if (isLinkTimeConstant) {
+    in.got->relocations.push_back({expr, target->symbolicRel, off, 0, &sym});
+    return;
+  }
+
+  // Otherwise, we emit a dynamic relocation to .rel[a].dyn so that
+  // the GOT slot will be fixed at load-time.
+  if (!sym.isTls() && !sym.isPreemptible && config->isPic && !isAbsolute(sym)) {
+    addRelativeReloc(in.got, off, &sym, 0, R_ABS, target->symbolicRel);
+    return;
+  }
+  mainPart->relaDyn->addReloc(
+      sym.isTls() ? target->tlsGotRel : target->gotRel, in.got, off, &sym, 0,
+      sym.isPreemptible ? R_ADDEND : R_ABS, target->symbolicRel);
+}
+
+// Return true if we can define a symbol in the executable that
+// contains the value/function of a symbol defined in a shared
+// library.
+static bool canDefineSymbolInExecutable(Symbol &sym) {
+  // If the symbol has default visibility the symbol defined in the
+  // executable will preempt it.
+  // Note that we want the visibility of the shared symbol itself, not
+  // the visibility of the symbol in the output file we are producing. That is
+  // why we use Sym.stOther.
+  if ((sym.stOther & 0x3) == STV_DEFAULT)
+    return true;
+
+  // If we are allowed to break address equality of functions, defining
+  // a plt entry will allow the program to call the function in the
+  // .so, but the .so and the executable will no agree on the address
+  // of the function. Similar logic for objects.
+  return ((sym.isFunc() && config->ignoreFunctionAddressEquality) ||
+          (sym.isObject() && config->ignoreDataAddressEquality));
+}
+
+// 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>
+static void processRelocAux(InputSectionBase &sec, RelExpr expr, RelType type,
+                            uint64_t offset, Symbol &sym, const RelTy &rel,
+                            int64_t addend) {
+  // If the relocation is known to be a link-time constant, we know no dynamic
+  // relocation will be created, pass the control to relocateAlloc() or
+  // relocateNonAlloc() to resolve it.
+  //
+  // The behavior of an undefined weak reference is implementation defined. If
+  // the relocation is to a weak undef, and we are producing an executable, let
+  // relocate{,Non}Alloc() resolve it.
+  if (isStaticLinkTimeConstant(expr, type, sym, sec, offset) ||
+      (!config->shared && sym.isUndefWeak())) {
+    sec.relocations.push_back({expr, type, offset, addend, &sym});
+    return;
+  }
+
+  bool canWrite = (sec.flags & SHF_WRITE) || !config->zText;
+  if (canWrite) {
+    RelType rel = target->getDynRel(type);
+    if (expr == R_GOT || (rel == target->symbolicRel && !sym.isPreemptible)) {
+      addRelativeReloc(&sec, offset, &sym, addend, expr, type);
+      return;
+    } else if (rel != 0) {
+      if (config->emachine == EM_MIPS && rel == target->symbolicRel)
+        rel = target->relativeRel;
+      sec.getPartition().relaDyn->addReloc(rel, &sec, offset, &sym, addend,
+                                           R_ADDEND, type);
+
+      // 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)
+        in.mipsGot->addEntry(*sec.file, sym, addend, expr);
+      return;
+    }
+  }
+
+  if (!canWrite && (config->isPic && !isRelExpr(expr))) {
+    error(
+        "can't create dynamic relocation " + toString(type) + " against " +
+        (sym.getName().empty() ? "local symbol" : "symbol: " + toString(sym)) +
+        " in readonly segment; recompile object files with -fPIC "
+        "or pass '-Wl,-z,notext' to allow text relocations in the output" +
+        getLocation(sec, sym, offset));
+    return;
+  }
+
+  // Copy relocations (for STT_OBJECT) and canonical PLT (for STT_FUNC) are only
+  // possible in an executable.
+  //
+  // Among R_ABS relocatoin types, symbolicRel has the same size as the word
+  // size. Others have fewer bits and may cause runtime overflow in -pie/-shared
+  // mode. Disallow them.
+  if (config->shared ||
+      (config->pie && expr == R_ABS && type != target->symbolicRel)) {
+    errorOrWarn(
+        "relocation " + toString(type) + " cannot be used against " +
+        (sym.getName().empty() ? "local symbol" : "symbol " + toString(sym)) +
+        "; recompile with -fPIC" + getLocation(sec, sym, offset));
+    return;
+  }
+
+  // If the symbol is undefined we already reported any relevant errors.
+  if (sym.isUndefined())
+    return;
+
+  if (!canDefineSymbolInExecutable(sym)) {
+    error("cannot preempt symbol: " + toString(sym) +
+          getLocation(sec, sym, offset));
+    return;
+  }
+
+  if (sym.isObject()) {
+    // Produce a copy relocation.
+    if (auto *ss = dyn_cast<SharedSymbol>(&sym)) {
+      if (!config->zCopyreloc)
+        error("unresolvable relocation " + toString(type) +
+              " against symbol '" + toString(*ss) +
+              "'; recompile with -fPIC or remove '-z nocopyreloc'" +
+              getLocation(sec, sym, offset));
+      addCopyRelSymbol<ELFT>(*ss);
+    }
+    sec.relocations.push_back({expr, type, offset, addend, &sym});
+    return;
+  }
+
+  if (sym.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 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).
+
+    // For position independent executable on i386, the plt entry requires ebx
+    // to be set. This causes two problems:
+    // * If some code has a direct reference to a function, it was probably
+    //   compiled without -fPIE/-fPIC and doesn't maintain ebx.
+    // * If a library definition gets preempted to the executable, it will have
+    //   the wrong ebx value.
+    if (config->pie && config->emachine == EM_386)
+      errorOrWarn("symbol '" + toString(sym) +
+                  "' cannot be preempted; recompile with -fPIE" +
+                  getLocation(sec, sym, offset));
+    if (!sym.isInPlt())
+      addPltEntry<ELFT>(in.plt, in.gotPlt, in.relaPlt, target->pltRel, sym);
+    if (!sym.isDefined())
+      replaceWithDefined(
+          sym, in.plt,
+          target->pltHeaderSize + target->pltEntrySize * sym.pltIndex, 0);
+    sym.needsPltAddr = true;
+    sec.relocations.push_back({expr, type, offset, addend, &sym});
+    return;
+  }
+
+  errorOrWarn("symbol '" + toString(sym) + "' has no type" +
+              getLocation(sec, sym, offset));
+}
+
+struct IRelativeReloc {
+  RelType type;
+  InputSectionBase *sec;
+  uint64_t offset;
+  Symbol *sym;
+};
+
+static std::vector<IRelativeReloc> iRelativeRelocs;
+
+template <class ELFT, class RelTy>
+static void scanReloc(InputSectionBase &sec, OffsetGetter &getOffset, RelTy *&i,
+                      RelTy *end) {
+  const RelTy &rel = *i;
+  uint32_t symIndex = rel.getSymbol(config->isMips64EL);
+  Symbol &sym = sec.getFile<ELFT>()->getSymbol(symIndex);
+  RelType type;
+
+  // Deal with MIPS oddity.
+  if (config->mipsN32Abi) {
+    type = getMipsN32RelType(i, end);
+  } else {
+    type = rel.getType(config->isMips64EL);
+    ++i;
+  }
+
+  // Get an offset in an output section this relocation is applied to.
+  uint64_t offset = getOffset.get(rel.r_offset);
+  if (offset == uint64_t(-1))
+    return;
+
+  // Error if the target symbol is undefined. Symbol index 0 may be used by
+  // marker relocations, e.g. R_*_NONE and R_ARM_V4BX. Don't error on them.
+  if (symIndex != 0 && maybeReportUndefined<ELFT>(sym, sec, rel.r_offset))
+    return;
+
+  const uint8_t *relocatedAddr = sec.data().begin() + rel.r_offset;
+  RelExpr expr = target->getRelExpr(type, sym, relocatedAddr);
+
+  // Ignore "hint" relocations because they are only markers for relaxation.
+  if (oneof<R_HINT, R_NONE>(expr))
+    return;
+
+  // We can separate the small code model relocations into 2 categories:
+  // 1) Those that access the compiler generated .toc sections.
+  // 2) Those that access the linker allocated got entries.
+  // lld allocates got entries to symbols on demand. Since we don't try to sort
+  // the got entries in any way, we don't have to track which objects have
+  // got-based small code model relocs. The .toc sections get placed after the
+  // end of the linker allocated .got section and we do sort those so sections
+  // addressed with small code model relocations come first.
+  if (config->emachine == EM_PPC64 && isPPC64SmallCodeModelTocReloc(type))
+    sec.file->ppc64SmallCodeModelTocRelocs = true;
+
+  if (sym.isGnuIFunc() && !config->zText && config->warnIfuncTextrel) {
+    warn("using ifunc symbols when text relocations are allowed may produce "
+         "a binary that will segfault, if the object file is linked with "
+         "old version of glibc (glibc 2.28 and earlier). If this applies to "
+         "you, consider recompiling the object files without -fPIC and "
+         "without -Wl,-z,notext option. Use -no-warn-ifunc-textrel to "
+         "turn off this warning." +
+         getLocation(sec, sym, offset));
+  }
+
+  // Read an addend.
+  int64_t addend = computeAddend<ELFT>(rel, end, sec, expr, sym.isLocal());
+
+  // Relax relocations.
+  //
+  // If we know that a PLT entry will be resolved within the same ELF module, we
+  // can skip PLT access and directly jump to the destination function. For
+  // example, if we are linking a main exectuable, all dynamic symbols that can
+  // be resolved within the executable will actually be resolved that way at
+  // runtime, because the main exectuable is always at the beginning of a search
+  // list. We can leverage that fact.
+  if (!sym.isPreemptible && (!sym.isGnuIFunc() || config->zIfuncNoplt)) {
+    if (expr == R_GOT_PC && !isAbsoluteValue(sym)) {
+      expr = target->adjustRelaxExpr(type, relocatedAddr, expr);
+    } else {
+      // Addend of R_PPC_PLTREL24 is used to choose call stub type. It should be
+      // ignored if optimized to R_PC.
+      if (config->emachine == EM_PPC && expr == R_PPC32_PLTREL)
+        addend = 0;
+      expr = fromPlt(expr);
+    }
+  }
+
+  // If the relocation does not emit a GOT or GOTPLT entry but its computation
+  // uses their addresses, we need GOT or GOTPLT to be created.
+  //
+  // The 4 types that relative GOTPLT are all x86 and x86-64 specific.
+  if (oneof<R_GOTPLTONLY_PC, R_GOTPLTREL, R_GOTPLT, R_TLSGD_GOTPLT>(expr)) {
+    in.gotPlt->hasGotPltOffRel = true;
+  } else if (oneof<R_GOTONLY_PC, R_GOTREL, R_PPC64_TOCBASE, R_PPC64_RELAX_TOC>(
+                 expr)) {
+    in.got->hasGotOffRel = true;
+  }
+
+  // Process some TLS relocations, including relaxing TLS relocations.
+  // Note that this function does not handle all TLS relocations.
+  if (unsigned processed =
+          handleTlsRelocation<ELFT>(type, sym, sec, offset, addend, expr)) {
+    i += (processed - 1);
+    return;
+  }
+
+  // We were asked not to generate PLT entries for ifuncs. Instead, pass the
+  // direct relocation on through.
+  if (sym.isGnuIFunc() && config->zIfuncNoplt) {
+    sym.exportDynamic = true;
+    mainPart->relaDyn->addReloc(type, &sec, offset, &sym, addend, R_ADDEND, type);
+    return;
+  }
+
+  // Non-preemptible ifuncs require special handling. First, handle the usual
+  // case where the symbol isn't one of these.
+  if (!sym.isGnuIFunc() || sym.isPreemptible) {
+    // If a relocation needs PLT, we create PLT and GOTPLT slots for the symbol.
+    if (needsPlt(expr) && !sym.isInPlt())
+      addPltEntry<ELFT>(in.plt, in.gotPlt, in.relaPlt, target->pltRel, sym);
+
+    // Create a GOT slot if a relocation needs GOT.
+    if (needsGot(expr)) {
+      if (config->emachine == EM_MIPS) {
+        // MIPS ABI has special rules to process GOT entries and doesn't
+        // require relocation entries for them. A special case is TLS
+        // relocations. In that case dynamic loader applies dynamic
+        // relocations to initialize TLS GOT entries.
+        // 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
+        in.mipsGot->addEntry(*sec.file, sym, addend, expr);
+      } else if (!sym.isInGot()) {
+        addGotEntry(sym);
+      }
+    }
+  } else {
+    // Handle a reference to a non-preemptible ifunc. These are special in a
+    // few ways:
+    //
+    // - Unlike most non-preemptible symbols, non-preemptible ifuncs do not have
+    //   a fixed value. But assuming that all references to the ifunc are
+    //   GOT-generating or PLT-generating, the handling of an ifunc is
+    //   relatively straightforward. We create a PLT entry in Iplt, which is
+    //   usually at the end of .plt, which makes an indirect call using a
+    //   matching GOT entry in igotPlt, which is usually at the end of .got.plt.
+    //   The GOT entry is relocated using an IRELATIVE relocation in relaIplt,
+    //   which is usually at the end of .rela.plt. Unlike most relocations in
+    //   .rela.plt, which may be evaluated lazily without -z now, dynamic
+    //   loaders evaluate IRELATIVE relocs eagerly, which means that for
+    //   IRELATIVE relocs only, GOT-generating relocations can point directly to
+    //   .got.plt without requiring a separate GOT entry.
+    //
+    // - Despite the fact that an ifunc does not have a fixed value, compilers
+    //   that are not passed -fPIC will assume that they do, and will emit
+    //   direct (non-GOT-generating, non-PLT-generating) relocations to the
+    //   symbol. This means that if a direct relocation to the symbol is
+    //   seen, the linker must set a value for the symbol, and this value must
+    //   be consistent no matter what type of reference is made to the symbol.
+    //   This can be done by creating a PLT entry for the symbol in the way
+    //   described above and making it canonical, that is, making all references
+    //   point to the PLT entry instead of the resolver. In lld we also store
+    //   the address of the PLT entry in the dynamic symbol table, which means
+    //   that the symbol will also have the same value in other modules.
+    //   Because the value loaded from the GOT needs to be consistent with
+    //   the value computed using a direct relocation, a non-preemptible ifunc
+    //   may end up with two GOT entries, one in .got.plt that points to the
+    //   address returned by the resolver and is used only by the PLT entry,
+    //   and another in .got that points to the PLT entry and is used by
+    //   GOT-generating relocations.
+    //
+    // - The fact that these symbols do not have a fixed value makes them an
+    //   exception to the general rule that a statically linked executable does
+    //   not require any form of dynamic relocation. To handle these relocations
+    //   correctly, the IRELATIVE relocations are stored in an array which a
+    //   statically linked executable's startup code must enumerate using the
+    //   linker-defined symbols __rela?_iplt_{start,end}.
+    //
+    // - An absolute relocation to a non-preemptible ifunc (such as a global
+    //   variable containing a pointer to the ifunc) needs to be relocated in
+    //   the exact same way as a GOT entry, so we can avoid needing to make the
+    //   PLT entry canonical by translating such relocations into IRELATIVE
+    //   relocations in the relaIplt.
+    if (!sym.isInPlt()) {
+      // Create PLT and GOTPLT slots for the symbol.
+      sym.isInIplt = true;
+
+      // Create a copy of the symbol to use as the target of the IRELATIVE
+      // relocation in the igotPlt. This is in case we make the PLT canonical
+      // later, which would overwrite the original symbol.
+      //
+      // FIXME: Creating a copy of the symbol here is a bit of a hack. All
+      // that's really needed to create the IRELATIVE is the section and value,
+      // so ideally we should just need to copy those.
+      auto *directSym = make<Defined>(cast<Defined>(sym));
+      addPltEntry<ELFT>(in.iplt, in.igotPlt, in.relaIplt, target->iRelativeRel,
+                        *directSym);
+      sym.pltIndex = directSym->pltIndex;
+    }
+    if (expr == R_ABS && addend == 0 && (sec.flags & SHF_WRITE)) {
+      // We might be able to represent this as an IRELATIVE. But we don't know
+      // yet whether some later relocation will make the symbol point to a
+      // canonical PLT, which would make this either a dynamic RELATIVE (PIC) or
+      // static (non-PIC) relocation. So we keep a record of the information
+      // required to process the relocation, and after scanRelocs() has been
+      // called on all relocations, the relocation is resolved by
+      // addIRelativeRelocs().
+      iRelativeRelocs.push_back({type, &sec, offset, &sym});
+      return;
+    }
+    if (needsGot(expr)) {
+      // Redirect GOT accesses to point to the Igot.
+      //
+      // This field is also used to keep track of whether we ever needed a GOT
+      // entry. If we did and we make the PLT canonical later, we'll need to
+      // create a GOT entry pointing to the PLT entry for Sym.
+      sym.gotInIgot = true;
+    } else if (!needsPlt(expr)) {
+      // Make the ifunc's PLT entry canonical by changing the value of its
+      // symbol to redirect all references to point to it.
+      unsigned entryOffset = sym.pltIndex * target->pltEntrySize;
+      if (config->zRetpolineplt)
+        entryOffset += target->pltHeaderSize;
+
+      auto &d = cast<Defined>(sym);
+      d.section = in.iplt;
+      d.value = entryOffset;
+      d.size = 0;
+      // It's important to set the symbol type here so that dynamic loaders
+      // don't try to call the PLT as if it were an ifunc resolver.
+      d.type = STT_FUNC;
+
+      if (sym.gotInIgot) {
+        // We previously encountered a GOT generating reference that we
+        // redirected to the Igot. Now that the PLT entry is canonical we must
+        // clear the redirection to the Igot and add a GOT entry. As we've
+        // changed the symbol type to STT_FUNC future GOT generating references
+        // will naturally use this GOT entry.
+        //
+        // We don't need to worry about creating a MIPS GOT here because ifuncs
+        // aren't a thing on MIPS.
+        sym.gotInIgot = false;
+        addGotEntry(sym);
+      }
+    }
+  }
+
+  processRelocAux<ELFT>(sec, expr, type, offset, sym, rel, addend);
+}
+
+template <class ELFT, class RelTy>
+static void scanRelocs(InputSectionBase &sec, ArrayRef<RelTy> rels) {
+  OffsetGetter getOffset(sec);
+
+  // Not all relocations end up in Sec.Relocations, but a lot do.
+  sec.relocations.reserve(rels.size());
+
+  for (auto i = rels.begin(), end = rels.end(); i != end;)
+    scanReloc<ELFT>(sec, getOffset, i, end);
+
+  // Sort relocations by offset for more efficient searching for
+  // R_RISCV_PCREL_HI20 and R_PPC64_ADDR64.
+  if (config->emachine == EM_RISCV ||
+      (config->emachine == EM_PPC64 && sec.name == ".toc"))
+    llvm::stable_sort(sec.relocations,
+                      [](const Relocation &lhs, const Relocation &rhs) {
+                        return lhs.offset < rhs.offset;
+                      });
+}
+
+template <class ELFT> void elf::scanRelocations(InputSectionBase &s) {
+  if (s.areRelocsRela)
+    scanRelocs<ELFT>(s, s.relas<ELFT>());
+  else
+    scanRelocs<ELFT>(s, s.rels<ELFT>());
+}
+
+// Figure out which representation to use for any absolute relocs to
+// non-preemptible ifuncs that we visited during scanRelocs().
+void elf::addIRelativeRelocs() {
+  for (IRelativeReloc &r : iRelativeRelocs) {
+    if (r.sym->type == STT_GNU_IFUNC)
+      in.relaIplt->addReloc(
+          {target->iRelativeRel, r.sec, r.offset, true, r.sym, 0});
+    else if (config->isPic)
+      addRelativeReloc(r.sec, r.offset, r.sym, 0, R_ABS, r.type);
+    else
+      r.sec->relocations.push_back({R_ABS, r.type, r.offset, 0, r.sym});
+  }
+  iRelativeRelocs.clear();
+}
+
+static bool mergeCmp(const InputSection *a, const InputSection *b) {
+  // std::merge requires a strict weak ordering.
+  if (a->outSecOff < b->outSecOff)
+    return true;
+
+  if (a->outSecOff == b->outSecOff) {
+    auto *ta = dyn_cast<ThunkSection>(a);
+    auto *tb = dyn_cast<ThunkSection>(b);
+
+    // Check if Thunk is immediately before any specific Target
+    // InputSection for example Mips LA25 Thunks.
+    if (ta && ta->getTargetInputSection() == b)
+      return true;
+
+    // Place Thunk Sections without specific targets before
+    // non-Thunk Sections.
+    if (ta && !tb && !ta->getTargetInputSection())
+      return true;
+  }
+
+  return false;
+}
+
+// Call Fn on every executable InputSection accessed via the linker script
+// InputSectionDescription::Sections.
+static void forEachInputSectionDescription(
+    ArrayRef<OutputSection *> outputSections,
+    llvm::function_ref<void(OutputSection *, InputSectionDescription *)> fn) {
+  for (OutputSection *os : outputSections) {
+    if (!(os->flags & SHF_ALLOC) || !(os->flags & SHF_EXECINSTR))
+      continue;
+    for (BaseCommand *bc : os->sectionCommands)
+      if (auto *isd = dyn_cast<InputSectionDescription>(bc))
+        fn(os, isd);
+  }
+}
+
+// Thunk Implementation
+//
+// Thunks (sometimes called stubs, veneers or branch islands) are small pieces
+// of code that the linker inserts inbetween a caller and a callee. The thunks
+// are added at link time rather than compile time as the decision on whether
+// a thunk is needed, such as the caller and callee being out of range, can only
+// be made at link time.
+//
+// It is straightforward to tell given the current state of the program when a
+// thunk is needed for a particular call. The more difficult part is that
+// the thunk needs to be placed in the program such that the caller can reach
+// the thunk and the thunk can reach the callee; furthermore, adding thunks to
+// the program alters addresses, which can mean more thunks etc.
+//
+// In lld we have a synthetic ThunkSection that can hold many Thunks.
+// The decision to have a ThunkSection act as a container means that we can
+// more easily handle the most common case of a single block of contiguous
+// Thunks by inserting just a single ThunkSection.
+//
+// The implementation of Thunks in lld is split across these areas
+// Relocations.cpp : Framework for creating and placing thunks
+// Thunks.cpp : The code generated for each supported thunk
+// Target.cpp : Target specific hooks that the framework uses to decide when
+//              a thunk is used
+// Synthetic.cpp : Implementation of ThunkSection
+// Writer.cpp : Iteratively call framework until no more Thunks added
+//
+// Thunk placement requirements:
+// Mips LA25 thunks. These must be placed immediately before the callee section
+// We can assume that the caller is in range of the Thunk. These are modelled
+// by Thunks that return the section they must precede with
+// getTargetInputSection().
+//
+// ARM interworking and range extension thunks. These thunks must be placed
+// within range of the caller. All implemented ARM thunks can always reach the
+// callee as they use an indirect jump via a register that has no range
+// restrictions.
+//
+// Thunk placement algorithm:
+// For Mips LA25 ThunkSections; the placement is explicit, it has to be before
+// getTargetInputSection().
+//
+// For thunks that must be placed within range of the caller there are many
+// possible choices given that the maximum range from the caller is usually
+// much larger than the average InputSection size. Desirable properties include:
+// - Maximize reuse of thunks by multiple callers
+// - Minimize number of ThunkSections to simplify insertion
+// - Handle impact of already added Thunks on addresses
+// - Simple to understand and implement
+//
+// In lld for the first pass, we pre-create one or more ThunkSections per
+// InputSectionDescription at Target specific intervals. A ThunkSection is
+// placed so that the estimated end of the ThunkSection is within range of the
+// start of the InputSectionDescription or the previous ThunkSection. For
+// example:
+// InputSectionDescription
+// Section 0
+// ...
+// Section N
+// ThunkSection 0
+// Section N + 1
+// ...
+// Section N + K
+// Thunk Section 1
+//
+// The intention is that we can add a Thunk to a ThunkSection that is well
+// spaced enough to service a number of callers without having to do a lot
+// of work. An important principle is that it is not an error if a Thunk cannot
+// be placed in a pre-created ThunkSection; when this happens we create a new
+// ThunkSection placed next to the caller. This allows us to handle the vast
+// majority of thunks simply, but also handle rare cases where the branch range
+// is smaller than the target specific spacing.
+//
+// The algorithm is expected to create all the thunks that are needed in a
+// single pass, with a small number of programs needing a second pass due to
+// the insertion of thunks in the first pass increasing the offset between
+// callers and callees that were only just in range.
+//
+// A consequence of allowing new ThunkSections to be created outside of the
+// pre-created ThunkSections is that in rare cases calls to Thunks that were in
+// range in pass K, are out of range in some pass > K due to the insertion of
+// more Thunks in between the caller and callee. When this happens we retarget
+// the relocation back to the original target and create another Thunk.
+
+// Remove ThunkSections that are empty, this should only be the initial set
+// precreated on pass 0.
+
+// Insert the Thunks for OutputSection OS into their designated place
+// in the Sections vector, and recalculate the InputSection output section
+// offsets.
+// This may invalidate any output section offsets stored outside of InputSection
+void ThunkCreator::mergeThunks(ArrayRef<OutputSection *> outputSections) {
+  forEachInputSectionDescription(
+      outputSections, [&](OutputSection *os, InputSectionDescription *isd) {
+        if (isd->thunkSections.empty())
+          return;
+
+        // Remove any zero sized precreated Thunks.
+        llvm::erase_if(isd->thunkSections,
+                       [](const std::pair<ThunkSection *, uint32_t> &ts) {
+                         return ts.first->getSize() == 0;
+                       });
+
+        // ISD->ThunkSections contains all created ThunkSections, including
+        // those inserted in previous passes. Extract the Thunks created this
+        // pass and order them in ascending outSecOff.
+        std::vector<ThunkSection *> newThunks;
+        for (const std::pair<ThunkSection *, uint32_t> ts : isd->thunkSections)
+          if (ts.second == pass)
+            newThunks.push_back(ts.first);
+        llvm::stable_sort(newThunks,
+                          [](const ThunkSection *a, const ThunkSection *b) {
+                            return a->outSecOff < b->outSecOff;
+                          });
+
+        // Merge sorted vectors of Thunks and InputSections by outSecOff
+        std::vector<InputSection *> tmp;
+        tmp.reserve(isd->sections.size() + newThunks.size());
+
+        std::merge(isd->sections.begin(), isd->sections.end(),
+                   newThunks.begin(), newThunks.end(), std::back_inserter(tmp),
+                   mergeCmp);
+
+        isd->sections = std::move(tmp);
+      });
+}
+
+// Find or create a ThunkSection within the InputSectionDescription (ISD) that
+// is in range of Src. An ISD maps to a range of InputSections described by a
+// linker script section pattern such as { .text .text.* }.
+ThunkSection *ThunkCreator::getISDThunkSec(OutputSection *os, InputSection *isec,
+                                           InputSectionDescription *isd,
+                                           uint32_t type, uint64_t src) {
+  for (std::pair<ThunkSection *, uint32_t> tp : isd->thunkSections) {
+    ThunkSection *ts = tp.first;
+    uint64_t tsBase = os->addr + ts->outSecOff;
+    uint64_t tsLimit = tsBase + ts->getSize();
+    if (target->inBranchRange(type, src, (src > tsLimit) ? tsBase : tsLimit))
+      return ts;
+  }
+
+  // No suitable ThunkSection exists. This can happen when there is a branch
+  // with lower range than the ThunkSection spacing or when there are too
+  // many Thunks. Create a new ThunkSection as close to the InputSection as
+  // possible. Error if InputSection is so large we cannot place ThunkSection
+  // anywhere in Range.
+  uint64_t thunkSecOff = isec->outSecOff;
+  if (!target->inBranchRange(type, src, os->addr + thunkSecOff)) {
+    thunkSecOff = isec->outSecOff + isec->getSize();
+    if (!target->inBranchRange(type, src, os->addr + thunkSecOff))
+      fatal("InputSection too large for range extension thunk " +
+            isec->getObjMsg(src - (os->addr + isec->outSecOff)));
+  }
+  return addThunkSection(os, isd, thunkSecOff);
+}
+
+// Add a Thunk that needs to be placed in a ThunkSection that immediately
+// precedes its Target.
+ThunkSection *ThunkCreator::getISThunkSec(InputSection *isec) {
+  ThunkSection *ts = thunkedSections.lookup(isec);
+  if (ts)
+    return ts;
+
+  // Find InputSectionRange within Target Output Section (TOS) that the
+  // InputSection (IS) that we need to precede is in.
+  OutputSection *tos = isec->getParent();
+  for (BaseCommand *bc : tos->sectionCommands) {
+    auto *isd = dyn_cast<InputSectionDescription>(bc);
+    if (!isd || isd->sections.empty())
+      continue;
+
+    InputSection *first = isd->sections.front();
+    InputSection *last = isd->sections.back();
+
+    if (isec->outSecOff < first->outSecOff || last->outSecOff < isec->outSecOff)
+      continue;
+
+    ts = addThunkSection(tos, isd, isec->outSecOff);
+    thunkedSections[isec] = ts;
+    return ts;
+  }
+
+  return nullptr;
+}
+
+// Create one or more ThunkSections per OS that can be used to place Thunks.
+// We attempt to place the ThunkSections using the following desirable
+// properties:
+// - Within range of the maximum number of callers
+// - Minimise the number of ThunkSections
+//
+// We follow a simple but conservative heuristic to place ThunkSections at
+// offsets that are multiples of a Target specific branch range.
+// For an InputSectionDescription that is smaller than the range, a single
+// ThunkSection at the end of the range will do.
+//
+// For an InputSectionDescription that is more than twice the size of the range,
+// we place the last ThunkSection at range bytes from the end of the
+// InputSectionDescription in order to increase the likelihood that the
+// distance from a thunk to its target will be sufficiently small to
+// allow for the creation of a short thunk.
+void ThunkCreator::createInitialThunkSections(
+    ArrayRef<OutputSection *> outputSections) {
+  uint32_t thunkSectionSpacing = target->getThunkSectionSpacing();
+
+  forEachInputSectionDescription(
+      outputSections, [&](OutputSection *os, InputSectionDescription *isd) {
+        if (isd->sections.empty())
+          return;
+
+        uint32_t isdBegin = isd->sections.front()->outSecOff;
+        uint32_t isdEnd =
+            isd->sections.back()->outSecOff + isd->sections.back()->getSize();
+        uint32_t lastThunkLowerBound = -1;
+        if (isdEnd - isdBegin > thunkSectionSpacing * 2)
+          lastThunkLowerBound = isdEnd - thunkSectionSpacing;
+
+        uint32_t isecLimit;
+        uint32_t prevIsecLimit = isdBegin;
+        uint32_t thunkUpperBound = isdBegin + thunkSectionSpacing;
+
+        for (const InputSection *isec : isd->sections) {
+          isecLimit = isec->outSecOff + isec->getSize();
+          if (isecLimit > thunkUpperBound) {
+            addThunkSection(os, isd, prevIsecLimit);
+            thunkUpperBound = prevIsecLimit + thunkSectionSpacing;
+          }
+          if (isecLimit > lastThunkLowerBound)
+            break;
+          prevIsecLimit = isecLimit;
+        }
+        addThunkSection(os, isd, isecLimit);
+      });
+}
+
+ThunkSection *ThunkCreator::addThunkSection(OutputSection *os,
+                                            InputSectionDescription *isd,
+                                            uint64_t off) {
+  auto *ts = make<ThunkSection>(os, off);
+  ts->partition = os->partition;
+  isd->thunkSections.push_back({ts, pass});
+  return ts;
+}
+
+static bool isThunkSectionCompatible(InputSection *source,
+                                     SectionBase *target) {
+  // We can't reuse thunks in different loadable partitions because they might
+  // not be loaded. But partition 1 (the main partition) will always be loaded.
+  if (source->partition != target->partition)
+    return target->partition == 1;
+  return true;
+}
+
+std::pair<Thunk *, bool> ThunkCreator::getThunk(InputSection *isec,
+                                                Relocation &rel, uint64_t src) {
+  std::vector<Thunk *> *thunkVec = nullptr;
+
+  // We use (section, offset) pair to find the thunk position if possible so
+  // that we create only one thunk for aliased symbols or ICFed sections.
+  if (auto *d = dyn_cast<Defined>(rel.sym))
+    if (!d->isInPlt() && d->section)
+      thunkVec = &thunkedSymbolsBySection[{d->section->repl, d->value}];
+  if (!thunkVec)
+    thunkVec = &thunkedSymbols[rel.sym];
+
+  // Check existing Thunks for Sym to see if they can be reused
+  for (Thunk *t : *thunkVec)
+    if (isThunkSectionCompatible(isec, t->getThunkTargetSym()->section) &&
+        t->isCompatibleWith(*isec, rel) &&
+        target->inBranchRange(rel.type, src, t->getThunkTargetSym()->getVA()))
+      return std::make_pair(t, false);
+
+  // No existing compatible Thunk in range, create a new one
+  Thunk *t = addThunk(*isec, rel);
+  thunkVec->push_back(t);
+  return std::make_pair(t, true);
+}
+
+// Return true if the relocation target is an in range Thunk.
+// Return false if the relocation is not to a Thunk. If the relocation target
+// was originally to a Thunk, but is no longer in range we revert the
+// relocation back to its original non-Thunk target.
+bool ThunkCreator::normalizeExistingThunk(Relocation &rel, uint64_t src) {
+  if (Thunk *t = thunks.lookup(rel.sym)) {
+    if (target->inBranchRange(rel.type, src, rel.sym->getVA()))
+      return true;
+    rel.sym = &t->destination;
+    if (rel.sym->isInPlt())
+      rel.expr = toPlt(rel.expr);
+  }
+  return false;
+}
+
+// Process all relocations from the InputSections that have been assigned
+// to InputSectionDescriptions and redirect through Thunks if needed. The
+// function should be called iteratively until it returns false.
+//
+// PreConditions:
+// All InputSections that may need a Thunk are reachable from
+// OutputSectionCommands.
+//
+// All OutputSections have an address and all InputSections have an offset
+// within the OutputSection.
+//
+// The offsets between caller (relocation place) and callee
+// (relocation target) will not be modified outside of createThunks().
+//
+// PostConditions:
+// If return value is true then ThunkSections have been inserted into
+// OutputSections. All relocations that needed a Thunk based on the information
+// available to createThunks() on entry have been redirected to a Thunk. Note
+// that adding Thunks changes offsets between caller and callee so more Thunks
+// may be required.
+//
+// If return value is false then no more Thunks are needed, and createThunks has
+// made no changes. If the target requires range extension thunks, currently
+// ARM, then any future change in offset between caller and callee risks a
+// relocation out of range error.
+bool ThunkCreator::createThunks(ArrayRef<OutputSection *> outputSections) {
+  bool addressesChanged = false;
+
+  if (pass == 0 && target->getThunkSectionSpacing())
+    createInitialThunkSections(outputSections);
+
+  // With Thunk Size much smaller than branch range we expect to
+  // converge quickly; if we get to 10 something has gone wrong.
+  if (pass == 10)
+    fatal("thunk creation not converged");
+
+  // Create all the Thunks and insert them into synthetic ThunkSections. The
+  // ThunkSections are later inserted back into InputSectionDescriptions.
+  // We separate the creation of ThunkSections from the insertion of the
+  // ThunkSections as ThunkSections are not always inserted into the same
+  // InputSectionDescription as the caller.
+  forEachInputSectionDescription(
+      outputSections, [&](OutputSection *os, InputSectionDescription *isd) {
+        for (InputSection *isec : isd->sections)
+          for (Relocation &rel : isec->relocations) {
+            uint64_t src = isec->getVA(rel.offset);
+
+            // If we are a relocation to an existing Thunk, check if it is
+            // still in range. If not then Rel will be altered to point to its
+            // original target so another Thunk can be generated.
+            if (pass > 0 && normalizeExistingThunk(rel, src))
+              continue;
+
+            if (!target->needsThunk(rel.expr, rel.type, isec->file, src,
+                                    *rel.sym))
+              continue;
+
+            Thunk *t;
+            bool isNew;
+            std::tie(t, isNew) = getThunk(isec, rel, src);
+
+            if (isNew) {
+              // Find or create a ThunkSection for the new Thunk
+              ThunkSection *ts;
+              if (auto *tis = t->getTargetInputSection())
+                ts = getISThunkSec(tis);
+              else
+                ts = getISDThunkSec(os, isec, isd, rel.type, src);
+              ts->addThunk(t);
+              thunks[t->getThunkTargetSym()] = t;
+            }
+
+            // Redirect relocation to Thunk, we never go via the PLT to a Thunk
+            rel.sym = t->getThunkTargetSym();
+            rel.expr = fromPlt(rel.expr);
+
+            // The addend of R_PPC_PLTREL24 should be ignored after changing to
+            // R_PC.
+            if (config->emachine == EM_PPC && rel.type == R_PPC_PLTREL24)
+              rel.addend = 0;
+          }
+
+        for (auto &p : isd->thunkSections)
+          addressesChanged |= p.first->assignOffsets();
+      });
+
+  for (auto &p : thunkedSections)
+    addressesChanged |= p.second->assignOffsets();
+
+  // Merge all created synthetic ThunkSections back into OutputSection
+  mergeThunks(outputSections);
+  ++pass;
+  return addressesChanged;
+}
+
+template void elf::scanRelocations<ELF32LE>(InputSectionBase &);
+template void elf::scanRelocations<ELF32BE>(InputSectionBase &);
+template void elf::scanRelocations<ELF64LE>(InputSectionBase &);
+template void elf::scanRelocations<ELF64BE>(InputSectionBase &);
+template void elf::reportUndefinedSymbols<ELF32LE>();
+template void elf::reportUndefinedSymbols<ELF32BE>();
+template void elf::reportUndefinedSymbols<ELF64LE>();
+template void elf::reportUndefinedSymbols<ELF64BE>();