846 lines
34 KiB
C++
846 lines
34 KiB
C++
//===- Relocations.cpp ----------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains platform-independent functions to process relocations.
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// I'll describe the overview of this file here.
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//
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// Simple relocations are easy to handle for the linker. For example,
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// for R_X86_64_PC64 relocs, the linker just has to fix up locations
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// with the relative offsets to the target symbols. It would just be
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// reading records from relocation sections and applying them to output.
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//
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// But not all relocations are that easy to handle. For example, for
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// R_386_GOTOFF relocs, the linker has to create new GOT entries for
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// symbols if they don't exist, and fix up locations with GOT entry
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// offsets from the beginning of GOT section. So there is more than
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// fixing addresses in relocation processing.
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//
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// ELF defines a large number of complex relocations.
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//
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// The functions in this file analyze relocations and do whatever needs
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// to be done. It includes, but not limited to, the following.
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//
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// - create GOT/PLT entries
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// - create new relocations in .dynsym to let the dynamic linker resolve
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// them at runtime (since ELF supports dynamic linking, not all
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// relocations can be resolved at link-time)
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// - create COPY relocs and reserve space in .bss
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// - replace expensive relocs (in terms of runtime cost) with cheap ones
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// - error out infeasible combinations such as PIC and non-relative relocs
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//
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// Note that the functions in this file don't actually apply relocations
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// because it doesn't know about the output file nor the output file buffer.
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// It instead stores Relocation objects to InputSection's Relocations
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// vector to let it apply later in InputSection::writeTo.
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//
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//===----------------------------------------------------------------------===//
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#include "Relocations.h"
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#include "Config.h"
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#include "OutputSections.h"
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#include "Strings.h"
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#include "SymbolTable.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "Thunks.h"
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#include "llvm/Support/Endian.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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using namespace llvm::ELF;
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using namespace llvm::object;
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using namespace llvm::support::endian;
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namespace lld {
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namespace elf {
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static bool refersToGotEntry(RelExpr Expr) {
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return isRelExprOneOf<R_GOT, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE, R_MIPS_GOT_OFF,
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R_MIPS_GOT_OFF32, R_MIPS_TLSGD, R_MIPS_TLSLD,
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R_GOT_PAGE_PC, R_GOT_PC, R_GOT_FROM_END, R_TLSGD,
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R_TLSGD_PC, R_TLSDESC, R_TLSDESC_PAGE>(Expr);
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}
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static bool isPreemptible(const SymbolBody &Body, uint32_t Type) {
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// In case of MIPS GP-relative relocations always resolve to a definition
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// in a regular input file, ignoring the one-definition rule. So we,
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// for example, should not attempt to create a dynamic relocation even
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// if the target symbol is preemptible. There are two two MIPS GP-relative
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// relocations R_MIPS_GPREL16 and R_MIPS_GPREL32. But only R_MIPS_GPREL16
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// can be against a preemptible symbol.
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// To get MIPS relocation type we apply 0xff mask. In case of O32 ABI all
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// relocation types occupy eight bit. In case of N64 ABI we extract first
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// relocation from 3-in-1 packet because only the first relocation can
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// be against a real symbol.
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if (Config->EMachine == EM_MIPS && (Type & 0xff) == R_MIPS_GPREL16)
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return false;
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return Body.isPreemptible();
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}
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// This function is similar to the `handleTlsRelocation`. ARM and MIPS do not
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// support any relaxations for TLS relocations so by factoring out ARM and MIPS
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// handling in to the separate function we can simplify the code and do not
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// pollute `handleTlsRelocation` by ARM and MIPS `ifs` statements.
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template <class ELFT, class GOT>
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static unsigned handleNoRelaxTlsRelocation(
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GOT *Got, uint32_t Type, SymbolBody &Body, InputSectionBase<ELFT> &C,
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typename ELFT::uint Offset, typename ELFT::uint Addend, RelExpr Expr) {
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typedef typename ELFT::uint uintX_t;
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auto addModuleReloc = [](SymbolBody &Body, GOT *Got, uintX_t Off, bool LD) {
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// The Dynamic TLS Module Index Relocation can be statically resolved to 1
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// if we know that we are linking an executable. For ARM we resolve the
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// relocation when writing the Got. MIPS has a custom Got implementation
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// that writes the Module index in directly.
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if (!Body.isPreemptible() && !Config->Pic && Config->EMachine == EM_ARM)
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Got->Relocations.push_back(
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{R_ABS, Target->TlsModuleIndexRel, Off, 0, &Body});
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else {
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SymbolBody *Dest = LD ? nullptr : &Body;
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In<ELFT>::RelaDyn->addReloc(
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{Target->TlsModuleIndexRel, Got, Off, false, Dest, 0});
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}
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};
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if (Expr == R_MIPS_TLSLD || Expr == R_TLSLD_PC) {
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if (Got->addTlsIndex() && (Config->Pic || Config->EMachine == EM_ARM))
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addModuleReloc(Body, Got, Got->getTlsIndexOff(), true);
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C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
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return 1;
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}
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if (Target->isTlsGlobalDynamicRel(Type)) {
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if (Got->addDynTlsEntry(Body) &&
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(Body.isPreemptible() || Config->EMachine == EM_ARM)) {
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uintX_t Off = Got->getGlobalDynOffset(Body);
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addModuleReloc(Body, Got, Off, false);
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if (Body.isPreemptible())
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In<ELFT>::RelaDyn->addReloc({Target->TlsOffsetRel, Got,
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Off + (uintX_t)sizeof(uintX_t), false,
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&Body, 0});
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}
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C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
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return 1;
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}
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return 0;
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}
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// Returns the number of relocations processed.
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template <class ELFT>
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static unsigned handleTlsRelocation(uint32_t Type, SymbolBody &Body,
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InputSectionBase<ELFT> &C,
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typename ELFT::uint Offset,
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typename ELFT::uint Addend, RelExpr Expr) {
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if (!(C.Flags & SHF_ALLOC))
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return 0;
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if (!Body.isTls())
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return 0;
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typedef typename ELFT::uint uintX_t;
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if (Config->EMachine == EM_ARM)
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return handleNoRelaxTlsRelocation<ELFT>(In<ELFT>::Got, Type, Body, C,
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Offset, Addend, Expr);
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if (Config->EMachine == EM_MIPS)
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return handleNoRelaxTlsRelocation<ELFT>(In<ELFT>::MipsGot, Type, Body, C,
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Offset, Addend, Expr);
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bool IsPreemptible = isPreemptible(Body, Type);
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if ((Expr == R_TLSDESC || Expr == R_TLSDESC_PAGE || Expr == R_TLSDESC_CALL) &&
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Config->Shared) {
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if (In<ELFT>::Got->addDynTlsEntry(Body)) {
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uintX_t Off = In<ELFT>::Got->getGlobalDynOffset(Body);
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In<ELFT>::RelaDyn->addReloc({Target->TlsDescRel, In<ELFT>::Got, Off,
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!IsPreemptible, &Body, 0});
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}
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if (Expr != R_TLSDESC_CALL)
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C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
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return 1;
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}
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if (Expr == R_TLSLD_PC || Expr == R_TLSLD) {
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// Local-Dynamic relocs can be relaxed to Local-Exec.
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if (!Config->Shared) {
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C.Relocations.push_back(
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{R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
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return 2;
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}
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if (In<ELFT>::Got->addTlsIndex())
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In<ELFT>::RelaDyn->addReloc({Target->TlsModuleIndexRel, In<ELFT>::Got,
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In<ELFT>::Got->getTlsIndexOff(), false,
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nullptr, 0});
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C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
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return 1;
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}
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// Local-Dynamic relocs can be relaxed to Local-Exec.
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if (Target->isTlsLocalDynamicRel(Type) && !Config->Shared) {
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C.Relocations.push_back(
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{R_RELAX_TLS_LD_TO_LE, Type, Offset, Addend, &Body});
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return 1;
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}
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if (Expr == R_TLSDESC_PAGE || Expr == R_TLSDESC || Expr == R_TLSDESC_CALL ||
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Target->isTlsGlobalDynamicRel(Type)) {
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if (Config->Shared) {
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if (In<ELFT>::Got->addDynTlsEntry(Body)) {
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uintX_t Off = In<ELFT>::Got->getGlobalDynOffset(Body);
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In<ELFT>::RelaDyn->addReloc(
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{Target->TlsModuleIndexRel, In<ELFT>::Got, Off, false, &Body, 0});
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// If the symbol is preemptible we need the dynamic linker to write
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// the offset too.
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uintX_t OffsetOff = Off + (uintX_t)sizeof(uintX_t);
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if (IsPreemptible)
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In<ELFT>::RelaDyn->addReloc({Target->TlsOffsetRel, In<ELFT>::Got,
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OffsetOff, false, &Body, 0});
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else
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In<ELFT>::Got->Relocations.push_back(
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{R_ABS, Target->TlsOffsetRel, OffsetOff, 0, &Body});
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}
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C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
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return 1;
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}
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// Global-Dynamic relocs can be relaxed to Initial-Exec or Local-Exec
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// depending on the symbol being locally defined or not.
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if (IsPreemptible) {
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C.Relocations.push_back(
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{Target->adjustRelaxExpr(Type, nullptr, R_RELAX_TLS_GD_TO_IE), Type,
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Offset, Addend, &Body});
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if (!Body.isInGot()) {
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In<ELFT>::Got->addEntry(Body);
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In<ELFT>::RelaDyn->addReloc({Target->TlsGotRel, In<ELFT>::Got,
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Body.getGotOffset<ELFT>(), false, &Body,
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0});
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}
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return Target->TlsGdRelaxSkip;
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}
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C.Relocations.push_back(
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{Target->adjustRelaxExpr(Type, nullptr, R_RELAX_TLS_GD_TO_LE), Type,
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Offset, Addend, &Body});
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return Target->TlsGdRelaxSkip;
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}
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// Initial-Exec relocs can be relaxed to Local-Exec if the symbol is locally
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// defined.
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if (Target->isTlsInitialExecRel(Type) && !Config->Shared && !IsPreemptible) {
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C.Relocations.push_back(
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{R_RELAX_TLS_IE_TO_LE, Type, Offset, Addend, &Body});
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return 1;
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}
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return 0;
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}
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template <endianness E> static int16_t readSignedLo16(const uint8_t *Loc) {
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return read32<E>(Loc) & 0xffff;
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}
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template <class RelTy>
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static uint32_t getMipsPairType(const RelTy *Rel, const SymbolBody &Sym) {
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switch (Rel->getType(Config->Mips64EL)) {
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case R_MIPS_HI16:
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return R_MIPS_LO16;
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case R_MIPS_GOT16:
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return Sym.isLocal() ? R_MIPS_LO16 : R_MIPS_NONE;
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case R_MIPS_PCHI16:
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return R_MIPS_PCLO16;
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case R_MICROMIPS_HI16:
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return R_MICROMIPS_LO16;
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default:
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return R_MIPS_NONE;
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}
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}
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template <class ELFT, class RelTy>
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static int32_t findMipsPairedAddend(const uint8_t *Buf, const uint8_t *BufLoc,
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SymbolBody &Sym, const RelTy *Rel,
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const RelTy *End) {
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uint32_t SymIndex = Rel->getSymbol(Config->Mips64EL);
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uint32_t Type = getMipsPairType(Rel, Sym);
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// Some MIPS relocations use addend calculated from addend of the relocation
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// itself and addend of paired relocation. ABI requires to compute such
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// combined addend in case of REL relocation record format only.
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// See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
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if (RelTy::IsRela || Type == R_MIPS_NONE)
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return 0;
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for (const RelTy *RI = Rel; RI != End; ++RI) {
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if (RI->getType(Config->Mips64EL) != Type)
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continue;
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if (RI->getSymbol(Config->Mips64EL) != SymIndex)
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continue;
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const endianness E = ELFT::TargetEndianness;
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return ((read32<E>(BufLoc) & 0xffff) << 16) +
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readSignedLo16<E>(Buf + RI->r_offset);
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}
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warn("can't find matching " + toString(Type) + " relocation for " +
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toString(Rel->getType(Config->Mips64EL)));
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return 0;
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}
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// True if non-preemptable symbol always has the same value regardless of where
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// the DSO is loaded.
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template <class ELFT> static bool isAbsolute(const SymbolBody &Body) {
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if (Body.isUndefined())
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return !Body.isLocal() && Body.symbol()->isWeak();
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if (const auto *DR = dyn_cast<DefinedRegular<ELFT>>(&Body))
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return DR->Section == nullptr; // Absolute symbol.
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return false;
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}
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template <class ELFT> static bool isAbsoluteValue(const SymbolBody &Body) {
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return isAbsolute<ELFT>(Body) || Body.isTls();
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}
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static bool needsPlt(RelExpr Expr) {
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return isRelExprOneOf<R_PLT_PC, R_PPC_PLT_OPD, R_PLT, R_PLT_PAGE_PC,
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R_THUNK_PLT_PC>(Expr);
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}
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// True if this expression is of the form Sym - X, where X is a position in the
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// file (PC, or GOT for example).
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static bool isRelExpr(RelExpr Expr) {
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return isRelExprOneOf<R_PC, R_GOTREL, R_GOTREL_FROM_END, R_MIPS_GOTREL,
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R_PAGE_PC, R_RELAX_GOT_PC, R_THUNK_PC, R_THUNK_PLT_PC>(
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Expr);
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}
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template <class ELFT>
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static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
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const SymbolBody &Body,
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InputSectionBase<ELFT> &S,
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typename ELFT::uint RelOff) {
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// These expressions always compute a constant
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if (isRelExprOneOf<R_SIZE, R_GOT_FROM_END, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE,
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R_MIPS_GOT_OFF, R_MIPS_GOT_OFF32, R_MIPS_TLSGD,
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R_GOT_PAGE_PC, R_GOT_PC, R_PLT_PC, R_TLSGD_PC, R_TLSGD,
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R_PPC_PLT_OPD, R_TLSDESC_CALL, R_TLSDESC_PAGE, R_HINT,
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R_THUNK_PC, R_THUNK_PLT_PC>(E))
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return true;
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// These never do, except if the entire file is position dependent or if
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// only the low bits are used.
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if (E == R_GOT || E == R_PLT || E == R_TLSDESC)
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return Target->usesOnlyLowPageBits(Type) || !Config->Pic;
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if (isPreemptible(Body, Type))
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return false;
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if (!Config->Pic)
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return true;
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bool AbsVal = isAbsoluteValue<ELFT>(Body);
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bool RelE = isRelExpr(E);
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if (AbsVal && !RelE)
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return true;
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if (!AbsVal && RelE)
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return true;
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// Relative relocation to an absolute value. This is normally unrepresentable,
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// but if the relocation refers to a weak undefined symbol, we allow it to
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// resolve to the image base. This is a little strange, but it allows us to
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// link function calls to such symbols. Normally such a call will be guarded
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// with a comparison, which will load a zero from the GOT.
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// Another special case is MIPS _gp_disp symbol which represents offset
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// between start of a function and '_gp' value and defined as absolute just
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// to simplify the code.
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if (AbsVal && RelE) {
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if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak())
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return true;
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if (&Body == ElfSym<ELFT>::MipsGpDisp)
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return true;
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error(S.getLocation(RelOff) + ": relocation " + toString(Type) +
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" cannot refer to absolute symbol '" + toString(Body) +
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"' defined in " + toString(Body.File));
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return true;
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}
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return Target->usesOnlyLowPageBits(Type);
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}
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static RelExpr toPlt(RelExpr Expr) {
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if (Expr == R_PPC_OPD)
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return R_PPC_PLT_OPD;
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if (Expr == R_PC)
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return R_PLT_PC;
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if (Expr == R_PAGE_PC)
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return R_PLT_PAGE_PC;
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if (Expr == R_ABS)
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return R_PLT;
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return Expr;
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}
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static RelExpr fromPlt(RelExpr Expr) {
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// We decided not to use a plt. Optimize a reference to the plt to a
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// reference to the symbol itself.
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if (Expr == R_PLT_PC)
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return R_PC;
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if (Expr == R_PPC_PLT_OPD)
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return R_PPC_OPD;
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if (Expr == R_PLT)
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return R_ABS;
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return Expr;
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}
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template <class ELFT> static uint32_t getAlignment(SharedSymbol<ELFT> *SS) {
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typedef typename ELFT::uint uintX_t;
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uintX_t SecAlign = SS->file()->getSection(SS->Sym)->sh_addralign;
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uintX_t SymValue = SS->Sym.st_value;
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int TrailingZeros =
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std::min(countTrailingZeros(SecAlign), countTrailingZeros(SymValue));
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return 1 << TrailingZeros;
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}
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template <class ELFT> static bool isReadOnly(SharedSymbol<ELFT> *SS) {
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typedef typename ELFT::uint uintX_t;
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typedef typename ELFT::Phdr Elf_Phdr;
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// Determine if the symbol is read-only by scanning the DSO's program headers.
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uintX_t Value = SS->Sym.st_value;
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for (const Elf_Phdr &Phdr : check(SS->file()->getObj().program_headers()))
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if ((Phdr.p_type == ELF::PT_LOAD || Phdr.p_type == ELF::PT_GNU_RELRO) &&
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!(Phdr.p_flags & ELF::PF_W) && Value >= Phdr.p_vaddr &&
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Value < Phdr.p_vaddr + Phdr.p_memsz)
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return true;
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return false;
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}
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// Reserve space in .bss or .bss.rel.ro for copy relocation.
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template <class ELFT> static void addCopyRelSymbol(SharedSymbol<ELFT> *SS) {
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typedef typename ELFT::uint uintX_t;
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typedef typename ELFT::Sym Elf_Sym;
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// Copy relocation against zero-sized symbol doesn't make sense.
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uintX_t SymSize = SS->template getSize<ELFT>();
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if (SymSize == 0)
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fatal("cannot create a copy relocation for symbol " + toString(*SS));
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// See if this symbol is in a read-only segment. If so, preserve the symbol's
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// memory protection by reserving space in the .bss.rel.ro section.
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bool IsReadOnly = isReadOnly(SS);
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OutputSection<ELFT> *CopySec =
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IsReadOnly ? Out<ELFT>::BssRelRo : Out<ELFT>::Bss;
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|
|
|
uintX_t Alignment = getAlignment(SS);
|
|
uintX_t Off = alignTo(CopySec->Size, Alignment);
|
|
CopySec->Size = Off + SymSize;
|
|
CopySec->updateAlignment(Alignment);
|
|
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()->getGlobalSymbols()) {
|
|
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->CopyIsInBssRelRo = IsReadOnly;
|
|
Alias->CopyOffset = Off;
|
|
Alias->NeedsCopyOrPltAddr = true;
|
|
Alias->symbol()->IsUsedInRegularObj = true;
|
|
}
|
|
In<ELFT>::RelaDyn->addReloc({Target->CopyRel, CopySec, Off, false, SS, 0});
|
|
}
|
|
|
|
template <class ELFT>
|
|
static RelExpr adjustExpr(const elf::ObjectFile<ELFT> &File, SymbolBody &Body,
|
|
bool IsWrite, RelExpr Expr, uint32_t Type,
|
|
const uint8_t *Data, InputSectionBase<ELFT> &S,
|
|
typename ELFT::uint RelOff) {
|
|
bool Preemptible = isPreemptible(Body, Type);
|
|
if (Body.isGnuIFunc()) {
|
|
Expr = toPlt(Expr);
|
|
} else if (!Preemptible) {
|
|
if (needsPlt(Expr))
|
|
Expr = fromPlt(Expr);
|
|
if (Expr == R_GOT_PC && !isAbsoluteValue<ELFT>(Body))
|
|
Expr = Target->adjustRelaxExpr(Type, Data, Expr);
|
|
}
|
|
Expr = Target->getThunkExpr(Expr, Type, File, Body);
|
|
|
|
if (IsWrite || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body, S, RelOff))
|
|
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))) {
|
|
error(S.getLocation(RelOff) + ": can't create dynamic relocation " +
|
|
toString(Type) + " against " +
|
|
(Body.getName().empty() ? "local symbol in readonly segment"
|
|
: "symbol '" + toString(Body) + "'") +
|
|
" defined in " + toString(Body.File));
|
|
return Expr;
|
|
}
|
|
if (Body.getVisibility() != STV_DEFAULT) {
|
|
error(S.getLocation(RelOff) + ": cannot preempt symbol '" + toString(Body) +
|
|
"' defined in " + toString(Body.File));
|
|
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 '" + toString(Body) + "' defined in " + toString(Body.File) +
|
|
" 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_MIPS_GOTREL && Body.isLocal())
|
|
Addend += File.MipsGp0;
|
|
}
|
|
if (Config->Pic && Config->EMachine == EM_PPC64 && Type == R_PPC64_TOC)
|
|
Addend += getPPC64TocBase();
|
|
return Addend;
|
|
}
|
|
|
|
template <class ELFT>
|
|
static void reportUndefined(SymbolBody &Sym, InputSectionBase<ELFT> &S,
|
|
typename ELFT::uint Offset) {
|
|
if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore)
|
|
return;
|
|
|
|
if (Config->Shared && Sym.symbol()->Visibility == STV_DEFAULT &&
|
|
Config->UnresolvedSymbols != UnresolvedPolicy::NoUndef)
|
|
return;
|
|
|
|
std::string Msg =
|
|
S.getLocation(Offset) + ": undefined symbol '" + toString(Sym) + "'";
|
|
|
|
if (Config->UnresolvedSymbols == UnresolvedPolicy::Warn)
|
|
warn(Msg);
|
|
else
|
|
error(Msg);
|
|
}
|
|
|
|
template <class RelTy>
|
|
static std::pair<uint32_t, uint32_t>
|
|
mergeMipsN32RelTypes(uint32_t Type, uint32_t Offset, RelTy *I, RelTy *E) {
|
|
// 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.
|
|
uint32_t Processed = 0;
|
|
for (; I != E && Offset == I->r_offset; ++I) {
|
|
++Processed;
|
|
Type |= I->getType(Config->Mips64EL) << (8 * Processed);
|
|
}
|
|
return std::make_pair(Type, Processed);
|
|
}
|
|
|
|
// 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 scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
|
|
typedef typename ELFT::uint uintX_t;
|
|
|
|
bool IsWrite = C.Flags & SHF_WRITE;
|
|
|
|
auto AddDyn = [=](const DynamicReloc<ELFT> &Reloc) {
|
|
In<ELFT>::RelaDyn->addReloc(Reloc);
|
|
};
|
|
|
|
const elf::ObjectFile<ELFT> *File = C.getFile();
|
|
ArrayRef<uint8_t> SectionData = C.Data;
|
|
const uint8_t *Buf = SectionData.begin();
|
|
|
|
ArrayRef<EhSectionPiece> Pieces;
|
|
if (auto *Eh = dyn_cast<EhInputSection<ELFT>>(&C))
|
|
Pieces = Eh->Pieces;
|
|
|
|
ArrayRef<EhSectionPiece>::iterator PieceI = Pieces.begin();
|
|
ArrayRef<EhSectionPiece>::iterator PieceE = Pieces.end();
|
|
|
|
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);
|
|
|
|
if (Config->MipsN32Abi) {
|
|
uint32_t Processed;
|
|
std::tie(Type, Processed) =
|
|
mergeMipsN32RelTypes(Type, RI.r_offset, I + 1, E);
|
|
I += Processed;
|
|
}
|
|
|
|
// We only report undefined symbols if they are referenced somewhere in the
|
|
// code.
|
|
if (!Body.isLocal() && Body.isUndefined() && !Body.symbol()->isWeak())
|
|
reportUndefined(Body, C, RI.r_offset);
|
|
|
|
RelExpr Expr = Target->getRelExpr(Type, Body);
|
|
bool Preemptible = isPreemptible(Body, Type);
|
|
Expr = adjustExpr(*File, Body, IsWrite, Expr, Type, Buf + RI.r_offset, C,
|
|
RI.r_offset);
|
|
if (ErrorCount)
|
|
continue;
|
|
|
|
// Skip a relocation that points to a dead piece
|
|
// in a eh_frame section.
|
|
while (PieceI != PieceE &&
|
|
(PieceI->InputOff + PieceI->size() <= RI.r_offset))
|
|
++PieceI;
|
|
|
|
// Compute the offset of this section in the output section. We do it here
|
|
// to try to compute it only once.
|
|
uintX_t Offset;
|
|
if (PieceI != PieceE) {
|
|
assert(PieceI->InputOff <= RI.r_offset && "Relocation not in any piece");
|
|
if (PieceI->OutputOff == -1)
|
|
continue;
|
|
Offset = PieceI->OutputOff + RI.r_offset - PieceI->InputOff;
|
|
} else {
|
|
Offset = RI.r_offset;
|
|
}
|
|
|
|
// 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_GOTONLY_PC_FROM_END ||
|
|
Expr == R_GOTREL || Expr == R_GOTREL_FROM_END || Expr == R_PPC_TOC)
|
|
In<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;
|
|
}
|
|
|
|
// Ignore "hint" and TLS Descriptor call relocation because they are
|
|
// only markers for relaxation.
|
|
if (isRelExprOneOf<R_HINT, R_TLSDESC_CALL>(Expr))
|
|
continue;
|
|
|
|
if (needsPlt(Expr) ||
|
|
isRelExprOneOf<R_THUNK_ABS, R_THUNK_PC, R_THUNK_PLT_PC>(Expr) ||
|
|
refersToGotEntry(Expr) || !isPreemptible(Body, Type)) {
|
|
// If the relocation points to something in the file, we can process it.
|
|
bool Constant =
|
|
isStaticLinkTimeConstant<ELFT>(Expr, Type, Body, C, RI.r_offset);
|
|
|
|
// 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, 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.
|
|
if (!Target->isPicRel(Type))
|
|
error(C.getLocation(Offset) + ": relocation " + toString(Type) +
|
|
" cannot be used against shared object; recompile with -fPIC.");
|
|
AddDyn({Target->getDynRel(Type), &C, 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)
|
|
In<ELFT>::MipsGot->addEntry(Body, Addend, Expr);
|
|
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;
|
|
|
|
if (Body.isGnuIFunc() && !Preemptible) {
|
|
In<ELFT>::Iplt->addEntry(Body);
|
|
In<ELFT>::IgotPlt->addEntry(Body);
|
|
In<ELFT>::RelaIplt->addReloc({Target->IRelativeRel, In<ELFT>::IgotPlt,
|
|
Body.getGotPltOffset<ELFT>(),
|
|
!Preemptible, &Body, 0});
|
|
} else {
|
|
In<ELFT>::Plt->addEntry(Body);
|
|
In<ELFT>::GotPlt->addEntry(Body);
|
|
In<ELFT>::RelaPlt->addReloc({Target->PltRel, In<ELFT>::GotPlt,
|
|
Body.getGotPltOffset<ELFT>(), !Preemptible,
|
|
&Body, 0});
|
|
}
|
|
continue;
|
|
}
|
|
|
|
if (refersToGotEntry(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<ELFT>::MipsGot->addEntry(Body, Addend, Expr);
|
|
if (Body.isTls() && Body.isPreemptible())
|
|
AddDyn({Target->TlsGotRel, In<ELFT>::MipsGot,
|
|
Body.getGotOffset<ELFT>(), false, &Body, 0});
|
|
continue;
|
|
}
|
|
|
|
if (Body.isInGot())
|
|
continue;
|
|
|
|
In<ELFT>::Got->addEntry(Body);
|
|
uintX_t Off = Body.getGotOffset<ELFT>();
|
|
uint32_t DynType;
|
|
RelExpr GotRE = R_ABS;
|
|
if (Body.isTls()) {
|
|
DynType = Target->TlsGotRel;
|
|
GotRE = R_TLS;
|
|
} else if (!Preemptible && Config->Pic && !isAbsolute<ELFT>(Body))
|
|
DynType = Target->RelativeRel;
|
|
else
|
|
DynType = Target->GotRel;
|
|
|
|
// FIXME: this logic is almost duplicated above.
|
|
bool Constant = !Preemptible && !(Config->Pic && !isAbsolute<ELFT>(Body));
|
|
if (!Constant)
|
|
AddDyn({DynType, In<ELFT>::Got, Off, !Preemptible, &Body, 0});
|
|
if (Constant || (!RelTy::IsRela && !Preemptible))
|
|
In<ELFT>::Got->Relocations.push_back({GotRE, DynType, Off, 0, &Body});
|
|
continue;
|
|
}
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void scanRelocations(InputSectionBase<ELFT> &S) {
|
|
if (S.AreRelocsRela)
|
|
scanRelocs(S, S.relas());
|
|
else
|
|
scanRelocs(S, S.rels());
|
|
}
|
|
|
|
template <class ELFT, class RelTy>
|
|
static void createThunks(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
|
|
const elf::ObjectFile<ELFT> *File = C.getFile();
|
|
for (const RelTy &Rel : Rels) {
|
|
SymbolBody &Body = File->getRelocTargetSym(Rel);
|
|
uint32_t Type = Rel.getType(Config->Mips64EL);
|
|
RelExpr Expr = Target->getRelExpr(Type, Body);
|
|
if (!isPreemptible(Body, Type) && needsPlt(Expr))
|
|
Expr = fromPlt(Expr);
|
|
Expr = Target->getThunkExpr(Expr, Type, *File, Body);
|
|
// 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, and ARM which requires interworking.
|
|
if (Expr == R_THUNK_ABS || Expr == R_THUNK_PC || Expr == R_THUNK_PLT_PC) {
|
|
auto *Sec = cast<InputSection<ELFT>>(&C);
|
|
addThunk<ELFT>(Type, Body, *Sec);
|
|
}
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void createThunks(InputSectionBase<ELFT> &S) {
|
|
if (S.AreRelocsRela)
|
|
createThunks(S, S.relas());
|
|
else
|
|
createThunks(S, S.rels());
|
|
}
|
|
|
|
template void scanRelocations<ELF32LE>(InputSectionBase<ELF32LE> &);
|
|
template void scanRelocations<ELF32BE>(InputSectionBase<ELF32BE> &);
|
|
template void scanRelocations<ELF64LE>(InputSectionBase<ELF64LE> &);
|
|
template void scanRelocations<ELF64BE>(InputSectionBase<ELF64BE> &);
|
|
|
|
template void createThunks<ELF32LE>(InputSectionBase<ELF32LE> &);
|
|
template void createThunks<ELF32BE>(InputSectionBase<ELF32BE> &);
|
|
template void createThunks<ELF64LE>(InputSectionBase<ELF64LE> &);
|
|
template void createThunks<ELF64BE>(InputSectionBase<ELF64BE> &);
|
|
}
|
|
}
|