230 lines · cpp
1//===- OutputSegment.cpp --------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "OutputSegment.h"10#include "ConcatOutputSection.h"11#include "InputSection.h"12#include "Sections.h"13#include "Symbols.h"14#include "SyntheticSections.h"15 16#include "lld/Common/Memory.h"17#include "llvm/ADT/StringSwitch.h"18#include "llvm/BinaryFormat/MachO.h"19 20using namespace llvm;21using namespace llvm::MachO;22using namespace lld;23using namespace lld::macho;24 25static uint32_t initProt(StringRef name) {26 auto it = find_if(27 config->segmentProtections,28 [&](const SegmentProtection &segprot) { return segprot.name == name; });29 if (it != config->segmentProtections.end())30 return it->initProt;31 32 if (name == segment_names::text)33 return VM_PROT_READ | VM_PROT_EXECUTE;34 if (name == segment_names::pageZero)35 return 0;36 if (name == segment_names::linkEdit)37 return VM_PROT_READ;38 return VM_PROT_READ | VM_PROT_WRITE;39}40 41static uint32_t maxProt(StringRef name) {42 assert(config->arch() != AK_i386 &&43 "TODO: i386 has different maxProt requirements");44 auto it = find_if(45 config->segmentProtections,46 [&](const SegmentProtection &segprot) { return segprot.name == name; });47 if (it != config->segmentProtections.end())48 return it->maxProt;49 50 return initProt(name);51}52 53static uint32_t flags(StringRef name) {54 // If we ever implement shared cache output support, SG_READ_ONLY should not55 // be used for dylibs that can be placed in it.56 return name == segment_names::dataConst ? (uint32_t)SG_READ_ONLY : 0;57}58 59size_t OutputSegment::numNonHiddenSections() const {60 size_t count = 0;61 for (const OutputSection *osec : sections)62 count += (!osec->isHidden() ? 1 : 0);63 return count;64}65 66void OutputSegment::addOutputSection(OutputSection *osec) {67 inputOrder = std::min(inputOrder, osec->inputOrder);68 69 osec->parent = this;70 sections.push_back(osec);71 72 for (const SectionAlign §Align : config->sectionAlignments)73 if (sectAlign.segName == name && sectAlign.sectName == osec->name)74 osec->align = sectAlign.align;75}76 77template <typename T, typename F> static auto compareByOrder(F ord) {78 return [=](T a, T b) { return ord(a) < ord(b); };79}80 81static int segmentOrder(OutputSegment *seg) {82 return StringSwitch<int>(seg->name)83 .Case(segment_names::pageZero, -4)84 .Case(segment_names::text, -3)85 .Case(segment_names::dataConst, -2)86 .Case(segment_names::data, -1)87 .Case(segment_names::llvm, std::numeric_limits<int>::max() - 1)88 // Make sure __LINKEDIT is the last segment (i.e. all its hidden89 // sections must be ordered after other sections).90 .Case(segment_names::linkEdit, std::numeric_limits<int>::max())91 .Default(seg->inputOrder);92}93 94static int sectionOrder(OutputSection *osec) {95 StringRef segname = osec->parent->name;96 // Sections are uniquely identified by their segment + section name.97 if (segname == segment_names::text) {98 if (osec->name == section_names::header)99 return -7;100 // `__text` needs to precede the other code sections since its101 // expected to be the largest. This means in effect that it will102 // be the section that determines whether we need thunks or not.103 if (osec->name == section_names::text)104 return -6;105 106 // Prioritize specific section ordering based on our knowledge. This ensures107 // that certain sections are placed in a particular order, even if they108 // are also categorized as code sections. This explicit ordering takes109 // precedence over the general code section ordering.110 int knownPriority =111 StringSwitch<int>(osec->name)112 .Case(section_names::stubs, -4)113 .Case(section_names::stubHelper, -3)114 .Case(section_names::objcStubs, -2)115 .Case(section_names::initOffsets, -1)116 .Case(section_names::unwindInfo,117 std::numeric_limits<int>::max() - 1)118 .Case(section_names::ehFrame, std::numeric_limits<int>::max())119 .Default(0);120 121 if (knownPriority != 0)122 return knownPriority;123 124 // Ensure all code sections are contiguous with `__text` for thunk125 // calculations.126 if (sections::isCodeSection(osec->name, segment_names::text, osec->flags)) {127 return -5;128 }129 130 return osec->inputOrder;131 } else if (segname == segment_names::data ||132 segname == segment_names::dataConst) {133 // For each thread spawned, dyld will initialize its TLVs by copying the134 // address range from the start of the first thread-local data section to135 // the end of the last one. We therefore arrange these sections contiguously136 // to minimize the amount of memory used. Additionally, since zerofill137 // sections must be at the end of their segments, and since TLV data138 // sections can be zerofills, we end up putting all TLV data sections at the139 // end of the segment.140 switch (sectionType(osec->flags)) {141 case S_THREAD_LOCAL_VARIABLE_POINTERS:142 return std::numeric_limits<int>::max() - 3;143 case S_THREAD_LOCAL_REGULAR:144 return std::numeric_limits<int>::max() - 2;145 case S_THREAD_LOCAL_ZEROFILL:146 return std::numeric_limits<int>::max() - 1;147 case S_ZEROFILL:148 return std::numeric_limits<int>::max();149 default:150 return StringSwitch<int>(osec->name)151 .Case(section_names::got, -3)152 .Case(section_names::lazySymbolPtr, -2)153 .Case(section_names::const_, -1)154 .Default(osec->inputOrder);155 }156 } else if (segname == segment_names::linkEdit) {157 return StringSwitch<int>(osec->name)158 .Case(section_names::chainFixups, -11)159 .Case(section_names::rebase, -10)160 .Case(section_names::binding, -9)161 .Case(section_names::weakBinding, -8)162 .Case(section_names::lazyBinding, -7)163 .Case(section_names::export_, -6)164 .Case(section_names::functionStarts, -5)165 .Case(section_names::dataInCode, -4)166 .Case(section_names::symbolTable, -3)167 .Case(section_names::indirectSymbolTable, -2)168 .Case(section_names::stringTable, -1)169 .Case(section_names::codeSignature, std::numeric_limits<int>::max())170 .Default(osec->inputOrder);171 }172 // ZeroFill sections must always be the at the end of their segments:173 // dyld checks if a segment's file size is smaller than its in-memory174 // size to detect if a segment has zerofill sections, and if so it maps175 // the missing tail as zerofill.176 if (sectionType(osec->flags) == S_ZEROFILL)177 return std::numeric_limits<int>::max();178 return osec->inputOrder;179}180 181void OutputSegment::sortOutputSections() {182 // Must be stable_sort() to keep special sections such as183 // S_THREAD_LOCAL_REGULAR in input order.184 llvm::stable_sort(sections, compareByOrder<OutputSection *>(sectionOrder));185}186 187void OutputSegment::assignAddressesToStartEndSymbols() {188 for (Defined *d : segmentStartSymbols)189 d->value = addr;190 for (Defined *d : segmentEndSymbols)191 d->value = addr + vmSize;192}193 194void macho::sortOutputSegments() {195 llvm::stable_sort(outputSegments,196 compareByOrder<OutputSegment *>(segmentOrder));197}198 199static DenseMap<StringRef, OutputSegment *> nameToOutputSegment;200std::vector<OutputSegment *> macho::outputSegments;201 202void macho::resetOutputSegments() {203 outputSegments.clear();204 nameToOutputSegment.clear();205}206 207static StringRef maybeRenameSegment(StringRef name) {208 auto newName = config->segmentRenameMap.find(name);209 if (newName != config->segmentRenameMap.end())210 return newName->second;211 return name;212}213 214OutputSegment *macho::getOrCreateOutputSegment(StringRef name) {215 name = maybeRenameSegment(name);216 217 OutputSegment *&segRef = nameToOutputSegment[name];218 if (segRef)219 return segRef;220 221 segRef = make<OutputSegment>();222 segRef->name = name;223 segRef->maxProt = maxProt(name);224 segRef->initProt = initProt(name);225 segRef->flags = flags(name);226 227 outputSegments.push_back(segRef);228 return segRef;229}230