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fuchsia / third_party / llvm-project / 59731eebf8f24e3e90dc77e91a08d068b529cfc5 / . / lld / ELF / LinkerScript.cpp
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//===- LinkerScript.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 the parser/evaluator of the linker script.
//
//===----------------------------------------------------------------------===//
#include "LinkerScript.h"
#include "Config.h"
#include "InputFiles.h"
#include "InputSection.h"
#include "OutputSections.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Writer.h"
#include "lld/Common/CommonLinkerContext.h"
#include "lld/Common/Strings.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/TimeProfiler.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <limits>
#include <string>
#include <vector>
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
static bool isSectionPrefix(StringRef prefix, StringRef name) {
return name.consume_front(prefix) && (name.empty() || name[0] == '.');
}
StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
// This is for --emit-relocs and -r. If .text.foo is emitted as .text.bar, we
// want to emit .rela.text.foo as .rela.text.bar for consistency (this is not
// technically required, but not doing it is odd). This code guarantees that.
if (auto *isec = dyn_cast<InputSection>(s)) {
if (InputSectionBase *rel = isec->getRelocatedSection()) {
OutputSection *out = rel->getOutputSection();
if (!out) {
assert(config->relocatable && (rel->flags & SHF_LINK_ORDER));
return s->name;
}
if (s->type == SHT_CREL)
return saver().save(".crel" + out->name);
if (s->type == SHT_RELA)
return saver().save(".rela" + out->name);
return saver().save(".rel" + out->name);
}
}
if (config->relocatable)
return s->name;
// A BssSection created for a common symbol is identified as "COMMON" in
// linker scripts. It should go to .bss section.
if (s->name == "COMMON")
return ".bss";
if (hasSectionsCommand)
return s->name;
// When no SECTIONS is specified, emulate GNU ld's internal linker scripts
// by grouping sections with certain prefixes.
// GNU ld places text sections with prefix ".text.hot.", ".text.unknown.",
// ".text.unlikely.", ".text.startup." or ".text.exit." before others.
// We provide an option -z keep-text-section-prefix to group such sections
// into separate output sections. This is more flexible. See also
// sortISDBySectionOrder().
// ".text.unknown" means the hotness of the section is unknown. When
// SampleFDO is used, if a function doesn't have sample, it could be very
// cold or it could be a new function never being sampled. Those functions
// will be kept in the ".text.unknown" section.
// ".text.split." holds symbols which are split out from functions in other
// input sections. For example, with -fsplit-machine-functions, placing the
// cold parts in .text.split instead of .text.unlikely mitigates against poor
// profile inaccuracy. Techniques such as hugepage remapping can make
// conservative decisions at the section granularity.
if (isSectionPrefix(".text", s->name)) {
if (config->zKeepTextSectionPrefix)
for (StringRef v : {".text.hot", ".text.unknown", ".text.unlikely",
".text.startup", ".text.exit", ".text.split"})
if (isSectionPrefix(v.substr(5), s->name.substr(5)))
return v;
return ".text";
}
for (StringRef v : {".data.rel.ro", ".data", ".rodata",
".bss.rel.ro", ".bss", ".ldata",
".lrodata", ".lbss", ".gcc_except_table",
".init_array", ".fini_array", ".tbss",
".tdata", ".ARM.exidx", ".ARM.extab",
".ctors", ".dtors", ".sbss",
".sdata", ".srodata"})
if (isSectionPrefix(v, s->name))
return v;
return s->name;
}
uint64_t ExprValue::getValue() const {
if (sec)
return alignToPowerOf2(sec->getOutputSection()->addr + sec->getOffset(val),
alignment);
return alignToPowerOf2(val, alignment);
}
uint64_t ExprValue::getSecAddr() const {
return sec ? sec->getOutputSection()->addr + sec->getOffset(0) : 0;
}
uint64_t ExprValue::getSectionOffset() const {
return getValue() - getSecAddr();
}
OutputDesc *LinkerScript::createOutputSection(StringRef name,
StringRef location) {
OutputDesc *&secRef = nameToOutputSection[CachedHashStringRef(name)];
OutputDesc *sec;
if (secRef && secRef->osec.location.empty()) {
// There was a forward reference.
sec = secRef;
} else {
sec = make<OutputDesc>(name, SHT_PROGBITS, 0);
if (!secRef)
secRef = sec;
}
sec->osec.location = std::string(location);
return sec;
}
OutputDesc *LinkerScript::getOrCreateOutputSection(StringRef name) {
OutputDesc *&cmdRef = nameToOutputSection[CachedHashStringRef(name)];
if (!cmdRef)
cmdRef = make<OutputDesc>(name, SHT_PROGBITS, 0);
return cmdRef;
}
// Expands the memory region by the specified size.
static void expandMemoryRegion(MemoryRegion *memRegion, uint64_t size,
StringRef secName) {
memRegion->curPos += size;
}
void LinkerScript::expandMemoryRegions(uint64_t size) {
if (state->memRegion)
expandMemoryRegion(state->memRegion, size, state->outSec->name);
// Only expand the LMARegion if it is different from memRegion.
if (state->lmaRegion && state->memRegion != state->lmaRegion)
expandMemoryRegion(state->lmaRegion, size, state->outSec->name);
}
void LinkerScript::expandOutputSection(uint64_t size) {
state->outSec->size += size;
expandMemoryRegions(size);
}
void LinkerScript::setDot(Expr e, const Twine &loc, bool inSec) {
uint64_t val = e().getValue();
// If val is smaller and we are in an output section, record the error and
// report it if this is the last assignAddresses iteration. dot may be smaller
// if there is another assignAddresses iteration.
if (val < dot && inSec) {
recordError(loc + ": unable to move location counter (0x" +
Twine::utohexstr(dot) + ") backward to 0x" +
Twine::utohexstr(val) + " for section '" + state->outSec->name +
"'");
}
// Update to location counter means update to section size.
if (inSec)
expandOutputSection(val - dot);
dot = val;
}
// Used for handling linker symbol assignments, for both finalizing
// their values and doing early declarations. Returns true if symbol
// should be defined from linker script.
static bool shouldDefineSym(SymbolAssignment *cmd) {
if (cmd->name == ".")
return false;
return !cmd->provide || LinkerScript::shouldAddProvideSym(cmd->name);
}
// Called by processSymbolAssignments() to assign definitions to
// linker-script-defined symbols.
void LinkerScript::addSymbol(SymbolAssignment *cmd) {
if (!shouldDefineSym(cmd))
return;
// Define a symbol.
ExprValue value = cmd->expression();
SectionBase *sec = value.isAbsolute() ? nullptr : value.sec;
uint8_t visibility = cmd->hidden ? STV_HIDDEN : STV_DEFAULT;
// When this function is called, section addresses have not been
// fixed yet. So, we may or may not know the value of the RHS
// expression.
//
// For example, if an expression is `x = 42`, we know x is always 42.
// However, if an expression is `x = .`, there's no way to know its
// value at the moment.
//
// We want to set symbol values early if we can. This allows us to
// use symbols as variables in linker scripts. Doing so allows us to
// write expressions like this: `alignment = 16; . = ALIGN(., alignment)`.
uint64_t symValue = value.sec ? 0 : value.getValue();
Defined newSym(createInternalFile(cmd->location), cmd->name, STB_GLOBAL,
visibility, value.type, symValue, 0, sec);
Symbol *sym = symtab.insert(cmd->name);
sym->mergeProperties(newSym);
newSym.overwrite(*sym);
sym->isUsedInRegularObj = true;
cmd->sym = cast<Defined>(sym);
}
// This function is called from LinkerScript::declareSymbols.
// It creates a placeholder symbol if needed.
static void declareSymbol(SymbolAssignment *cmd) {
if (!shouldDefineSym(cmd))
return;
uint8_t visibility = cmd->hidden ? STV_HIDDEN : STV_DEFAULT;
Defined newSym(ctx.internalFile, cmd->name, STB_GLOBAL, visibility,
STT_NOTYPE, 0, 0, nullptr);
// If the symbol is already defined, its order is 0 (with absence indicating
// 0); otherwise it's assigned the order of the SymbolAssignment.
Symbol *sym = symtab.insert(cmd->name);
if (!sym->isDefined())
ctx.scriptSymOrder.insert({sym, cmd->symOrder});
// We can't calculate final value right now.
sym->mergeProperties(newSym);
newSym.overwrite(*sym);
cmd->sym = cast<Defined>(sym);
cmd->provide = false;
sym->isUsedInRegularObj = true;
sym->scriptDefined = true;
}
using SymbolAssignmentMap =
DenseMap<const Defined *, std::pair<SectionBase *, uint64_t>>;
// Collect section/value pairs of linker-script-defined symbols. This is used to
// check whether symbol values converge.
static SymbolAssignmentMap
getSymbolAssignmentValues(ArrayRef<SectionCommand *> sectionCommands) {
SymbolAssignmentMap ret;
for (SectionCommand *cmd : sectionCommands) {
if (auto *assign = dyn_cast<SymbolAssignment>(cmd)) {
if (assign->sym) // sym is nullptr for dot.
ret.try_emplace(assign->sym, std::make_pair(assign->sym->section,
assign->sym->value));
continue;
}
if (isa<SectionClassDesc>(cmd))
continue;
for (SectionCommand *subCmd : cast<OutputDesc>(cmd)->osec.commands)
if (auto *assign = dyn_cast<SymbolAssignment>(subCmd))
if (assign->sym)
ret.try_emplace(assign->sym, std::make_pair(assign->sym->section,
assign->sym->value));
}
return ret;
}
// Returns the lexicographical smallest (for determinism) Defined whose
// section/value has changed.
static const Defined *
getChangedSymbolAssignment(const SymbolAssignmentMap &oldValues) {
const Defined *changed = nullptr;
for (auto &it : oldValues) {
const Defined *sym = it.first;
if (std::make_pair(sym->section, sym->value) != it.second &&
(!changed || sym->getName() < changed->getName()))
changed = sym;
}
return changed;
}
// Process INSERT [AFTER|BEFORE] commands. For each command, we move the
// specified output section to the designated place.
void LinkerScript::processInsertCommands() {
SmallVector<OutputDesc *, 0> moves;
for (const InsertCommand &cmd : insertCommands) {
if (config->enableNonContiguousRegions)
error("INSERT cannot be used with --enable-non-contiguous-regions");
for (StringRef name : cmd.names) {
// If base is empty, it may have been discarded by
// adjustOutputSections(). We do not handle such output sections.
auto from = llvm::find_if(sectionCommands, [&](SectionCommand *subCmd) {
return isa<OutputDesc>(subCmd) &&
cast<OutputDesc>(subCmd)->osec.name == name;
});
if (from == sectionCommands.end())
continue;
moves.push_back(cast<OutputDesc>(*from));
sectionCommands.erase(from);
}
auto insertPos =
llvm::find_if(sectionCommands, [&cmd](SectionCommand *subCmd) {
auto *to = dyn_cast<OutputDesc>(subCmd);
return to != nullptr && to->osec.name == cmd.where;
});
if (insertPos == sectionCommands.end()) {
error("unable to insert " + cmd.names[0] +
(cmd.isAfter ? " after " : " before ") + cmd.where);
} else {
if (cmd.isAfter)
++insertPos;
sectionCommands.insert(insertPos, moves.begin(), moves.end());
}
moves.clear();
}
}
// Symbols defined in script should not be inlined by LTO. At the same time
// we don't know their final values until late stages of link. Here we scan
// over symbol assignment commands and create placeholder symbols if needed.
void LinkerScript::declareSymbols() {
assert(!state);
for (SectionCommand *cmd : sectionCommands) {
if (auto *assign = dyn_cast<SymbolAssignment>(cmd)) {
declareSymbol(assign);
continue;
}
if (isa<SectionClassDesc>(cmd))
continue;
// If the output section directive has constraints,
// we can't say for sure if it is going to be included or not.
// Skip such sections for now. Improve the checks if we ever
// need symbols from that sections to be declared early.
const OutputSection &sec = cast<OutputDesc>(cmd)->osec;
if (sec.constraint != ConstraintKind::NoConstraint)
continue;
for (SectionCommand *cmd : sec.commands)
if (auto *assign = dyn_cast<SymbolAssignment>(cmd))
declareSymbol(assign);
}
}
// This function is called from assignAddresses, while we are
// fixing the output section addresses. This function is supposed
// to set the final value for a given symbol assignment.
void LinkerScript::assignSymbol(SymbolAssignment *cmd, bool inSec) {
if (cmd->name == ".") {
setDot(cmd->expression, cmd->location, inSec);
return;
}
if (!cmd->sym)
return;
ExprValue v = cmd->expression();
if (v.isAbsolute()) {
cmd->sym->section = nullptr;
cmd->sym->value = v.getValue();
} else {
cmd->sym->section = v.sec;
cmd->sym->value = v.getSectionOffset();
}
cmd->sym->type = v.type;
}
static inline StringRef getFilename(const InputFile *file) {
return file ? file->getNameForScript() : StringRef();
}
bool InputSectionDescription::matchesFile(const InputFile *file) const {
if (filePat.isTrivialMatchAll())
return true;
if (!matchesFileCache || matchesFileCache->first != file)
matchesFileCache.emplace(file, filePat.match(getFilename(file)));
return matchesFileCache->second;
}
bool SectionPattern::excludesFile(const InputFile *file) const {
if (excludedFilePat.empty())
return false;
if (!excludesFileCache || excludesFileCache->first != file)
excludesFileCache.emplace(file, excludedFilePat.match(getFilename(file)));
return excludesFileCache->second;
}
bool LinkerScript::shouldKeep(InputSectionBase *s) {
for (InputSectionDescription *id : keptSections)
if (id->matchesFile(s->file))
for (SectionPattern &p : id->sectionPatterns)
if (p.sectionPat.match(s->name) &&
(s->flags & id->withFlags) == id->withFlags &&
(s->flags & id->withoutFlags) == 0)
return true;
return false;
}
// A helper function for the SORT() command.
static bool matchConstraints(ArrayRef<InputSectionBase *> sections,
ConstraintKind kind) {
if (kind == ConstraintKind::NoConstraint)
return true;
bool isRW = llvm::any_of(
sections, [](InputSectionBase *sec) { return sec->flags & SHF_WRITE; });
return (isRW && kind == ConstraintKind::ReadWrite) ||
(!isRW && kind == ConstraintKind::ReadOnly);
}
static void sortSections(MutableArrayRef<InputSectionBase *> vec,
SortSectionPolicy k) {
auto alignmentComparator = [](InputSectionBase *a, InputSectionBase *b) {
// ">" is not a mistake. Sections with larger alignments are placed
// before sections with smaller alignments in order to reduce the
// amount of padding necessary. This is compatible with GNU.
return a->addralign > b->addralign;
};
auto nameComparator = [](InputSectionBase *a, InputSectionBase *b) {
return a->name < b->name;
};
auto priorityComparator = [](InputSectionBase *a, InputSectionBase *b) {
return getPriority(a->name) < getPriority(b->name);
};
switch (k) {
case SortSectionPolicy::Default:
case SortSectionPolicy::None:
return;
case SortSectionPolicy::Alignment:
return llvm::stable_sort(vec, alignmentComparator);
case SortSectionPolicy::Name:
return llvm::stable_sort(vec, nameComparator);
case SortSectionPolicy::Priority:
return llvm::stable_sort(vec, priorityComparator);
case SortSectionPolicy::Reverse:
return std::reverse(vec.begin(), vec.end());
}
}
// Sort sections as instructed by SORT-family commands and --sort-section
// option. Because SORT-family commands can be nested at most two depth
// (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command
// line option is respected even if a SORT command is given, the exact
// behavior we have here is a bit complicated. Here are the rules.
//
// 1. If two SORT commands are given, --sort-section is ignored.
// 2. If one SORT command is given, and if it is not SORT_NONE,
// --sort-section is handled as an inner SORT command.
// 3. If one SORT command is given, and if it is SORT_NONE, don't sort.
// 4. If no SORT command is given, sort according to --sort-section.
static void sortInputSections(MutableArrayRef<InputSectionBase *> vec,
SortSectionPolicy outer,
SortSectionPolicy inner) {
if (outer == SortSectionPolicy::None)
return;
if (inner == SortSectionPolicy::Default)
sortSections(vec, config->sortSection);
else
sortSections(vec, inner);
sortSections(vec, outer);
}
// Compute and remember which sections the InputSectionDescription matches.
SmallVector<InputSectionBase *, 0>
LinkerScript::computeInputSections(const InputSectionDescription *cmd,
ArrayRef<InputSectionBase *> sections,
const SectionBase &outCmd) {
SmallVector<InputSectionBase *, 0> ret;
DenseSet<InputSectionBase *> spills;
// Returns whether an input section's flags match the input section
// description's specifiers.
auto flagsMatch = [cmd](InputSectionBase *sec) {
return (sec->flags & cmd->withFlags) == cmd->withFlags &&
(sec->flags & cmd->withoutFlags) == 0;
};
// Collects all sections that satisfy constraints of Cmd.
if (cmd->classRef.empty()) {
DenseSet<size_t> seen;
size_t sizeAfterPrevSort = 0;
SmallVector<size_t, 0> indexes;
auto sortByPositionThenCommandLine = [&](size_t begin, size_t end) {
llvm::sort(MutableArrayRef<size_t>(indexes).slice(begin, end - begin));
for (size_t i = begin; i != end; ++i)
ret[i] = sections[indexes[i]];
sortInputSections(
MutableArrayRef<InputSectionBase *>(ret).slice(begin, end - begin),
config->sortSection, SortSectionPolicy::None);
};
for (const SectionPattern &pat : cmd->sectionPatterns) {
size_t sizeBeforeCurrPat = ret.size();
for (size_t i = 0, e = sections.size(); i != e; ++i) {
// Skip if the section is dead or has been matched by a previous pattern
// in this input section description.
InputSectionBase *sec = sections[i];
if (!sec->isLive() || seen.contains(i))
continue;
// For --emit-relocs we have to ignore entries like
// .rela.dyn : { *(.rela.data) }
// which are common because they are in the default bfd script.
// We do not ignore SHT_REL[A] linker-synthesized sections here because
// want to support scripts that do custom layout for them.
if (isa<InputSection>(sec) &&
cast<InputSection>(sec)->getRelocatedSection())
continue;
// Check the name early to improve performance in the common case.
if (!pat.sectionPat.match(sec->name))
continue;
if (!cmd->matchesFile(sec->file) || pat.excludesFile(sec->file) ||
sec->parent == &outCmd || !flagsMatch(sec))
continue;
if (sec->parent) {
// Skip if not allowing multiple matches.
if (!config->enableNonContiguousRegions)
continue;
// Disallow spilling into /DISCARD/; special handling would be needed
// for this in address assignment, and the semantics are nebulous.
if (outCmd.name == "/DISCARD/")
continue;
// Class definitions cannot contain spills, nor can a class definition
// generate a spill in a subsequent match. Those behaviors belong to
// class references and additional matches.
if (!isa<SectionClass>(outCmd) && !isa<SectionClass>(sec->parent))
spills.insert(sec);
}
ret.push_back(sec);
indexes.push_back(i);
seen.insert(i);
}
if (pat.sortOuter == SortSectionPolicy::Default)
continue;
// Matched sections are ordered by radix sort with the keys being (SORT*,
// --sort-section, input order), where SORT* (if present) is most
// significant.
//
// Matched sections between the previous SORT* and this SORT* are sorted
// by (--sort-alignment, input order).
sortByPositionThenCommandLine(sizeAfterPrevSort, sizeBeforeCurrPat);
// Matched sections by this SORT* pattern are sorted using all 3 keys.
// ret[sizeBeforeCurrPat,ret.size()) are already in the input order, so we
// just sort by sortOuter and sortInner.
sortInputSections(
MutableArrayRef<InputSectionBase *>(ret).slice(sizeBeforeCurrPat),
pat.sortOuter, pat.sortInner);
sizeAfterPrevSort = ret.size();
}
// Matched sections after the last SORT* are sorted by (--sort-alignment,
// input order).
sortByPositionThenCommandLine(sizeAfterPrevSort, ret.size());
} else {
SectionClassDesc *scd =
sectionClasses.lookup(CachedHashStringRef(cmd->classRef));
if (!scd) {
errorOrWarn("undefined section class '" + cmd->classRef + "'");
return ret;
}
if (!scd->sc.assigned) {
errorOrWarn("section class '" + cmd->classRef + "' referenced by '" +
outCmd.name + "' before class definition");
return ret;
}
for (InputSectionDescription *isd : scd->sc.commands) {
for (InputSectionBase *sec : isd->sectionBases) {
if (sec->parent == &outCmd || !flagsMatch(sec))
continue;
bool isSpill = sec->parent && isa<OutputSection>(sec->parent);
if (!sec->parent || (isSpill && outCmd.name == "/DISCARD/")) {
errorOrWarn("section '" + sec->name +
"' cannot spill from/to /DISCARD/");
continue;
}
if (isSpill)
spills.insert(sec);
ret.push_back(sec);
}
}
}
// The flag --enable-non-contiguous-regions or the section CLASS syntax may
// cause sections to match an InputSectionDescription in more than one
// OutputSection. Matches after the first were collected in the spills set, so
// replace these with potential spill sections.
if (!spills.empty()) {
for (InputSectionBase *&sec : ret) {
if (!spills.contains(sec))
continue;
// Append the spill input section to the list for the input section,
// creating it if necessary.
PotentialSpillSection *pss = make<PotentialSpillSection>(
*sec, const_cast<InputSectionDescription &>(*cmd));
auto [it, inserted] =
potentialSpillLists.try_emplace(sec, PotentialSpillList{pss, pss});
if (!inserted) {
PotentialSpillSection *&tail = it->second.tail;
tail = tail->next = pss;
}
sec = pss;
}
}
return ret;
}
void LinkerScript::discard(InputSectionBase &s) {
if (&s == in.shStrTab.get())
error("discarding " + s.name + " section is not allowed");
s.markDead();
s.parent = nullptr;
for (InputSection *sec : s.dependentSections)
discard(*sec);
}
void LinkerScript::discardSynthetic(OutputSection &outCmd) {
for (Partition &part : partitions) {
if (!part.armExidx || !part.armExidx->isLive())
continue;
SmallVector<InputSectionBase *, 0> secs(
part.armExidx->exidxSections.begin(),
part.armExidx->exidxSections.end());
for (SectionCommand *cmd : outCmd.commands)
if (auto *isd = dyn_cast<InputSectionDescription>(cmd))
for (InputSectionBase *s : computeInputSections(isd, secs, outCmd))
discard(*s);
}
}
SmallVector<InputSectionBase *, 0>
LinkerScript::createInputSectionList(OutputSection &outCmd) {
SmallVector<InputSectionBase *, 0> ret;
for (SectionCommand *cmd : outCmd.commands) {
if (auto *isd = dyn_cast<InputSectionDescription>(cmd)) {
isd->sectionBases = computeInputSections(isd, ctx.inputSections, outCmd);
for (InputSectionBase *s : isd->sectionBases)
s->parent = &outCmd;
ret.insert(ret.end(), isd->sectionBases.begin(), isd->sectionBases.end());
}
}
return ret;
}
// Create output sections described by SECTIONS commands.
void LinkerScript::processSectionCommands() {
auto process = [this](OutputSection *osec) {
SmallVector<InputSectionBase *, 0> v = createInputSectionList(*osec);
// The output section name `/DISCARD/' is special.
// Any input section assigned to it is discarded.
if (osec->name == "/DISCARD/") {
for (InputSectionBase *s : v)
discard(*s);
discardSynthetic(*osec);
osec->commands.clear();
return false;
}
// This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive
// ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
// sections satisfy a given constraint. If not, a directive is handled
// as if it wasn't present from the beginning.
//
// Because we'll iterate over SectionCommands many more times, the easy
// way to "make it as if it wasn't present" is to make it empty.
if (!matchConstraints(v, osec->constraint)) {
for (InputSectionBase *s : v)
s->parent = nullptr;
osec->commands.clear();
return false;
}
// Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
// is given, input sections are aligned to that value, whether the
// given value is larger or smaller than the original section alignment.
if (osec->subalignExpr) {
uint32_t subalign = osec->subalignExpr().getValue();
for (InputSectionBase *s : v)
s->addralign = subalign;
}
// Set the partition field the same way OutputSection::recordSection()
// does. Partitions cannot be used with the SECTIONS command, so this is
// always 1.
osec->partition = 1;
return true;
};
// Process OVERWRITE_SECTIONS first so that it can overwrite the main script
// or orphans.
if (config->enableNonContiguousRegions && !overwriteSections.empty())
error("OVERWRITE_SECTIONS cannot be used with "
"--enable-non-contiguous-regions");
DenseMap<CachedHashStringRef, OutputDesc *> map;
size_t i = 0;
for (OutputDesc *osd : overwriteSections) {
OutputSection *osec = &osd->osec;
if (process(osec) &&
!map.try_emplace(CachedHashStringRef(osec->name), osd).second)
warn("OVERWRITE_SECTIONS specifies duplicate " + osec->name);
}
for (SectionCommand *&base : sectionCommands) {
if (auto *osd = dyn_cast<OutputDesc>(base)) {
OutputSection *osec = &osd->osec;
if (OutputDesc *overwrite = map.lookup(CachedHashStringRef(osec->name))) {
log(overwrite->osec.location + " overwrites " + osec->name);
overwrite->osec.sectionIndex = i++;
base = overwrite;
} else if (process(osec)) {
osec->sectionIndex = i++;
}
} else if (auto *sc = dyn_cast<SectionClassDesc>(base)) {
for (InputSectionDescription *isd : sc->sc.commands) {
isd->sectionBases =
computeInputSections(isd, ctx.inputSections, sc->sc);
for (InputSectionBase *s : isd->sectionBases) {
// A section class containing a section with different parent isn't
// necessarily an error due to --enable-non-contiguous-regions. Such
// sections all become potential spills when the class is referenced.
if (!s->parent)
s->parent = &sc->sc;
}
}
sc->sc.assigned = true;
}
}
// Check that input sections cannot spill into or out of INSERT,
// since the semantics are nebulous. This is also true for OVERWRITE_SECTIONS,
// but no check is needed, since the order of processing ensures they cannot
// legally reference classes.
if (!potentialSpillLists.empty()) {
DenseSet<StringRef> insertNames;
for (InsertCommand &ic : insertCommands)
insertNames.insert(ic.names.begin(), ic.names.end());
for (SectionCommand *&base : sectionCommands) {
auto *osd = dyn_cast<OutputDesc>(base);
if (!osd)
continue;
OutputSection *os = &osd->osec;
if (!insertNames.contains(os->name))
continue;
for (SectionCommand *sc : os->commands) {
auto *isd = dyn_cast<InputSectionDescription>(sc);
if (!isd)
continue;
for (InputSectionBase *isec : isd->sectionBases)
if (isa<PotentialSpillSection>(isec) ||
potentialSpillLists.contains(isec))
errorOrWarn("section '" + isec->name +
"' cannot spill from/to INSERT section '" + os->name +
"'");
}
}
}
// If an OVERWRITE_SECTIONS specified output section is not in
// sectionCommands, append it to the end. The section will be inserted by
// orphan placement.
for (OutputDesc *osd : overwriteSections)
if (osd->osec.partition == 1 && osd->osec.sectionIndex == UINT32_MAX)
sectionCommands.push_back(osd);
// Input sections cannot have a section class parent past this point; they
// must have been assigned to an output section.
for (const auto &[_, sc] : sectionClasses) {
for (InputSectionDescription *isd : sc->sc.commands) {
for (InputSectionBase *sec : isd->sectionBases) {
if (sec->parent && isa<SectionClass>(sec->parent)) {
errorOrWarn("section class '" + sec->parent->name +
"' is unreferenced");
goto nextClass;
}
}
}
nextClass:;
}
}
void LinkerScript::processSymbolAssignments() {
// Dot outside an output section still represents a relative address, whose
// sh_shndx should not be SHN_UNDEF or SHN_ABS. Create a dummy aether section
// that fills the void outside a section. It has an index of one, which is
// indistinguishable from any other regular section index.
aether = make<OutputSection>("", 0, SHF_ALLOC);
aether->sectionIndex = 1;
// `st` captures the local AddressState and makes it accessible deliberately.
// This is needed as there are some cases where we cannot just thread the
// current state through to a lambda function created by the script parser.
AddressState st;
state = &st;
st.outSec = aether;
for (SectionCommand *cmd : sectionCommands) {
if (auto *assign = dyn_cast<SymbolAssignment>(cmd))
addSymbol(assign);
else if (auto *osd = dyn_cast<OutputDesc>(cmd))
for (SectionCommand *subCmd : osd->osec.commands)
if (auto *assign = dyn_cast<SymbolAssignment>(subCmd))
addSymbol(assign);
}
state = nullptr;
}
static OutputSection *findByName(ArrayRef<SectionCommand *> vec,
StringRef name) {
for (SectionCommand *cmd : vec)
if (auto *osd = dyn_cast<OutputDesc>(cmd))
if (osd->osec.name == name)
return &osd->osec;
return nullptr;
}
static OutputDesc *createSection(InputSectionBase *isec, StringRef outsecName) {
OutputDesc *osd = ctx.script->createOutputSection(outsecName, "<internal>");
osd->osec.recordSection(isec);
return osd;
}
static OutputDesc *addInputSec(StringMap<TinyPtrVector<OutputSection *>> &map,
InputSectionBase *isec, StringRef outsecName) {
// Sections with SHT_GROUP or SHF_GROUP attributes reach here only when the -r
// option is given. A section with SHT_GROUP defines a "section group", and
// its members have SHF_GROUP attribute. Usually these flags have already been
// stripped by InputFiles.cpp as section groups are processed and uniquified.
// However, for the -r option, we want to pass through all section groups
// as-is because adding/removing members or merging them with other groups
// change their semantics.
if (isec->type == SHT_GROUP || (isec->flags & SHF_GROUP))
return createSection(isec, outsecName);
// Imagine .zed : { *(.foo) *(.bar) } script. Both foo and bar may have
// relocation sections .rela.foo and .rela.bar for example. Most tools do
// not allow multiple REL[A] sections for output section. Hence we
// should combine these relocation sections into single output.
// We skip synthetic sections because it can be .rela.dyn/.rela.plt or any
// other REL[A] sections created by linker itself.
if (!isa<SyntheticSection>(isec) && isStaticRelSecType(isec->type)) {
auto *sec = cast<InputSection>(isec);
OutputSection *out = sec->getRelocatedSection()->getOutputSection();
if (auto *relSec = out->relocationSection) {
relSec->recordSection(sec);
return nullptr;
}
OutputDesc *osd = createSection(isec, outsecName);
out->relocationSection = &osd->osec;
return osd;
}
// The ELF spec just says
// ----------------------------------------------------------------
// In the first phase, input sections that match in name, type and
// attribute flags should be concatenated into single sections.
// ----------------------------------------------------------------
//
// However, it is clear that at least some flags have to be ignored for
// section merging. At the very least SHF_GROUP and SHF_COMPRESSED have to be
// ignored. We should not have two output .text sections just because one was
// in a group and another was not for example.
//
// It also seems that wording was a late addition and didn't get the
// necessary scrutiny.
//
// Merging sections with different flags is expected by some users. One
// reason is that if one file has
//
// int *const bar __attribute__((section(".foo"))) = (int *)0;
//
// gcc with -fPIC will produce a read only .foo section. But if another
// file has
//
// int zed;
// int *const bar __attribute__((section(".foo"))) = (int *)&zed;
//
// gcc with -fPIC will produce a read write section.
//
// Last but not least, when using linker script the merge rules are forced by
// the script. Unfortunately, linker scripts are name based. This means that
// expressions like *(.foo*) can refer to multiple input sections with
// different flags. We cannot put them in different output sections or we
// would produce wrong results for
//
// start = .; *(.foo.*) end = .; *(.bar)
//
// and a mapping of .foo1 and .bar1 to one section and .foo2 and .bar2 to
// another. The problem is that there is no way to layout those output
// sections such that the .foo sections are the only thing between the start
// and end symbols.
//
// Given the above issues, we instead merge sections by name and error on
// incompatible types and flags.
TinyPtrVector<OutputSection *> &v = map[outsecName];
for (OutputSection *sec : v) {
if (sec->partition != isec->partition)
continue;
if (config->relocatable && (isec->flags & SHF_LINK_ORDER)) {
// Merging two SHF_LINK_ORDER sections with different sh_link fields will
// change their semantics, so we only merge them in -r links if they will
// end up being linked to the same output section. The casts are fine
// because everything in the map was created by the orphan placement code.
auto *firstIsec = cast<InputSectionBase>(
cast<InputSectionDescription>(sec->commands[0])->sectionBases[0]);
OutputSection *firstIsecOut =
(firstIsec->flags & SHF_LINK_ORDER)
? firstIsec->getLinkOrderDep()->getOutputSection()
: nullptr;
if (firstIsecOut != isec->getLinkOrderDep()->getOutputSection())
continue;
}
sec->recordSection(isec);
return nullptr;
}
OutputDesc *osd = createSection(isec, outsecName);
v.push_back(&osd->osec);
return osd;
}
// Add sections that didn't match any sections command.
void LinkerScript::addOrphanSections() {
StringMap<TinyPtrVector<OutputSection *>> map;
SmallVector<OutputDesc *, 0> v;
auto add = [&](InputSectionBase *s) {
if (s->isLive() && !s->parent) {
orphanSections.push_back(s);
StringRef name = getOutputSectionName(s);
if (config->unique) {
v.push_back(createSection(s, name));
} else if (OutputSection *sec = findByName(sectionCommands, name)) {
sec->recordSection(s);
} else {
if (OutputDesc *osd = addInputSec(map, s, name))
v.push_back(osd);
assert(isa<MergeInputSection>(s) ||
s->getOutputSection()->sectionIndex == UINT32_MAX);
}
}
};
// For further --emit-reloc handling code we need target output section
// to be created before we create relocation output section, so we want
// to create target sections first. We do not want priority handling
// for synthetic sections because them are special.
size_t n = 0;
for (InputSectionBase *isec : ctx.inputSections) {
// Process InputSection and MergeInputSection.
if (LLVM_LIKELY(isa<InputSection>(isec)))
ctx.inputSections[n++] = isec;
// In -r links, SHF_LINK_ORDER sections are added while adding their parent
// sections because we need to know the parent's output section before we
// can select an output section for the SHF_LINK_ORDER section.
if (config->relocatable && (isec->flags & SHF_LINK_ORDER))
continue;
if (auto *sec = dyn_cast<InputSection>(isec))
if (InputSectionBase *rel = sec->getRelocatedSection())
if (auto *relIS = dyn_cast_or_null<InputSectionBase>(rel->parent))
add(relIS);
add(isec);
if (config->relocatable)
for (InputSectionBase *depSec : isec->dependentSections)
if (depSec->flags & SHF_LINK_ORDER)
add(depSec);
}
// Keep just InputSection.
ctx.inputSections.resize(n);
// If no SECTIONS command was given, we should insert sections commands
// before others, so that we can handle scripts which refers them,
// for example: "foo = ABSOLUTE(ADDR(.text)));".
// When SECTIONS command is present we just add all orphans to the end.
if (hasSectionsCommand)
sectionCommands.insert(sectionCommands.end(), v.begin(), v.end());
else
sectionCommands.insert(sectionCommands.begin(), v.begin(), v.end());
}
void LinkerScript::diagnoseOrphanHandling() const {
llvm::TimeTraceScope timeScope("Diagnose orphan sections");
if (config->orphanHandling == OrphanHandlingPolicy::Place ||
!hasSectionsCommand)
return;
for (const InputSectionBase *sec : orphanSections) {
// .relro_padding is inserted before DATA_SEGMENT_RELRO_END, if present,
// automatically. The section is not supposed to be specified by scripts.
if (sec == in.relroPadding.get())
continue;
// Input SHT_REL[A] retained by --emit-relocs are ignored by
// computeInputSections(). Don't warn/error.
if (isa<InputSection>(sec) &&
cast<InputSection>(sec)->getRelocatedSection())
continue;
StringRef name = getOutputSectionName(sec);
if (config->orphanHandling == OrphanHandlingPolicy::Error)
error(toString(sec) + " is being placed in '" + name + "'");
else
warn(toString(sec) + " is being placed in '" + name + "'");
}
}
void LinkerScript::diagnoseMissingSGSectionAddress() const {
if (!config->cmseImplib || !in.armCmseSGSection->isNeeded())
return;
OutputSection *sec = findByName(sectionCommands, ".gnu.sgstubs");
if (sec && !sec->addrExpr && !config->sectionStartMap.count(".gnu.sgstubs"))
error("no address assigned to the veneers output section " + sec->name);
}
// This function searches for a memory region to place the given output
// section in. If found, a pointer to the appropriate memory region is
// returned in the first member of the pair. Otherwise, a nullptr is returned.
// The second member of the pair is a hint that should be passed to the
// subsequent call of this method.
std::pair<MemoryRegion *, MemoryRegion *>
LinkerScript::findMemoryRegion(OutputSection *sec, MemoryRegion *hint) {
// Non-allocatable sections are not part of the process image.
if (!(sec->flags & SHF_ALLOC)) {
bool hasInputOrByteCommand =
sec->hasInputSections ||
llvm::any_of(sec->commands, [](SectionCommand *comm) {
return ByteCommand::classof(comm);
});
if (!sec->memoryRegionName.empty() && hasInputOrByteCommand)
warn("ignoring memory region assignment for non-allocatable section '" +
sec->name + "'");
return {nullptr, nullptr};
}
// If a memory region name was specified in the output section command,
// then try to find that region first.
if (!sec->memoryRegionName.empty()) {
if (MemoryRegion *m = memoryRegions.lookup(sec->memoryRegionName))
return {m, m};
error("memory region '" + sec->memoryRegionName + "' not declared");
return {nullptr, nullptr};
}
// If at least one memory region is defined, all sections must
// belong to some memory region. Otherwise, we don't need to do
// anything for memory regions.
if (memoryRegions.empty())
return {nullptr, nullptr};
// An orphan section should continue the previous memory region.
if (sec->sectionIndex == UINT32_MAX && hint)
return {hint, hint};
// See if a region can be found by matching section flags.
for (auto &pair : memoryRegions) {
MemoryRegion *m = pair.second;
if (m->compatibleWith(sec->flags))
return {m, nullptr};
}
// Otherwise, no suitable region was found.
error("no memory region specified for section '" + sec->name + "'");
return {nullptr, nullptr};
}
static OutputSection *findFirstSection(PhdrEntry *load) {
for (OutputSection *sec : ctx.outputSections)
if (sec->ptLoad == load)
return sec;
return nullptr;
}
// Assign addresses to an output section and offsets to its input sections and
// symbol assignments. Return true if the output section's address has changed.
bool LinkerScript::assignOffsets(OutputSection *sec) {
const bool isTbss = (sec->flags & SHF_TLS) && sec->type == SHT_NOBITS;
const bool sameMemRegion = state->memRegion == sec->memRegion;
const bool prevLMARegionIsDefault = state->lmaRegion == nullptr;
const uint64_t savedDot = dot;
bool addressChanged = false;
state->memRegion = sec->memRegion;
state->lmaRegion = sec->lmaRegion;
if (!(sec->flags & SHF_ALLOC)) {
// Non-SHF_ALLOC sections have zero addresses.
dot = 0;
} else if (isTbss) {
// Allow consecutive SHF_TLS SHT_NOBITS output sections. The address range
// starts from the end address of the previous tbss section.
if (state->tbssAddr == 0)
state->tbssAddr = dot;
else
dot = state->tbssAddr;
} else {
if (state->memRegion)
dot = state->memRegion->curPos;
if (sec->addrExpr)
setDot(sec->addrExpr, sec->location, false);
// If the address of the section has been moved forward by an explicit
// expression so that it now starts past the current curPos of the enclosing
// region, we need to expand the current region to account for the space
// between the previous section, if any, and the start of this section.
if (state->memRegion && state->memRegion->curPos < dot)
expandMemoryRegion(state->memRegion, dot - state->memRegion->curPos,
sec->name);
}
state->outSec = sec;
if (!(sec->addrExpr && hasSectionsCommand)) {
// ALIGN is respected. sec->alignment is the max of ALIGN and the maximum of
// input section alignments.
const uint64_t pos = dot;
dot = alignToPowerOf2(dot, sec->addralign);
expandMemoryRegions(dot - pos);
}
addressChanged = sec->addr != dot;
sec->addr = dot;
// state->lmaOffset is LMA minus VMA. If LMA is explicitly specified via AT()
// or AT>, recompute state->lmaOffset; otherwise, if both previous/current LMA
// region is the default, and the two sections are in the same memory region,
// reuse previous lmaOffset; otherwise, reset lmaOffset to 0. This emulates
// heuristics described in
// https://sourceware.org/binutils/docs/ld/Output-Section-LMA.html
if (sec->lmaExpr) {
state->lmaOffset = sec->lmaExpr().getValue() - dot;
} else if (MemoryRegion *mr = sec->lmaRegion) {
uint64_t lmaStart = alignToPowerOf2(mr->curPos, sec->addralign);
if (mr->curPos < lmaStart)
expandMemoryRegion(mr, lmaStart - mr->curPos, sec->name);
state->lmaOffset = lmaStart - dot;
} else if (!sameMemRegion || !prevLMARegionIsDefault) {
state->lmaOffset = 0;
}
// Propagate state->lmaOffset to the first "non-header" section.
if (PhdrEntry *l = sec->ptLoad)
if (sec == findFirstSection(l))
l->lmaOffset = state->lmaOffset;
// We can call this method multiple times during the creation of
// thunks and want to start over calculation each time.
sec->size = 0;
// We visited SectionsCommands from processSectionCommands to
// layout sections. Now, we visit SectionsCommands again to fix
// section offsets.
for (SectionCommand *cmd : sec->commands) {
// This handles the assignments to symbol or to the dot.
if (auto *assign = dyn_cast<SymbolAssignment>(cmd)) {
assign->addr = dot;
assignSymbol(assign, true);
assign->size = dot - assign->addr;
continue;
}
// Handle BYTE(), SHORT(), LONG(), or QUAD().
if (auto *data = dyn_cast<ByteCommand>(cmd)) {
data->offset = dot - sec->addr;
dot += data->size;
expandOutputSection(data->size);
continue;
}
// Handle a single input section description command.
// It calculates and assigns the offsets for each section and also
// updates the output section size.
auto &sections = cast<InputSectionDescription>(cmd)->sections;
for (InputSection *isec : sections) {
assert(isec->getParent() == sec);
if (isa<PotentialSpillSection>(isec))
continue;
const uint64_t pos = dot;
dot = alignToPowerOf2(dot, isec->addralign);
isec->outSecOff = dot - sec->addr;
dot += isec->getSize();
// Update output section size after adding each section. This is so that
// SIZEOF works correctly in the case below:
// .foo { *(.aaa) a = SIZEOF(.foo); *(.bbb) }
expandOutputSection(dot - pos);
}
}
// If .relro_padding is present, round up the end to a common-page-size
// boundary to protect the last page.
if (in.relroPadding && sec == in.relroPadding->getParent())
expandOutputSection(alignToPowerOf2(dot, config->commonPageSize) - dot);
// Non-SHF_ALLOC sections do not affect the addresses of other OutputSections
// as they are not part of the process image.
if (!(sec->flags & SHF_ALLOC)) {
dot = savedDot;
} else if (isTbss) {
// NOBITS TLS sections are similar. Additionally save the end address.
state->tbssAddr = dot;
dot = savedDot;
}
return addressChanged;
}
static bool isDiscardable(const OutputSection &sec) {
if (sec.name == "/DISCARD/")
return true;
// We do not want to remove OutputSections with expressions that reference
// symbols even if the OutputSection is empty. We want to ensure that the
// expressions can be evaluated and report an error if they cannot.
if (sec.expressionsUseSymbols)
return false;
// OutputSections may be referenced by name in ADDR and LOADADDR expressions,
// as an empty Section can has a valid VMA and LMA we keep the OutputSection
// to maintain the integrity of the other Expression.
if (sec.usedInExpression)
return false;
for (SectionCommand *cmd : sec.commands) {
if (auto assign = dyn_cast<SymbolAssignment>(cmd))
// Don't create empty output sections just for unreferenced PROVIDE
// symbols.
if (assign->name != "." && !assign->sym)
continue;
if (!isa<InputSectionDescription>(*cmd))
return false;
}
return true;
}
static void maybePropagatePhdrs(OutputSection &sec,
SmallVector<StringRef, 0> &phdrs) {
if (sec.phdrs.empty()) {
// To match the bfd linker script behaviour, only propagate program
// headers to sections that are allocated.
if (sec.flags & SHF_ALLOC)
sec.phdrs = phdrs;
} else {
phdrs = sec.phdrs;
}
}
void LinkerScript::adjustOutputSections() {
// If the output section contains only symbol assignments, create a
// corresponding output section. The issue is what to do with linker script
// like ".foo : { symbol = 42; }". One option would be to convert it to
// "symbol = 42;". That is, move the symbol out of the empty section
// description. That seems to be what bfd does for this simple case. The
// problem is that this is not completely general. bfd will give up and
// create a dummy section too if there is a ". = . + 1" inside the section
// for example.
// Given that we want to create the section, we have to worry what impact
// it will have on the link. For example, if we just create a section with
// 0 for flags, it would change which PT_LOADs are created.
// We could remember that particular section is dummy and ignore it in
// other parts of the linker, but unfortunately there are quite a few places
// that would need to change:
// * The program header creation.
// * The orphan section placement.
// * The address assignment.
// The other option is to pick flags that minimize the impact the section
// will have on the rest of the linker. That is why we copy the flags from
// the previous sections. We copy just SHF_ALLOC and SHF_WRITE to keep the
// impact low. We do not propagate SHF_EXECINSTR as in some cases this can
// lead to executable writeable section.
uint64_t flags = SHF_ALLOC;
SmallVector<StringRef, 0> defPhdrs;
bool seenRelro = false;
for (SectionCommand *&cmd : sectionCommands) {
if (!isa<OutputDesc>(cmd))
continue;
auto *sec = &cast<OutputDesc>(cmd)->osec;
// Handle align (e.g. ".foo : ALIGN(16) { ... }").
if (sec->alignExpr)
sec->addralign =
std::max<uint32_t>(sec->addralign, sec->alignExpr().getValue());
bool isEmpty = (getFirstInputSection(sec) == nullptr);
bool discardable = isEmpty && isDiscardable(*sec);
// If sec has at least one input section and not discarded, remember its
// flags to be inherited by subsequent output sections. (sec may contain
// just one empty synthetic section.)
if (sec->hasInputSections && !discardable)
flags = sec->flags;
// We do not want to keep any special flags for output section
// in case it is empty.
if (isEmpty) {
sec->flags =
flags & ((sec->nonAlloc ? 0 : (uint64_t)SHF_ALLOC) | SHF_WRITE);
sec->sortRank = getSectionRank(*sec);
}
// The code below may remove empty output sections. We should save the
// specified program headers (if exist) and propagate them to subsequent
// sections which do not specify program headers.
// An example of such a linker script is:
// SECTIONS { .empty : { *(.empty) } :rw
// .foo : { *(.foo) } }
// Note: at this point the order of output sections has not been finalized,
// because orphans have not been inserted into their expected positions. We
// will handle them in adjustSectionsAfterSorting().
if (sec->sectionIndex != UINT32_MAX)
maybePropagatePhdrs(*sec, defPhdrs);
// Discard .relro_padding if we have not seen one RELRO section. Note: when
// .tbss is the only RELRO section, there is no associated PT_LOAD segment
// (needsPtLoad), so we don't append .relro_padding in the case.
if (in.relroPadding && in.relroPadding->getParent() == sec && !seenRelro)
discardable = true;
if (discardable) {
sec->markDead();
cmd = nullptr;
} else {
seenRelro |=
sec->relro && !(sec->type == SHT_NOBITS && (sec->flags & SHF_TLS));
}
}
// It is common practice to use very generic linker scripts. So for any
// given run some of the output sections in the script will be empty.
// We could create corresponding empty output sections, but that would
// clutter the output.
// We instead remove trivially empty sections. The bfd linker seems even
// more aggressive at removing them.
llvm::erase_if(sectionCommands, [&](SectionCommand *cmd) { return !cmd; });
}
void LinkerScript::adjustSectionsAfterSorting() {
// Try and find an appropriate memory region to assign offsets in.
MemoryRegion *hint = nullptr;
for (SectionCommand *cmd : sectionCommands) {
if (auto *osd = dyn_cast<OutputDesc>(cmd)) {
OutputSection *sec = &osd->osec;
if (!sec->lmaRegionName.empty()) {
if (MemoryRegion *m = memoryRegions.lookup(sec->lmaRegionName))
sec->lmaRegion = m;
else
error("memory region '" + sec->lmaRegionName + "' not declared");
}
std::tie(sec->memRegion, hint) = findMemoryRegion(sec, hint);
}
}
// If output section command doesn't specify any segments,
// and we haven't previously assigned any section to segment,
// then we simply assign section to the very first load segment.
// Below is an example of such linker script:
// PHDRS { seg PT_LOAD; }
// SECTIONS { .aaa : { *(.aaa) } }
SmallVector<StringRef, 0> defPhdrs;
auto firstPtLoad = llvm::find_if(phdrsCommands, [](const PhdrsCommand &cmd) {
return cmd.type == PT_LOAD;
});
if (firstPtLoad != phdrsCommands.end())
defPhdrs.push_back(firstPtLoad->name);
// Walk the commands and propagate the program headers to commands that don't
// explicitly specify them.
for (SectionCommand *cmd : sectionCommands)
if (auto *osd = dyn_cast<OutputDesc>(cmd))
maybePropagatePhdrs(osd->osec, defPhdrs);
}
// When the SECTIONS command is used, try to find an address for the file and
// program headers output sections, which can be added to the first PT_LOAD
// segment when program headers are created.
//
// We check if the headers fit below the first allocated section. If there isn't
// enough space for these sections, we'll remove them from the PT_LOAD segment,
// and we'll also remove the PT_PHDR segment.
void LinkerScript::allocateHeaders(SmallVector<PhdrEntry *, 0> &phdrs) {
uint64_t min = std::numeric_limits<uint64_t>::max();
for (OutputSection *sec : ctx.outputSections)
if (sec->flags & SHF_ALLOC)
min = std::min<uint64_t>(min, sec->addr);
auto it = llvm::find_if(
phdrs, [](const PhdrEntry *e) { return e->p_type == PT_LOAD; });
if (it == phdrs.end())
return;
PhdrEntry *firstPTLoad = *it;
bool hasExplicitHeaders =
llvm::any_of(phdrsCommands, [](const PhdrsCommand &cmd) {
return cmd.hasPhdrs || cmd.hasFilehdr;
});
bool paged = !config->omagic && !config->nmagic;
uint64_t headerSize = getHeaderSize();
uint64_t base = 0;
// If SECTIONS is present and the linkerscript is not explicit about program
// headers, only allocate program headers if that would not add a page.
if (hasSectionsCommand && !hasExplicitHeaders)
base = alignDown(min, config->maxPageSize);
if ((paged || hasExplicitHeaders) && headerSize <= min - base) {
min = alignDown(min - headerSize, config->maxPageSize);
ctx.out.elfHeader->addr = min;
ctx.out.programHeaders->addr = min + ctx.out.elfHeader->size;
return;
}
// Error if we were explicitly asked to allocate headers.
if (hasExplicitHeaders)
error("could not allocate headers");
ctx.out.elfHeader->ptLoad = nullptr;
ctx.out.programHeaders->ptLoad = nullptr;
firstPTLoad->firstSec = findFirstSection(firstPTLoad);
llvm::erase_if(phdrs,
[](const PhdrEntry *e) { return e->p_type == PT_PHDR; });
}
LinkerScript::AddressState::AddressState() {
for (auto &mri : ctx.script->memoryRegions) {
MemoryRegion *mr = mri.second;
mr->curPos = (mr->origin)().getValue();
}
}
// Here we assign addresses as instructed by linker script SECTIONS
// sub-commands. Doing that allows us to use final VA values, so here
// we also handle rest commands like symbol assignments and ASSERTs.
// Return an output section that has changed its address or null, and a symbol
// that has changed its section or value (or nullptr if no symbol has changed).
std::pair<const OutputSection *, const Defined *>
LinkerScript::assignAddresses() {
if (hasSectionsCommand) {
// With a linker script, assignment of addresses to headers is covered by
// allocateHeaders().
dot = config->imageBase.value_or(0);
} else {
// Assign addresses to headers right now.
dot = ctx.target->getImageBase();
ctx.out.elfHeader->addr = dot;
ctx.out.programHeaders->addr = dot + ctx.out.elfHeader->size;
dot += getHeaderSize();
}
OutputSection *changedOsec = nullptr;
AddressState st;
state = &st;
errorOnMissingSection = true;
st.outSec = aether;
recordedErrors.clear();
SymbolAssignmentMap oldValues = getSymbolAssignmentValues(sectionCommands);
for (SectionCommand *cmd : sectionCommands) {
if (auto *assign = dyn_cast<SymbolAssignment>(cmd)) {
assign->addr = dot;
assignSymbol(assign, false);
assign->size = dot - assign->addr;
continue;
}
if (isa<SectionClassDesc>(cmd))
continue;
if (assignOffsets(&cast<OutputDesc>(cmd)->osec) && !changedOsec)
changedOsec = &cast<OutputDesc>(cmd)->osec;
}
state = nullptr;
return {changedOsec, getChangedSymbolAssignment(oldValues)};
}
static bool hasRegionOverflowed(MemoryRegion *mr) {
if (!mr)
return false;
return mr->curPos - mr->getOrigin() > mr->getLength();
}
// Spill input sections in reverse order of address assignment to (potentially)
// bring memory regions out of overflow. The size savings of a spill can only be
// estimated, since general linker script arithmetic may occur afterwards.
// Under-estimates may cause unnecessary spills, but over-estimates can always
// be corrected on the next pass.
bool LinkerScript::spillSections() {
if (potentialSpillLists.empty())
return false;
bool spilled = false;
for (SectionCommand *cmd : reverse(sectionCommands)) {
auto *osd = dyn_cast<OutputDesc>(cmd);
if (!osd)
continue;
OutputSection *osec = &osd->osec;
if (!osec->memRegion)
continue;
// Input sections that have replaced a potential spill and should be removed
// from their input section description.
DenseSet<InputSection *> spilledInputSections;
for (SectionCommand *cmd : reverse(osec->commands)) {
if (!hasRegionOverflowed(osec->memRegion) &&
!hasRegionOverflowed(osec->lmaRegion))
break;
auto *isd = dyn_cast<InputSectionDescription>(cmd);
if (!isd)
continue;
for (InputSection *isec : reverse(isd->sections)) {
// Potential spill locations cannot be spilled.
if (isa<PotentialSpillSection>(isec))
continue;
// Find the next potential spill location and remove it from the list.
auto it = potentialSpillLists.find(isec);
if (it == potentialSpillLists.end())
continue;
PotentialSpillList &list = it->second;
PotentialSpillSection *spill = list.head;
if (spill->next)
list.head = spill->next;
else
potentialSpillLists.erase(isec);
// Replace the next spill location with the spilled section and adjust
// its properties to match the new location. Note that the alignment of
// the spill section may have diverged from the original due to e.g. a
// SUBALIGN. Correct assignment requires the spill's alignment to be
// used, not the original.
spilledInputSections.insert(isec);
*llvm::find(spill->isd->sections, spill) = isec;
isec->parent = spill->parent;
isec->addralign = spill->addralign;
// Record the (potential) reduction in the region's end position.
osec->memRegion->curPos -= isec->getSize();
if (osec->lmaRegion)
osec->lmaRegion->curPos -= isec->getSize();
// Spilling continues until the end position no longer overflows the
// region. Then, another round of address assignment will either confirm
// the spill's success or lead to yet more spilling.
if (!hasRegionOverflowed(osec->memRegion) &&
!hasRegionOverflowed(osec->lmaRegion))
break;
}
// Remove any spilled input sections to complete their move.
if (!spilledInputSections.empty()) {
spilled = true;
llvm::erase_if(isd->sections, [&](InputSection *isec) {
return spilledInputSections.contains(isec);
});
}
}
}
return spilled;
}
// Erase any potential spill sections that were not used.
void LinkerScript::erasePotentialSpillSections() {
if (potentialSpillLists.empty())
return;
// Collect the set of input section descriptions that contain potential
// spills.
DenseSet<InputSectionDescription *> isds;
for (const auto &[_, list] : potentialSpillLists)
for (PotentialSpillSection *s = list.head; s; s = s->next)
isds.insert(s->isd);
for (InputSectionDescription *isd : isds)
llvm::erase_if(isd->sections, [](InputSection *s) {
return isa<PotentialSpillSection>(s);
});
potentialSpillLists.clear();
}
// Creates program headers as instructed by PHDRS linker script command.
SmallVector<PhdrEntry *, 0> LinkerScript::createPhdrs() {
SmallVector<PhdrEntry *, 0> ret;
// Process PHDRS and FILEHDR keywords because they are not
// real output sections and cannot be added in the following loop.
for (const PhdrsCommand &cmd : phdrsCommands) {
PhdrEntry *phdr = make<PhdrEntry>(cmd.type, cmd.flags.value_or(PF_R));
if (cmd.hasFilehdr)
phdr->add(ctx.out.elfHeader);
if (cmd.hasPhdrs)
phdr->add(ctx.out.programHeaders);
if (cmd.lmaExpr) {
phdr->p_paddr = cmd.lmaExpr().getValue();
phdr->hasLMA = true;
}
ret.push_back(phdr);
}
// Add output sections to program headers.
for (OutputSection *sec : ctx.outputSections) {
// Assign headers specified by linker script
for (size_t id : getPhdrIndices(sec)) {
ret[id]->add(sec);
if (!phdrsCommands[id].flags)
ret[id]->p_flags |= sec->getPhdrFlags();
}
}
return ret;
}
// Returns true if we should emit an .interp section.
//
// We usually do. But if PHDRS commands are given, and
// no PT_INTERP is there, there's no place to emit an
// .interp, so we don't do that in that case.
bool LinkerScript::needsInterpSection() {
if (phdrsCommands.empty())
return true;
for (PhdrsCommand &cmd : phdrsCommands)
if (cmd.type == PT_INTERP)
return true;
return false;
}
ExprValue LinkerScript::getSymbolValue(StringRef name, const Twine &loc) {
if (name == ".") {
if (state)
return {state->outSec, false, dot - state->outSec->addr, loc};
error(loc + ": unable to get location counter value");
return 0;
}
if (Symbol *sym = symtab.find(name)) {
if (auto *ds = dyn_cast<Defined>(sym)) {
ExprValue v{ds->section, false, ds->value, loc};
// Retain the original st_type, so that the alias will get the same
// behavior in relocation processing. Any operation will reset st_type to
// STT_NOTYPE.
v.type = ds->type;
return v;
}
if (isa<SharedSymbol>(sym))
if (!errorOnMissingSection)
return {nullptr, false, 0, loc};
}
error(loc + ": symbol not found: " + name);
return 0;
}
// Returns the index of the segment named Name.
static std::optional<size_t> getPhdrIndex(ArrayRef<PhdrsCommand> vec,
StringRef name) {
for (size_t i = 0; i < vec.size(); ++i)
if (vec[i].name == name)
return i;
return std::nullopt;
}
// Returns indices of ELF headers containing specific section. Each index is a
// zero based number of ELF header listed within PHDRS {} script block.
SmallVector<size_t, 0> LinkerScript::getPhdrIndices(OutputSection *cmd) {
SmallVector<size_t, 0> ret;
for (StringRef s : cmd->phdrs) {
if (std::optional<size_t> idx = getPhdrIndex(phdrsCommands, s))
ret.push_back(*idx);
else if (s != "NONE")
error(cmd->location + ": program header '" + s +
"' is not listed in PHDRS");
}
return ret;
}
void LinkerScript::printMemoryUsage(raw_ostream& os) {
auto printSize = [&](uint64_t size) {
if ((size & 0x3fffffff) == 0)
os << format_decimal(size >> 30, 10) << " GB";
else if ((size & 0xfffff) == 0)
os << format_decimal(size >> 20, 10) << " MB";
else if ((size & 0x3ff) == 0)
os << format_decimal(size >> 10, 10) << " KB";
else
os << " " << format_decimal(size, 10) << " B";
};
os << "Memory region Used Size Region Size %age Used\n";
for (auto &pair : memoryRegions) {
MemoryRegion *m = pair.second;
uint64_t usedLength = m->curPos - m->getOrigin();
os << right_justify(m->name, 16) << ": ";
printSize(usedLength);
uint64_t length = m->getLength();
if (length != 0) {
printSize(length);
double percent = usedLength * 100.0 / length;
os << " " << format("%6.2f%%", percent);
}
os << '\n';
}
}
void LinkerScript::recordError(const Twine &msg) {
auto &str = recordedErrors.emplace_back();
msg.toVector(str);
}
static void checkMemoryRegion(const MemoryRegion *region,
const OutputSection *osec, uint64_t addr) {
uint64_t osecEnd = addr + osec->size;
uint64_t regionEnd = region->getOrigin() + region->getLength();
if (osecEnd > regionEnd) {
error("section '" + osec->name + "' will not fit in region '" +
region->name + "': overflowed by " + Twine(osecEnd - regionEnd) +
" bytes");
}
}
void LinkerScript::checkFinalScriptConditions() const {
for (StringRef err : recordedErrors)
errorOrWarn(err);
for (const OutputSection *sec : ctx.outputSections) {
if (const MemoryRegion *memoryRegion = sec->memRegion)
checkMemoryRegion(memoryRegion, sec, sec->addr);
if (const MemoryRegion *lmaRegion = sec->lmaRegion)
checkMemoryRegion(lmaRegion, sec, sec->getLMA());
}
}
void LinkerScript::addScriptReferencedSymbolsToSymTable() {
// Some symbols (such as __ehdr_start) are defined lazily only when there
// are undefined symbols for them, so we add these to trigger that logic.
auto reference = [](StringRef name) {
Symbol *sym = symtab.addUnusedUndefined(name);
sym->isUsedInRegularObj = true;
sym->referenced = true;
};
for (StringRef name : referencedSymbols)
reference(name);
// Keeps track of references from which PROVIDE symbols have been added to the
// symbol table.
DenseSet<StringRef> added;
SmallVector<const SmallVector<StringRef, 0> *, 0> symRefsVec;
for (const auto &[name, symRefs] : provideMap)
if (LinkerScript::shouldAddProvideSym(name) && added.insert(name).second)
symRefsVec.push_back(&symRefs);
while (symRefsVec.size()) {
for (StringRef name : *symRefsVec.pop_back_val()) {
reference(name);
// Prevent the symbol from being discarded by --gc-sections.
referencedSymbols.push_back(name);
auto it = provideMap.find(name);
if (it != provideMap.end() && shouldAddProvideSym(name) &&
added.insert(name).second) {
symRefsVec.push_back(&it->second);
}
}
}
}
bool LinkerScript::shouldAddProvideSym(StringRef symName) {
Symbol *sym = symtab.find(symName);
return sym && !sym->isDefined() && !sym->isCommon();
}