forked from OSchip/llvm-project
1159 lines
40 KiB
C++
1159 lines
40 KiB
C++
//===- LinkerScript.cpp ---------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains the parser/evaluator of the linker script.
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//
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//===----------------------------------------------------------------------===//
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#include "LinkerScript.h"
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#include "Config.h"
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#include "InputSection.h"
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#include "OutputSections.h"
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#include "SymbolTable.h"
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#include "Symbols.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "Writer.h"
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#include "lld/Common/Memory.h"
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#include "lld/Common/Strings.h"
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#include "lld/Common/Threads.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/BinaryFormat/ELF.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Endian.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/FileSystem.h"
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#include "llvm/Support/Path.h"
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#include <algorithm>
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#include <cassert>
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#include <cstddef>
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#include <cstdint>
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#include <iterator>
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#include <limits>
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#include <string>
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#include <vector>
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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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using namespace lld;
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using namespace lld::elf;
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LinkerScript *elf::script;
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static uint64_t getOutputSectionVA(SectionBase *inputSec, StringRef loc) {
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if (OutputSection *os = inputSec->getOutputSection())
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return os->addr;
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error(loc + ": unable to evaluate expression: input section " +
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inputSec->name + " has no output section assigned");
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return 0;
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}
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uint64_t ExprValue::getValue() const {
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if (sec)
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return alignTo(sec->getOffset(val) + getOutputSectionVA(sec, loc),
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alignment);
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return alignTo(val, alignment);
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}
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uint64_t ExprValue::getSecAddr() const {
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if (sec)
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return sec->getOffset(0) + getOutputSectionVA(sec, loc);
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return 0;
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}
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uint64_t ExprValue::getSectionOffset() const {
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// If the alignment is trivial, we don't have to compute the full
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// value to know the offset. This allows this function to succeed in
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// cases where the output section is not yet known.
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if (alignment == 1 && (!sec || !sec->getOutputSection()))
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return val;
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return getValue() - getSecAddr();
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}
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OutputSection *LinkerScript::createOutputSection(StringRef name,
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StringRef location) {
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OutputSection *&secRef = nameToOutputSection[name];
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OutputSection *sec;
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if (secRef && secRef->location.empty()) {
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// There was a forward reference.
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sec = secRef;
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} else {
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sec = make<OutputSection>(name, SHT_PROGBITS, 0);
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if (!secRef)
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secRef = sec;
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}
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sec->location = location;
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return sec;
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}
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OutputSection *LinkerScript::getOrCreateOutputSection(StringRef name) {
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OutputSection *&cmdRef = nameToOutputSection[name];
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if (!cmdRef)
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cmdRef = make<OutputSection>(name, SHT_PROGBITS, 0);
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return cmdRef;
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}
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// Expands the memory region by the specified size.
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static void expandMemoryRegion(MemoryRegion *memRegion, uint64_t size,
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StringRef regionName, StringRef secName) {
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memRegion->curPos += size;
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uint64_t newSize = memRegion->curPos - memRegion->origin;
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if (newSize > memRegion->length)
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error("section '" + secName + "' will not fit in region '" + regionName +
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"': overflowed by " + Twine(newSize - memRegion->length) + " bytes");
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}
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void LinkerScript::expandMemoryRegions(uint64_t size) {
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if (ctx->memRegion)
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expandMemoryRegion(ctx->memRegion, size, ctx->memRegion->name,
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ctx->outSec->name);
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// Only expand the LMARegion if it is different from memRegion.
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if (ctx->lmaRegion && ctx->memRegion != ctx->lmaRegion)
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expandMemoryRegion(ctx->lmaRegion, size, ctx->lmaRegion->name,
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ctx->outSec->name);
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}
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void LinkerScript::expandOutputSection(uint64_t size) {
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ctx->outSec->size += size;
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expandMemoryRegions(size);
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}
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void LinkerScript::setDot(Expr e, const Twine &loc, bool inSec) {
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uint64_t val = e().getValue();
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if (val < dot && inSec)
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error(loc + ": unable to move location counter backward for: " +
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ctx->outSec->name);
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// Update to location counter means update to section size.
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if (inSec)
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expandOutputSection(val - dot);
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dot = val;
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}
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// Used for handling linker symbol assignments, for both finalizing
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// their values and doing early declarations. Returns true if symbol
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// should be defined from linker script.
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static bool shouldDefineSym(SymbolAssignment *cmd) {
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if (cmd->name == ".")
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return false;
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if (!cmd->provide)
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return true;
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// If a symbol was in PROVIDE(), we need to define it only
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// when it is a referenced undefined symbol.
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Symbol *b = symtab->find(cmd->name);
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if (b && !b->isDefined())
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return true;
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return false;
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}
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// This function is called from processSectionCommands,
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// while we are fixing the output section layout.
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void LinkerScript::addSymbol(SymbolAssignment *cmd) {
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if (!shouldDefineSym(cmd))
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return;
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// Define a symbol.
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ExprValue value = cmd->expression();
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SectionBase *sec = value.isAbsolute() ? nullptr : value.sec;
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uint8_t visibility = cmd->hidden ? STV_HIDDEN : STV_DEFAULT;
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// When this function is called, section addresses have not been
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// fixed yet. So, we may or may not know the value of the RHS
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// expression.
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//
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// For example, if an expression is `x = 42`, we know x is always 42.
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// However, if an expression is `x = .`, there's no way to know its
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// value at the moment.
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//
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// We want to set symbol values early if we can. This allows us to
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// use symbols as variables in linker scripts. Doing so allows us to
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// write expressions like this: `alignment = 16; . = ALIGN(., alignment)`.
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uint64_t symValue = value.sec ? 0 : value.getValue();
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Defined New(nullptr, cmd->name, STB_GLOBAL, visibility, STT_NOTYPE, symValue,
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0, sec);
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Symbol *sym = symtab->insert(cmd->name);
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sym->mergeProperties(New);
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sym->replace(New);
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cmd->sym = cast<Defined>(sym);
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}
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// This function is called from LinkerScript::declareSymbols.
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// It creates a placeholder symbol if needed.
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static void declareSymbol(SymbolAssignment *cmd) {
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if (!shouldDefineSym(cmd))
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return;
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uint8_t visibility = cmd->hidden ? STV_HIDDEN : STV_DEFAULT;
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Defined New(nullptr, cmd->name, STB_GLOBAL, visibility, STT_NOTYPE, 0, 0,
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nullptr);
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// We can't calculate final value right now.
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Symbol *sym = symtab->insert(cmd->name);
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sym->mergeProperties(New);
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sym->replace(New);
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cmd->sym = cast<Defined>(sym);
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cmd->provide = false;
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sym->scriptDefined = true;
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}
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// This method is used to handle INSERT AFTER statement. Here we rebuild
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// the list of script commands to mix sections inserted into.
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void LinkerScript::processInsertCommands() {
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std::vector<BaseCommand *> v;
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auto insert = [&](std::vector<BaseCommand *> &from) {
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v.insert(v.end(), from.begin(), from.end());
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from.clear();
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};
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for (BaseCommand *base : sectionCommands) {
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if (auto *os = dyn_cast<OutputSection>(base)) {
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insert(insertBeforeCommands[os->name]);
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v.push_back(base);
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insert(insertAfterCommands[os->name]);
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continue;
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}
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v.push_back(base);
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}
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for (auto &cmds : {insertBeforeCommands, insertAfterCommands})
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for (const std::pair<StringRef, std::vector<BaseCommand *>> &p : cmds)
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if (!p.second.empty())
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error("unable to INSERT AFTER/BEFORE " + p.first +
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": section not defined");
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sectionCommands = std::move(v);
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}
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// Symbols defined in script should not be inlined by LTO. At the same time
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// we don't know their final values until late stages of link. Here we scan
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// over symbol assignment commands and create placeholder symbols if needed.
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void LinkerScript::declareSymbols() {
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assert(!ctx);
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for (BaseCommand *base : sectionCommands) {
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if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
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declareSymbol(cmd);
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continue;
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}
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// If the output section directive has constraints,
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// we can't say for sure if it is going to be included or not.
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// Skip such sections for now. Improve the checks if we ever
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// need symbols from that sections to be declared early.
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auto *sec = cast<OutputSection>(base);
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if (sec->constraint != ConstraintKind::NoConstraint)
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continue;
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for (BaseCommand *base2 : sec->sectionCommands)
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if (auto *cmd = dyn_cast<SymbolAssignment>(base2))
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declareSymbol(cmd);
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}
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}
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// This function is called from assignAddresses, while we are
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// fixing the output section addresses. This function is supposed
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// to set the final value for a given symbol assignment.
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void LinkerScript::assignSymbol(SymbolAssignment *cmd, bool inSec) {
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if (cmd->name == ".") {
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setDot(cmd->expression, cmd->location, inSec);
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return;
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}
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if (!cmd->sym)
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return;
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ExprValue v = cmd->expression();
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if (v.isAbsolute()) {
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cmd->sym->section = nullptr;
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cmd->sym->value = v.getValue();
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} else {
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cmd->sym->section = v.sec;
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cmd->sym->value = v.getSectionOffset();
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}
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}
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static std::string getFilename(InputFile *file) {
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if (!file)
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return "";
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if (file->archiveName.empty())
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return file->getName();
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return (file->archiveName + "(" + file->getName() + ")").str();
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}
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bool LinkerScript::shouldKeep(InputSectionBase *s) {
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if (keptSections.empty())
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return false;
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std::string filename = getFilename(s->file);
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for (InputSectionDescription *id : keptSections)
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if (id->filePat.match(filename))
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for (SectionPattern &p : id->sectionPatterns)
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if (p.sectionPat.match(s->name))
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return true;
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return false;
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}
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// A helper function for the SORT() command.
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static std::function<bool(InputSectionBase *, InputSectionBase *)>
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getComparator(SortSectionPolicy k) {
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switch (k) {
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case SortSectionPolicy::Alignment:
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return [](InputSectionBase *a, InputSectionBase *b) {
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// ">" is not a mistake. Sections with larger alignments are placed
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// before sections with smaller alignments in order to reduce the
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// amount of padding necessary. This is compatible with GNU.
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return a->alignment > b->alignment;
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};
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case SortSectionPolicy::Name:
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return [](InputSectionBase *a, InputSectionBase *b) {
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return a->name < b->name;
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};
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case SortSectionPolicy::Priority:
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return [](InputSectionBase *a, InputSectionBase *b) {
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return getPriority(a->name) < getPriority(b->name);
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};
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default:
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llvm_unreachable("unknown sort policy");
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}
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}
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// A helper function for the SORT() command.
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static bool matchConstraints(ArrayRef<InputSection *> sections,
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ConstraintKind kind) {
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if (kind == ConstraintKind::NoConstraint)
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return true;
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bool isRW = llvm::any_of(
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sections, [](InputSection *sec) { return sec->flags & SHF_WRITE; });
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return (isRW && kind == ConstraintKind::ReadWrite) ||
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(!isRW && kind == ConstraintKind::ReadOnly);
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}
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static void sortSections(MutableArrayRef<InputSection *> vec,
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SortSectionPolicy k) {
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if (k != SortSectionPolicy::Default && k != SortSectionPolicy::None)
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llvm::stable_sort(vec, getComparator(k));
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}
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// Sort sections as instructed by SORT-family commands and --sort-section
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// option. Because SORT-family commands can be nested at most two depth
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// (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command
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// line option is respected even if a SORT command is given, the exact
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// behavior we have here is a bit complicated. Here are the rules.
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//
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// 1. If two SORT commands are given, --sort-section is ignored.
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// 2. If one SORT command is given, and if it is not SORT_NONE,
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// --sort-section is handled as an inner SORT command.
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// 3. If one SORT command is given, and if it is SORT_NONE, don't sort.
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// 4. If no SORT command is given, sort according to --sort-section.
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static void sortInputSections(MutableArrayRef<InputSection *> vec,
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const SectionPattern &pat) {
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if (pat.sortOuter == SortSectionPolicy::None)
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return;
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if (pat.sortInner == SortSectionPolicy::Default)
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sortSections(vec, config->sortSection);
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else
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sortSections(vec, pat.sortInner);
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sortSections(vec, pat.sortOuter);
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}
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// Compute and remember which sections the InputSectionDescription matches.
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std::vector<InputSection *>
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LinkerScript::computeInputSections(const InputSectionDescription *cmd) {
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std::vector<InputSection *> ret;
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// Collects all sections that satisfy constraints of Cmd.
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for (const SectionPattern &pat : cmd->sectionPatterns) {
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size_t sizeBefore = ret.size();
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for (InputSectionBase *sec : inputSections) {
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if (!sec->isLive() || sec->assigned)
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continue;
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// For -emit-relocs we have to ignore entries like
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// .rela.dyn : { *(.rela.data) }
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// which are common because they are in the default bfd script.
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// We do not ignore SHT_REL[A] linker-synthesized sections here because
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// want to support scripts that do custom layout for them.
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if (auto *isec = dyn_cast<InputSection>(sec))
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if (isec->getRelocatedSection())
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continue;
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std::string filename = getFilename(sec->file);
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if (!cmd->filePat.match(filename) ||
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pat.excludedFilePat.match(filename) ||
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!pat.sectionPat.match(sec->name))
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continue;
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// It is safe to assume that Sec is an InputSection
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// because mergeable or EH input sections have already been
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// handled and eliminated.
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ret.push_back(cast<InputSection>(sec));
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sec->assigned = true;
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}
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sortInputSections(MutableArrayRef<InputSection *>(ret).slice(sizeBefore),
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pat);
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}
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return ret;
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}
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void LinkerScript::discard(ArrayRef<InputSection *> v) {
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for (InputSection *s : v) {
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if (s == in.shStrTab || s == mainPart->relaDyn || s == mainPart->relrDyn)
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error("discarding " + s->name + " section is not allowed");
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// You can discard .hash and .gnu.hash sections by linker scripts. Since
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// they are synthesized sections, we need to handle them differently than
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// other regular sections.
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if (s == mainPart->gnuHashTab)
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mainPart->gnuHashTab = nullptr;
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if (s == mainPart->hashTab)
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mainPart->hashTab = nullptr;
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s->assigned = false;
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s->markDead();
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discard(s->dependentSections);
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}
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}
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std::vector<InputSection *>
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LinkerScript::createInputSectionList(OutputSection &outCmd) {
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std::vector<InputSection *> ret;
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for (BaseCommand *base : outCmd.sectionCommands) {
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if (auto *cmd = dyn_cast<InputSectionDescription>(base)) {
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cmd->sections = computeInputSections(cmd);
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ret.insert(ret.end(), cmd->sections.begin(), cmd->sections.end());
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}
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}
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return ret;
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}
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void LinkerScript::processSectionCommands() {
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// A symbol can be assigned before any section is mentioned in the linker
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// script. In an DSO, the symbol values are addresses, so the only important
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// section values are:
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// * SHN_UNDEF
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// * SHN_ABS
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// * Any value meaning a regular section.
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// To handle that, create a dummy aether section that fills the void before
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// the linker scripts switches to another section. It has an index of one
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// which will map to whatever the first actual section is.
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aether = make<OutputSection>("", 0, SHF_ALLOC);
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aether->sectionIndex = 1;
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// Ctx captures the local AddressState and makes it accessible deliberately.
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// This is needed as there are some cases where we cannot just
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// thread the current state through to a lambda function created by the
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// script parser.
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auto deleter = make_unique<AddressState>();
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ctx = deleter.get();
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ctx->outSec = aether;
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size_t i = 0;
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// Add input sections to output sections.
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for (BaseCommand *base : sectionCommands) {
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// Handle symbol assignments outside of any output section.
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if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
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addSymbol(cmd);
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continue;
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}
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if (auto *sec = dyn_cast<OutputSection>(base)) {
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std::vector<InputSection *> v = createInputSectionList(*sec);
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// The output section name `/DISCARD/' is special.
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// Any input section assigned to it is discarded.
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if (sec->name == "/DISCARD/") {
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discard(v);
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sec->sectionCommands.clear();
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continue;
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}
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// This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive
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// ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
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// sections satisfy a given constraint. If not, a directive is handled
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// as if it wasn't present from the beginning.
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//
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// Because we'll iterate over SectionCommands many more times, the easy
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// way to "make it as if it wasn't present" is to make it empty.
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if (!matchConstraints(v, sec->constraint)) {
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for (InputSectionBase *s : v)
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s->assigned = false;
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sec->sectionCommands.clear();
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continue;
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}
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// A directive may contain symbol definitions like this:
|
|
// ".foo : { ...; bar = .; }". Handle them.
|
|
for (BaseCommand *base : sec->sectionCommands)
|
|
if (auto *outCmd = dyn_cast<SymbolAssignment>(base))
|
|
addSymbol(outCmd);
|
|
|
|
// 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 (sec->subalignExpr) {
|
|
uint32_t subalign = sec->subalignExpr().getValue();
|
|
for (InputSectionBase *s : v)
|
|
s->alignment = subalign;
|
|
}
|
|
|
|
// Add input sections to an output section.
|
|
for (InputSection *s : v)
|
|
sec->addSection(s);
|
|
|
|
sec->sectionIndex = i++;
|
|
if (sec->noload)
|
|
sec->type = SHT_NOBITS;
|
|
if (sec->nonAlloc)
|
|
sec->flags &= ~(uint64_t)SHF_ALLOC;
|
|
}
|
|
}
|
|
ctx = nullptr;
|
|
}
|
|
|
|
static OutputSection *findByName(ArrayRef<BaseCommand *> vec,
|
|
StringRef name) {
|
|
for (BaseCommand *base : vec)
|
|
if (auto *sec = dyn_cast<OutputSection>(base))
|
|
if (sec->name == name)
|
|
return sec;
|
|
return nullptr;
|
|
}
|
|
|
|
static OutputSection *createSection(InputSectionBase *isec,
|
|
StringRef outsecName) {
|
|
OutputSection *sec = script->createOutputSection(outsecName, "<internal>");
|
|
sec->addSection(cast<InputSection>(isec));
|
|
return sec;
|
|
}
|
|
|
|
static OutputSection *
|
|
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) &&
|
|
(isec->type == SHT_REL || isec->type == SHT_RELA)) {
|
|
auto *sec = cast<InputSection>(isec);
|
|
OutputSection *out = sec->getRelocatedSection()->getOutputSection();
|
|
|
|
if (out->relocationSection) {
|
|
out->relocationSection->addSection(sec);
|
|
return nullptr;
|
|
}
|
|
|
|
out->relocationSection = createSection(isec, outsecName);
|
|
return out->relocationSection;
|
|
}
|
|
|
|
// When control reaches here, mergeable sections have already been merged into
|
|
// synthetic sections. For relocatable case we want to create one output
|
|
// section per syntetic section so that they have a valid sh_entsize.
|
|
if (config->relocatable && (isec->flags & SHF_MERGE))
|
|
return createSection(isec, outsecName);
|
|
|
|
// 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;
|
|
sec->addSection(cast<InputSection>(isec));
|
|
return nullptr;
|
|
}
|
|
|
|
OutputSection *sec = createSection(isec, outsecName);
|
|
v.push_back(sec);
|
|
return sec;
|
|
}
|
|
|
|
// Add sections that didn't match any sections command.
|
|
void LinkerScript::addOrphanSections() {
|
|
StringMap<TinyPtrVector<OutputSection *>> map;
|
|
std::vector<OutputSection *> v;
|
|
|
|
auto add = [&](InputSectionBase *s) {
|
|
if (!s->isLive() || s->parent)
|
|
return;
|
|
|
|
StringRef name = getOutputSectionName(s);
|
|
|
|
if (config->orphanHandling == OrphanHandlingPolicy::Error)
|
|
error(toString(s) + " is being placed in '" + name + "'");
|
|
else if (config->orphanHandling == OrphanHandlingPolicy::Warn)
|
|
warn(toString(s) + " is being placed in '" + name + "'");
|
|
|
|
if (OutputSection *sec = findByName(sectionCommands, name)) {
|
|
sec->addSection(cast<InputSection>(s));
|
|
return;
|
|
}
|
|
|
|
if (OutputSection *os = addInputSec(map, s, name))
|
|
v.push_back(os);
|
|
assert(s->getOutputSection()->sectionIndex == UINT32_MAX);
|
|
};
|
|
|
|
// For futher --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.
|
|
for (InputSectionBase *isec : inputSections) {
|
|
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 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());
|
|
}
|
|
|
|
uint64_t LinkerScript::advance(uint64_t size, unsigned alignment) {
|
|
bool isTbss =
|
|
(ctx->outSec->flags & SHF_TLS) && ctx->outSec->type == SHT_NOBITS;
|
|
uint64_t start = isTbss ? dot + ctx->threadBssOffset : dot;
|
|
start = alignTo(start, alignment);
|
|
uint64_t end = start + size;
|
|
|
|
if (isTbss)
|
|
ctx->threadBssOffset = end - dot;
|
|
else
|
|
dot = end;
|
|
return end;
|
|
}
|
|
|
|
void LinkerScript::output(InputSection *s) {
|
|
assert(ctx->outSec == s->getParent());
|
|
uint64_t before = advance(0, 1);
|
|
uint64_t pos = advance(s->getSize(), s->alignment);
|
|
s->outSecOff = pos - s->getSize() - ctx->outSec->addr;
|
|
|
|
// 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(pos - before);
|
|
}
|
|
|
|
void LinkerScript::switchTo(OutputSection *sec) {
|
|
ctx->outSec = sec;
|
|
|
|
uint64_t before = advance(0, 1);
|
|
ctx->outSec->addr = advance(0, ctx->outSec->alignment);
|
|
expandMemoryRegions(ctx->outSec->addr - before);
|
|
}
|
|
|
|
// 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. Otherwise, a nullptr is returned.
|
|
MemoryRegion *LinkerScript::findMemoryRegion(OutputSection *sec) {
|
|
// 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;
|
|
error("memory region '" + sec->memoryRegionName + "' not declared");
|
|
return 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;
|
|
|
|
// See if a region can be found by matching section flags.
|
|
for (auto &pair : memoryRegions) {
|
|
MemoryRegion *m = pair.second;
|
|
if ((m->flags & sec->flags) && (m->negFlags & sec->flags) == 0)
|
|
return m;
|
|
}
|
|
|
|
// Otherwise, no suitable region was found.
|
|
if (sec->flags & SHF_ALLOC)
|
|
error("no memory region specified for section '" + sec->name + "'");
|
|
return nullptr;
|
|
}
|
|
|
|
static OutputSection *findFirstSection(PhdrEntry *load) {
|
|
for (OutputSection *sec : outputSections)
|
|
if (sec->ptLoad == load)
|
|
return sec;
|
|
return nullptr;
|
|
}
|
|
|
|
// This function assigns offsets to input sections and an output section
|
|
// for a single sections command (e.g. ".text { *(.text); }").
|
|
void LinkerScript::assignOffsets(OutputSection *sec) {
|
|
if (!(sec->flags & SHF_ALLOC))
|
|
dot = 0;
|
|
|
|
ctx->memRegion = sec->memRegion;
|
|
ctx->lmaRegion = sec->lmaRegion;
|
|
if (ctx->memRegion)
|
|
dot = ctx->memRegion->curPos;
|
|
|
|
if ((sec->flags & SHF_ALLOC) && sec->addrExpr)
|
|
setDot(sec->addrExpr, sec->location, false);
|
|
|
|
switchTo(sec);
|
|
|
|
if (sec->lmaExpr)
|
|
ctx->lmaOffset = sec->lmaExpr().getValue() - dot;
|
|
|
|
if (MemoryRegion *mr = sec->lmaRegion)
|
|
ctx->lmaOffset = mr->curPos - dot;
|
|
|
|
// If neither AT nor AT> is specified for an allocatable section, the linker
|
|
// will set the LMA such that the difference between VMA and LMA for the
|
|
// section is the same as the preceding output section in the same region
|
|
// https://sourceware.org/binutils/docs-2.20/ld/Output-Section-LMA.html
|
|
// This, however, should only be done by the first "non-header" section
|
|
// in the segment.
|
|
if (PhdrEntry *l = ctx->outSec->ptLoad)
|
|
if (sec == findFirstSection(l))
|
|
l->lmaOffset = ctx->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 (BaseCommand *base : sec->sectionCommands) {
|
|
// This handles the assignments to symbol or to the dot.
|
|
if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
|
|
cmd->addr = dot;
|
|
assignSymbol(cmd, true);
|
|
cmd->size = dot - cmd->addr;
|
|
continue;
|
|
}
|
|
|
|
// Handle BYTE(), SHORT(), LONG(), or QUAD().
|
|
if (auto *cmd = dyn_cast<ByteCommand>(base)) {
|
|
cmd->offset = dot - ctx->outSec->addr;
|
|
dot += cmd->size;
|
|
expandOutputSection(cmd->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.
|
|
for (InputSection *sec : cast<InputSectionDescription>(base)->sections)
|
|
output(sec);
|
|
}
|
|
}
|
|
|
|
static bool isDiscardable(OutputSection &sec) {
|
|
if (sec.name == "/DISCARD/")
|
|
return true;
|
|
|
|
// We do not remove empty sections that are explicitly
|
|
// assigned to any segment.
|
|
if (!sec.phdrs.empty())
|
|
return false;
|
|
|
|
// 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 (BaseCommand *base : sec.sectionCommands) {
|
|
if (auto cmd = dyn_cast<SymbolAssignment>(base))
|
|
// Don't create empty output sections just for unreferenced PROVIDE
|
|
// symbols.
|
|
if (cmd->name != "." && !cmd->sym)
|
|
continue;
|
|
|
|
if (!isa<InputSectionDescription>(*base))
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
void LinkerScript::adjustSectionsBeforeSorting() {
|
|
// 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. Only a few flags are needed to keep the impact low.
|
|
uint64_t flags = SHF_ALLOC;
|
|
|
|
for (BaseCommand *&cmd : sectionCommands) {
|
|
auto *sec = dyn_cast<OutputSection>(cmd);
|
|
if (!sec)
|
|
continue;
|
|
|
|
// Handle align (e.g. ".foo : ALIGN(16) { ... }").
|
|
if (sec->alignExpr)
|
|
sec->alignment =
|
|
std::max<uint32_t>(sec->alignment, sec->alignExpr().getValue());
|
|
|
|
// The input section might have been removed (if it was an empty synthetic
|
|
// section), but we at least know the flags.
|
|
if (sec->hasInputSections)
|
|
flags = sec->flags;
|
|
|
|
// We do not want to keep any special flags for output section
|
|
// in case it is empty.
|
|
bool isEmpty = getInputSections(sec).empty();
|
|
if (isEmpty)
|
|
sec->flags = flags & ((sec->nonAlloc ? 0 : (uint64_t)SHF_ALLOC) |
|
|
SHF_WRITE | SHF_EXECINSTR);
|
|
|
|
if (isEmpty && isDiscardable(*sec)) {
|
|
sec->markDead();
|
|
cmd = nullptr;
|
|
} else if (!sec->isLive()) {
|
|
sec->markLive();
|
|
}
|
|
}
|
|
|
|
// 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, [&](BaseCommand *base) { return !base; });
|
|
}
|
|
|
|
void LinkerScript::adjustSectionsAfterSorting() {
|
|
// Try and find an appropriate memory region to assign offsets in.
|
|
for (BaseCommand *base : sectionCommands) {
|
|
if (auto *sec = dyn_cast<OutputSection>(base)) {
|
|
if (!sec->lmaRegionName.empty()) {
|
|
if (MemoryRegion *m = memoryRegions.lookup(sec->lmaRegionName))
|
|
sec->lmaRegion = m;
|
|
else
|
|
error("memory region '" + sec->lmaRegionName + "' not declared");
|
|
}
|
|
sec->memRegion = findMemoryRegion(sec);
|
|
}
|
|
}
|
|
|
|
// 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) } }
|
|
std::vector<StringRef> 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 (BaseCommand *base : sectionCommands) {
|
|
auto *sec = dyn_cast<OutputSection>(base);
|
|
if (!sec)
|
|
continue;
|
|
|
|
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 = defPhdrs;
|
|
} else {
|
|
defPhdrs = sec->phdrs;
|
|
}
|
|
}
|
|
}
|
|
|
|
static uint64_t computeBase(uint64_t min, bool allocateHeaders) {
|
|
// If there is no SECTIONS or if the linkerscript is explicit about program
|
|
// headers, do our best to allocate them.
|
|
if (!script->hasSectionsCommand || allocateHeaders)
|
|
return 0;
|
|
// Otherwise only allocate program headers if that would not add a page.
|
|
return alignDown(min, config->maxPageSize);
|
|
}
|
|
|
|
// Try to find an address for the file and program headers output sections,
|
|
// which were unconditionally added to the first PT_LOAD segment earlier.
|
|
//
|
|
// When using the default layout, we check if the headers fit below the first
|
|
// allocated section. When using a linker script, we also check if the headers
|
|
// are covered by the output section. This allows omitting the headers by not
|
|
// leaving enough space for them in the linker script; this pattern is common
|
|
// in embedded systems.
|
|
//
|
|
// 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(std::vector<PhdrEntry *> &phdrs) {
|
|
uint64_t min = std::numeric_limits<uint64_t>::max();
|
|
for (OutputSection *sec : 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();
|
|
if ((paged || hasExplicitHeaders) &&
|
|
headerSize <= min - computeBase(min, hasExplicitHeaders)) {
|
|
min = alignDown(min - headerSize, config->maxPageSize);
|
|
Out::elfHeader->addr = min;
|
|
Out::programHeaders->addr = min + Out::elfHeader->size;
|
|
return;
|
|
}
|
|
|
|
// Error if we were explicitly asked to allocate headers.
|
|
if (hasExplicitHeaders)
|
|
error("could not allocate headers");
|
|
|
|
Out::elfHeader->ptLoad = nullptr;
|
|
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 : script->memoryRegions) {
|
|
MemoryRegion *mr = mri.second;
|
|
mr->curPos = mr->origin;
|
|
}
|
|
}
|
|
|
|
static uint64_t getInitialDot() {
|
|
// By default linker scripts use an initial value of 0 for '.',
|
|
// but prefer -image-base if set.
|
|
if (script->hasSectionsCommand)
|
|
return config->imageBase ? *config->imageBase : 0;
|
|
|
|
uint64_t startAddr = UINT64_MAX;
|
|
// The sections with -T<section> have been sorted in order of ascending
|
|
// address. We must lower startAddr if the lowest -T<section address> as
|
|
// calls to setDot() must be monotonically increasing.
|
|
for (auto &kv : config->sectionStartMap)
|
|
startAddr = std::min(startAddr, kv.second);
|
|
return std::min(startAddr, target->getImageBase() + elf::getHeaderSize());
|
|
}
|
|
|
|
// 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.
|
|
void LinkerScript::assignAddresses() {
|
|
dot = getInitialDot();
|
|
|
|
auto deleter = make_unique<AddressState>();
|
|
ctx = deleter.get();
|
|
errorOnMissingSection = true;
|
|
switchTo(aether);
|
|
|
|
for (BaseCommand *base : sectionCommands) {
|
|
if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
|
|
cmd->addr = dot;
|
|
assignSymbol(cmd, false);
|
|
cmd->size = dot - cmd->addr;
|
|
continue;
|
|
}
|
|
assignOffsets(cast<OutputSection>(base));
|
|
}
|
|
ctx = nullptr;
|
|
}
|
|
|
|
// Creates program headers as instructed by PHDRS linker script command.
|
|
std::vector<PhdrEntry *> LinkerScript::createPhdrs() {
|
|
std::vector<PhdrEntry *> 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 ? *cmd.flags : PF_R);
|
|
|
|
if (cmd.hasFilehdr)
|
|
phdr->add(Out::elfHeader);
|
|
if (cmd.hasPhdrs)
|
|
phdr->add(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 : outputSections) {
|
|
// Assign headers specified by linker script
|
|
for (size_t id : getPhdrIndices(sec)) {
|
|
ret[id]->add(sec);
|
|
if (!phdrsCommands[id].flags.hasValue())
|
|
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 (ctx)
|
|
return {ctx->outSec, false, dot - ctx->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))
|
|
return {ds->section, false, ds->value, loc};
|
|
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 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 None;
|
|
}
|
|
|
|
// Returns indices of ELF headers containing specific section. Each index is a
|
|
// zero based number of ELF header listed within PHDRS {} script block.
|
|
std::vector<size_t> LinkerScript::getPhdrIndices(OutputSection *cmd) {
|
|
std::vector<size_t> ret;
|
|
|
|
for (StringRef s : cmd->phdrs) {
|
|
if (Optional<size_t> idx = getPhdrIndex(phdrsCommands, s))
|
|
ret.push_back(*idx);
|
|
else if (s != "NONE")
|
|
error(cmd->location + ": section header '" + s +
|
|
"' is not listed in PHDRS");
|
|
}
|
|
return ret;
|
|
}
|