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Differential D103303 Diff 351738 lld/ELF/LinkerScript.cpp

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lld/ELF/LinkerScript.cpp

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} }
// Process INSERT [AFTER|BEFORE] commands. For each command, we move the // Process INSERT [AFTER|BEFORE] commands. For each command, we move the
// specified output section to the designated place. // specified output section to the designated place.
void LinkerScript::processInsertCommands() { void LinkerScript::processInsertCommands() {
for (const InsertCommand &cmd : insertCommands) { for (const InsertCommand &cmd : insertCommands) {
// If cmd.os is empty, it may have been discarded by // If cmd.os is empty, it may have been discarded by
// adjustSectionsBeforeSorting(). We do not handle such output sections. // adjustSectionsBeforeSorting(). We do not handle such output sections.
auto from = llvm::find(sectionCommands, cmd.os); auto from = llvm::find_if(sectionCommands, [&](BaseCommand *base) {
return isa<OutputSection>(base) &&
cast<OutputSection>(base)->name == cmd.name;
});
if (from == sectionCommands.end()) if (from == sectionCommands.end())
continue; continue;
OutputSection *osec = cast<OutputSection>(*from);
sectionCommands.erase(from); sectionCommands.erase(from);
auto insertPos = llvm::find_if(sectionCommands, [&cmd](BaseCommand *base) { auto insertPos = llvm::find_if(sectionCommands, [&cmd](BaseCommand *base) {
auto *to = dyn_cast<OutputSection>(base); auto *to = dyn_cast<OutputSection>(base);
return to != nullptr && to->name == cmd.where; return to != nullptr && to->name == cmd.where;
}); });
if (insertPos == sectionCommands.end()) { if (insertPos == sectionCommands.end()) {
error("unable to insert " + cmd.os->name + error("unable to insert " + osec->name +
(cmd.isAfter ? " after " : " before ") + cmd.where); (cmd.isAfter ? " after " : " before ") + cmd.where);
} else { } else {
if (cmd.isAfter) if (cmd.isAfter)
++insertPos; ++insertPos;
sectionCommands.insert(insertPos, cmd.os); sectionCommands.insert(insertPos, osec);
} }
} }
} }
// Symbols defined in script should not be inlined by LTO. At the same time // 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 // 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. // over symbol assignment commands and create placeholder symbols if needed.
void LinkerScript::declareSymbols() { void LinkerScript::declareSymbols() {
▲ Show 20 Lines • Show All 261 Lines • ▼ Show 20 Lines if (auto *cmd = dyn_cast<InputSectionDescription>(base)) {
ret.insert(ret.end(), cmd->sectionBases.begin(), cmd->sectionBases.end()); ret.insert(ret.end(), cmd->sectionBases.begin(), cmd->sectionBases.end());
} }
} }
return ret; return ret;
} }
// Create output sections described by SECTIONS commands. // Create output sections described by SECTIONS commands.
void LinkerScript::processSectionCommands() { void LinkerScript::processSectionCommands() {
size_t i = 0; auto process = [this](OutputSection *osec) {
for (BaseCommand *base : sectionCommands) { std::vector<InputSectionBase *> v = createInputSectionList(*osec);
if (auto *sec = dyn_cast<OutputSection>(base)) {
std::vector<InputSectionBase *> v = createInputSectionList(*sec);
// The output section name `/DISCARD/' is special. // The output section name `/DISCARD/' is special.
// Any input section assigned to it is discarded. // Any input section assigned to it is discarded.
if (sec->name == "/DISCARD/") { if (osec->name == "/DISCARD/") {
for (InputSectionBase *s : v) for (InputSectionBase *s : v)
discard(s); discard(s);
discardSynthetic(*sec); discardSynthetic(*osec);
sec->sectionCommands.clear(); osec->sectionCommands.clear();
continue; return false;
} }
// This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive // 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 // ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
// sections satisfy a given constraint. If not, a directive is handled // sections satisfy a given constraint. If not, a directive is handled
// as if it wasn't present from the beginning. // as if it wasn't present from the beginning.
// //
// Because we'll iterate over SectionCommands many more times, the easy // 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. // way to "make it as if it wasn't present" is to make it empty.
if (!matchConstraints(v, sec->constraint)) { if (!matchConstraints(v, osec->constraint)) {
for (InputSectionBase *s : v) for (InputSectionBase *s : v)
s->parent = nullptr; s->parent = nullptr;
sec->sectionCommands.clear(); osec->sectionCommands.clear();
continue; return false;
} }
// Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign // Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
// is given, input sections are aligned to that value, whether the // is given, input sections are aligned to that value, whether the
// given value is larger or smaller than the original section alignment. // given value is larger or smaller than the original section alignment.
if (sec->subalignExpr) { if (osec->subalignExpr) {
uint32_t subalign = sec->subalignExpr().getValue(); uint32_t subalign = osec->subalignExpr().getValue();
for (InputSectionBase *s : v) for (InputSectionBase *s : v)
s->alignment = subalign; s->alignment = subalign;
} }
// Set the partition field the same way OutputSection::recordSection() // Set the partition field the same way OutputSection::recordSection()
// does. Partitions cannot be used with the SECTIONS command, so this is // does. Partitions cannot be used with the SECTIONS command, so this is
// always 1. // always 1.
sec->partition = 1; osec->partition = 1;
return true;
};
sec->sectionIndex = i++; // Process OVERWRITE_SECTIONS first so that it can overwrite the main script
// or orphans.
DenseMap<StringRef, OutputSection *> map;
size_t i = 0;
for (OutputSection *osec : overwriteSections)
if (process(osec) && !map.try_emplace(osec->name, osec).second)
warn("OVERWRITE_SECTIONS specifies duplicate " + osec->name);
for (BaseCommand *&base : sectionCommands)
if (auto *osec = dyn_cast<OutputSection>(base)) {
if (OutputSection *overwrite = map.lookup(osec->name)) {
log(overwrite->location + " overwrites " + osec->name);
overwrite->sectionIndex = i++;
base = overwrite;
} else if (process(osec)) {
osec->sectionIndex = i++;
} }
} }
// 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 (OutputSection *osec : overwriteSections)
if (osec->partition == 1 && osec->sectionIndex == UINT32_MAX)
sectionCommands.push_back(osec);
} }
void LinkerScript::processSymbolAssignments() { void LinkerScript::processSymbolAssignments() {
// Dot outside an output section still represents a relative address, whose // 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 // 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 // that fills the void outside a section. It has an index of one, which is
// indistinguishable from any other regular section index. // indistinguishable from any other regular section index.
aether = make<OutputSection>("", 0, SHF_ALLOC); aether = make<OutputSection>("", 0, SHF_ALLOC);
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