[lld] [lld][ELF] Add --debug-names to create merged .debug_names. (PR #86508)
David Blaikie via llvm-commits
llvm-commits at lists.llvm.org
Sun Apr 14 20:43:17 PDT 2024
================
@@ -2711,6 +2714,606 @@ static uint32_t computeGdbHash(StringRef s) {
return h;
}
+// 4-byte alignment ensures that values in the hash lookup table and the name
+// table are aligned.
+DebugNamesBaseSection::DebugNamesBaseSection()
+ : SyntheticSection(0, SHT_PROGBITS, 4, ".debug_names") {}
+
+// Get the size of the .debug_names section header in bytes for DWARF32:
+static uint32_t getDebugNamesHeaderSize(uint32_t augmentationStringSize) {
+ return /* unit length */ 4 +
+ /* version */ 2 +
+ /* padding */ 2 +
+ /* CU count */ 4 +
+ /* TU count */ 4 +
+ /* Foreign TU count */ 4 +
+ /* Bucket Count */ 4 +
+ /* Name Count */ 4 +
+ /* Abbrev table size */ 4 +
+ /* Augmentation string size */ 4 +
+ /* Augmentation string */ augmentationStringSize;
+}
+
+void DebugNamesBaseSection::parseDebugNames(
+ InputChunk &inputChunk, OutputChunk &chunk,
+ DWARFDataExtractor &namesExtractor, DataExtractor &strExtractor,
+ function_ref<SmallVector<uint32_t, 0>(
+ const DWARFDebugNames::Header &,
+ const DWARFDebugNames::DWARFDebugNamesOffsets &)>
+ readOffsets) {
+ const LLDDWARFSection namesSec = inputChunk.section;
+ DenseMap<uint32_t, IndexEntry *> offsetMap;
+ for (const DWARFDebugNames::NameIndex &ni : *inputChunk.llvmDebugNames) {
+ NameData &nd = inputChunk.nameData.emplace_back();
+ nd.hdr = ni.getHeader();
+ if (nd.hdr.Format != DwarfFormat::DWARF32) {
+ errorOrWarn(toString(namesSec.sec) + Twine(": unsupported DWARF64"));
+ return;
+ }
+ if (nd.hdr.Version != 5) {
+ errorOrWarn(toString(namesSec.sec) + Twine(": unsupported version ") +
+ Twine(nd.hdr.Version));
+ return;
+ }
+ const uint32_t dwarfSize =
+ dwarf::getDwarfOffsetByteSize(DwarfFormat::DWARF32);
+ const uint32_t hdrSize =
+ getDebugNamesHeaderSize(nd.hdr.AugmentationStringSize);
+ auto locs = findDebugNamesOffsets(hdrSize, nd.hdr);
+ if (locs.EntriesBase > namesExtractor.getData().size()) {
+ errorOrWarn(toString(namesSec.sec) +
+ Twine(": index entry is out of bounds"));
+ return;
+ }
+
+ SmallVector<uint32_t, 0> entryOffsets = readOffsets(nd.hdr, locs);
+
+ // Read the entry pool.
+ offsetMap.clear();
+ nd.nameEntries.resize(nd.hdr.NameCount);
+ for (auto i : seq(nd.hdr.NameCount)) {
+ NameEntry &ne = nd.nameEntries[i];
+ uint64_t strOffset = locs.StringOffsetsBase + i * dwarfSize;
+ ne.stringOffset = strOffset;
+ uint64_t strp = namesExtractor.getRelocatedValue(dwarfSize, &strOffset);
+ StringRef name = strExtractor.getCStrRef(&strp);
+ ne.name = name.data();
+ ne.hashValue = caseFoldingDjbHash(name);
+
+ // Read a series of index entries that end with abbreviation code 0.
+ const char *errMsg = nullptr;
+ uint64_t offset = locs.EntriesBase + entryOffsets[i];
+ while (offset < namesSec.Data.size() && namesSec.Data[offset] != 0) {
+ // Read & store all entries (for the same string).
+ auto ie = makeThreadLocal<IndexEntry>();
+ ie->poolOffset = offset;
+ Error err = Error::success();
+ ie->abbrevCode =
+ static_cast<uint32_t>(namesExtractor.getULEB128(&offset, &err));
+ if (err) {
+ consumeError(std::move(err));
+ errMsg = ": invalid abbrev code in entry";
+ break;
+ }
+ auto it = ni.getAbbrevs().find_as(ie->abbrevCode);
+ if (it == ni.getAbbrevs().end()) {
+ errMsg = ": invalid abbrev code in entry";
+ break;
+ }
+
+ AttrValue attr, cuAttr = {0, 0};
+ for (DWARFDebugNames::AttributeEncoding a : it->Attributes) {
+ if (a.Index == dwarf::DW_IDX_parent) {
+ if (a.Form == dwarf::DW_FORM_ref4) {
+ attr.attrValue = namesExtractor.getU32(&offset, &err);
+ attr.attrSize = 4;
+ ie->parentOffset = locs.EntriesBase + attr.attrValue;
+ } else if (a.Form != DW_FORM_flag_present) {
+ errMsg = ": invalid form for DW_IDX_parent";
+ }
+ } else {
+ switch (a.Form) {
+ case DW_FORM_data1:
+ case DW_FORM_ref1: {
+ attr.attrValue = namesExtractor.getU8(&offset, &err);
+ attr.attrSize = 1;
+ break;
+ }
+ case DW_FORM_data2:
+ case DW_FORM_ref2: {
+ attr.attrValue = namesExtractor.getU16(&offset, &err);
+ attr.attrSize = 2;
+ break;
+ }
+ case DW_FORM_data4:
+ case DW_FORM_ref4: {
+ attr.attrValue = namesExtractor.getU32(&offset, &err);
+ attr.attrSize = 4;
+ break;
+ }
+ default:
+ errorOrWarn(toString(namesSec.sec) +
+ Twine(": unrecognized form encoding ") +
+ Twine(a.Form) + Twine(" in abbrev table"));
+ return;
+ }
+ }
+ if (err) {
+ errorOrWarn(toString(namesSec.sec) +
+ Twine(": error while reading attributes: ") +
+ toString(std::move(err)));
+ return;
+ }
+ if (a.Index == DW_IDX_compile_unit)
+ cuAttr = attr;
+ else if (a.Form != DW_FORM_flag_present)
+ ie->attrValues.push_back(attr);
+ }
+
+ // Canonicalize abbrev by placing the CU/TU index at the end.
+ ie->attrValues.push_back(cuAttr);
+ ne.indexEntries.push_back(std::move(ie));
+ }
+ if (offset >= namesSec.Data.size())
+ errMsg = ": index entry is out of bounds";
+ if (errMsg)
+ errorOrWarn(toString(namesSec.sec) + Twine(errMsg));
+
+ for (IndexEntry &ie : ne.entries())
+ offsetMap[ie.poolOffset] = &ie;
+ }
+
+ // Assign parent pointers, which will be used to update DW_IDX_parent index
+ // attributes. Note: offsetMap[0] does not exist, so parentOffset == 0 will
+ // get parentEntry == null as well.
+ for (NameEntry &ne : nd.nameEntries)
+ for (IndexEntry &ie : ne.entries())
+ ie.parentEntry = offsetMap.lookup(ie.parentOffset);
+ }
+}
+
+// Compute the form for output DW_IDX_compile_unit attributes, similar to
+// DIEInteger::BestForm. The input form (often DW_FORM_data1) may not hold all
+// the merged CU indices.
+std::pair<uint8_t, dwarf::Form> static getMergedCuCountForm(
+ uint32_t compUnitCount) {
+ if (compUnitCount > UINT16_MAX)
+ return {4, DW_FORM_data4};
+ if (compUnitCount > UINT8_MAX)
+ return {2, DW_FORM_data2};
+ return {1, DW_FORM_data1};
+}
+
+void DebugNamesBaseSection::computeHdrAndAbbrevTable(
+ MutableArrayRef<InputChunk> inputChunks) {
+ TimeTraceScope timeScope("Merge .debug_names", "hdr and abbrev table");
+ size_t numCu = 0;
+ hdr.Format = DwarfFormat::DWARF32;
+ hdr.Version = 5;
+ hdr.CompUnitCount = 0;
+ hdr.LocalTypeUnitCount = 0;
+ hdr.ForeignTypeUnitCount = 0;
+ hdr.AugmentationStringSize = 0;
+
+ // Compute CU and TU counts.
+ for (auto i : seq(numChunks)) {
+ InputChunk &inputChunk = inputChunks[i];
+ inputChunk.baseCuIdx = numCu;
+ numCu += chunks[i].compUnits.size();
+ for (const NameData &nd : inputChunk.nameData) {
+ hdr.CompUnitCount += nd.hdr.CompUnitCount;
+ hdr.LocalTypeUnitCount += nd.hdr.LocalTypeUnitCount;
+ hdr.ForeignTypeUnitCount += nd.hdr.ForeignTypeUnitCount;
+ // If augmentation strings are not identical, use an empty string.
+ if (i == 0) {
+ hdr.AugmentationStringSize = nd.hdr.AugmentationStringSize;
+ hdr.AugmentationString = nd.hdr.AugmentationString;
+ } else if (hdr.AugmentationString != nd.hdr.AugmentationString) {
+ // There are conflicting augmentation strings, so it's best for the
+ // merged index to not use an augmentation string.
+ hdr.AugmentationStringSize = 0;
+ hdr.AugmentationString.clear();
+ }
+ }
+ }
+
+ // Create the merged abbrev table, uniquifyinng the input abbrev tables and
+ // computing mapping from old (per-cu) abbrev codes to new (merged) abbrev
+ // codes.
+ FoldingSet<Abbrev> abbrevSet;
+ // Determine the form for the DW_IDX_compile_unit attributes in the merged
+ // index. The input form may not be big enough for all CU indices.
+ const dwarf::Form cuAttrForm = getMergedCuCountForm(hdr.CompUnitCount).second;
+ for (InputChunk &inputChunk : inputChunks) {
+ for (auto [i, ni] : enumerate(*inputChunk.llvmDebugNames)) {
+ for (const DWARFDebugNames::Abbrev &oldAbbrev : ni.getAbbrevs()) {
+ // Canonicalize abbrev by placing the CU/TU index at the end,
+ // similar to 'parseDebugNames'.
+ Abbrev abbrev;
+ DWARFDebugNames::AttributeEncoding cuAttr(DW_IDX_compile_unit,
+ cuAttrForm);
+ abbrev.code = oldAbbrev.Code;
+ abbrev.tag = oldAbbrev.Tag;
+ for (DWARFDebugNames::AttributeEncoding a : oldAbbrev.Attributes) {
+ if (a.Index == DW_IDX_compile_unit)
+ cuAttr.Index = a.Index;
+ else
+ abbrev.attributes.push_back({a.Index, a.Form});
+ }
+ // Put the CU/TU index at the end of the attributes list.
+ abbrev.attributes.push_back(cuAttr);
+
+ // Profile the abbrev, get or assign a new code, then record the abbrev
+ // code mapping.
+ FoldingSetNodeID id;
+ abbrev.Profile(id);
+ uint32_t newCode;
+ void *insertPos;
+ if (Abbrev *existing = abbrevSet.FindNodeOrInsertPos(id, insertPos)) {
+ // Found it; we've already seen an identical abbreviation.
+ newCode = existing->code;
+ } else {
+ Abbrev *abbrev2 =
+ new (abbrevAlloc.Allocate()) Abbrev(std::move(abbrev));
+ abbrevSet.InsertNode(abbrev2, insertPos);
+ abbrevTable.push_back(abbrev2);
+ newCode = abbrevTable.size();
+ abbrev2->code = newCode;
+ }
+ inputChunk.nameData[i].abbrevCodeMap[oldAbbrev.Code] = newCode;
+ }
+ }
+ }
+
+ // Compute the merged abbrev table.
+ raw_svector_ostream os(abbrevTableBuf);
+ for (Abbrev *abbrev : abbrevTable) {
+ encodeULEB128(abbrev->code, os);
+ encodeULEB128(abbrev->tag, os);
+ for (DWARFDebugNames::AttributeEncoding a : abbrev->attributes) {
+ encodeULEB128(a.Index, os);
+ encodeULEB128(a.Form, os);
+ }
+ os.write("\0", 2); // attribute specification end
+ }
+ os.write(0); // abbrev table end
+ hdr.AbbrevTableSize = abbrevTableBuf.size();
+}
+
+void DebugNamesBaseSection::Abbrev::Profile(FoldingSetNodeID &id) const {
+ id.AddInteger(tag);
+ for (const DWARFDebugNames::AttributeEncoding &attr : attributes) {
+ id.AddInteger(attr.Index);
+ id.AddInteger(attr.Form);
+ }
+}
+
+std::pair<uint32_t, uint32_t> DebugNamesBaseSection::computeEntryPool(
+ MutableArrayRef<InputChunk> inputChunks) {
+ TimeTraceScope timeScope("Merge .debug_names", "entry pool");
+ // Collect and de-duplicate all the names (preserving all the entries).
+ // Speed it up using multithreading, as the number of symbols can be in the
+ // order of millions.
+ const size_t concurrency =
+ bit_floor(std::min<size_t>(config->threadCount, numShards));
+ const size_t shift = 32 - countr_zero(numShards);
+ const uint8_t cuAttrSize = getMergedCuCountForm(hdr.CompUnitCount).first;
+ DenseMap<CachedHashStringRef, size_t> maps[numShards];
+
+ parallelFor(0, concurrency, [&](size_t threadId) {
+ for (auto i : seq(numChunks)) {
+ InputChunk &inputChunk = inputChunks[i];
+ for (NameData &nd : inputChunk.nameData) {
+ // Deduplicate the NameEntry records (based on the string/name),
+ // appending all IndexEntries from duplicate NameEntry records to
+ // the single preserved copy.
+ for (NameEntry &ne : nd.nameEntries) {
+ auto shardId = ne.hashValue >> shift;
+ if ((shardId & (concurrency - 1)) != threadId)
+ continue;
+
+ ne.chunkIdx = i;
+ for (IndexEntry &ie : ne.entries()) {
+ // Update the IndexEntry's abbrev code to match the merged
+ // abbreviations.
+ ie.abbrevCode = nd.abbrevCodeMap[ie.abbrevCode];
+ // Update the DW_IDX_compile_unit attribute (the last one after
+ // canonicalization) to have correct merged offset value and size.
+ auto &back = ie.attrValues.back();
+ back.attrValue += inputChunk.baseCuIdx;
+ back.attrSize = cuAttrSize;
+ }
+
+ auto &nameVec = nameVecs[shardId];
+ auto [it, inserted] = maps[shardId].try_emplace(
+ CachedHashStringRef(ne.name, ne.hashValue), nameVec.size());
+ if (inserted)
+ nameVec.push_back(std::move(ne));
+ else
+ nameVec[it->second].indexEntries.append(std::move(ne.indexEntries));
+ }
+ }
+ }
+ });
+
+ // Compute entry offsets in parallel. First, comptute offsets relative to the
+ // current shard.
+ uint32_t offsets[numShards];
+ parallelFor(0, numShards, [&](size_t shard) {
+ uint32_t offset = 0;
+ for (NameEntry &ne : nameVecs[shard]) {
+ ne.entryOffset = offset;
+ for (IndexEntry &ie : ne.entries()) {
+ ie.poolOffset = offset;
+ offset += getULEB128Size(ie.abbrevCode);
+ for (AttrValue value : ie.attrValues)
+ offset += value.attrSize;
+ }
+ ++offset; // index entry sentinel
+ }
+ offsets[shard] = offset;
+ });
+ // Then add shard offsets.
+ std::partial_sum(offsets, std::end(offsets), offsets);
+ parallelFor(1, numShards, [&](size_t shard) {
+ uint32_t offset = offsets[shard - 1];
+ for (NameEntry &ne : nameVecs[shard]) {
+ ne.entryOffset += offset;
+ for (IndexEntry &ie : ne.entries())
+ ie.poolOffset += offset;
+ }
+ });
+
+ // Update the DW_IDX_parent entries that refer to real parents (have
+ // DW_FORM_ref4).
+ parallelFor(0, numShards, [&](size_t shard) {
+ for (NameEntry &ne : nameVecs[shard]) {
+ for (IndexEntry &ie : ne.entries()) {
+ if (!ie.parentEntry)
+ continue;
+ // Abbrevs are indexed starting at 1; vector starts at 0. (abbrevCode
+ // corresponds to position in the merged table vector).
+ const Abbrev *abbrev = abbrevTable[ie.abbrevCode - 1];
+ for (auto i : seq(abbrev->attributes.size())) {
+ DWARFDebugNames::AttributeEncoding a = abbrev->attributes[i];
+ if (a.Index == DW_IDX_parent && a.Form == DW_FORM_ref4)
+ ie.attrValues[i].attrValue = ie.parentEntry->poolOffset;
+ }
+ }
+ }
+ });
+
+ // Return (entry pool size, number of entries).
+ uint32_t num = 0;
+ for (auto &map : maps)
+ num += map.size();
+ return {offsets[numShards - 1], num};
+}
+
+void DebugNamesBaseSection::init(
+ function_ref<void(InputFile *, InputChunk &, OutputChunk &)> parseFile) {
+ TimeTraceScope timeScope("Merge .debug_names");
+ // Collect and remove input .debug_names sections. Save InputSection pointers
+ // to relocate string offsets in `writeTo`.
+ SetVector<InputFile *> files;
+ for (InputSectionBase *s : ctx.inputSections) {
+ InputSection *isec = dyn_cast<InputSection>(s);
+ if (!isec)
+ continue;
+ if (!(s->flags & SHF_ALLOC) && s->name == ".debug_names") {
+ s->markDead();
+ inputSections.push_back(isec);
+ files.insert(isec->file);
+ }
+ }
+
+ // Parse input .debug_names sections and extract InputChunk and OutputChunk
+ // data. OutputChunk contains CU information, which will be needed by
+ // `writeTo`.
+ auto inputChunksPtr = std::make_unique<InputChunk[]>(files.size());
+ MutableArrayRef<InputChunk> inputChunks(inputChunksPtr.get(), files.size());
+ numChunks = files.size();
+ chunks = std::make_unique<OutputChunk[]>(files.size());
+ {
+ TimeTraceScope timeScope("Merge .debug_names", "parse");
+ parallelFor(0, files.size(), [&](size_t i) {
+ parseFile(files[i], inputChunks[i], chunks[i]);
+ });
+ }
+
+ // Compute section header (except unit_length), abbrev table, and entry pool.
+ computeHdrAndAbbrevTable(inputChunks);
+ uint32_t entryPoolSize;
+ std::tie(entryPoolSize, hdr.NameCount) = computeEntryPool(inputChunks);
+ hdr.BucketCount = dwarf::getDebugNamesBucketCount(hdr.NameCount);
+
+ // Compute the section size. Subtract 4 to get the unit_length for DWARF32.
+ uint32_t hdrSize = getDebugNamesHeaderSize(hdr.AugmentationStringSize);
+ size = findDebugNamesOffsets(hdrSize, hdr).EntriesBase + entryPoolSize;
+ hdr.UnitLength = size - 4;
+}
+
+template <class ELFT> DebugNamesSection<ELFT>::DebugNamesSection() {
+ init([](InputFile *f, InputChunk &inputChunk, OutputChunk &chunk) {
+ auto *file = cast<ObjFile<ELFT>>(f);
+ DWARFContext dwarf(std::make_unique<LLDDwarfObj<ELFT>>(file));
+ auto &dobj = static_cast<const LLDDwarfObj<ELFT> &>(dwarf.getDWARFObj());
+ chunk.infoSec = dobj.getInfoSection();
+ DWARFDataExtractor namesExtractor(dobj, dobj.getNamesSection(),
+ ELFT::Endianness == endianness::little,
+ ELFT::Is64Bits ? 8 : 4);
+ // .debug_str is needed to get symbol names from string offsets.
+ DataExtractor strExtractor(dobj.getStrSection(),
+ ELFT::Endianness == endianness::little,
+ ELFT::Is64Bits ? 8 : 4);
+ inputChunk.section = dobj.getNamesSection();
+
+ inputChunk.llvmDebugNames.emplace(namesExtractor, strExtractor);
+ if (Error e = inputChunk.llvmDebugNames->extract()) {
+ errorOrWarn(toString(dobj.getNamesSection().sec) + Twine(": ") +
+ toString(std::move(e)));
+ }
+ parseDebugNames(
+ inputChunk, chunk, namesExtractor, strExtractor,
+ [&chunk, namesData = dobj.getNamesSection().Data.data()](
+ const DWARFDebugNames::Header &hdr,
+ const DWARFDebugNames::DWARFDebugNamesOffsets &locs) {
+ // Read CU offsets.
+ const char *p = namesData + locs.CUsBase;
+ chunk.compUnits.resize_for_overwrite(hdr.CompUnitCount);
+ for (auto i : seq(hdr.CompUnitCount))
+ chunk.compUnits[i] =
+ endian::readNext<uint32_t, ELFT::Endianness, unaligned>(p);
+
+ // Read entry offsets.
+ p = namesData + locs.EntryOffsetsBase;
+ SmallVector<uint32_t, 0> entryOffsets;
+ entryOffsets.resize_for_overwrite(hdr.NameCount);
+ for (auto i : seq(hdr.NameCount))
+ entryOffsets[i] =
+ endian::readNext<uint32_t, ELFT::Endianness, unaligned>(p);
+ return entryOffsets;
+ });
+ });
+}
+
+template <class ELFT>
+template <class RelTy>
+void DebugNamesSection<ELFT>::getNameRelocs(
+ InputSection *sec, ArrayRef<RelTy> rels,
+ DenseMap<uint32_t, uint32_t> &relocs) {
+ for (const RelTy &rel : rels) {
+ Symbol &sym = sec->file->getRelocTargetSym(rel);
+ relocs[rel.r_offset] = sym.getVA(getAddend<ELFT>(rel));
+ }
+}
+
+template <class ELFT> void DebugNamesSection<ELFT>::finalizeContents() {
+ // Get relocations of .debug_names sections.
+ auto relocs = std::make_unique<DenseMap<uint32_t, uint32_t>[]>(numChunks);
+ parallelFor(0, numChunks, [&](size_t i) {
+ InputSection *sec = inputSections[i];
+ auto rels = sec->template relsOrRelas<ELFT>();
+ if (rels.areRelocsRel())
+ getNameRelocs(sec, rels.rels, relocs.get()[i]);
+ else
+ getNameRelocs(sec, rels.relas, relocs.get()[i]);
+ });
+
+ // Relocate string offsets in the name table.
+ parallelForEach(nameVecs, [&](auto &nameVec) {
+ for (NameEntry &ne : nameVec)
+ ne.stringOffset = relocs.get()[ne.chunkIdx][ne.stringOffset];
+ });
+}
+
+template <class ELFT> void DebugNamesSection<ELFT>::writeTo(uint8_t *buf) {
+ [[maybe_unused]] uint8_t *oldBuf = buf;
----------------
dwblaikie wrote:
maybe `beginBuf` rather than `oldBuf`, to make it more self-documenting?
https://github.com/llvm/llvm-project/pull/86508
More information about the llvm-commits
mailing list