Create minimal remap table for symbol binary search.
ELF symbols are not sorted by address. Create remap table which reshuffles the indices into sorted-by-address order. This saves over 6x of memory (the remap table needs just uint32_t per entry, as opposed the FuncInfo cache entry). ART symbols are sorted. Make use of that fact. Bug: 110133331 Test: libunwindstack_test Test: art/test.py -b --host -r -t 137-cfi Change-Id: I1812d2dd3ad6a69ae93ed50ca387749c649289b9
This commit is contained in:
David Srbecky
parent
451197cb64
commit
af41960acb
3 changed files with 122 additions and 70 deletions
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@ -19,6 +19,7 @@
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#include <algorithm>
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#include <string>
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#include <vector>
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#include <unwindstack/Memory.h>
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@ -29,23 +30,55 @@ namespace unwindstack {
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Symbols::Symbols(uint64_t offset, uint64_t size, uint64_t entry_size, uint64_t str_offset,
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uint64_t str_size)
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: cur_offset_(offset),
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offset_(offset),
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end_(offset + size),
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: offset_(offset),
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count_(entry_size != 0 ? size / entry_size : 0),
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entry_size_(entry_size),
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str_offset_(str_offset),
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str_end_(str_offset_ + str_size) {}
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const Symbols::Info* Symbols::GetInfoFromCache(uint64_t addr) {
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// Binary search the table.
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template <typename SymType>
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static bool IsFunc(const SymType* entry) {
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return entry->st_shndx != SHN_UNDEF && ELF32_ST_TYPE(entry->st_info) == STT_FUNC;
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}
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// Read symbol entry from memory and cache it so we don't have to read it again.
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template <typename SymType>
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inline __attribute__((__always_inline__)) const Symbols::Info* Symbols::ReadFuncInfo(
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uint32_t symbol_index, Memory* elf_memory) {
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auto it = symbols_.find(symbol_index);
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if (it != symbols_.end()) {
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return &it->second;
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}
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SymType sym;
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if (!elf_memory->ReadFully(offset_ + symbol_index * entry_size_, &sym, sizeof(sym))) {
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return nullptr;
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}
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if (!IsFunc(&sym)) {
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// We need the address for binary search, but we don't want it to be matched.
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sym.st_size = 0;
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}
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Info info{.addr = sym.st_value, .size = static_cast<uint32_t>(sym.st_size), .name = sym.st_name};
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return &symbols_.emplace(symbol_index, info).first->second;
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}
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// Binary search the symbol table to find function containing the given address.
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// Without remap, the symbol table is assumed to be sorted and accessed directly.
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// If the symbol table is not sorted this method might fail but should not crash.
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// When the indices are remapped, they are guaranteed to be sorted by address.
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template <typename SymType, bool RemapIndices>
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const Symbols::Info* Symbols::BinarySearch(uint64_t addr, Memory* elf_memory) {
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size_t first = 0;
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size_t last = symbols_.size();
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size_t last = RemapIndices ? remap_->size() : count_;
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while (first < last) {
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size_t current = first + (last - first) / 2;
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const Info* info = &symbols_[current];
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if (addr < info->start_offset) {
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size_t symbol_index = RemapIndices ? remap_.value()[current] : current;
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const Info* info = ReadFuncInfo<SymType>(symbol_index, elf_memory);
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if (info == nullptr) {
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return nullptr;
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}
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if (addr < info->addr) {
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last = current;
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} else if (addr < info->end_offset) {
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} else if (addr < info->addr + info->size) {
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return info;
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} else {
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first = current + 1;
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@ -54,64 +87,72 @@ const Symbols::Info* Symbols::GetInfoFromCache(uint64_t addr) {
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return nullptr;
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}
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// Create remapping table which allows us to access symbols as if they were sorted by address.
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template <typename SymType>
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bool Symbols::GetName(uint64_t addr, Memory* elf_memory, std::string* name, uint64_t* func_offset) {
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if (symbols_.size() != 0) {
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const Info* info = GetInfoFromCache(addr);
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if (info) {
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CHECK(addr >= info->start_offset && addr <= info->end_offset);
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*func_offset = addr - info->start_offset;
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return elf_memory->ReadString(info->str_offset, name, str_end_ - info->str_offset);
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void Symbols::BuildRemapTable(Memory* elf_memory) {
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std::vector<uint64_t> addrs; // Addresses of all symbols (addrs[i] == symbols[i].st_value).
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addrs.reserve(count_);
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remap_.emplace(); // Construct the optional remap table.
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remap_->reserve(count_);
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for (size_t symbol_idx = 0; symbol_idx < count_;) {
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// Read symbols from memory. We intentionally bypass the cache to save memory.
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// Do the reads in batches so that we minimize the number of memory read calls.
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uint8_t buffer[1024];
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size_t read = std::min<size_t>(sizeof(buffer), (count_ - symbol_idx) * entry_size_);
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size_t size = elf_memory->Read(offset_ + symbol_idx * entry_size_, buffer, read);
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if (size < sizeof(SymType)) {
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break; // Stop processing, something looks like it is corrupted.
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}
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}
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bool symbol_added = false;
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bool return_value = false;
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while (cur_offset_ + entry_size_ <= end_) {
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SymType entry;
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if (!elf_memory->ReadFully(cur_offset_, &entry, sizeof(entry))) {
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// Stop all processing, something looks like it is corrupted.
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cur_offset_ = UINT64_MAX;
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return false;
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}
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cur_offset_ += entry_size_;
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if (entry.st_shndx != SHN_UNDEF && ELF32_ST_TYPE(entry.st_info) == STT_FUNC) {
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// Treat st_value as virtual address.
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uint64_t start_offset = entry.st_value;
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uint64_t end_offset = start_offset + entry.st_size;
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// Cache the value.
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symbols_.emplace_back(start_offset, end_offset, str_offset_ + entry.st_name);
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symbol_added = true;
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if (addr >= start_offset && addr < end_offset) {
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*func_offset = addr - start_offset;
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uint64_t offset = str_offset_ + entry.st_name;
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if (offset < str_end_) {
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return_value = elf_memory->ReadString(offset, name, str_end_ - offset);
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}
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break;
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for (size_t offset = 0; offset + sizeof(SymType) <= size; offset += entry_size_, symbol_idx++) {
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SymType sym;
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memcpy(&sym, &buffer[offset], sizeof(SymType)); // Copy to ensure alignment.
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addrs.push_back(sym.st_value); // Always insert so it is indexable by symbol index.
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if (IsFunc(&sym)) {
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remap_->push_back(symbol_idx); // Indices of function symbols only.
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}
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}
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}
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// Sort by address to make the remap list binary searchable (stable due to the a<b tie break).
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auto comp = [&addrs](auto a, auto b) { return std::tie(addrs[a], a) < std::tie(addrs[b], b); };
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std::sort(remap_->begin(), remap_->end(), comp);
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// Remove duplicate entries (methods de-duplicated by the linker).
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auto pred = [&addrs](auto a, auto b) { return addrs[a] == addrs[b]; };
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remap_->erase(std::unique(remap_->begin(), remap_->end(), pred), remap_->end());
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remap_->shrink_to_fit();
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}
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if (symbol_added) {
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std::sort(symbols_.begin(), symbols_.end(),
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[](const Info& a, const Info& b) { return a.start_offset < b.start_offset; });
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template <typename SymType>
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bool Symbols::GetName(uint64_t addr, Memory* elf_memory, std::string* name, uint64_t* func_offset) {
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const Info* info;
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if (!remap_.has_value()) {
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// Assume the symbol table is sorted. If it is not, this will gracefully fail.
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info = BinarySearch<SymType, false>(addr, elf_memory);
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if (info == nullptr) {
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// Create the remapping table and retry the search.
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BuildRemapTable<SymType>(elf_memory);
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symbols_.clear(); // Remove cached symbols since the access pattern will be different.
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info = BinarySearch<SymType, true>(addr, elf_memory);
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}
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} else {
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// Fast search using the previously created remap table.
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info = BinarySearch<SymType, true>(addr, elf_memory);
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}
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return return_value;
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if (info == nullptr) {
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return false;
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}
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// Read the function name from the string table.
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*func_offset = addr - info->addr;
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uint64_t str = str_offset_ + info->name;
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return str < str_end_ && elf_memory->ReadString(str, name, str_end_ - str);
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}
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template <typename SymType>
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bool Symbols::GetGlobal(Memory* elf_memory, const std::string& name, uint64_t* memory_address) {
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uint64_t cur_offset = offset_;
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while (cur_offset + entry_size_ <= end_) {
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for (uint32_t i = 0; i < count_; i++) {
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SymType entry;
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if (!elf_memory->ReadFully(cur_offset, &entry, sizeof(entry))) {
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if (!elf_memory->ReadFully(offset_ + i * entry_size_, &entry, sizeof(entry))) {
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return false;
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}
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cur_offset += entry_size_;
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if (entry.st_shndx != SHN_UNDEF && ELF32_ST_TYPE(entry.st_info) == STT_OBJECT &&
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ELF32_ST_BIND(entry.st_info) == STB_GLOBAL) {
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@ -19,8 +19,9 @@
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#include <stdint.h>
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#include <optional>
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#include <string>
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#include <vector>
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#include <unordered_map>
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namespace unwindstack {
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@ -29,11 +30,9 @@ class Memory;
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class Symbols {
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struct Info {
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Info(uint64_t start_offset, uint64_t end_offset, uint64_t str_offset)
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: start_offset(start_offset), end_offset(end_offset), str_offset(str_offset) {}
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uint64_t start_offset;
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uint64_t end_offset;
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uint64_t str_offset;
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uint64_t addr; // Symbol address.
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uint32_t size; // Symbol size in bytes. Zero if not a function.
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uint32_t name; // Offset in .strtab.
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};
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public:
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@ -41,8 +40,6 @@ class Symbols {
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uint64_t str_size);
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virtual ~Symbols() = default;
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const Info* GetInfoFromCache(uint64_t addr);
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template <typename SymType>
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bool GetName(uint64_t addr, Memory* elf_memory, std::string* name, uint64_t* func_offset);
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@ -51,18 +48,27 @@ class Symbols {
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void ClearCache() {
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symbols_.clear();
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cur_offset_ = offset_;
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remap_.reset();
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}
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private:
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uint64_t cur_offset_;
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uint64_t offset_;
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uint64_t end_;
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uint64_t entry_size_;
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uint64_t str_offset_;
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uint64_t str_end_;
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template <typename SymType>
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const Info* ReadFuncInfo(uint32_t symbol_index, Memory* elf_memory);
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std::vector<Info> symbols_;
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template <typename SymType, bool RemapIndices>
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const Info* BinarySearch(uint64_t addr, Memory* elf_memory);
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template <typename SymType>
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void BuildRemapTable(Memory* elf_memory);
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const uint64_t offset_;
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const uint64_t count_;
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const uint64_t entry_size_;
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const uint64_t str_offset_;
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const uint64_t str_end_;
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std::unordered_map<uint32_t, Info> symbols_; // Cache of read symbols (keyed by symbol index).
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std::optional<std::vector<uint32_t>> remap_; // Indices of function symbols sorted by address.
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};
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} // namespace unwindstack
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@ -185,18 +185,21 @@ TYPED_TEST_P(SymbolsTest, multiple_entries_nonstandard_size) {
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std::string fake_name;
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this->InitSym(&sym, 0x5000, 0x10, 0x40);
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this->memory_.SetMemoryBlock(offset, entry_size, 0);
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this->memory_.SetMemory(offset, &sym, sizeof(sym));
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fake_name = "function_one";
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this->memory_.SetMemory(0x2040, fake_name.c_str(), fake_name.size() + 1);
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offset += entry_size;
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this->InitSym(&sym, 0x3004, 0x200, 0x100);
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this->memory_.SetMemoryBlock(offset, entry_size, 0);
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this->memory_.SetMemory(offset, &sym, sizeof(sym));
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fake_name = "function_two";
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this->memory_.SetMemory(0x2100, fake_name.c_str(), fake_name.size() + 1);
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offset += entry_size;
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this->InitSym(&sym, 0xa010, 0x20, 0x230);
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this->memory_.SetMemoryBlock(offset, entry_size, 0);
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this->memory_.SetMemory(offset, &sym, sizeof(sym));
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fake_name = "function_three";
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this->memory_.SetMemory(0x2230, fake_name.c_str(), fake_name.size() + 1);
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@ -274,7 +277,9 @@ TYPED_TEST_P(SymbolsTest, symtab_read_cached) {
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// Do call that should cache all of the entries (except the string data).
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std::string name;
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uint64_t func_offset;
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ASSERT_FALSE(symbols.GetName<TypeParam>(0x6000, &this->memory_, &name, &func_offset));
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ASSERT_FALSE(symbols.GetName<TypeParam>(0x5000, &this->memory_, &name, &func_offset));
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ASSERT_FALSE(symbols.GetName<TypeParam>(0x2000, &this->memory_, &name, &func_offset));
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ASSERT_FALSE(symbols.GetName<TypeParam>(0x1000, &this->memory_, &name, &func_offset));
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this->memory_.Clear();
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ASSERT_FALSE(symbols.GetName<TypeParam>(0x6000, &this->memory_, &name, &func_offset));
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