/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_
#define ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_
#include <unordered_set>
#include <vector>
#include "compiled_method.h"
#include "debug/dwarf/debug_line_opcode_writer.h"
#include "debug/dwarf/headers.h"
#include "debug/elf_compilation_unit.h"
#include "dex_file-inl.h"
#include "elf_builder.h"
#include "stack_map.h"
namespace art {
namespace debug {
typedef std::vector<DexFile::PositionInfo> PositionInfos;
static bool PositionInfoCallback(void* ctx, const DexFile::PositionInfo& entry) {
static_cast<PositionInfos*>(ctx)->push_back(entry);
return false;
}
template<typename ElfTypes>
class ElfDebugLineWriter {
using Elf_Addr = typename ElfTypes::Addr;
public:
explicit ElfDebugLineWriter(ElfBuilder<ElfTypes>* builder) : builder_(builder) {
}
void Start() {
builder_->GetDebugLine()->Start();
}
// Write line table for given set of methods.
// Returns the number of bytes written.
size_t WriteCompilationUnit(ElfCompilationUnit& compilation_unit) {
const InstructionSet isa = builder_->GetIsa();
const bool is64bit = Is64BitInstructionSet(isa);
const Elf_Addr base_address = compilation_unit.is_code_address_text_relative
? builder_->GetText()->GetAddress()
: 0;
compilation_unit.debug_line_offset = builder_->GetDebugLine()->GetSize();
std::vector<dwarf::FileEntry> files;
std::unordered_map<std::string, size_t> files_map;
std::vector<std::string> directories;
std::unordered_map<std::string, size_t> directories_map;
int code_factor_bits_ = 0;
int dwarf_isa = -1;
switch (isa) {
case kArm: // arm actually means thumb2.
case kThumb2:
code_factor_bits_ = 1; // 16-bit instuctions
dwarf_isa = 1; // DW_ISA_ARM_thumb.
break;
case kArm64:
case kMips:
case kMips64:
code_factor_bits_ = 2; // 32-bit instructions
break;
case kNone:
case kX86:
case kX86_64:
break;
}
std::unordered_set<uint64_t> seen_addresses(compilation_unit.methods.size());
dwarf::DebugLineOpCodeWriter<> opcodes(is64bit, code_factor_bits_);
for (const MethodDebugInfo* mi : compilation_unit.methods) {
// Ignore function if we have already generated line table for the same address.
// It would confuse the debugger and the DWARF specification forbids it.
// We allow the line table for method to be replicated in different compilation unit.
// This ensures that each compilation unit contains line table for all its methods.
if (!seen_addresses.insert(mi->code_address).second) {
continue;
}
uint32_t prologue_end = std::numeric_limits<uint32_t>::max();
std::vector<SrcMapElem> pc2dex_map;
if (mi->code_info != nullptr) {
// Use stack maps to create mapping table from pc to dex.
const CodeInfo code_info(mi->code_info);
const CodeInfoEncoding encoding = code_info.ExtractEncoding();
pc2dex_map.reserve(code_info.GetNumberOfStackMaps(encoding));
for (uint32_t s = 0; s < code_info.GetNumberOfStackMaps(encoding); s++) {
StackMap stack_map = code_info.GetStackMapAt(s, encoding);
DCHECK(stack_map.IsValid());
const uint32_t pc = stack_map.GetNativePcOffset(encoding.stack_map.encoding, isa);
const int32_t dex = stack_map.GetDexPc(encoding.stack_map.encoding);
pc2dex_map.push_back({pc, dex});
if (stack_map.HasDexRegisterMap(encoding.stack_map.encoding)) {
// Guess that the first map with local variables is the end of prologue.
prologue_end = std::min(prologue_end, pc);
}
}
std::sort(pc2dex_map.begin(), pc2dex_map.end());
}
if (pc2dex_map.empty()) {
continue;
}
// Compensate for compiler's off-by-one-instruction error.
//
// The compiler generates stackmap with PC *after* the branch instruction
// (because this is the PC which is easier to obtain when unwinding).
//
// However, the debugger is more clever and it will ask us for line-number
// mapping at the location of the branch instruction (since the following
// instruction could belong to other line, this is the correct thing to do).
//
// So we really want to just decrement the PC by one instruction so that the
// branch instruction is covered as well. However, we do not know the size
// of the previous instruction, and we can not subtract just a fixed amount
// (the debugger would trust us that the PC is valid; it might try to set
// breakpoint there at some point, and setting breakpoint in mid-instruction
// would make the process crash in spectacular way).
//
// Therefore, we say that the PC which the compiler gave us for the stackmap
// is the end of its associated address range, and we use the PC from the
// previous stack map as the start of the range. This ensures that the PC is
// valid and that the branch instruction is covered.
//
// This ensures we have correct line number mapping at call sites (which is
// important for backtraces), but there is nothing we can do for non-call
// sites (so stepping through optimized code in debugger is not possible).
//
// We do not adjust the stackmaps if the code was compiled as debuggable.
// In that case, the stackmaps should accurately cover all instructions.
if (!mi->is_native_debuggable) {
for (size_t i = pc2dex_map.size() - 1; i > 0; --i) {
pc2dex_map[i].from_ = pc2dex_map[i - 1].from_;
}
pc2dex_map[0].from_ = 0;
}
Elf_Addr method_address = base_address + mi->code_address;
PositionInfos dex2line_map;
DCHECK(mi->dex_file != nullptr);
const DexFile* dex = mi->dex_file;
if (!dex->DecodeDebugPositionInfo(mi->code_item, PositionInfoCallback, &dex2line_map)) {
continue;
}
if (dex2line_map.empty()) {
continue;
}
opcodes.SetAddress(method_address);
if (dwarf_isa != -1) {
opcodes.SetISA(dwarf_isa);
}
// Get and deduplicate directory and filename.
int file_index = 0; // 0 - primary source file of the compilation.
auto& dex_class_def = dex->GetClassDef(mi->class_def_index);
const char* source_file = dex->GetSourceFile(dex_class_def);
if (source_file != nullptr) {
std::string file_name(source_file);
size_t file_name_slash = file_name.find_last_of('/');
std::string class_name(dex->GetClassDescriptor(dex_class_def));
size_t class_name_slash = class_name.find_last_of('/');
std::string full_path(file_name);
// Guess directory from package name.
int directory_index = 0; // 0 - current directory of the compilation.
if (file_name_slash == std::string::npos && // Just filename.
class_name.front() == 'L' && // Type descriptor for a class.
class_name_slash != std::string::npos) { // Has package name.
std::string package_name = class_name.substr(1, class_name_slash - 1);
auto it = directories_map.find(package_name);
if (it == directories_map.end()) {
directory_index = 1 + directories.size();
directories_map.emplace(package_name, directory_index);
directories.push_back(package_name);
} else {
directory_index = it->second;
}
full_path = package_name + "/" + file_name;
}
// Add file entry.
auto it2 = files_map.find(full_path);
if (it2 == files_map.end()) {
file_index = 1 + files.size();
files_map.emplace(full_path, file_index);
files.push_back(dwarf::FileEntry {
file_name,
directory_index,
0, // Modification time - NA.
0, // File size - NA.
});
} else {
file_index = it2->second;
}
}
opcodes.SetFile(file_index);
// Generate mapping opcodes from PC to Java lines.
if (file_index != 0) {
// If the method was not compiled as native-debuggable, we still generate all available
// lines, but we try to prevent the debugger from stepping and setting breakpoints since
// the information is too inaccurate for that (breakpoints would be set after the calls).
const bool default_is_stmt = mi->is_native_debuggable;
bool first = true;
for (SrcMapElem pc2dex : pc2dex_map) {
uint32_t pc = pc2dex.from_;
int dex_pc = pc2dex.to_;
// Find mapping with address with is greater than our dex pc; then go back one step.
auto dex2line = std::upper_bound(
dex2line_map.begin(),
dex2line_map.end(),
dex_pc,
[](uint32_t address, const DexFile::PositionInfo& entry) {
return address < entry.address_;
});
// Look for first valid mapping after the prologue.
if (dex2line != dex2line_map.begin() && pc >= prologue_end) {
int line = (--dex2line)->line_;
if (first) {
first = false;
if (pc > 0) {
// Assume that any preceding code is prologue.
int first_line = dex2line_map.front().line_;
// Prologue is not a sensible place for a breakpoint.
opcodes.SetIsStmt(false);
opcodes.AddRow(method_address, first_line);
opcodes.SetPrologueEnd();
}
opcodes.SetIsStmt(default_is_stmt);
opcodes.AddRow(method_address + pc, line);
} else if (line != opcodes.CurrentLine()) {
opcodes.SetIsStmt(default_is_stmt);
opcodes.AddRow(method_address + pc, line);
}
}
}
} else {
// line 0 - instruction cannot be attributed to any source line.
opcodes.AddRow(method_address, 0);
}
opcodes.AdvancePC(method_address + mi->code_size);
opcodes.EndSequence();
}
std::vector<uint8_t> buffer;
buffer.reserve(opcodes.data()->size() + KB);
size_t offset = builder_->GetDebugLine()->GetSize();
WriteDebugLineTable(directories, files, opcodes, offset, &buffer, &debug_line_patches_);
builder_->GetDebugLine()->WriteFully(buffer.data(), buffer.size());
return buffer.size();
}
void End(bool write_oat_patches) {
builder_->GetDebugLine()->End();
if (write_oat_patches) {
builder_->WritePatches(".debug_line.oat_patches",
ArrayRef<const uintptr_t>(debug_line_patches_));
}
}
private:
ElfBuilder<ElfTypes>* builder_;
std::vector<uintptr_t> debug_line_patches_;
};
} // namespace debug
} // namespace art
#endif // ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_