diff --git a/src/student/ld.cpp b/src/student/ld.cpp index 508a666..3f46ad0 100644 --- a/src/student/ld.cpp +++ b/src/student/ld.cpp @@ -1,30 +1,151 @@ -#include "fle.hpp" #include #include #include +#include #include #include +#include "fle.hpp" +#include "string_utils.hpp" + +FLEObject FLE_ld(const std::vector& input_objects) { + // 1. 合并段并收集符号 + // - 遍历每个输入对象的段 + // - 按段名合并并计算各段的偏移量 + // - 设置段的读/写/执行属性 + auto local_symbol_sets = std::vector>(); // 存储每个目标文件的局部符号 + for (const auto& obj : input_objects) { + local_symbol_sets.push_back(std::set()); + for (const auto& symbol : obj.symbols) { + if (symbol.type == SymbolType::LOCAL) + local_symbol_sets.back().insert(symbol.name); + } + } + + // 创建目标 FLEObject + auto linked_object = FLEObject(); + auto global_symbols = std::map(); + auto segment_names = std::vector{".text", ".rodata", ".data", ".bss"}; + auto segment_flags = std::vector{5, 4, 6, 6}; // 设置段的权限标志 + auto segment_vaddr = std::vector(4, 0); // 各段的虚拟地址 + size_t virtual_address = 0x400000; // 初始化虚拟内存基址 + + // 所有段并合并 + for (int i = 0; i < 4; i++) { + auto current_segment_name = segment_names[i]; + FLESection current_merged_section; + current_merged_section.has_symbols = false; + size_t section_offset = 0; // 当前段内的偏移量 + segment_vaddr[i] = virtual_address; + + // 遍历每个输入文件 + for (size_t j = 0; j < input_objects.size(); j++) { + auto current_object = input_objects[j]; + for (const auto& section_with_name : current_object.sections) { + auto current_subsection_name = section_with_name.first; + if (!starts_with(current_subsection_name, current_segment_name)) // 处理类似 .rodata.str1.1 的情况 + continue; + + auto current_section = section_with_name.second; + size_t section_size = 0; + + // 获取当前段的大小 + for (const auto& section_header : current_object.shdrs) { + if (section_header.name == current_subsection_name) { + section_size = section_header.size; + break; + } + } + + // 将当前段的数据复制到合并段 + current_merged_section.data.insert(current_merged_section.data.end(), current_section.data.begin(), current_section.data.end()); + + // 合并符号表 + for (auto symbol : current_object.symbols) { + if (symbol.section != current_subsection_name) + continue; + if (symbol.type == SymbolType::LOCAL) // 对本地符号进行重命名 + symbol.name = symbol.name + "@" + current_object.name; + symbol.offset += virtual_address; + + auto existing_symbol = global_symbols.find(symbol.name); + if (existing_symbol == global_symbols.end() || + (existing_symbol->second.type == SymbolType::UNDEFINED && (symbol.type == SymbolType::GLOBAL || symbol.type == SymbolType::WEAK)) || + (existing_symbol->second.type == SymbolType::WEAK && symbol.type == SymbolType::GLOBAL)) { + global_symbols[symbol.name] = symbol; + } + + if (existing_symbol != global_symbols.end() && + existing_symbol->second.type == SymbolType::GLOBAL && + symbol.type == SymbolType::GLOBAL) { + throw std::runtime_error("Multiple definitions of strong symbol: " + symbol.name); + } + current_merged_section.has_symbols = true; + } + + // 合并重定位项 + for (auto reloc : current_section.relocs) { + reloc.offset += section_offset; + if (local_symbol_sets[j].count(reloc.symbol) == 1) // 对本地符号重命名 + reloc.symbol = reloc.symbol + "@" + current_object.name; + current_merged_section.relocs.push_back(reloc); + } + + // 更新当前段偏移量和虚拟地址 + section_offset += section_size; + virtual_address += section_size; + } + } + + // 更新最终的可执行文件中的段 + linked_object.sections[current_segment_name] = current_merged_section; + ProgramHeader header; + header.name = current_segment_name; + header.vaddr = segment_vaddr[i]; + header.size = section_offset; + header.flags = segment_flags[i]; + linked_object.phdrs.push_back(header); + + // 对齐虚拟地址 + virtual_address = (virtual_address + 0xfff) & ~0xfff; + } + + // 3. 处理重定位 + for (int i = 0; i < 4; i++) { + auto section_name = segment_names[i]; + auto& section = linked_object.sections[section_name]; + for (const auto& reloc : section.relocs) { + if (global_symbols.count(reloc.symbol) == 0) { + auto symbol_name = reloc.symbol; + symbol_name = symbol_name.substr(0, symbol_name.find('@')); // 重命名回本地符号 + throw std::runtime_error("Undefined symbol: " + symbol_name); + } + + auto symbol = global_symbols.at(reloc.symbol); + assert(symbol.type != SymbolType::UNDEFINED); + int size = reloc.type == RelocationType::R_X86_64_64 ? 8 : 4; + + symbol.offset -= reloc.type == RelocationType::R_X86_64_PC32 ? segment_vaddr[i] + reloc.offset : 0; + symbol.offset += reloc.addend; + + // 写入重定位值（按小端序存储） + for (int j = 0; j < size; j++) { + section.data[reloc.offset + j] = symbol.offset & 0xff; + symbol.offset >>= 8; + } + } + + // 清空当前段的重定位项 + section.relocs.clear(); + } + + // 4. 设置程序入口点并返回可执行文件 + linked_object.type = ".exe"; + for (const auto& symbol : global_symbols) { + if (symbol.second.name == "_start") { + linked_object.entry = symbol.second.offset; + break; + } + } -FLEObject FLE_ld(const std::vector& objects) -{ - // TODO: 实现链接器 - // 1. 收集和合并段 - // - 遍历所有输入对象的段 - // - 按段名分组并计算偏移量 - // - 设置段的属性（读/写/执行） - - // 2. 处理符号 - // - 收集所有全局符号和局部符号 - // - 处理符号冲突（强符号/弱符号） - - // 3. 重定位 - // - 遍历所有重定位项 - // - 计算并填充重定位值 - // - 注意不同重定位类型的处理 - - // 4. 生成可执行文件 - // - 设置程序入口点（_start） - // - 确保所有必要的段都已正确设置 - - throw std::runtime_error("Not implemented"); -} \ No newline at end of file + return linked_object; +}