Update ld.cpp

src/student/ld.cpp

@@ -1,30 +1,151 @@
-#include "fle.hpp"
 #include <cassert>
 #include <iostream>
 #include <map>
+#include <set>
 #include <stdexcept>
 #include <vector>
+#include "fle.hpp"
+#include "string_utils.hpp"
+
+FLEObject FLE_ld(const std::vector<FLEObject>& 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<std::set<std::string>>();  // 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<std::string>());
+        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<std::string, Symbol>();
+    auto segment_names = std::vector<std::string>{".text", ".rodata", ".data", ".bss"};
+    auto segment_flags = std::vector<uint32_t>{5, 4, 6, 6};  // 设置段的权限标志
+    auto segment_vaddr = std::vector<size_t>(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<FLEObject>& 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");
-}
+    return linked_object;
+}