diff options
Diffstat (limited to 'tools/elf/elfkill.cpp')
| -rw-r--r-- | tools/elf/elfkill.cpp | 293 |
1 files changed, 293 insertions, 0 deletions
diff --git a/tools/elf/elfkill.cpp b/tools/elf/elfkill.cpp new file mode 100644 index 00000000..da4d77d1 --- /dev/null +++ b/tools/elf/elfkill.cpp @@ -0,0 +1,293 @@ +#include <iostream> // cout, cerr, endl +#include <iomanip> // setw +#include <vector> // vector +#include <string> // string +#include <unordered_set> // unordered_set +#include <cstring> // strcmp, strncpy +#include <fstream> // ifstream +#include <cstdio> // remove + +#include <elfio/elfio.hpp> +#include <elfio/elfio_dump.hpp> + +#define VERSION "1.0" + +using namespace ELFIO; + +struct SymbolSection { + Elf_Half index; + section *elfSection; + std::string name; + + bool Get(const elfio &elf, Elf_Half index) { + this->index = index; + + elfSection = elf.sections[index]; + if (elfSection == nullptr) { + std::cerr << "Failed to get section " << index << std::endl; + return false; + } + + name = elfSection->get_name(); + return true; + } + + bool SetName(const elfio &elf, const std::string &name) { + elfSection->set_name(name); + this->name = name; + + Elf_Word nameIndex = elfSection->get_name_string_offset(); + + section *shstrtab = elf.sections[".shstrtab"]; + if (shstrtab == nullptr) { + std::cerr << "Failed to get string section" << std::endl; + return false; + } + + string_section_accessor strAccessor(shstrtab); + const char *tabStr = strAccessor.get_string(nameIndex); + size_t len = strlen(tabStr); + + if (len < name.length()) { + std::cerr << "Cannot rename section " << tabStr << " because it is shorter than " << name << std::endl; + return false; + } + + // HACK: Strings shorter than `name` can't be renamed due to lack of space + strncpy((char*) tabStr, name.c_str(), len); + return true; + } +}; + +struct Symbol { + Elf_Xword index; + std::string name; + Elf64_Addr value; + Elf_Xword size; + unsigned char bind; + unsigned char type; + SymbolSection section; + unsigned char other; + + bool Get(const elfio &elf, const symbol_section_accessor &accessor, Elf_Xword index) { + this->index = index; + + if (!accessor.get_symbol(index, name, value, size, bind, type, section.index, other)) { + std::cerr << "Failed to get symbol at index " << index << std::endl; + return false; + } + + if (!section.Get(elf, section.index)) { + std::cerr << "...for symbol '" << name << "'" << std::endl; + return false; + } + + return true; + } + + static void PrintHeader() { + std::cout + << std::setw(75) << "name" + << std::setw(6) << "value" + << std::setw(6) << "size" + << std::setw(5) << "bind" + << std::setw(5) << "type" + << std::setw(8) << "section" + << std::setw(12) << "" + << std::setw(6) << "other" + << std::endl; + } + + void Print() const { + std::cout + << std::setw(75) << name + << std::setw(6) << value + << std::setw(6) << size + << std::setw(5) << (int) bind + << std::setw(5) << (int) type + << std::setw(5) << section.index << ' ' + << std::setw(14) << std::left << section.name << std::right + << std::setw(6) << (int) other + << std::endl; + } +}; + +bool GetFunctionSymbols(const elfio &elf, std::vector<Symbol> &outSymbols) { + section *symtab = elf.sections[".symtab"]; + if (symtab == nullptr) { + std::cerr << "No section called .symtab" << std::endl; + return false; + } + + symbol_section_accessor symAccessor(elf, symtab); + std::vector<Symbol> symbols; + for (Elf_Xword i = 0; i < symAccessor.get_symbols_num(); ++i) { + Symbol symbol; + if (!symbol.Get(elf, symAccessor, i)) return false; + + if (symbol.name.find("@", 0) == 0) continue; + if (symbol.name.find("$", 0) == 0) continue; + if (symbol.name.find(".", 0) == 0) continue; + if (symbol.section.name != ".text") continue; + + symbols.push_back(symbol); + } + + outSymbols = symbols; + return true; +} + +bool FindSymbolsToKill(const char *srcFile, std::unordered_set<std::string> &outSymbolsToKill) { + std::ifstream file(srcFile); + + const std::string killMacro = "KILL("; + std::string line; + size_t row = 0; + std::unordered_set<std::string> symbolsToKill; + while (std::getline(file, line)) { + row += 1; + size_t endOffset = 0; + while (true) { + size_t macroOffset = line.find(killMacro, endOffset); + if (macroOffset == std::string::npos) break; + + size_t symbolOffset = macroOffset + killMacro.length(); + symbolOffset = line.find_first_not_of(" \t", symbolOffset); + if (symbolOffset == std::string::npos) { + std::cerr + << srcFile << ':' << row << ':' << macroOffset + 1 + << ": Expected non-whitespace character after " << killMacro << std::endl; + return false; + } + + endOffset = line.find_first_of(" \t)", symbolOffset); + if (endOffset == std::string::npos) { + std::cerr + << srcFile << ':' << row << ':' << symbolOffset + 1 + << ": Expected whitespace character or ')' after kill symbol" << std::endl; + return false; + } + + std::string symbolToKill = line.substr(symbolOffset, endOffset - symbolOffset); + symbolsToKill.insert(symbolToKill); + } + } + + file.close(); + outSymbolsToKill = symbolsToKill; + return true; +} + +bool KillFunctionSymbols( + const elfio &elf, + std::vector<Symbol> &symbols, + std::unordered_set<std::string> &symbolsToKill, + const char *srcFile +) { + for (Symbol &symbol : symbols) { + auto it = symbolsToKill.find(symbol.name); + if (it == symbolsToKill.end()) continue; + + if (!symbol.section.SetName(elf, ".dead")) return false; + symbolsToKill.erase(it); + } + + if (symbolsToKill.empty()) return true; + + std::cerr << srcFile << ": the following functions couldn't be killed because they do not exist:\n"; + for (const std::string &symbolToKill : symbolsToKill) { + std::cerr << " " << symbolToKill << '\n'; + } + std::cerr << std::endl; + return false; +} + +bool DeleteElf(const char *elfFile) { + // Delete ELF file so the Makefile doesn't skip elfkill on next build + if (std::remove(elfFile) == 0) return true; + std::cerr << "Failed to delete ELF '" << elfFile << "' upon previous error" << std::endl; + return false; +} + +void PrintUsage(const char *program) { + std::cout + << "elfkill " VERSION "\n" + << "\n" + << "Usage: " << program << " -s SRCFILE -e ELFFILE\n" + << " -s SRCFILE\tSource C/C++ file\n" + << " -e ELFFILE\tELF file corresponding to SRCFILE\n" + << std::endl; +} + +int main(int argc, const char **argv) { + const char *program = argv[0]; + if (argc == 1) { + PrintUsage(program); + return 0; + } + const char *srcFile = nullptr; + const char *elfFile = nullptr; + for (int i = 1; i < argc; ++i) { + if (strcmp(argv[i], "-s") == 0) { + if (++i >= argc) { + std::cerr << "Expected filename after -s" << std::endl; + return 1; + } + srcFile = argv[i]; + } else if (strcmp(argv[i], "-e") == 0) { + if (++i >= argc) { + std::cerr << "Expected filename after -e" << std::endl; + return 1; + } + elfFile = argv[i]; + } else { + std::cerr << "Unknown option '" << argv[i] << "'" << std::endl; + return 1; + } + } + if (srcFile == nullptr) { + PrintUsage(program); + std::cerr << "Please provide a source file, see usage above" << std::endl; + return 1; + } + if (elfFile == nullptr) { + PrintUsage(program); + std::cerr << "Please provide an ELF file, see usage above" << std::endl; + return 1; + } + + elfio elf; + if (!elf.load(elfFile)) { + std::cerr << "Failed to load ELF file '" << elfFile << "'" << std::endl; + return 1; + } + + std::vector<Symbol> symbols; + if (!GetFunctionSymbols(elf, symbols)) { + DeleteElf(elfFile); + return 1; + } + + // Symbol::PrintHeader(); + // for (const Symbol &symbol : symbols) { + // symbol.Print(); + // } + // return 0; + + std::unordered_set<std::string> symbolsToKill; + if (!FindSymbolsToKill(srcFile, symbolsToKill)) { + DeleteElf(elfFile); + return 1; + } + if (!KillFunctionSymbols(elf, symbols, symbolsToKill, srcFile)) { + DeleteElf(elfFile); + return 1; + } + + // Symbol::PrintHeader(); + // for (const Symbol &symbol : symbols) { + // symbol.Print(); + // } + + elf.save(elfFile); +} |