diff options
| -rw-r--r-- | elf.cpp | 69 | ||||
| -rw-r--r-- | elf.h | 14 | ||||
| -rw-r--r-- | test-elf.cpp | 2 |
3 files changed, 72 insertions, 13 deletions
@@ -2,17 +2,25 @@ #include "file.h" +// TODO //#include <boost/endian/conversion.hpp> #include <cstring> +// We need at least 4096 bytes aligment. Otherwise we get segfaults at startup +#define PAD 0x1000 + // Helper Functions namespace { void AddFileHeader(std::vector<uint8_t>& data, const std::vector<uint8_t>& code) { Elf::FileHeader fh; - fh.e_shoff = sizeof(fh) + sizeof(Elf::ProgramHeader) + code.size() + 16; +#ifdef PAD + fh.e_shoff = PAD + code.size() + 17; +#else + fh.e_shoff = sizeof(fh) + sizeof(Elf::ProgramHeader) + code.size() + 17; +#endif size_t old_size {data.size()}; data.resize(old_size + sizeof(fh)); @@ -23,7 +31,12 @@ namespace { { Elf::ProgramHeader ph; +#ifdef PAD + ph.p_offset = PAD; + ph.p_align = PAD; +#else ph.p_offset = sizeof(Elf::FileHeader) + sizeof(Elf::ProgramHeader); +#endif ph.p_filesz = code.size(); ph.p_memsz = code.size(); @@ -32,13 +45,35 @@ namespace { std::memcpy(data.data() + old_size, reinterpret_cast<void*>(&ph), sizeof(ph)); } - void AddSectionHeaderText(std::vector<uint8_t>& data, const std::vector<uint8_t>& code) + void AddSectionHeaderNull(std::vector<uint8_t>& data, const std::vector<uint8_t>& code) { Elf::SectionHeader sh; sh.sh_name = 0; // offset in section + sh.sh_size = 0; + sh.sh_type = 0; // <null> + sh.sh_flags = 0; + sh.sh_addr = 0; + sh.sh_offset = 0; + + size_t old_size {data.size()}; + data.resize(old_size + sizeof(sh)); + std::memcpy(data.data() + old_size, reinterpret_cast<void*>(&sh), sizeof(sh)); + } + + void AddSectionHeaderText(std::vector<uint8_t>& data, const std::vector<uint8_t>& code) + { + Elf::SectionHeader sh; + + sh.sh_name = 1; // offset in section sh.sh_size = code.size(); sh.sh_type = 1; // program +#ifdef PAD + sh.sh_offset = PAD; +#else + sh.sh_offset = sizeof(Elf::FileHeader) + sizeof(Elf::ProgramHeader); +#endif + sh.sh_addralign = 1; size_t old_size {data.size()}; data.resize(old_size + sizeof(sh)); @@ -49,15 +84,30 @@ namespace { { Elf::SectionHeader sh; - sh.sh_name = 0; // offset in section - sh.sh_size = 16; + sh.sh_name = 7; // offset in section + sh.sh_size = 17; sh.sh_type = 3; // section names sh.sh_flags = 0; + sh.sh_addr = 0; +#ifdef PAD + sh.sh_offset = PAD + code.size(); +#else + sh.sh_offset = sizeof(Elf::FileHeader) + sizeof(Elf::ProgramHeader) + code.size(); +#endif + sh.sh_addralign = 1; size_t old_size {data.size()}; data.resize(old_size + sizeof(sh)); std::memcpy(data.data() + old_size, reinterpret_cast<void*>(&sh), sizeof(sh)); } + + void PadUpTo(std::vector<uint8_t>& data, size_t size) + { + if (data.size() < size) { + data.resize(size); + } else + throw std::runtime_error("Padding not possible. Too many bytes already."); + } } void Elf::Write(const std::filesystem::path& path, const std::vector<uint8_t>& code) @@ -67,13 +117,21 @@ void Elf::Write(const std::filesystem::path& path, const std::vector<uint8_t>& c AddFileHeader(data, code); AddProgramHeader(data, code); +#ifdef PAD + PadUpTo(data, PAD); +#endif + data.insert(data.end(), code.begin(), code.end()); - std::string section_names(".text\0.shstrtab\0", 16); + std::string section_names("\0.text\0.shstrtab\0", 17); + if (section_names.size() != 17) + throw std::runtime_error("Bad size"); + size_t old_size {data.size()}; data.resize(old_size + section_names.size()); std::memcpy(data.data() + old_size, section_names.data(), section_names.size()); + AddSectionHeaderNull(data, code); AddSectionHeaderText(data, code); AddSectionHeaderSectionNames(data, code); @@ -88,3 +146,4 @@ std::vector<uint8_t> Elf::Read(const std::filesystem::path& path) return result; } + @@ -29,7 +29,7 @@ struct FileHeader 2, // 64 bit 1, // little endian 1, // Version: default == 1 - 3, // Linux + 0, // SysV, 3=Linux 0, // EI_ABIVERSION 0,0,0,0,0,0,0 // pad }; @@ -39,13 +39,13 @@ struct FileHeader uint64_t e_entry{0x0000000000401000}; uint64_t e_phoff{0x40}; uint64_t e_shoff{}; // section header table offset - uint32_t e_flags{0x00000112}; // EXEC_P, HAS_SYMS, D_PAGED + uint32_t e_flags{}; uint16_t e_ehsize{0x40}; // size of this header uint16_t e_phentsize{0x38}; // size of program header uint16_t e_phnum{1}; // 1 program header uint16_t e_shentsize{0x40}; // size of section header - uint16_t e_shnum{2}; // number of section headers - uint16_t e_shstrndx{1}; // 1st section header contains section names + uint16_t e_shnum{3}; // number of section headers + uint16_t e_shstrndx{2}; // 1st section header contains section names }; // Segment @@ -53,12 +53,12 @@ struct ProgramHeader { uint32_t p_type{1}; // Loadable segment uint32_t p_flags{5}; // X=1 | W=2 | R=4 - uint64_t p_offset{0x0}; // offset in file + uint64_t p_offset{}; // offset in file uint64_t p_vaddr{0x401000}; // virtual address uint64_t p_paddr{0x401000}; // physical address, not really relevant uint64_t p_filesz{}; // size of segment in file, e.g. size of code uint64_t p_memsz{}; // size of segment in memory - uint64_t p_align{0}; // alignment + uint64_t p_align{}; // alignment }; struct SectionHeader @@ -67,7 +67,7 @@ struct SectionHeader uint32_t sh_type{1}; // program data uint64_t sh_flags{6}; // ALLOC, EXE uint64_t sh_addr{0x401000}; // virtual address - uint64_t sh_offset{0x1000}; + uint64_t sh_offset{}; uint64_t sh_size{}; // section size uint32_t sh_link{}; uint32_t sh_info{}; diff --git a/test-elf.cpp b/test-elf.cpp index dba220e..d3fa9a9 100644 --- a/test-elf.cpp +++ b/test-elf.cpp @@ -49,7 +49,7 @@ TEST_F(ElfTest, write) { { 0x48, 0xc7, 0xc0, 0x3c, 0x00, 0x00, 0x00, // mov $0x3c,%rax # syscall 60 0x48, 0x31, 0xff, // xor %rdi,%rdi # exit code 0 - 0x0f, 0x05 // syscall + 0x0f, 0x05, // syscall }); ASSERT_TRUE(fs::exists(TempFilename())); |