Cider Isn't Darwin Emulation, Really
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#include <string>#include <iostream>#include <set>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <elf.h>#include <errno.h>#include <dlfcn.h>#include <sys/mman.h>#include <sstream>#include <stdexcept>#include <fstream>#include <link.h>
#ifndef PATH_MAX# define PATH_MAX 4096#endif
// This is a generator of assembly code for Mach-O// libraries wrapping ELF libraries.
// TODO: use wrapgen32 to generate 32-bit wrappers.
void parse_elf(const char* elf, std::string& soname_out, std::set<std::string>& functions_out, std::set<std::string>& vars_out);void generate_wrapper(std::ofstream& output, const char* soname, const std::set<std::string>& symbols);void generate_var_wrappers(std::ofstream& output, std::ofstream& outputHeader, const std::set<std::string>& vars);Elf64_Off vaddr_to_offset(const Elf64_Ehdr* ehdr, Elf64_Addr vaddr);
int main(int argc, const char** argv){ std::string elfLibrary; std::set<std::string> functions, vars; std::string soname; std::ofstream output;
if (argc != 4) { std::cerr << "Usage: " << argv[0] << " <library-name> <output-file> <var-access-header>\n"; return 1; }
elfLibrary = argv[1]; output.open(argv[2]);
try { if (!output.is_open()) throw std::runtime_error("Cannot open output file");
if (access(elfLibrary.c_str(), R_OK) == -1) { // Try loading the library and then ask the loader where it found the library. // It is simpler than parsing /etc/ld.so.conf.
void* handle = dlopen(elfLibrary.c_str(), RTLD_LAZY | RTLD_LOCAL); struct link_map* lm = NULL;
if (!handle) { std::stringstream ss; ss << "Cannot load " << elfLibrary << ": " << dlerror(); throw std::runtime_error(ss.str()); }
if (dlinfo(handle, RTLD_DI_LINKMAP, &lm) == 0) { elfLibrary = lm->l_name; } else { std::stringstream ss; std::cerr << "Cannot locate " << elfLibrary << ": " << dlerror(); throw std::runtime_error(ss.str()); }
dlclose(handle); }
parse_elf(elfLibrary.c_str(), soname, functions, vars); generate_wrapper(output, soname.c_str(), functions);
if (!vars.empty()) { std::ofstream outputHeader(argv[3]); if (!outputHeader.is_open()) throw std::runtime_error("Cannot open output macro header file");
generate_var_wrappers(output, outputHeader, vars); } } catch (const std::exception& e) { std::cerr << e.what() << std::endl; return 1; }
return 0;}
void parse_elf(const char* elf, std::string& soname, std::set<std::string>& symbols, std::set<std::string>& vars){ int fd; const Elf64_Ehdr* ehdr; const char* strings = NULL; uint64_t length;
fd = open(elf, O_RDONLY); if (fd < 0) { std::stringstream ss; ss << "Error opening " << elf << ": " << strerror(errno); throw std::runtime_error(ss.str()); }
length = lseek(fd, 0, SEEK_END);
ehdr = (Elf64_Ehdr*) mmap(NULL, length, PROT_READ, MAP_SHARED, fd, 0); if (ehdr == MAP_FAILED) { std::stringstream ss; ss << "Cannot mmap ELF file: " << strerror(errno); throw std::runtime_error(ss.str()); }
close(fd);
if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0 || ehdr->e_ident[EI_CLASS] != ELFCLASS64) { std::stringstream ss; ss << elf << " is not a 64-bit ELF"; throw std::runtime_error(ss.str()); }
if (ehdr->e_type != ET_DYN) { std::stringstream ss; ss << elf << " is not a dynamic library ELF"; throw std::runtime_error(ss.str()); }
if (ehdr->e_machine != EM_X86_64) { std::stringstream ss; ss << elf << " is not an ELF for x86-64"; throw std::runtime_error(ss.str()); }
// Now read program headers, find a PT_DYNAMIC segment type for (int i = 0; i < ehdr->e_phnum; i++) { const Elf64_Phdr* phdr;
phdr = (const Elf64_Phdr*) (((char*) ehdr) + ehdr->e_phoff + (i * ehdr->e_phentsize));
if (phdr->p_type == PT_DYNAMIC) { Elf64_Xword off_strtab, off_soname;
off_strtab = off_soname = 0;
for (int j = 0; j < phdr->p_filesz; j += sizeof(Elf64_Dyn)) { const Elf64_Dyn* dyn;
dyn = (const Elf64_Dyn*) (((char*) ehdr) + phdr->p_offset + j); switch (dyn->d_tag) { case DT_STRTAB: off_strtab = vaddr_to_offset(ehdr, dyn->d_un.d_val); break; case DT_SONAME: off_soname = vaddr_to_offset(ehdr, dyn->d_un.d_val); break; case DT_NULL: goto end_dyn; } }end_dyn:
if (off_strtab != 0) { strings = (const char*) ((char*) ehdr) + off_strtab;
if (off_soname != 0) { // Read DT_SONAME value from the string table soname = strings + off_soname; } }
break; } }
if (strings != NULL) { // Load symbol list const Elf64_Shdr* shdr;
for (int i = 0; i < ehdr->e_shnum; i++) { shdr = (const Elf64_Shdr*) (((char*) ehdr) + ehdr->e_shoff + (i * ehdr->e_shentsize)); if (shdr->sh_type == SHT_DYNSYM) { for (int j = 0; j < shdr->sh_size; j += sizeof(Elf64_Sym)) { const Elf64_Sym* sym;
sym = (const Elf64_Sym*) (((char*) ehdr) + shdr->sh_offset + j);
if (ELF64_ST_TYPE(sym->st_info) != STT_OBJECT && ELF64_ST_TYPE(sym->st_info) != STT_FUNC) continue; if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL) continue; if (sym->st_shndx == SHN_UNDEF || sym->st_value == 0) continue; if (ELF64_ST_VISIBILITY(sym->st_other) != STV_DEFAULT) continue;
if (ELF64_ST_TYPE(sym->st_info) == STT_FUNC) symbols.insert(strings + sym->st_name); else vars.insert(strings + sym->st_name); }
break; } } }
if (soname.empty()) { std::cerr << "WARNING: No DT_SONAME in " << elf << ".\n";
const char* slash = strrchr(elf, '/'); if (slash != NULL) soname = slash + 1; else soname = elf; } if (symbols.empty()) { std::stringstream ss; ss << "No symbols found in " << elf; throw std::runtime_error(ss.str()); }
munmap((void*) ehdr, length);}
void generate_wrapper(std::ofstream& output, const char* soname, const std::set<std::string>& symbols){ output << "#include <elfcalls.h>\n" "extern struct elf_calls* _elfcalls;\n\n" "extern const char __elfname[];\n\n";
output << "static void* lib_handle;\n" "__attribute__((constructor)) static void initializer() {\n" "\tlib_handle = _elfcalls->dlopen_fatal(__elfname);\n" "}\n\n";
output << "__attribute__((destructor)) static void destructor() {\n" "\t_elfcalls->dlclose_fatal(lib_handle);\n" "}\n\n"; for (const std::string& sym : symbols) { output << "void* " << sym << "() {\n" "\t__asm__(\".symbol_resolver _" << sym << "\");\n" "\treturn _elfcalls->dlsym_fatal(lib_handle, \"" << sym << "\");\n" "}\n\n"; } output << "asm(\".section __TEXT,__elfname\\n" ".private_extern ___elfname\\n" "___elfname: .asciz \\\"" << soname << "\\\"\");\n";}
void generate_var_wrappers(std::ofstream& output, std::ofstream& outputHeader, const std::set<std::string>& vars){ outputHeader << "#pragma once\n\n"; outputHeader << "#ifdef __cplusplus\n" "extern \"C\" {\n" "#endif\n\n";
for (const std::string& sym : vars) { output << "void* __elf_get_" << sym << "(void) {\n" "\treturn _elfcalls->dlsym_fatal(lib_handle, \"" << sym << "\");\n" "}\n\n"; outputHeader << "extern __typeof(" << sym << ")* __elf_get_" << sym << "(void);\n" "#define " << sym << " (*__elf_get_" << sym << "())\n\n"; }
outputHeader << "\n\n#ifdef __cplusplus\n" "}\n" "#endif\n\n";}
Elf64_Off vaddr_to_offset(const Elf64_Ehdr* ehdr, Elf64_Xword vaddr){ for (int i = 0; i < ehdr->e_phnum; i++) { const Elf64_Phdr* phdr; Elf64_Addr vstart, vend;
phdr = (const Elf64_Phdr*) (((char*) ehdr) + ehdr->e_phoff + (i * ehdr->e_phentsize)); vstart = phdr->p_vaddr; vend = phdr->p_vaddr + phdr->p_memsz; if (vstart <= vaddr && vaddr < vend) { return phdr->p_offset + vaddr - vstart; } }
return 0;}