/* From http://www.hanshq.net/making-executables.html */ #include #include #include #include static const uint8_t rot13_program[] = { /* read: */ 0xb8,0x03,0x00,0x00,0x00, /* movl $3,%eax */ 0x31,0xdb, /* xorl %ebx,%ebx */ 0xb9,0x00,0xa0,0x04,0x08, /* movl $buffer,%ecx */ 0xba,0x00,0x10,0x00,0x00, /* movl $4096,%edx */ 0xcd,0x80, /* int $0x80 */ 0x85,0xc0, /* testl %eax,%eax */ 0x7e,0x21, /* jle end */ 0x89,0xc2, /* movl %eax,%edx */ /* rot13: */ 0x0f,0xb6,0x19, /* movzbl (%ecx),%ebx */ 0x8a,0x9b,0x00,0x90,0x04,0x08, /* movb rot13_table(%ebx),%bl */ 0x88,0x19, /* movb %bl,(%ecx) */ 0x41, /* incl %ecx */ 0x48, /* decl %eax */ 0x75,0xf1, /* jnz rot13 */ 0xb8,0x04,0x00,0x00,0x00, /* movl $4,%eax */ 0xbb,0x01,0x00,0x00,0x00, /* movl $1,%ebx */ 0x29,0xd1, /* subl %edx,%ecx */ 0xcd,0x80, /* int $0x80 */ 0xeb,0xc8, /* jmp read */ /* end: */ 0xb8,0x01,0x00,0x00,0x00, /* movl $1,%eax */ 0x31,0xdb, /* xorl %ebx,%ebx */ 0xcd,0x80 /* int $0x80 */ }; static const uint8_t rot13_table[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 91, 92, 93, 94, 95, 96, 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255 }; /* Write an 8-bit value to file. */ static void write8(FILE *file, uint8_t value) { if (fputc(value, file) == EOF) { perror("fputc"); exit(1); } } /* Write a 16-bit value in little-endian to file. */ static void write16(FILE *file, uint16_t value) { write8(file, (value >> 0) & 0xff); write8(file, (value >> 8) & 0xff); } /* Write a 32-bit value in little-endian to file. */ static void write32(FILE *file, uint32_t value) { write8(file, (value >> 0) & 0xff); write8(file, (value >> 8) & 0xff); write8(file, (value >> 16) & 0xff); write8(file, (value >> 24) & 0xff); } /* Seek to offset in file. */ static void seek(FILE *file, long offset) { if (fseek(file, offset, SEEK_SET) == -1) { perror("fseek"); exit(1); } } #define TEXT_ADDR 0x08048000 #define RDATA_ADDR 0x08049000 #define BSS_ADDR 0x0804a000 #define TEXT_SIZE sizeof(rot13_program) #define RDATA_SIZE sizeof(rot13_table) #define BSS_SIZE 4096 #define EHSIZE 52 /* ELF header size. */ #define PHSIZE 32 /* Program header size. */ #define PAGE_SIZE 4096 /* Round value up to alignment. */ static uint32_t align_to(uint32_t value, uint32_t alignment) { uint32_t remainder = value % alignment; if (remainder == 0) { return value; } return value + (alignment - remainder); } int main(int argc, char **argv) { FILE *f; size_t i; if (argc != 2) { fprintf(stderr, "Usage: %s \n", argv[0]); exit(1); } f = fopen(argv[1], "wb"); if (f == NULL) { perror("fopen"); exit(1); } /* ELF header. */ write8(f, 0x7f); /* EI_MAG0 */ write8(f, 'E'); /* EI_MAG1 */ write8(f, 'L'); /* EI_MAG2 */ write8(f, 'F'); /* EI_MAG3 */ write8(f, 1); /* EI_CLASS: 32-bit */ write8(f, 1); /* EI_DATA: Little-endian */ write8(f, 1); /* EI_VERSION: Current */ write8(f, 0); /* EI_OSABI: No extensions */ write8(f, 0); /* EI_ABIVERSION */ write8(f, 0); /* EI_PAD ... (7 bytes) */ write8(f, 0); write8(f, 0); write8(f, 0); write8(f, 0); write8(f, 0); write8(f, 0); /* ELF header (continued). */ write16(f, 2); /* e_type: ET_EXEC */ write16(f, 3); /* e_machine: EM_386 */ write32(f, 1); /* e_version: EV_CURRENT */ write32(f, TEXT_ADDR); /* e_entry */ write32(f, EHSIZE); /* e_phoff */ write32(f, 0); /* e_shoff */ write32(f, 0); /* e_flags */ write16(f, EHSIZE); /* e_ehsize */ write16(f, PHSIZE); /* e_phentsize */ write16(f, 3); /* e_phnum */ write16(f, 40); /* e_shentsize */ write16(f, 0); /* e_shnum */ write16(f, 0); /* e_shstrndx */ assert(RDATA_ADDR - TEXT_ADDR >= TEXT_SIZE); assert(BSS_ADDR - RDATA_ADDR >= RDATA_SIZE); uint32_t text_offset = align_to(EHSIZE + 3 * PHSIZE, PAGE_SIZE); uint32_t rdata_offset = align_to(text_offset + TEXT_SIZE, PAGE_SIZE); /* Program header 1 (TEXT). */ write32(f, 1); /* p_type: PT_LOAD */ write32(f, text_offset); /* p_offset */ write32(f, TEXT_ADDR); /* p_vaddr */ write32(f, 0); /* p_paddr */ write32(f, TEXT_SIZE); /* p_filesz */ write32(f, TEXT_SIZE); /* p_memsz */ write32(f, 0x4 | 0x1); /* p_flags: PF_R | PF_X */ write32(f, PAGE_SIZE); /* p_align */ /* Program header 2 (RDATA). */ write32(f, 1); /* p_type: PT_LOAD */ write32(f, rdata_offset); /* p_offset */ write32(f, RDATA_ADDR); /* p_vaddr */ write32(f, 0); /* p_paddr */ write32(f, RDATA_SIZE); /* p_filesz */ write32(f, RDATA_SIZE); /* p_memsz */ write32(f, 0x4); /* p_flags: PF_R */ write32(f, PAGE_SIZE); /* p_align */ /* Program header 3 (BSS). */ write32(f, 1); /* p_type: PT_LOAD */ write32(f, 0); /* p_offset */ write32(f, BSS_ADDR); /* p_vaddr */ write32(f, 0); /* p_paddr */ write32(f, 0); /* p_filesz */ write32(f, BSS_SIZE); /* p_memsz */ write32(f, 0x4 | 0x2); /* p_flags: PF_R | PF_W */ write32(f, PAGE_SIZE); /* p_align */ /* Write the TEXT segment. */ seek(f, text_offset); for (i = 0; i < sizeof(rot13_program); i++) { write8(f, rot13_program[i]); } /* Write the RDATA segment. */ seek(f, rdata_offset); for (i = 0; i < sizeof(rot13_table); i++) { write8(f, rot13_table[i]); } if (fclose(f) == EOF) { perror("fclose"); exit(1); } return 0; }