# Assign addresses (co-ordinates) to instructions (landmarks) in a program # (landscape). # Use the addresses assigned to: # a) replace labels # b) add segment headers containing the initial address # # To build (from the subx/ directory): # $ ./subx translate *.subx apps/survey.subx -o apps/survey # # The expected input is a stream of bytes with segment headers, comments and # some interspersed labels. # $ cat x # == code 0x1 # l1: # aa bb l1/imm8 # cc dd l2/disp32 # l2: # ee foo/imm32 # == data 0x10 # foo: # 00 # # The output is the stream of bytes without segment headers or label definitions, # and with label references replaced with numeric values/displacements. # # $ cat x |./subx run apps/assort # ...ELF header bytes... # # ELF header above will specify that code segment begins at this offset # aa bb nn # some computed address # cc dd nn nn nn nn # some computed displacement # ee nn nn nn nn # some computed address # # ELF header above will specify that data segment begins at this offset # 00 == code # instruction effective address register displacement immediate # . op subop mod rm32 base index scale r32 # . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes Entry: # initialize heap # . Heap = new-segment(64KB) # . . push args 68/push Heap/imm32 68/push 0x10000/imm32/64KB # . . call e8/call new-segment/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # for debugging: run a single test #? e8/call test-convert/disp32 #? 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX #? eb/jump $main:end/disp8 # run tests if necessary, convert stdin if not # . prolog 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP # initialize heap # - if argc > 1 and argv[1] == "test", then return run_tests() # . argc > 1 81 7/subop/compare 1/mod/*+disp8 5/rm32/EBP . . . . 0/disp8 1/imm32 # compare *EBP 7e/jump-if-lesser-or-equal $run-main/disp8 # . argv[1] == "test" # . . push args 68/push "test"/imm32 ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 8/disp8 . # push *(EBP+8) # . . call e8/call kernel-string-equal?/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # . check result 3d/compare-EAX-and 1/imm32 75/jump-if-not-equal $run-main/disp8 # . run-tests() e8/call run-tests/disp32 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX eb/jump $main:end/disp8 $run-main: # - otherwise convert stdin # var ed/EAX : exit-descriptor 81 5/subop/subtract 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # subtract from ESP 89/copy 3/mod/direct 0/rm32/EAX . . . 4/r32/ESP . . # copy ESP to EAX # configure ed to really exit() # . ed->target = 0 c7 0/subop/copy 0/mod/direct 0/rm32/EAX . . . . . 0/imm32 # copy to *EAX # return convert(Stdin, 1/stdout, 2/stderr, ed) # . . push args 50/push-EAX/ed 68/push Stderr/imm32 68/push Stdout/imm32 68/push Stdin/imm32 # . . call e8/call convert/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0x10/imm32 # add to ESP # . syscall(exit, 0) bb/copy-to-EBX 0/imm32 $main:end: b8/copy-to-EAX 1/imm32/exit cd/syscall 0x80/imm8 convert: # in : (address buffered-file), out : (address buffered-file) -> # . prolog 55/push-EBP 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP # . save registers $convert:end: # . reclaim locals # . restore registers # . epilog 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP 5d/pop-to-EBP c3/return ## helpers == data Segment-size: 0x1000/imm32/4KB # This block of bytes gets copied to the start of the output ELF file, with # some fields filled in. # http://www.sco.com/developers/gabi/latest/ch4.eheader.html Elf_header: # - length 0x34/imm32 # - data $e_ident: 7f 45/E 4c/L 46/F 01/32-bit 01/little-endian 01/file-version 00/no-os-extensions 00 00 00 00 00 00 00 00 # 8 bytes of padding $e_type: 02 00 $e_machine: 03 00 $e_version: 1/imm32 Elf_e_entry: 0x09000000/imm32 # approximate default; must be updated $e_phoff: 0x34/imm32 # offset for the 'program header table' containing segment headers $e_shoff: 0/imm32 # no sections $e_flags: 0/imm32 # unused $e_ehsize: 0x34 00 $e_phentsize: 0x20 00 Elf_e_phnum: 00 00 # number of segments; must be updated $e_shentsize: 00 00 # no sections $e_shnum: 00 00 $e_shstrndx: 00 00 # This block of bytes gets copied after the Elf_header once for each segment. # Some fields need filling in each time. # https://docs.oracle.com/cd/E19683-01/816-1386/chapter6-83432/index.html Elf_program_header_entry: # - length 0x20/imm32 # - data $p_type: 1/imm32/PT_LOAD Elf_p_offset: 0/imm32 # byte offset in the file at which a segment begins; must be updated Elf_p_vaddr: 0/imm32 # starting address to store the segment at before running the program Elf_p_paddr: 0/imm32 # should have same value as Elf_p_vaddr Elf_p_filesz: 0/imm32 Elf_p_memsz: 0/imm32 # should have same value as Elf_p_filesz Elf_p_flags: 6/imm32/rw- # read/write/execute permissions for the segment; must be updated for the code segment Elf_p_align: # we hold this constant; changing it will require adjusting the way we # compute the starting address for each segment 0x1000/imm32 # . . vim:nowrap:textwidth=0