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# 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) -> <void>
# . 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
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