298 lines
13 KiB
Plaintext
298 lines
13 KiB
Plaintext
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# Assign addresses (co-ordinates) to instructions (landmarks) in a program
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# (landscape).
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# Use the addresses assigned to:
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# a) replace labels
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# b) add segment headers containing the initial address
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#
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# To build (from the subx/ directory):
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# $ ./subx translate *.subx apps/survey.subx -o apps/survey
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#
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# The expected input is a stream of bytes with segment headers, comments and
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# some interspersed labels.
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# $ cat x
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# == code 0x1
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# l1:
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# aa bb l1/imm8
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# cc dd l2/disp32
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# l2:
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# ee foo/imm32
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# == data 0x10
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# foo:
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# 00
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#
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# The output is the stream of bytes without segment headers or label definitions,
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# and with label references replaced with numeric values/displacements.
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#
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# $ cat x |./subx run apps/assort
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# ...ELF header bytes...
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# # ELF header above will specify that code segment begins at this offset
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# aa bb nn # some computed address
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# cc dd nn nn nn nn # some computed displacement
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# ee nn nn nn nn # some computed address
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# # ELF header above will specify that data segment begins at this offset
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# 00
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== code
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# instruction effective address register displacement immediate
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# . op subop mod rm32 base index scale r32
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# . 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
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Entry:
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# initialize heap
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# . Heap = new-segment(64KB)
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# . . push args
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68/push Heap/imm32
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68/push 0x10000/imm32/64KB
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# . . call
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e8/call new-segment/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# for debugging: run a single test
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#? e8/call test-convert/disp32
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#? 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX
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#? eb/jump $main:end/disp8
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# run tests if necessary, convert stdin if not
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# . prolog
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89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
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# initialize heap
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# - if argc > 1 and argv[1] == "test", then return run_tests()
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# . argc > 1
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81 7/subop/compare 1/mod/*+disp8 5/rm32/EBP . . . . 0/disp8 1/imm32 # compare *EBP
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7e/jump-if-lesser-or-equal $run-main/disp8
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# . argv[1] == "test"
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# . . push args
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68/push "test"/imm32
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ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 8/disp8 . # push *(EBP+8)
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# . . call
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e8/call kernel-string-equal?/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# . check result
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3d/compare-EAX-and 1/imm32
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75/jump-if-not-equal $run-main/disp8
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# . run-tests()
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e8/call run-tests/disp32
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8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX
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eb/jump $main:end/disp8
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$run-main:
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# - otherwise convert stdin
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# var ed/EAX : exit-descriptor
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81 5/subop/subtract 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # subtract from ESP
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89/copy 3/mod/direct 0/rm32/EAX . . . 4/r32/ESP . . # copy ESP to EAX
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# configure ed to really exit()
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# . ed->target = 0
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c7 0/subop/copy 0/mod/direct 0/rm32/EAX . . . . . 0/imm32 # copy to *EAX
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# return convert(Stdin, 1/stdout, 2/stderr, ed)
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# . . push args
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50/push-EAX/ed
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68/push Stderr/imm32
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68/push Stdout/imm32
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68/push Stdin/imm32
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# . . call
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e8/call convert/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0x10/imm32 # add to ESP
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# . syscall(exit, 0)
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bb/copy-to-EBX 0/imm32
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$main:end:
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b8/copy-to-EAX 1/imm32/exit
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cd/syscall 0x80/imm8
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convert: # in : (address buffered-file), out : (address buffered-file) -> <void>
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# . prolog
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55/push-EBP
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89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
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# . save registers
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$convert:end:
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# . reclaim locals
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# . restore registers
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# . epilog
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89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
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5d/pop-to-EBP
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c3/return
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## helpers
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# TODO: pass in an allocation descriptor
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get-or-insert-segment: # table : (address stream row), s : (address slice), n : int -> EAX : (address stream)
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# pseudocode:
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# curr = table->data
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# max = &table->data[table->write]
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# while curr < max
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# if slice-equal?(s, *curr)
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# return *(curr+4)
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# curr += 8
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# if table->write < table->length
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# *max = slice-to-string(Heap, s)
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# result = new-stream(Heap, n, 1)
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# *(max+4) = result
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# table->write += 8
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# return result
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# return 0
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#
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# . prolog
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55/push-EBP
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89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
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# . save registers
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51/push-ECX
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52/push-EDX
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56/push-ESI
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# ESI = table
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8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 6/r32/ESI 8/disp8 . # copy *(EBP+8) to ESI
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# curr/ECX = table->data
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8d/copy-address 1/mod/*+disp8 6/rm32/ESI . . . 1/r32/ECX 0xc/disp8 . # copy ESI+12 to ECX
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# max/EDX = table->data + table->write
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8b/copy 0/mod/indirect 6/rm32/ESI . . . 2/r32/EDX . . # copy *ESI to EDX
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8d/copy-address 0/mod/indirect 4/rm32/sib 1/base/ECX 2/index/EDX . 2/r32/EDX . . # copy ECX+EDX to EDX
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$get-or-insert-segment:search-loop:
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# if (curr >= max) break
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39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX
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7d/jump-if-greater-or-equal $get-or-insert-segment:not-found/disp8
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# if (slice-equal?(s, *curr)) return *(curr+4)
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# . EAX = slice-equal?(s, *curr)
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# . . push args
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ff 6/subop/push 0/mod/indirect 1/rm32/ECX . . . . . . # push *ECX
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ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 0xc/disp8 . # push *(EBP+12)
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# . . call
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e8/call slice-equal?/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# . if (EAX != 0) return EAX = *(curr+4)
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3d/compare-EAX-and 0/imm32
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74/jump-if-equal $get-or-insert-segment:mismatch/disp8
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8b/copy 1/mod/*+disp8 1/rm32/ECX . . . 0/r32/EAX 4/disp8 . # copy *(ECX+4) to EAX
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eb/jump $get-or-insert-segment:end/disp8
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$get-or-insert-segment:mismatch:
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# curr += 8
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81 0/subop/add 3/mod/direct 1/rm32/ECX . . . . . 8/imm32 # add to ECX
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# loop
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eb/jump $get-or-insert-segment:search-loop/disp8
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$get-or-insert-segment:not-found:
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# result/EAX = 0
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31/xor 3/mod/direct 0/rm32/EAX . . . 0/r32/EAX . . # clear EAX
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# if (table->write >= table->length) abort
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8b/copy 0/mod/indirect 6/rm32/ESI . . . 1/r32/ECX . . # copy *ESI to ECX
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3b/compare 1/mod/*+disp8 6/rm32/ESI . . . 1/r32/ECX 8/disp8 . # compare ECX with *(ESI+8)
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7d/jump-if-greater-or-equal $get-or-insert-segment:abort/disp8
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# *max = slice-to-string(Heap, s)
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# . EAX = slice-to-string(Heap, s)
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# . . push args
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ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 0xc/disp8 . # push *(EBP+12)
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68/push Heap/imm32
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# . . call
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e8/call slice-to-string/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# . *max = EAX
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89/copy 0/mod/indirect 2/rm32/EDX . . . 0/r32/EAX . . # copy EAX to *EDX
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# result/EAX = new-stream(Heap, n, 1)
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# . . push args
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68/push 1/imm32
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ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 0x10/disp8 . # push *(EBP+16)
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68/push Heap/imm32
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# . . call
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e8/call new-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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# *(max+4) = result
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89/copy 1/mod/*+disp8 2/rm32/EDX . . . 0/r32/EAX 4/disp8 . # copy EAX to *(EDX+4)
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# table->write += 8
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81 0/subop/add 0/mod/indirect 6/rm32/ESI . . . . . 8/imm32 # add to *ESI
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$get-or-insert-segment:end:
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# . restore registers
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5e/pop-to-ESI
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5a/pop-to-EDX
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59/pop-to-ECX
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# . epilog
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89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
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5d/pop-to-EBP
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c3/return
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$get-or-insert-segment:abort:
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# . _write(2/stderr, error)
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# . . push args
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68/push "get-or-insert-segment: too many segments"/imm32
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68/push 2/imm32/stderr
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# . . call
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e8/call _write/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# . syscall(exit, 1)
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bb/copy-to-EBX 1/imm32
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b8/copy-to-EAX 1/imm32/exit
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cd/syscall 0x80/imm8
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# never gets here
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== data
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Segment-size:
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0x1000/imm32/4KB
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Heap:
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# curr
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0/imm32
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# limit
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0/imm32
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# This block of bytes gets copied to the start of the output ELF file, with
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# some fields filled in.
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# http://www.sco.com/developers/gabi/latest/ch4.eheader.html
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Elf_header:
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$e_ident:
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7f 45/E 4c/L 46/F
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01/32-bit 01/little-endian 01/file-version 00/no-os-extensions
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00 00 00 00 00 00 00 00 # 8 bytes of padding
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$e_type:
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02 00
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$e_machine:
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03 00
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$e_version:
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1/imm32
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Elf_e_entry:
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0x09000000/imm32 # approximate default; must be updated
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$e_phoff:
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0x34/imm32 # offset for the 'program header table' containing segment headers
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$e_shoff:
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0/imm32 # no sections
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$e_flags:
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0/imm32 # unused
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$e_ehsize:
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0x34 00
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$e_phentsize:
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0x20 00
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Elf_e_phnum:
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00 00 # number of segments; must be updated
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$e_shentsize:
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00 00 # no sections
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$e_shnum:
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00 00
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$e_shstrndx:
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00 00
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# This block of bytes gets copied after the Elf_header once for each segment.
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# Some fields need filling in each time.
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# https://docs.oracle.com/cd/E19683-01/816-1386/chapter6-83432/index.html
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Elf_program_header_entry:
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$p_type:
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1/imm32/PT_LOAD
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Elf_p_offset:
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0/imm32 # byte offset in the file at which a segment begins; must be updated
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Elf_p_vaddr:
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0/imm32 # starting address to store the segment at before running the program
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Elf_p_paddr:
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0/imm32 # should have same value as Elf_p_vaddr
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Elf_p_filesz:
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0/imm32
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Elf_p_memsz:
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0/imm32 # should have same value as Elf_p_filesz
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Elf_p_flags:
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6/imm32/rw- # read/write/execute permissions for the segment; must be updated for the code segment
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Elf_p_align:
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# we hold this constant; changing it will require adjusting the way we
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# compute the starting address for each segment
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0x1000/imm32
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# . . vim:nowrap:textwidth=0
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