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Diffstat (limited to 'examples/ex11.subx')
| -rw-r--r-- | examples/ex11.subx | 357 |
1 files changed, 357 insertions, 0 deletions
diff --git a/examples/ex11.subx b/examples/ex11.subx new file mode 100644 index 00000000..ba75c1d3 --- /dev/null +++ b/examples/ex11.subx @@ -0,0 +1,357 @@ +# Null-terminated vs length-prefixed ascii strings. +# +# By default we create strings with a 4-byte length prefix rather than a null suffix. +# However we still need null-prefixed strings when interacting with the Linux +# kernel in a few places. This layer implements a function for comparing +# a null-terminated 'kernel string' with a length-prefixed 'SubX string'. +# +# To run (from the subx directory): +# $ ./subx translate examples/ex11.subx -o examples/ex11 +# $ ./subx run examples/ex11 # runs a series of tests +# ...... # all tests pass +# +# (We can't yet run the tests when given a "test" commandline argument, +# because checking for it would require the function being tested! Breakage +# would cause tests to not run, rather than to fail as we'd like.) + +== code 0x09000000 +# 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: # run all tests + e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'. + # syscall(exit, EAX) + 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX + b8/copy-to-EAX 1/imm32/exit + cd/syscall 0x80/imm8 + +# compare a null-terminated ascii string with a more idiomatic length-prefixed byte array +# reason for the name: the only place we should have null-terminated ascii strings is from commandline args +kernel-string-equal?: # s : null-terminated ascii string, benchmark : length-prefixed ascii string -> EAX : boolean + # pseudocode: + # n = benchmark->length + # s1 = s + # s2 = benchmark->data + # i = 0 + # while i < n + # c1 = *s1 + # c2 = *s2 + # if (c1 == 0) return false + # if (c1 != c2) return false + # ++s1, ++s2, ++i + # return *s1 == 0 + # + # registers: + # i: ECX + # n: EDX + # s1: EDI + # s2: ESI + # c1: EAX + # c2: EBX + # + # . prolog + 55/push-EBP + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # . save registers + 51/push-ECX + 52/push-EDX + 53/push-EBX + 56/push-ESI + 57/push-EDI + # s1/EDI = s + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 7/r32/EDI 8/disp8 . # copy *(EBP+8) to EDI + # n/EDX = benchmark->length + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 2/r32/EDX 0xc/disp8 . # copy *(EBP+12) to EDX + 8b/copy 0/mod/indirect 2/rm32/EDX . . . 2/r32/EDX . . # copy *EDX to EDX + # s2/ESI = benchmark->data + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 6/r32/ESI 0xc/disp8 . # copy *(EBP+12) to ESI + 81 0/subop/add 3/mod/direct 6/rm32/ESI . . . . . 4/imm32 # add to ESI + # i/ECX = c1/EAX = c2/EBX = 0 + b9/copy-to-ECX 0/imm32/exit + b8/copy-to-EAX 0/imm32 + bb/copy-to-EBX 0/imm32 +$kernel-string-equal?:loop: + # if (i >= n) break + 39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX + 7d/jump-if-greater-or-equal $kernel-string-equal?:break/disp8 + # c1 = *s1 + 8a/copy-byte 0/mod/indirect 7/rm32/EDI . . . 0/r32/AL . . # copy byte at *EDI to AL + # c2 = *s2 + 8a/copy-byte 0/mod/indirect 6/rm32/ESI . . . 3/r32/BL . . # copy byte at *ESI to BL + # if (c1 == 0) return false + 3d/compare-EAX-and 0/imm32 + 74/jump-if-equal $kernel-string-equal?:false/disp8 + # if (c1 != c2) return false + 39/compare 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # compare EAX and EBX + 75/jump-if-not-equal $kernel-string-equal?:false/disp8 + # ++i + 41/increment-ECX + # ++s1 + 47/increment-EDI + # ++s2 + 46/increment-ESI + eb/jump $kernel-string-equal?:loop/disp8 +$kernel-string-equal?:break: + # return *s1 == 0 + 8a/copy-byte 0/mod/indirect 7/rm32/EDI . . . 0/r32/AL . . # copy byte at *EDI to AL + 3d/compare-EAX-and 0/imm32 + 75/jump-if-not-equal $kernel-string-equal?:false/disp8 +$kernel-string-equal?:true: + b8/copy-to-EAX 1/imm32 + eb/jump $kernel-string-equal?:end/disp8 +$kernel-string-equal?:false: + b8/copy-to-EAX 0/imm32 +$kernel-string-equal?:end: + # . restore registers + 5f/pop-to-EDI + 5e/pop-to-ESI + 5b/pop-to-EBX + 5a/pop-to-EDX + 59/pop-to-ECX + # . epilog + 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP + 5d/pop-to-EBP + c3/return + +# - tests + +test-compare-null-kernel-string-with-empty-array: + # EAX = kernel-string-equal?(Null-kernel-string, "") + # . . push args + 68/push ""/imm32 + 68/push Null-kernel-string/imm32 + # . . 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-ints-equal(EAX, 1, msg) + # . . push args + 68/push "F - test-compare-null-kernel-string-with-empty-array"/imm32 + 68/push 1/imm32/true + 50/push-EAX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + c3/return + +test-compare-null-kernel-string-with-non-empty-array: + # EAX = kernel-string-equal?(Null-kernel-string, "Abc") + # . . push args + 68/push "Abc"/imm32 + 68/push Null-kernel-string/imm32 + # . . 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-ints-equal(EAX, 0, msg) + # . . push args + 68/push "F - test-compare-null-kernel-string-with-non-empty-array"/imm32 + 68/push 0/imm32/false + 50/push-EAX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + c3/return + +test-compare-kernel-string-with-equal-array: + # EAX = kernel-string-equal?(_test-Abc-kernel-string, "Abc") + # . . push args + 68/push "Abc"/imm32 + 68/push _test-Abc-kernel-string/imm32 + # . . 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-ints-equal(EAX, 1, msg) + # . . push args + 68/push "F - test-compare-kernel-string-with-equal-array"/imm32 + 68/push 1/imm32/true + 50/push-EAX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + c3/return + +test-compare-kernel-string-with-inequal-array: + # EAX = kernel-string-equal?(_test-Abc-kernel-string, "Adc") + # . . push args + 68/push "Adc"/imm32 + 68/push _test-Abc-kernel-string/imm32 + # . . 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-ints-equal(EAX, 0, msg) + # . . push args + 68/push "F - test-compare-kernel-string-with-equal-array"/imm32 + 68/push 0/imm32/false + 50/push-EAX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + c3/return + +test-compare-kernel-string-with-empty-array: + # EAX = kernel-string-equal?(_test-Abc-kernel-string, "") + # . . push args + 68/push ""/imm32 + 68/push _test-Abc-kernel-string/imm32 + # . . 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-ints-equal(EAX, 0, msg) + # . . push args + 68/push "F - test-compare-kernel-string-with-equal-array"/imm32 + 68/push 0/imm32/false + 50/push-EAX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + c3/return + +test-compare-kernel-string-with-shorter-array: + # EAX = kernel-string-equal?(_test-Abc-kernel-string, "Ab") + # . . push args + 68/push "Ab"/imm32 + 68/push _test-Abc-kernel-string/imm32 + # . . 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-ints-equal(EAX, 0, msg) + # . . push args + 68/push "F - test-compare-kernel-string-with-shorter-array"/imm32 + 68/push 0/imm32/false + 50/push-EAX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + c3/return + +test-compare-kernel-string-with-longer-array: + # EAX = kernel-string-equal?(_test-Abc-kernel-string, "Abcd") + # . . push args + 68/push "Abcd"/imm32 + 68/push _test-Abc-kernel-string/imm32 + # . . 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-ints-equal(EAX, 0, msg) + # . . push args + 68/push "F - test-compare-kernel-string-with-longer-array"/imm32 + 68/push 0/imm32/false + 50/push-EAX + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP + c3/return + +# - helpers + +# print msg to stderr if a != b, otherwise print "." +check-ints-equal: # (a : int, b : int, msg : (address array byte)) -> boolean + # . prolog + 55/push-EBP + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # . save registers + 51/push-ECX + 53/push-EBX + # load args into EAX, EBX and ECX + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 0/r32/EAX 8/disp8 . # copy *(EBP+8) to EAX + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 3/r32/EBX 0xc/disp8 . # copy *(EBP+12) to EBX + # if (EAX == b/EBX) print('.') and return + 39/compare 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # compare EAX and EBX + 75/jump-if-unequal $check-ints-equal:else/disp8 + # . write-stderr('.') + # . . push args + 68/push "."/imm32 + # . . call + e8/call write-stderr/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP + # . return + eb/jump $check-ints-equal:end/disp8 + # otherwise print(msg) +$check-ints-equal:else: + # copy msg into ECX + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 1/r32/ECX 0x10/disp8 . # copy *(EBP+16) to ECX + # print(ECX) + # . . push args + 51/push-ECX + # . . call + e8/call write-stderr/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP + # print newline + # . . push args + 68/push Newline/imm32 + # . . call + e8/call write-stderr/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP +$check-ints-equal:end: + # . restore registers + 5b/pop-to-EBX + 59/pop-to-ECX + # end + 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP + 5d/pop-to-EBP + c3/return + +write-stderr: # s : (address array byte) -> <void> + # . prolog + 55/push-EBP + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # . save registers + 50/push-EAX + 51/push-ECX + 52/push-EDX + 53/push-EBX + # syscall(write, 2/stderr, (data) s+4, (size) *s) + # . . fd = 2 (stderr) + bb/copy-to-EBX 2/imm32 + # . . x = s+4 + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 1/r32/ECX 8/disp8 . # copy *(EBP+8) to ECX + 81 0/subop/add 3/mod/direct 1/rm32/ECX . . . . . 4/imm32 # add to ECX + # . . size = *s + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 2/r32/EDX 8/disp8 . # copy *(EBP+8) to EDX + 8b/copy 0/mod/indirect 2/rm32/EDX . . . 2/r32/EDX . . # copy *EDX to EDX + # . . syscall + b8/copy-to-EAX 4/imm32/write + cd/syscall 0x80/imm8 + # . restore registers + 5b/pop-to-EBX + 5a/pop-to-EDX + 59/pop-to-ECX + 58/pop-to-EAX + # . end + 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP + 5d/pop-to-EBP + c3/return + +== data 0x0a000000 + +Newline: + # size + 1/imm32 + # data + 0a/newline + +# for kernel-string-equal tests +Null-kernel-string: + 00/null + +_test-Abc-kernel-string: + 41/A 62/b 63/c 00/null + +# . . vim:nowrap:textwidth=0 |