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author | Kartik Agaram <vc@akkartik.com> | 2018-10-01 14:13:53 -0700 |
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committer | Kartik Agaram <vc@akkartik.com> | 2018-10-01 14:21:27 -0700 |
commit | 1666b12f37b2714e136d07db52e115ab14b06a20 (patch) | |
tree | 0920a4f4dec408b564ecb076f1f42820b1c4d8bf /subx/052kernel_string_equal.subx | |
parent | fb7e66fd4b30cc4c0aa9abcdf64ab7e33a0e9ef3 (diff) | |
download | mu-1666b12f37b2714e136d07db52e115ab14b06a20.tar.gz |
4641
Diffstat (limited to 'subx/052kernel_string_equal.subx')
-rw-r--r-- | subx/052kernel_string_equal.subx | 258 |
1 files changed, 258 insertions, 0 deletions
diff --git a/subx/052kernel_string_equal.subx b/subx/052kernel_string_equal.subx new file mode 100644 index 00000000..59bf56c5 --- /dev/null +++ b/subx/052kernel_string_equal.subx @@ -0,0 +1,258 @@ +## Checking null-terminated 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 05[0-2]*.subx -o /tmp/tmp52 +# $ subx run /tmp/tmp52 # 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 + +# instruction effective address operand 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 + +# main: (if this is the last file loaded) + e8/call run_tests/disp32 # 'run_tests' is a function created automatically by SubX. It calls all functions that start with 'test_'. + # exit(EAX) + 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX + b8/copy . . . . . . . 1/imm32 # copy 1 to EAX + 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 + # 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 + + # pseudocode: + # initialize n = b.length + # initialize s1 = s + # initialize s2 = b.data + # i = 0 + # for (i = 0; i < n; ++n) + # c1 = *s1 + # c2 = *s2 + # if c1 == 0 + # return false + # if c1 != c2 + # return false + # return *s1 == 0 + # initialize s into EDI + 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 7/r32/EDI 8/disp8 . # copy *(EBP+8) to EDI + # initialize benchmark length n into EDX + 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 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 + # initialize benchmark data into ESI + 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 6/r32/ESI 0xc/disp8 . # copy *(EBP+12) to ESI + 81 0/subop/add 3/mod/direct 6/rm32/ESI . . . . . 4/imm32 # add 4 to ESI + # initialize loop counter i into ECX + b9/copy . . . . . . . 0/imm32/exit # copy 1 to ECX + # while (i/ECX < n/EDX) +$kernel_string_loop: + 39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX + 74/jump-if-equal $kernel_string_break/disp8 + # c1/EAX, c2/EBX = *s, *benchmark + b8/copy 0/imm32 # clear EAX + 8a/copy 0/mod/indirect 7/rm32/EDI . . . 0/r32/EAX . . # copy byte at *EDI to lower byte of EAX + bb/copy 0/imm32 # clear EBX + 8a/copy 0/mod/indirect 6/rm32/ESI . . . 3/r32/EBX . . # copy byte at *ESI to lower byte of EBX + # if (c1 == 0) return false + 3d/compare . . . . . . . 0/imm32 # compare EAX with 0 + 74/jump-if-equal $kernel_string_fail/disp8 + # if (c1 != c2) return false + 39/compare 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # compare EAX with EBX + 75/jump-if-not-equal $kernel_string_fail/disp8 + # ++s1, ++s2, ++i + 41/inc-ECX + 46/inc-ESI + 47/inc-EDI + # end while + eb/jump $kernel_string_loop/disp8 +$kernel_string_break: + # if (*s/EDI == 0) return true + b8/copy 0/imm32 # clear EAX + 8a/copy 0/mod/indirect 7/rm32/EDI . . . 0/r32/EAX . . # copy byte at *EDI to lower byte of EAX + 81 7/subop/compare 3/mod/direct 0/rm32/EAX . . . . . 0/imm32 # compare EAX with 0 + 75/jump-if-not-equal $kernel_string_fail/disp8 + b8/copy . . . . . . . 1/imm32 # copy 1 to EAX + eb/jump $kernel_string_end/disp8 + # return false +$kernel_string_fail: + b8/copy . . . . . . . 0/imm32 # copy 0 to EAX + +$kernel_string_end: + # restore registers + 5f/pop-to-EDI + 5e/pop-to-ESI + 5b/pop-to-EBX + 5a/pop-to-EDX + 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 + +## 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 8 to ESP + # call 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 12 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 8 to ESP + # call 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 12 to ESP + c3/return + +test_compare_kernel_string_with_equal_array: + # EAX = kernel_string_equal(Abc_kernel_string, "Abc") + # push args + 68/push "Abc"/imm32 + 68/push 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 8 to ESP + # call 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 12 to ESP + c3/return + +test_compare_kernel_string_with_inequal_array: + # EAX = kernel_string_equal(Abc_kernel_string, "Adc") + # push args + 68/push "Adc"/imm32 + 68/push 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 8 to ESP + # call 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 12 to ESP + c3/return + +test_compare_kernel_string_with_empty_array: + # EAX = kernel_string_equal(Abc_kernel_string, "") + # push args + 68/push ""/imm32 + 68/push 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 8 to ESP + # call check_ints_equal(EAX, 0) + # 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 12 to ESP + c3/return + +test_compare_kernel_string_with_shorter_array: + # EAX = kernel_string_equal(Abc_kernel_string, "Ab") + # push args + 68/push "Ab"/imm32 + 68/push 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 8 to ESP + # call check_ints_equal(EAX, 0) + # 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 12 to ESP + c3/return + +test_compare_kernel_string_with_longer_array: + # EAX = kernel_string_equal(Abc_kernel_string, "Abcd") + # push args + 68/push "Abcd"/imm32 + 68/push 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 8 to ESP + # call check_ints_equal(EAX, 0) + # 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 12 to ESP + c3/return + +== data + +Null_kernel_string: + 00/null +Abc_kernel_string: + 41/A 62/b 63/c 00/null |