diff options
author | Kartik Agaram <vc@akkartik.com> | 2019-01-03 17:02:17 -0800 |
---|---|---|
committer | Kartik Agaram <vc@akkartik.com> | 2019-01-03 17:02:17 -0800 |
commit | 634b162a980f72ae1d822e593f7975fa8e1ad3e8 (patch) | |
tree | 9f3cd2b8c3a6445c36268392fc8ef2bf820401d6 /subx/052kernel-string-equal.subx | |
parent | 1ffb27a045c63217336e2c926058360e9521afc9 (diff) | |
download | mu-634b162a980f72ae1d822e593f7975fa8e1ad3e8.tar.gz |
4901
Diffstat (limited to 'subx/052kernel-string-equal.subx')
-rw-r--r-- | subx/052kernel-string-equal.subx | 260 |
1 files changed, 260 insertions, 0 deletions
diff --git a/subx/052kernel-string-equal.subx b/subx/052kernel-string-equal.subx new file mode 100644 index 00000000..67e9695e --- /dev/null +++ b/subx/052kernel-string-equal.subx @@ -0,0 +1,260 @@ +# 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 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 + +# main: + e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'. + # syscall(exit, Num-test-failures) + 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures 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 + # . 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 5/rm32/EBP . . . 7/r32/EDI 8/disp8 . # copy *(EBP+8) to EDI + # initialize benchmark length n into EDX + 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 + # initialize benchmark data into ESI + 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 + # initialize loop counter i into ECX + b9/copy-to-ECX 0/imm32/exit + # while (i/ECX < n/EDX) +$kernel-string-equal:loop: + 39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX + 74/jump-if-equal $kernel-string-equal:break/disp8 + # c1/EAX, c2/EBX = *s, *benchmark + b8/copy-to-EAX 0/imm32 + 8a/copy 0/mod/indirect 7/rm32/EDI . . . 0/r32/EAX . . # copy byte at *EDI to lower byte of EAX + bb/copy-to-EBX 0/imm32 + 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-EAX 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 with EBX + 75/jump-if-not-equal $kernel-string-equal:false/disp8 + # ++s1, ++s2, ++i + 41/inc-ECX + 46/inc-ESI + 47/inc-EDI + # end while + eb/jump $kernel-string-equal:loop/disp8 +$kernel-string-equal:break: + # if (*s/EDI == 0) return true + b8/copy-to-EAX 0/imm32 + 8a/copy 0/mod/indirect 7/rm32/EDI . . . 0/r32/EAX . . # copy byte at *EDI to lower byte of EAX + 3d/compare-EAX 0/imm32 + 75/jump-if-not-equal $kernel-string-equal:false/disp8 +$kernel-string-equal:true: + b8/copy-to-EAX 1/imm32 + eb/jump $kernel-string-equal:end/disp8 + # return false +$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(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 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(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 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(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 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(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 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(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 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 + +== data + +Null-kernel-string: + 00/null +Abc-kernel-string: + 41/A 62/b 63/c 00/null + +# . . vim:nowrap:textwidth=0 |