diff options
Diffstat (limited to 'linux/103kernel-string-equal.subx')
| -rw-r--r-- | linux/103kernel-string-equal.subx | 269 |
1 files changed, 269 insertions, 0 deletions
diff --git a/linux/103kernel-string-equal.subx b/linux/103kernel-string-equal.subx new file mode 100644 index 00000000..7e1b9d6f --- /dev/null +++ b/linux/103kernel-string-equal.subx @@ -0,0 +1,269 @@ +# Checking null-terminated strings. +# +# By default we create strings as arrays of bytes, and all arrays have a 4-byte +# size prefix. +# +# However, we sometimes need to deal with null-terminated strings when +# interacting with the Linux kernel. This layer implements a function for +# comparing a null-terminated 'kernel string' with a size-prefixed 'SubX +# string'. +# +# To run (from the subx directory): +# $ ./bootstrap translate 05[0-2]*.subx -o /tmp/tmp52 +# $ ./bootstrap 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 + +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, Num-test-failures) + 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/ebx Num-test-failures/disp32 # copy *Num-test-failures to ebx + e8/call syscall_exit/disp32 + +kernel-string-equal?: # s: (addr kernel-string), benchmark: (addr array byte) -> result/eax: boolean + # pseudocode: + # n = benchmark->size + # 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 + # + # . prologue + 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 + # var s1/edi: (addr byte) = s + 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 7/r32/edi 8/disp8 . # copy *(ebp+8) to edi + # var n/edx: int = benchmark->size + 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 + # var s2/esi: (addr byte) = 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 + # var i/ecx: int = 0 + b9/copy-to-ecx 0/imm32/exit + # var c1/eax: byte = 0 + b8/copy-to-eax 0/imm32 + # var c2/ebx: byte = 0 + 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->= $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/null + 74/jump-if-= $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-!= $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/null + 75/jump-if-!= $kernel-string-equal?:false/disp8 +$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 + # . epilogue + 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 + +== data + +Null-kernel-string: # (addr kernel-string) + 00/null + +_test-Abc-kernel-string: # (addr kernel-string) + 41/A 62/b 63/c 00/null + +# . . vim:nowrap:textwidth=0 |