## Null-terminated vs length-prefixed ascii strings. # # By default we create strings with a 4-byte length prefix rather than a null suffix. # However, commandline arguments come null-prefixed from the Linux kernel. # This example shows a helper that can compare a commandline argument with the # (length-prefixed) literal string "target". # # To run: # $ subx translate ex11.subx ex11 # $ subx run 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 # 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: 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 argv_equal: # s : null-terminated ascii string, benchmark : length-prefixed ascii string -> EAX : boolean # 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 4/base/ESP 4/index/none . 7/r32/EDI 8/disp8 . # copy *(ESP+8) to EDI # initialize benchmark length n into EDX 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 2/r32/EDX 4/disp8 . # copy *(ESP+4) 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 4/base/ESP 4/index/none . 6/r32/ESI 4/disp8 . # copy *(ESP+4) 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) $argv_loop: 39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX 74/jump-if-equal $argv_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 $argv_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 $argv_fail/disp8 # ++s1, ++s2, ++i 41/inc-ECX 46/inc-ESI 47/inc-EDI # end while eb/jump $argv_loop/disp8 $argv_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 $argv_fail/disp8 b8/copy . . . . . . . 1/imm32 # copy 1 to EAX c3/return # return false $argv_fail: b8/copy . . . . . . . 0/imm32 # copy 0 to EAX c3/return ## tests test_compare_null_argv_with_empty_array: # EAX = argv_equal(Null_argv, "") # push args 68/push Null_argv/imm32 68/push ""/imm32 # call e8/call argv_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) 50/push-EAX 68/push 1/imm32/true 68/push "F - test_compare_null_argv_with_empty_array"/imm32 # 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_argv_with_non_empty_array: # EAX = argv_equal(Null_argv, "Abc") # push args 68/push Null_argv/imm32 68/push "Abc"/imm32 # call e8/call argv_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) 50/push-EAX 68/push 0/imm32/false 68/push "F - test_compare_null_argv_with_non_empty_array"/imm32 # 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_argv_with_equal_array: # EAX = argv_equal(Abc_argv, "Abc") # push args 68/push Abc_argv/imm32 68/push "Abc"/imm32 # call e8/call argv_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) 50/push-EAX 68/push 1/imm32/true 68/push "F - test_compare_argv_with_equal_array"/imm32 # 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_argv_with_inequal_array: # EAX = argv_equal(Abc_argv, "Adc") # push args 68/push Abc_argv/imm32 68/push "Adc"/imm32 # call e8/call argv_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) 50/push-EAX 68/push 0/imm32/false 68/push "F - test_compare_argv_with_equal_array"/imm32 # 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_argv_with_empty_array: # EAX = argv_equal(Abc_argv, "") # push args 68/push Abc_argv/imm32 68/push ""/imm32 # call e8/call argv_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) 50/push-EAX 68/push 0/imm32/false 68/push "F - test_compare_argv_with_equal_array"/imm32 # 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_argv_with_shorter_array: # EAX = argv_equal(Abc_argv, "Ab") # push args 68/push Abc_argv/imm32 68/push "Ab"/imm32 # call e8/call argv_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) 50/push-EAX 68/push 0/imm32/false 68/push "F - test_compare_argv_with_shorter_array"/imm32 # 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_argv_with_longer_array: # EAX = argv_equal(Abc_argv, "Abcd") # push args 68/push Abc_argv/imm32 68/push "Abcd"/imm32 # call e8/call argv_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) 50/push-EAX 68/push 0/imm32/false 68/push "F - test_compare_argv_with_longer_array"/imm32 # 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 ## helpers # print msg to stderr if a != b, otherwise print "." check_ints_equal: # (a : int, b : int, msg : (address array byte)) -> boolean # load args into EAX, EBX and ECX 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 0/r32/EAX 0xc/disp8 . # copy *(ESP+12) to EAX 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 3/r32/EBX 0x8/disp8 . # copy *(ESP+8) to EBX # if EAX == b/EBX 39/compare 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # compare EAX and EBX 75/jump-if-unequal $check_ints_equal:else/disp8 # print('.') # push args 68/push "."/imm32 # call e8/call write_stderr/disp32 # discard arg 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add 4 to ESP # return c3/return # else: $check_ints_equal:else: # copy msg into ECX 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 1/r32/ECX 4/disp8 . # copy *(ESP+4) to ECX # print(ECX) # push args 51/push-ECX # call e8/call write_stderr/disp32 # discard arg 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add 4 to ESP # print newline # push args 68/push Newline/imm32 # call e8/call write_stderr/disp32 # discard arg 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add 4 to ESP # end c3/return write_stderr: # s : (address array byte) -> # save registers 50/push-EAX 51/push-ECX 52/push-EDX 53/push-EBX # write(2/stderr, (data) s+4, (size) *s) # fd = 2 (stderr) bb/copy . . . . . . . 2/imm32 # copy 2 to EBX # x = s+4 8b/copy 1/mod/*+disp8 4/rm32/SIB 4/base/ESP 4/index/none . 1/r32/ECX 0x14/disp8 . # copy *(ESP+20) to ECX 81 0/subop/add 3/mod/direct 1/rm32/ECX . . . . . 4/imm32 # add 4 to ECX # size = *s 8b/copy 1/mod/*+disp8 4/rm32/SIB 4/base/ESP 4/index/none . 2/r32/EDX 0x14/disp8 . # copy *(ESP+20) to EDX 8b/copy 0/mod/indirect 2/rm32/EDX . . . 2/r32/EDX . . # copy *EDX to EDX # call write() b8/copy . . . . . . . 4/imm32/write # copy 1 to EAX cd/syscall 0x80/imm8 # restore registers 5b/pop-EBX 5a/pop-EDX 59/pop-ECX 58/pop-EAX # end c3/return == data Newline: # size 01 00 00 00 # data 0a/newline # for argv_equal tests Null_argv: 00/null Abc_argv: 41/A 62/b 63/c 00/null # vim:ft=subx:nowrap:so=0