## 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) -> <void>
# 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