blob: 7ec862023dd3a0e944af5db866fbb1aae452452d (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
|
# String comparison: return 1 iff the two args passed in at the commandline are equal.
#
# To run:
# $ ./bootstrap translate init.linux apps/ex10.subx -o apps/ex10
# $ ./bootstrap run apps/ex10 abc abd
# Expected result:
# $ echo $?
# 0 # false
== 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: # return argv-equal(argv[1], argv[2])
# At the start of a SubX program:
# argc: *esp
# argv[0]: *(esp+4)
# argv[1]: *(esp+8)
# ...
# . prologue
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# argv-equal(argv[1], argv[2])
# . . push argv[2]
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12)
# . . push argv[1]
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
# . . call
e8/call argv-equal/disp32
# exit(eax)
89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
e8/call syscall_exit/disp32
# compare two null-terminated ascii strings
# reason for the name: the only place we should have null-terminated ascii strings is from commandline args
argv-equal: # (s1, s2): null-terminated ascii strings -> eax: boolean
# initialize s1 (ecx) and s2 (edx)
8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 1/r32/ecx 4/disp8 . # copy *(esp+4) to ecx
8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 8/disp8 . # copy *(esp+8) to edx
$argv-equal:loop:
# c1/eax, c2/ebx = *s1, *s2
b8/copy-to-eax 0/imm32
8a/copy-byte 0/mod/indirect 1/rm32/ecx . . . 0/r32/AL . . # copy byte at *ecx to AL
bb/copy-to-ebx 0/imm32
8a/copy-byte 0/mod/indirect 2/rm32/edx . . . 3/r32/BL . . # copy byte at *edx to BL
# if (c1 == 0) break
3d/compare-eax-and 0/imm32/null
74/jump-if-= $argv-equal:break/disp8
# if (c1 != c2) return false
39/compare 3/mod/direct 0/rm32/eax . . . 3/r32/ebx . . # compare eax and ebx
75/jump-if-!= $argv-equal:false/disp8
# ++s1, ++s2
41/increment-ecx
42/increment-edx
# end while
eb/jump $argv-equal:loop/disp8
$argv-equal:break:
# if (c2 == 0) return true
81 7/subop/compare 3/mod/direct 3/rm32/ebx . . . . . 0/imm32/null # compare ebx
75/jump-if-!= $argv-equal:false/disp8
$argv-equal:success:
b8/copy-to-eax 1/imm32
c3/return
# return false
$argv-equal:false:
b8/copy-to-eax 0/imm32
c3/return
# . . vim:nowrap:textwidth=0
|