blob: b8d5ca10b1e358d677dee992407e2274b9d905d3 (
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
|
## read a character from stdin, save it to a global, write it to stdout
#
# To run:
# $ subx translate ex4.subx ex4
# $ subx run ex4
== 0x08048074 # code segment, after leaving room for ELF header and segment headers
# 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
## read(stdin, x, 1)
# fd = 0 (stdin)
bb 0/imm32 # copy 0 to EBX
# set location to write to
b9 0x080490a7/imm32 # copy to ECX
# size = 1 character
ba 1/imm32 # copy 1 to EDX
# syscall = read
b8 3/imm32 # copy 3 to EAX
# call
cd 0x80/imm8 # int 80h
## write(stdout, x, 1)
# fd = 1 (stdout)
bb 1/imm32 # copy 1 to EBX
# set location to write to
b9 0x080490a7/imm32 # copy to ECX
# size = 1 character
ba 1/imm32 # copy 1 to EDX
# syscall = write
b8 4/imm32 # copy 4 to EAX
# call
cd 0x80/imm8 # int 80h
## exit(EBX)
b8 1/imm32 # copy 1 to EAX
cd 0x80/imm8 # int 80h
== 0x080490a7
00 00 00 00 # space for read() to write to
# vim:ft=subx:nowrap
|