about summary refs log tree commit diff stats
path: root/linux/ex4.subx
blob: ee78ce7d5bb1fc2e4d92f5c0573f820c0d047f05 (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
# Read a character from stdin, save it to a global, write it to stdout.
#
# To run:
#   $ bootstrap/bootstrap translate ex4.subx -o ex4
#   $ bootstrap/bootstrap run ex4

== data

# the global variable we save to
X:
    0/imm32  # space for read() to write to

== code

Entry:
# read(stdin, X, 1)
# . fd = 0 (stdin)
bb/copy-to-ebx  0/imm32
# . data = X (location to write result to)
b9/copy-to-ecx  X/imm32
# . size = 1 character
ba/copy-to-edx  1/imm32
# . syscall
e8/call  syscall_read/disp32

# write(stdout, X, 1)
# . fd = 1 (stdout)
bb/copy-to-ebx  1/imm32
# . initialize X (location to read from)
b9/copy-to-ecx  X/imm32
# . size = 1 character
ba/copy-to-edx  1/imm32
# . syscall
e8/call  syscall_write/disp32

# exit(ebx)
e8/call  syscall_exit/disp32

# . . vim:nowrap:textwidth=0