1 # Read a character from stdin, save it to a local on the stack, write it to stdout.
 2 #
 3 # To run (from the subx directory):
 4 #   $ ./subx translate examples/ex5.subx -o examples/ex5
 5 #   $ ./subx run examples/ex5
 6 
 7 == code
 8 #   instruction                     effective address                                                   register    displacement    immediate
 9 # . op          subop               mod             rm32          base        index         scale       r32
10 # . 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
11 
12 # main:
13     # allocate x on the stack
14     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # subtract from ESP
15 
16     # syscall(read, stdin, x, 1)
17     # . fd = 0 (stdin)
18     bb/copy-to-EBX  0/imm32
19     # . data = x (location to write result to)
20     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              1/r32/ECX   4/disp8         .                 # copy ESP+4 to ECX
21     # . size = 1 character
22     ba/copy-to-EDX  1/imm32
23     # . syscall
24     b8/copy-to-EAX  3/imm32/read
25     cd/syscall  0x80/imm8
26 
27     # syscall(write, stdout, x, 1)
28     # . fd = 1 (stdout)
29     bb/copy-to-EBX  1/imm32
30     # . data = x (location to read from)
31     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              1/r32/ECX   4/disp8         .                 # copy ESP+4 to ECX
32     # . size = 1 character
33     ba/copy-to-EDX  1/imm32
34     # . syscall
35     b8/copy-to-EAX  4/imm32/write
36     cd/syscall  0x80/imm8
37 
38     # syscall(exit, EBX)
39     b8/copy-to-EAX  1/imm32/exit
40     cd/syscall  0x80/imm8
41 
42 # . . vim:nowrap:textwidth=0