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 Entry:
13 
14     # allocate x on the stack
15     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # subtract from ESP
16 
17     # syscall(read, stdin, x, 1)
18     # . fd = 0 (stdin)
19     bb/copy-to-EBX  0/imm32
20     # . data = x (location to write result to)
21     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
22     # . size = 1 character
23     ba/copy-to-EDX  1/imm32
24     # . syscall
25     b8/copy-to-EAX  3/imm32/read
26     cd/syscall  0x80/imm8
27 
28     # syscall(write, stdout, x, 1)
29     # . fd = 1 (stdout)
30     bb/copy-to-EBX  1/imm32
31     # . data = x (location to read from)
32     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
33     # . size = 1 character
34     ba/copy-to-EDX  1/imm32
35     # . syscall
36     b8/copy-to-EAX  4/imm32/write
37     cd/syscall  0x80/imm8
38 
39     # syscall(exit, EBX)
40     b8/copy-to-EAX  1/imm32/exit
41     cd/syscall  0x80/imm8
42 
43 # . . vim:nowrap:textwidth=0