1 # Read a character from stdin, save it to a local on the stack, write it to stdout.
 2 #
 3 # To run:
 4 #   $ ./bootstrap translate init.linux apps/ex5.subx -o apps/ex5
 5 #   $ ./bootstrap run apps/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     # 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     e8/call  syscall_read/disp32
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     e8/call  syscall_write/disp32
36 
37     # exit(ebx)
38     e8/call  syscall_exit/disp32
39 
40 # . . vim:nowrap:textwidth=0