From 3350c34a74844e21ea69077e01efff3bae64bdcd Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Tue, 23 Mar 2021 17:31:08 -0700 Subject: . --- html/linux/ex9.subx.html | 114 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 114 insertions(+) create mode 100644 html/linux/ex9.subx.html (limited to 'html/linux/ex9.subx.html') diff --git a/html/linux/ex9.subx.html b/html/linux/ex9.subx.html new file mode 100644 index 00000000..019a2c60 --- /dev/null +++ b/html/linux/ex9.subx.html @@ -0,0 +1,114 @@ + + + + +Mu - linux/ex9.subx + + + + + + + + + + +https://github.com/akkartik/mu/blob/main/linux/ex9.subx +
+ 1 # Example showing arg order on the stack.
+ 2 #
+ 3 # Show difference between ascii codes of first letter of first arg and first
+ 4 # letter of second arg.
+ 5 #
+ 6 # To run:
+ 7 #   $ bootstrap/bootstrap translate apps/ex9.subx -o apps/ex9
+ 8 #   $ bootstrap/bootstrap run ex9 z x
+ 9 # Expected result:
+10 #   $ echo $?
+11 #   2
+12 #
+13 # At the start of a SubX program:
+14 #   argc: *esp
+15 #   argv[0]: *(esp+4)
+16 #   argv[1]: *(esp+8)
+17 #   ...
+18 # Locals start from esp-4 downwards.
+19 
+20 == code
+21 #   instruction                     effective address                                                   register    displacement    immediate
+22 # . op          subop               mod             rm32          base        index         scale       r32
+23 # . 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
+24 
+25 Entry:
+26     # . prologue
+27     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+28     # ascii-difference(argv[1], argv[2])
+29     # . . push argv[2]
+30     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
+31     # . . push argv[1]
+32     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
+33     # . . call
+34     e8/call  ascii-difference/disp32
+35     # . . discard args
+36     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+37     # exit(eax)
+38     89/copy                         3/mod/direct    3/rm32/ebx    .           .             .           0/r32/eax   .               .                 # copy eax to ebx
+39     e8/call  syscall_exit/disp32
+40 
+41 ascii-difference:  # (s1, s2): null-terminated ascii strings
+42     # a = first letter of s1 (ecx)
+43     8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/esp  4/index/none  .           0/r32/eax   4/disp8         .                 # copy *(esp+4) to eax
+44     8b/copy                         0/mod/indirect  0/rm32/eax    .           .             .           0/r32/eax   .               .                 # copy *eax to eax
+45     # b = first letter of s2 (edx)
+46     8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/esp  4/index/none  .           1/r32/ecx   8/disp8                           # copy *(esp+8) to ecx
+47     8b/copy                         0/mod/indirect  1/rm32/ecx    .           .             .           1/r32/ecx   .               .                 # copy *ecx to ecx
+48     # a-b
+49     29/subtract                     3/mod/direct    0/rm32/eax    .           .             .           1/r32/ecx   .               .                 # subtract ecx from eax
+50     c3/return
+51 
+52 # . . vim:nowrap:textwidth=0
+
+ + + -- cgit 1.4.1-2-gfad0