# From https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html :
# "-Og : optimize debugging"

https://www.ibm.com/developerworks/library/l-gas-nasm/index.html
google "NASM vs GAS" to see examples of the two styles
for representing assembly. Notice that they reverse the order of
arguments, e.g. "movl $1, %eax" vs "mov eax, 1".

See https://en.wikibooks.org/wiki/X86_Assembly/GAS_Syntax

 b  bytes  (8 bit)
 s  short  (16 bit integer, 32 bit float)
 w  word   (16 bit)
 l  long   (32 bit integer, 64 bit float)
 q  quad   (64 bit)
 t  ten    (ten bytes, 80 bits)

 example :
 movl  -8(%ebp, %edx, 4), %eax   # Full example: load *(ebp + (edx * 4) - 8) into eax

 If no letter suffix (i.e. "mov" rather than "movq"), use size of destination register.


$ gcc -Og swap.c -o swap
$ objdump -d swap > swap.objdjump

--- swap.objdump - (excerpt) ---------------------------------

0000000000400546 <swap>:
  400546:       8b 07                   mov    (%rdi),%eax
  400548:       8b 16                   mov    (%rsi),%edx
  40054a:       89 17                   mov    %edx,(%rdi)
  40054c:       89 06                   mov    %eax,(%rsi)
  40054e:       c3                      ret

000000000040054f <doit>:
  40054f:       48 83 ec 18             sub    $0x18,%rsp
  400553:       64 48 8b 04 25 28 00    mov    %fs:0x28,%rax
  40055a:       00 00
  40055c:       48 89 44 24 08          mov    %rax,0x8(%rsp)
  400561:       31 c0                   xor    %eax,%eax
  400563:       c7 04 24 7b 00 00 00    movl   $0x7b,(%rsp)
  40056a:       c7 44 24 04 c8 01 00    movl   $0x1c8,0x4(%rsp)
  400571:       00
  400572:       48 8d 74 24 04          lea    0x4(%rsp),%rsi
  400577:       48 89 e7                mov    %rsp,%rdi
  40057a:       e8 c7 ff ff ff          callq  400546 <swap>
  40057f:       8b 44 24 04             mov    0x4(%rsp),%eax
  400583:       03 04 24                add    (%rsp),%eax
  400586:       48 8b 54 24 08          mov    0x8(%rsp),%rdx
  40058b:       64 48 33 14 25 28 00    xor    %fs:0x28,%rdx
  400592:       00 00
  400594:       74 05                   je     40059b <doit+0x4c>
  400596:       e8 85 fe ff ff          callq  400420 <__stack_chk_fail@plt>
  40059b:       48 83 c4 18             add    $0x18,%rsp
  40059f:       c3                      retq

00000000004005a0 <main>:
  4005a0:       48 83 ec 08             sub    $0x8,%rsp
  4005a4:       b8 00 00 00 00          mov    $0x0,%eax
  4005a9:       e8 a1 ff ff ff          callq  40054f <doit>
  4005ae:       b8 00 00 00 00          mov    $0x0,%eax
  4005b3:       48 83 c4 08             add    $0x8,%rsp
  4005b7:       c3                      retq
  4005b8:       0f 1f 84 00 00 00 00    nopl   0x0(%rax,%rax,1)
  4005bf:       00

----------------------------------------------------------------

$ gdb swap
(gdb) break swap
(gdb) run
(gdb) disass swap
...
(gdb) info reg
...

----------------------------------------------------------------