.code16gccの有無で66の位置が変わる (gcc 4.8.1)

code16gcc_test.txt

YUKI.N>cat cbw.s
.code16gcc

_start:
        cbw
        cwde

YUKI.N>gcc -c -o cbw.o cbw.s

YUKI.N>objdump -Mi8086 -D cbw.o

cbw.o:     file format pe-i386


Disassembly of section .text:

00000000 <_start>:
   0:   98                      cbtw
   1:   66 98                   cwtl
   3:   90                      nop

YUKI.N>cat cbw2.s
_start:
        cbw
        cwde

YUKI.N>gcc -c -o cbw2.o cbw2.s

YUKI.N>objdump -D cbw2.o

cbw2.o:     file format pe-i386


Disassembly of section .text:

00000000 <_start>:
   0:   66 98                   cbtw
   2:   98                      cwtl
   3:   90                      nop

reference.md

• x86 instruction listings - Wikipedia, the free encyclopedia
• CBW/CWDE: Convert Byte to Word/Convert Word to Doubleword (x86 Instruction Set Reference)