While using objdump to disassemble a piece of 16-bit i386 code I noticed that
using Intel asm syntax leads to erroneous results for some opcodes.  The
command lines I used were as follows:
objdump -d -mi386 -Maddr16,data16 mbr.o (gas syntax)
objdump -d -mi386:intel -Maddr16,data16 mbr.o (Intel syntax)

The only little problem with gas syntax was that objdump showed
a sign-expanded immediate as a 32-bit value in its output:
  5a:   83 f9 ff                cmp    $0xffffffff,%cx

In Intel syntax there were more errors. I'll show them along with
corresponding gas-syntax output so the problems are clearly visible.
The most of the trouble seems related to indexing with registers.
Thanks!

=== start Intel syntax ===
00000048 <main.4>:
  48:   8a 14 89                mov    dl,BYTE PTR [ecx+ecx*4]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
0000004a <main.5>:
  4a:   89 e7                   mov    di,sp
  4c:   8a 74 01 8b             mov    dh,BYTE PTR [ecx+eax-117]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  50:   4c 02 bb 00 7c 80 fe    rex64X add    r15b,BYTE PTR [ebx-25134080]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  57:   ff 75 32                push   DWORD PTR [ebp+50]
  5a:   83 f9 ff                cmp    cx,0xffffffffffffffff
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  5d:   75 2d                   jne    8c <main.7>
  5f:   51                      push   rcx
  60:   53                      push   rbx
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  61:   bb aa 55                mov    bx,0x55aa
  64:   b4 41                   mov    ah,0x41
  66:   cd 13                   int    0x13
  68:   72 20                   jb     8a <main.6>
  6a:   81 fb 55 aa             cmp    bx,0xaa55
  6e:   75 1a                   jne    8a <main.6>
  70:   f6 c1 01                test   cl,0x1
  73:   74 15                   je     8a <main.6>
  75:   5b                      pop    rbx
  76:   66                      data32
  77:   6a 00                   push   0x0
  79:   66                      data32
  7a:   ff 74 08 06             push   DWORD PTR [eax+ecx+6]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  7e:   53                      push   rbx
  7f:   6a 01                   push   0x1
  81:   6a 10                   push   0x10
  83:   89 e6                   mov    si,sp
  85:   b8 00 42                mov    ax,0x4200
  88:   eb 05                   jmp    8f <main.8>

0000008a <main.6>:
  8a:   5b                      pop    rbx
  8b:   59                      pop    rcx
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

0000008c <main.7>:
  8c:   b8 01 02                mov    ax,0x201

0000008f <main.8>:
  8f:   cd 13                   int    0x13
  91:   89 fc                   mov    sp,di
  93:   72 0f                   jb     a4 <err_rd>
  95:   81 bf fe 01 55 aa 75    cmp    DWORD PTR [edi-1437269506],0xc75
  9c:   0c
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  9d:   ff e3                   jmp    bx

=== end Intel syntax ===

=== start gas syntax ===
00000048 <main.4>:
  48:   8a 14                   mov    (%si),%dl

0000004a <main.5>:
  4a:   89 e7                   mov    %sp,%di
  4c:   8a 74 01                mov    1(%si),%dh
  4f:   8b 4c 02                mov    2(%si),%cx
  52:   bb 00 7c                mov    $0x7c00,%bx
  55:   80 fe ff                cmp    $0xff,%dh
  58:   75 32                   jne    8c <main.7>
  5a:   83 f9 ff                cmp    $0xffffffff,%cx
  5d:   75 2d                   jne    8c <main.7>
  5f:   51                      push   %cx
  60:   53                      push   %bx
  61:   bb aa 55                mov    $0x55aa,%bx
  64:   b4 41                   mov    $0x41,%ah
  66:   cd 13                   int    $0x13
  68:   72 20                   jb     8a <main.6>
  6a:   81 fb 55 aa             cmp    $0xaa55,%bx
  6e:   75 1a                   jne    8a <main.6>
  70:   f6 c1 01                test   $0x1,%cl
  73:   74 15                   je     8a <main.6>
  75:   5b                      pop    %bx
  76:   66 6a 00                pushl  $0x0
  79:   66 ff 74 08             pushl  8(%si)
  7d:   06                      push   %es
  7e:   53                      push   %bx
  7f:   6a 01                   push   $0x1
  81:   6a 10                   push   $0x10
  83:   89 e6                   mov    %sp,%si
  85:   b8 00 42                mov    $0x4200,%ax
  88:   eb 05                   jmp    8f <main.8>

0000008a <main.6>:
  8a:   5b                      pop    %bx
  8b:   59                      pop    %cx

0000008c <main.7>:
  8c:   b8 01 02                mov    $0x201,%ax

0000008f <main.8>:
  8f:   cd 13                   int    $0x13
  91:   89 fc                   mov    %di,%sp
  93:   72 0f                   jb     a4 <err_rd>
  95:   81 bf fe 01 55 aa       cmpw   $0xaa55,510(%bx)
  9b:   75 0c                   jne    a9 <err_os>
  9d:   ff e3                   jmp    *%bx

=== end gas syntax ===