[Bug gdb/22869] New: set architecture i8068 has no effect on disassembly

["aidankhoury at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=22869

            Bug ID: 22869
           Summary: set architecture i8068 has no effect on disassembly
           Product: gdb
           Version: 8.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: aidankhoury at gmail dot com
  Target Milestone: ---

When specifying the current target architecture as i8086 using `set
architecture i8086`, GDB still disassembles in i386 protected mode.

Here is some example code compiled using NASM with BITS 16 specified:

; i386 instruction set
CPU 386

; Text section
SECTION .text

; 16 bit code
[BITS 16]

check_device:
    mov bx, 55AAh
    mov ah, 41h
    int 13h

    mov si, sDriveParamsBuffer
    mov word [si+DRIVE_PARAMS_EXTENDED.BufferSize], 16
    mov ah, 48h
    int 13h

Here is GDB's disassembly output at the correct location, which is clearly
being seen as 32 bit protected mode code
even though the target architecture is set for i8086:

(gdb) set architecture i8086
The target architecture is assumed to be i8086
(gdb) show architecture
The target architecture is assumed to be i8086
(gdb) disassemble /r $cs * 16 + $eip,+24
Dump of assembler code from 0x2033d to 0x20355:
   0x0002033d:  bb aa 55 b4 41          mov    ebx,0x41b455aa
   0x00020342:  cd 13                   int    0x13
   0x00020344:  72 78                   jb     0x203be
   0x00020346:  66 be a0 2f             mov    si,0x2fa0
   0x0002034a:  00 00                   add    BYTE PTR [eax],al
   0x0002034c:  c7 04 42 00 b4 48 cd    mov    DWORD PTR [edx+eax*2],0xcd48b400
   0x00020353:  13 72 68                adc    esi,DWORD PTR [edx+0x68]


Here are the current flags I use to configure the GDB project for build: 

./configure --enable-64-bit-bfd --disable-werror --disable-win32-registry
--disable-rpath --with-expat --with-zlib --with-lzma --enable-tui

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