Why is the gdb list subcommand output different for i686?

Issue

• Why is the gdb list subcommand output different for i686?

• i686:

  # gdb
  
  ...snip...
  
  (gdb) attach 27588
  
  ...snip...
  
  __kernel_vsyscall () at arch/x86/vdso/vdso32/int80.S:16
  16              ret
  Current language:  auto; currently asm
  Missing separate debuginfos, use: debuginfo-install glibc-2.10.90-26.i686
  (gdb) list
  11              .type __kernel_vsyscall,@function
  12              ALIGN
  13      __kernel_vsyscall:
  14      .LSTART_vsyscall:
  15              int $0x80
  16              ret
  17      .LEND_vsyscall:
  18              .size __kernel_vsyscall,.-.LSTART_vsyscall
  19              .previous
  20
  (gdb)
  

• x86_64:

  # gdb
  
  ...snip...
  
  (gdb) attach 2181
  
  ...snip...
  
  (gdb) list
  1       #include <unistd.h>
  2
  3       int main()
  4       {
  5               sleep (30);
  6       }
  (gdb) c
  Continuing.
  
  Program exited normally.
  (gdb)