Why does `disassemble` behave differently on Linux and Mac?

Hi,

https://visualgdb.com/gdbreference/commands/set_disassembly-flavor

I am trying to follow the above example, but it does behave the same
on Linux and Mac. Does anybody know how to make it work on Mac?
Thanks.

On Linux:

$ uname
Linux
$ cat func.c
int func(int a, int b) {
    return a + b;
}
$ gcc -c func.c
$ gdb -q func.o
Reading symbols from func.o...
(No debugging symbols found in func.o)
(gdb) show disassembly-flavor
The disassembly flavor is "att".
(gdb) disassemble func
Dump of assembler code for function func:
   0x0000000000000000 <+0>:	push   %rbp
   0x0000000000000001 <+1>:	mov    %rsp,%rbp
   0x0000000000000004 <+4>:	mov    %edi,-0x4(%rbp)
   0x0000000000000007 <+7>:	mov    %esi,-0x8(%rbp)
   0x000000000000000a <+10>:	mov    -0x4(%rbp),%edx
   0x000000000000000d <+13>:	mov    -0x8(%rbp),%eax
   0x0000000000000010 <+16>:	add    %edx,%eax
   0x0000000000000012 <+18>:	pop    %rbp
   0x0000000000000013 <+19>:	ret
End of assembler dump.

On Mac:

$ uname
Darwin
$ cat func.c
int func(int a, int b) {
    return a + b;
}
$ gcc -c func.c
$ gdb -q func.o
Reading symbols from func.o...
(No debugging symbols found in func.o)
(gdb) show disassembly-flavor
The disassembly flavor is "att".
(gdb) disassemble func
No symbol table is loaded.  Use the "file" command.

-- 
Regards,
Peng