int main()

int main()
{
	struct st {
		int aa:16;
		int bb:16;
	} s;
	s.aa = 1;
	s.bb = 2;
	return 0;
}
objdump -d:
elf64-x86-64
Disassembly of section .text:

0000000000000000 <main>:
   0:	55                   	push   %rbp
   1:	48 89 e5             	mov    %rsp,%rbp
   4:	48 81 ec 10 00 00 00 	sub    $0x10,%rsp
   b:	b8 01 00 00 00       	mov    $0x1,%eax
  10:	48 89 c1             	mov    %rax,%rcx
  13:	81 e1 ff ff 00 00    	and    $0xffff,%ecx
  19:	8b 55 fc             	mov    -0x4(%rbp),%edx
  1c:	81 e2 00 00 ff ff    	and    $0xffff0000,%edx
  22:	09 d1                	or     %edx,%ecx
  24:	89 4d fc             	mov    %ecx,-0x4(%rbp)
  27:	b8 02 00 00 00       	mov    $0x2,%eax
  2c:	48 89 c1             	mov    %rax,%rcx
  2f:	81 e1 ff ff 00 00    	and    $0xffff,%ecx
  35:	c1 e1 10             	shl    $0x10,%ecx
  38:	8b 55 fc             	mov    -0x4(%rbp),%edx
  3b:	81 e2 ff ff 00 00    	and    $0xffff,%edx
  41:	09 d1                	or     %edx,%ecx
  43:	89 4d fc             	mov    %ecx,-0x4(%rbp)
  46:	b8 00 00 00 00       	mov    $0x0,%eax
  4b:	e9 00 00 00 00       	jmpq   50 <main+0x50>
  50:	c9                   	leaveq
  51:	c3                   	retq

After the patch

Disassembly of section .text:

0000000000000000 <main>:
   0:	55                   	push   %rbp
   1:	48 89 e5             	mov    %rsp,%rbp
   4:	48 81 ec 10 00 00 00 	sub    $0x10,%rsp
   b:	8b 45 fc             	mov    -0x4(%rbp),%eax
   e:	81 e0 00 00 ff ff    	and    $0xffff0000,%eax
  14:	83 c8 01             	or     $0x1,%eax
  17:	89 45 fc             	mov    %eax,-0x4(%rbp)
  1a:	8b 45 fc             	mov    -0x4(%rbp),%eax
  1d:	81 e0 ff ff 00 00    	and    $0xffff,%eax
  23:	81 c8 00 00 02 00    	or     $0x20000,%eax
  29:	89 45 fc             	mov    %eax,-0x4(%rbp)
  2c:	b8 00 00 00 00       	mov    $0x0,%eax
  31:	e9 00 00 00 00       	jmpq   36 <main+0x36>
  36:	c9                   	leaveq
  37:	c3                   	retq