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

JIjiang committed 12 years ago