Re: [patch 3/4] Fix hw watchpoints #2: reordered / simultaneously hit

Jan Kratochvil
2009-11-17T15:31:13Z

On Tue, 17 Nov 2009 15:11:39 +0100, Joel Brobecker wrote:
> > ??? Why? What's wrong with bitfields that we should avoid them?
>
> It makes access to the field more difficult and require more instructions.

While true...

0000000000000000 <get>:
0: 0f b6 47 04 movzbl 0x4(%rdi),%eax
+ 4: 83 e0 01 and $0x1,%eax
c3 retq

0000000000000010 <set>:
- 10: c6 47 04 01 movb $0x1,0x4(%rdi)
+ 10: 80 4f 04 01 orb $0x1,0x4(%rdi)

... one may miss turning it to a flag for sharing the byte for other flags in
future possibly creating the struct needlessly larger.

But OK.

Regards,
Jan