> Looks the problem is worse than above, not only bitfields are affected, the
> adjacent fields might be involved too, see:
>
> http://lwn.net/Articles/478657/
Not mentioned in there is that even with x86/amd64 given
a struct with the following adjacent fields:
char a;
char b;
char c;
then foo->b |= 0x80; might do a 32bit RMW cycle.
This will (well might - but probably does) happen
if compiled to a 'BTS' instruction.
The x86 instruction set docs are actually unclear
as to whether the 32bit cycle might even be misaligned!
amd64 might do a 64bit cycle (not checked the docs).
David
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