On Tue, Aug 18, 2020 at 12:19 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, Aug 18, 2020 at 12:03 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote: > > > > I'm not saying "change the semantics", nor am I saying that playing > > whack-a-mole *for a limited time* is unreasonable. But I would like to go back > > to the compiler authors and get them to implement such a #pragma: "this > > freestanding implementation *does* support *this specific library function*, > > and you are free to call it." > > I'd much rather just see the library functions as builtins that always > do the right thing (with the fallback being "just call the standard > function"). > > IOW, there's nothing wrong with -ffreestanding if you then also have > __builtin_memcpy() etc, and they do the sane compiler optimizations > for memcpy(). > > What we want to avoid is the compiler making *assumptions* based on > standard names, because we may implement some of those things > differently. > > And honestly, a compiler that uses 'bcmp' is just broken. WTH? It's > the year 2020, we don't use bcmp. It's that simple. Fix your damn > broken compiler and use memcmp. The argument that memcmp is more > expensive than bcmp is garbage legacy thinking from four decades ago. > > It's likely the other way around, where people have actually spent > time on memcmp, but not on bcmp. > > If somebody really *wants* to use bcmp, give them the "Get off my > lawn" flag, and leave them alone. But never ever should "use bcmp" be > any kind of default behavior. That's some batshit crazy stuff. > > Linus You'll have to ask Clement about that. I'm not sure I ever saw the "faster bcmp than memcmp" implementation, but I was told "it exists" when I asked for a revert when all of our kernel builds went red. -- Thanks, ~Nick Desaulniers
