On Fri, May 27, 2016 at 07:58:06PM +0300, Yury Norov wrote: > So, we have 3 options for now: > 1. Clear top halves in entry.S which means we pass off_t as a pair. > The cost is performance (didn't measure it yet and doubt about it > makes serious impact). The advantage is simplicity and unification with > aarch32, as I mentioned above. And David likes it. And it mininizes > the amount of changes on glibc side. > 2. Clear top halves in in separated file hosted wrappers. > 3. Clear top halves in I-cache and tail optimization friendly in-site wrappers. > > 2 and 3 are the same from ABI point of view. > > 2 is the worst for me as it is the most complex in implementation and > I-cache and tail optimization non-friendly. But Heiko likes it. > > 3 is what Catalin is talking about, and it was my initial approach. > Though I didn't made compiler to do tail optimization, I think we can > do it. I don't fully understand the difference between 2 and 3. My comment was more around annotating the wrappers in (2) with __naked to no longer generate function prologue/epilogue. They would still be in a separate kernel/compat_wrapper.c file. I can't figure out how you would have in-place wrappers for all syscalls. You can indeed handle the current COMPAT_SYSCALL_DEFINE via __SC_DELOUSE (and penalising the AArch32/compat support slightly) but there is no solution for native SYSCALL_DEFINE functions to do it in-place. > But 2 is what we have now. And I'd choose it. We'll never get ilp32 done > if will roll back previously agreed decisions again and again. I would rather roll back a decision than going ahead with a wrong one. Note that this is *ABI*, not a driver that you can fix upstream later. Since yesterday, I realised that (2) requires further annotations and wrapping for the native and compat syscalls used by ILP32 just to cope with pointers. Also given davem's comments, (1) starts to look a bit more appealing (I don't like reverting such decisions either, I'd have to review the code again and again). -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
