So this looks clean, but I noticed something (that was true even of the old 64-bit accesses) On Tue, Feb 12, 2013 at 12:55 PM, tip-bot for H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> wrote: > + register __inttype(*(ptr)) __val_gu asm("%edx"); \ How does gcc even alllow this? On x86-32, you cannot put a 64-bit value in %edx. Where do the upper bits go? It clearly cannot be %edx:%eax, since we put the error value in %eax. So is the rule for x86-32 that naming "long long" register values names the first register, and the high bits go into the next one (I forget the crazy register numbering, I assume it's %ecx). Or what? This should have a comment. Also, come to think of it, we have tried the "named register variables" thing before, and it has resulted in problems with scope. In particular, two variables within the same scope and the same register have been problematic. And it *does* happen, when you have things like /* copy_user */ put_user(get_user(.., addr), addr2); and then things go downhill. Maybe we do not have these issues, but there are good reasons why we've tried very hard on x86 to avoid named register variables. (I realize that they happen, and some other architectures don't even have good support for naming registers any other way so they are way more common there, so I probably worry needlessly, but it does worry me). Linus -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html