On Wed, Nov 18, 2015 at 03:21:19PM +0000, David Laight wrote: > From: Will Deacon > > Sent: 18 November 2015 12:28 > > On Wed, Nov 18, 2015 at 12:11:25PM +0000, David Laight wrote: > > > From: Will Deacon > > > > http://lists.infradead.org/pipermail/linux-arm-kernel/2015-November/386094.html > > > > > > That patch forces a memory write-read and returns uninitialised stack > > > for short reads. > > > > Really? The disassembly looks fine to me. Do you have a concrete example > > of where you think it goes wrong, please? > > > > > Who knows what happens on big-endian systems. > > > > The same thing as READ_ONCE? I'll test it there to make sure, but I > > don't see a problem. > > Ah, god, it is absolutely horrid. But probably right :-( Yeah, I wasn't pretending it was nice :) FWIW, I've given it a reasonable testing in both little-endian and big-endian configurations and it seems to be happy. > Do all the lda variants zero extend to 64 bits ? Yes. > If so maybe you could use a single 64 bit variable for the result of the read > and then cast it to typeof(*p) to get the required sign extension for > small integer types. That was the original proposal from Arnd, but I want this to work with structures smaller than 64-bit (e.g. arch_spinlock_t), so that's why I decided to follow the approach laid down by READ_ONCE. Will -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
