Messages in this thread | | | Date | Wed, 8 Jun 2022 14:33:42 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] s390: disable -Warray-bounds |
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On Wed, Jun 08, 2022 at 01:07:05PM -0700, Linus Torvalds wrote: > Coming back to this, because my rc2 week tends to be quiet as people > take a breather, and as such a good time for me to do system upgrades. > > And gcc-12 dropped in Fedora 36, and shows problems on x86 too. > > So I suspect we'll have to disable -Warray-bounds globally on gcc-12, > not just on s390. > > Unless Kees has patches ready to go already.
I and others have been working through a bunch of them, though yes, they're not all fixed yet. I've been trying to track it here[1], but many of those fixes are only in -next.
> Some of the warnings look potentially simple, ie > > struct mbus_dram_target_info; > > in <linux/mbus.h> has the comment > > * [..] Peripherals are > * required to support at least 4 decode windows. > > and then as a result has > > int num_cs; > struct mbus_dram_window { > [..] > } cs[4]; > > and that "cs[4]" looks just bogus - it can be a much larger array, the > '4' is just a minimum. The real limit is that 'num_cs' one. > > But there's a *lot* of warnings, and many of them are due to this, and > while some are obvious, others aren't.
When I did a count in -next 2 weeks ago, there were 182 warnings (x86 allmodconfig) from GCC 12 where 153 were from -Warray-bounds. Today we're now down to 80 total (61 from -Warray-bounds), so we've solved over half of them.
> There are other things too in gcc-12 that seem half-baked. I was > interested to see the new '-Wdangling-pointer' thing, but then when I > looked at it, the two cases I looked at were just bogus, so ..
Yes, GCC 12 is very odd in places. Besides the literal-as-pointer issue that still causes problems for s390[2], there seem to be at least a few other bugs associated with the internal diagnostics infrastructure that informs -Warray-bounds, -Wstringop-overflow, etc. I narrowed down one recently with UBSAN_BOUNDS[3] (which therefore impacts all*config builds), but there is no GCC fix yet. :(
So, it's unclear to me if we want to try to get back to 0 warnings (where we were with v5.18 and GCC 11) in the next couple weeks, or if we need to just disable it for GCC 12 until everything is fixed again.
-Kees
[1] https://github.com/KSPP/linux/issues/190 [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578 [3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105679
-- Kees Cook
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