[RFC PATCH 4/8] mm: Separate fault info out of 'struct vm_fault'

[Will Deacon]

On Thu, Jan 14, 2021 at 01:11:12PM -0800, Linus Torvalds wrote:
> On Thu, Jan 14, 2021 at 11:41 AM Will Deacon <will at kernel.org> wrote:
> >
> > Sure enough, an arm64 defconfig builds perfectly alright with that change,
> > but it really shouldn't. I'm using clang 11.0.5, so I had another go with
> > GCC 9.2.1 and bang:
> 
> Ok, looks like a clang bug, but a reasonably benign one.
> 
> As long as we have sufficient coverage with gcc, we'll get error
> reporting in a timely manner for any new incorrect assignments, so I
> think we can do that constant anonymous struct even if it does mean
> that clang might let some bad cases through (I personally use gcc for
> build testing, and then clang for building my boot kernels, so I'd
> catch anything x86-64 allmodconfig in my build tests).
> 
> And keeping it unnamed it would avoid a lot of noisy churn..

Hmm. The feedback on the clang bug suggests that GCC is the one in the
wrong here (although the argument is based on C11 and I haven't trawled
through the standards to see how this has evolved):

https://bugs.llvm.org/show_bug.cgi?id=48755#c1

There is at least some sympathy to generating a warning, so that might
be good enough. Otherwise, I suppose we can explicitly mark the fields
as 'const' but I won't jump to that immediately.

Will