Linus Torvalds [off-list ref] writes:

On Mon, Jul 25, 2022 at 5:39 AM Michael Ellerman [off-list ref] wrote:

quoted

Further digging shows that the build failures only occur with compilers
that default to 64-bit long double.

Where the heck do we have 'long double' things anywhere in the kernel?

There's one or two uses, but not in any code that's relevant to this
issue AFAICS.

I tried to grep for it, and failed miserably. I found some constants
that would qualify, but they were in the v4l colorspaces-details.rst
doc file.

Strange.

It doesn't seem to matter if you use long double or not. It's just that
if the long double size is 64-bits the linker refuses to link a mixture
of soft/hard-float objects.

The 64-bit ABI says long double is 128-bits, so the compilers that are
using 64-bit long double are either not built correctly, or we are not
passing the correct flags to them.

There's an -mlong-double-128 flag which we can pass at build time which
seems to do the right thing, I will probably add that to the kernel
CFLAGS, but I want that to get a bit more testing.

cheers