On Mon, Nov 06, 2017 at 03:59:18PM +0000, Catalin Marinas wrote:

On Mon, Nov 06, 2017 at 10:31:51AM +0100, Jason A. Donenfeld wrote:

quoted

Versions of gcc prior to gcc 5 emitted a __multi3 function call when
dealing with TI types, resulting in failures when trying to link to
libgcc, and more generally, bad performance. However, since gcc 5,
the compiler supports actually emitting fast instructions, which means
we can at long last enable this option and receive the speedups.

The gcc commit that added proper Aarch64 support is:
https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=d1ae7bb994f49316f6f63e6173f2931e837a351d
This commit appears to be part of the gcc 5 release.

There are still a few instructions, __ashlti3 and __ashrti3, which
require libgcc, which is fine. Rather than linking to libgcc, we
simply provide them ourselves, since they're not that complicated.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

According to Arnd, linux-next (with this patch included) fails to build
with gcc-7 (config: https://pastebin.com/raw/sgvPe96e).

Will is managing the upcoming merging window for arm64 but is travelling
this week. I'll wait for couple of days, he'll probably catch up with
emails but my suggestion is that we revert the patch and push it back
again into -next after the 4.15 merging window.

So I pushed a fixup patch on top of for-next/core, but I suggest we
temporarily revert the- DCONFIG_ARCH_SUPPORTS_INT128 option if any other
issues crop up.

Cheers,

Will