On Fri, Nov 3, 2017 at 10:51 AM, Mark Rutland <mark.rutl...@arm.com> wrote: > I had to create an aarch64-linux-gnu-clang wrapper, too. I'm not sure if > there's build system help to avoid needing that?
Gah! So a BIG difference with Clang vs GCC for cross compiling is that Clang by default ships with all backends enabled, and uses a `-target <triple>` CFLAG to determine the arch to cross compile for, while GCC is configured at compile time to support one back end, IIUC. Clang _can_ be built with all other back ends disabled but one, but I have a problem with this approach: distributions of Clang are rarely configured this way (all backends enabled by default), and it seems we just found this past week that Clang if configured with just one backend, it will silently ignore -target flags for other backends and generate code for the configured backend (this led to: https://lkml.org/lkml/2017/11/2/892). I consider this a bug in Clang, so I just filed: https://bugs.llvm.org/show_bug.cgi?id=35196 > CC arch/arm64/crypto/aes-ce-cipher.o > fatal error: error in backend: Do not know how to split the result of this > operator! Yep, we've seen this. It was the FINAL bug in Clang for compiling the kernel for arm64. It was recently fixed upstream in llvm by g...@google.com, but so recent that you'll need to either compiler Clang from source from ToT or work around it like we have in Android with: https://android.googlesource.com/kernel/msm/+/9093342a0186dad05095b70f1806938310ace6e7 aka patch 7 in this series.
