default on LLVM_IAS=1

[nickdesaulniers]

now that we have LLVM_IAS=1 enabled for MIPS in CI, that leaves just s390 and powerpc without LLVM_IAS=1 support. Let's turn it on by default and have uses opt out explicitly via LLVM_IAS=0.

[nathanchance]

Something to keep in mind is that ARCH=arm and ARCH=riscv did not become buildable with LLVM_IAS=1 until LLVM 13.0.0. ARCH=arm64 and ARCH=x86_64 are buildable with LLVM_IAS=1 since LLVM 11.0.0 so a rhetorical question: should this be version dependent?

[nickdesaulniers]

It's a good point and question.

should this be version dependent?

I think we can simply require folks set LLVM_IAS=0 CROSS_COMPILE=arm-linux-gnueabihf- etc for those older toolchains. This encourages folks to upgrade their tools to have nice things; in this case, a shorter command line.

[nickdesaulniers]

v1: https://lore.kernel.org/lkml/20210802234304.3519577-1-ndesaulniers@google.com/

[nathanchance]

We should also check the various CI systems and see what versions of LLVM they are using along with how they are building the kernel, otherwise that patch could end up breaking them.

[nickdesaulniers]

I mentioned this to @gctucker on Tuesday's KernelCI meeting. If they're not using LLVM=1 when building s390 or ppc, they should be fine.

Perhaps worthwhile to reach out to 0day folks as well.

[nathanchance]

If they're not using LLVM=1 when building s390 or ppc, they should be fine.

Unless I am reading that patch wrong, that impacts CC=clang too.

[nickdesaulniers]

v2: https://lore.kernel.org/lkml/20210806172701.3993843-1-ndesaulniers@google.com/

(probably should have added a Link tag to here)

[nickdesaulniers]

accepted
1: https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git/commit/?h=for-next&id=52cc02b910284d6bddba46cce402044ab775f314
2: https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git/commit/?h=for-next&id=f12b034afeb3a977bbb1c6584dedc0f3dc666f14

[nickdesaulniers]

1. 52cc02b
2. f12b034