Re: git: 349cc55c9796 - main - Merge llvm-project main llvmorg-14-init-10186-gff7f2cfa959b

On 18 May 2022, at 02:33, Konstantin Belousov <kostikbel@gmail.com> wrote:
> 
> On Tue, May 17, 2022 at 10:56:14AM -0700, John Baldwin wrote:
>> On 5/16/22 8:09 PM, Charlie Li wrote:
>>> Brooks Davis wrote:
>>>> On Mon, May 16, 2022 at 10:47:49AM -0400, Charlie Li wrote:
>>>>> Dimitry Andric wrote:
>>>>>> This was also reported by another user, and it turned out they were
>>>>>> using WITHOUT_CROSS_COMPILER= in src.conf. If you also have that, try
>>>>>> removing it and rebuilding.
>>>>>> 
>>>>> Yeah I eventually figured that part out. Worked around (first attempt)
>>>>> by building with devel/llvm14 CROSS_TOOLCHAIN, but resulted in certain
>>>>> kernel modules (zfs and a few more) with malformed relocations.
>>>>> Subsequent rebuild with the new world's toolchain corrected that.
>>>> 
>>>> Does that mean we're missing patches in the port? Hopefully anything
>>>> this critical can be merged into LLVM 14.0.3.
>>>> 
>>> Probably:
>>> 
>>> May 15 22:34:08 current-builder kernel: ---<<BOOT>>---
>>> May 15 22:34:08 current-builder kernel: Copyright (c) 1992-2022 The
>>> FreeBSD Project.
>>> May 15 22:34:08 current-builder kernel: Copyright (c) 1979, 1980, 1983,
>>> 1986, 1988, 1989, 1991, 1992, 1993, 1994
>>> May 15 22:34:08 current-builder kernel: The Regents of the
>>> University of California. All rights reserved.
>>> May 15 22:34:08 current-builder kernel: FreeBSD is a registered
>>> trademark of The FreeBSD Foundation.
>>> May 15 22:34:08 current-builder kernel: FreeBSD 14.0-CURRENT #121
>>> main-n255657-48a1a6be196: Sun May 15 21:59:12 EDT 2022
>>> May 15 22:34:08 current-builder kernel:
>>> root@current-builder:/usr/obj/usr/src/amd64.amd64/sys/GENERIC-NODEBUG amd64
>>> May 15 22:34:08 current-builder kernel: clang version 14.0.2
>>> [...]
>>> May 15 22:34:08 current-builder kernel: kldload: unexpected relocation
>>> type 42, symbol index 8321
>> 
>> These are all type 42:
>> 
>> #define	R_X86_64_REX_GOTPCRELX	42
>> 
>> It's not a LLVM bug so much as it is probably missing support in the kernel and/or
>> loader for this type of relocation. kldxref might also need updating.
>> 
>> I suspect due to a mismatch of old lld with new clang or some such that the old
>> lld failed to resolve these relocations to some other type or something weird like
>> that?
> 
> I do think this is a toolchain bug, or at least new and undesired behavior.
> 
> For practical purposes, R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX are
> same as R_X86_64_GOTPCREL64, I believe, but we do not expect GOT relocations
> in the .o object modules on amd64.

I don't see this with clang 14.0.3 from base on 14-CURRENT. None of my
kernel modules has any of these relocations, and I also get no warnings
from kldxref.

Btw, I know that clang from ports will use /usr/local/bin/ld if it is
available, so this might be GNU ld specific behavior? Charlie, do you
have the binutils port installed?

That said, the lld release notes
<https://releases.llvm.org/14.0.0/tools/lld/docs/ReleaseNotes.html#elf-improvements>
say you can now use --no-relax for this:

> • For x86-64, --no-relax now suppresses R_X86_64_GOTPCRELX and
>   R_X86_64_REX_GOTPCRELX GOT optimization (D113615)

So maybe we can use this in sys/conf/kern.mk, or in kmod.mk?

-Dimitry