Re: [PATCH v11 00/15] kasan: x86: arm64: KASAN tag-based mode for x86

[Maciej Wieczor-Retman <m.wieczorretman@pm.me>]

On 2026-03-10 at 11:24:21 -0700, Andrew Morton wrote:
>On Tue, 10 Mar 2026 17:51:19 +0000 Maciej Wieczor-Retman <m.wieczorretman@pm.me> wrote:
>
>>
>> [1] Currently inline mode doesn't work on x86 due to things missing in
>> the compiler. I have written a patch for clang that seems to fix the
>> inline mode and I was able to boot and check that all patches regarding
>> the inline mode work as expected. My hope is to post the patch to LLVM
>> once this series is completed, and then make inline mode available in
>> the kernel config.
>>
>> [2] While I was able to boot the inline tag-based kernel with my
>> compiler changes in a simulated environment, due to toolchain
>> difficulties I couldn't get it to boot on the machine I had access to.
>> Also boot time results from the simulation seem too good to be true, and
>> they're much too worse for the generic case to be believable. Therefore
>> I'm posting only results from the physical server platform.
>>
>> ======= Compilation
>> Clang was used to compile the series (make LLVM=1) since gcc doesn't
>> seem to have support for KASAN tag-based compiler instrumentation on
>> x86. Patchset does seem to compile with gcc without an issue but doesn't
>> boot afterwards.
>
>So LLVM works partially and gcc doesn't work at all?

The non-working options are disabled in Kconfig so right now only outline KASAN
with LLVM works fully.

>Do we know which compiler people are using?  Google tells me that
>Android, ChromeOS, and OpenMandriva use LLVM.  That's pretty thin.

I don't have any numbers on this matter, from working on this I only got that
there is much more KASAN traffic around clang. So I thought that most KASAN
users prefer LLVM.

>This is all rather problematic and it isn't clear (to me) how to
>proceed at this time.  Do we have any projections on when all this will
>be fixed up?

My understanding is that there is something off in gcc support. I recall Andrey
Konovalov mentioning that gcc also doesn't work well with arm64's KASAN
tag-based mode. As for LLVM inline support I do know the codebase a bit so I got
some WIP patches there. But I wanted to see where this review process goes
before posting to LLVM.

>> The series is based on mm-new.
>
>I actually carry kexec patches in the mm-nonmm-[un]stable branches.
>But the series applies OK anyway.

Should I base this patchset on top of mm-nonmm-stable in the future? I was after
one patch by Andrey Ryabinin that was in mm-new and I needed to rebase on top of
it.

-- 
Kind regards
Maciej Wieczór-Retman