linux-kernel - Re: mainline build failure for x86

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Date:   Thu, 4 Aug 2022 11:52:09 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Sudip Mukherjee (Codethink)" <sudipm.mukherjee@...il.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: mainline build failure for x86_64 allmodconfig with clang

On Thu, Aug 4, 2022 at 11:37 AM Sudip Mukherjee (Codethink)
<sudipm.mukherjee@...il.com> wrote:
>
> git bisect points to 3876a8b5e241 ("drm/amd/display: Enable building new display engine with KCOV enabled").

Ahh. So that was presumably why it was disabled before - because it
presumably does disgusting things that make KCOV generate even bigger
stack frames than it already has.

Those functions do seem to have fairly big stack footprints already (I
didn't try to look into why, I assume it's partly due to aggressive
inlining, and probably some automatic structures on stack). But gcc
doesn't seem to make it all that much worse with KCOV (and my clang
build doesn't enable KCOV).

So it's presumably some KCOV-vs-clang thing. Nathan?

              Linus