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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Thu, 7 Jan 2021 21:41:09 +0100
Message-ID: <CAK8P3a1RZ3yUjG6eHKFh9E2fV9xkUtviGCQCaROOw-Sna7XCyA@mail.gmail.com>
Subject: Re: [PATCH] ubsan: disable unsigned-integer-overflow sanitizer with clang
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marco Elver <elver@google.com>,
        George Popescu <georgepope@android.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Thu, Jan 7, 2021 at 7:15 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
> On Thu, Jan 07, 2021 at 09:22:00AM -0800, Kees Cook wrote:

> > I think this is:
> > https://github.com/ClangBuiltLinux/linux/issues/256
> > and that bug needs re-opening? Or maybe there's a new bug I can't find?
>
> The problem is that applying the fix for that issue does not work, nor
> does converting p4d_index to a macro like mips and s390. I am not sure
> what exactly is going on there, it appears that clang cannot reason
> about ptrs_per_p4d because it is an extern variable with no assigned
> value in its translation unit?

Right, I tried the __always_inline trick already and concluded the same.

       Arnd