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Date:   Thu, 5 May 2022 13:36:29 +0100
From:   Mark Rutland <>
To:     Sami Tolvanen <>
Cc:     LKML <>,
        Kees Cook <>,
        Josh Poimboeuf <>,
        Peter Zijlstra <>, X86 ML <>,
        Catalin Marinas <>,
        Will Deacon <>,
        Nathan Chancellor <>,
        Nick Desaulniers <>,
        Joao Moreira <>,
        Sedat Dilek <>,
        Steven Rostedt <>,,
        linux-arm-kernel <>,
Subject: Re: [RFC PATCH 00/21] KCFI support

On Wed, May 04, 2022 at 01:17:25PM -0700, Sami Tolvanen wrote:
> On Wed, May 4, 2022 at 9:41 AM Sami Tolvanen <> wrote:
> >
> > Hi Mark,
> >
> > On Wed, May 4, 2022 at 9:18 AM Mark Rutland <> wrote:
> > > I wanted to give this a spin on arm64, but I'm seeing some very odd toolchain
> > > behaviour. I'm not sure if I've done something wrong, or if I'm just hitting an
> > > edge-case, but it looks like using -fsanitize=kcfi causes the toolchain to hit
> > > out-of-memory errors and other issues which look like they could be memory
> > > corruption.
> >
> > Thanks for the detailed bug report! It definitely looks like something
> > is wrong with the recent switch from std::string to Twine in the Clang
> > code. I didn't see this issue when compiling the arm64 kernel, but
> > I'll take a closer look and see if I can reproduce it.
> I was able to reproduce this by turning off assertions in Clang. It
> seems to work fine with -DLLVM_ENABLE_ASSERTIONS=ON. I'll go fix.

FWIW, a `-DLLVM_ENABLE_ASSERTIONS=ON` build also seems to work for me when
building a kernel with CONFIG_CFI_CLANG=y. It's much slower than a regular
Release build, so I'm still waiting for that to finish building a kernel, but
it has gotten much further through the build without issues.


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