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Date:   Tue, 17 May 2022 10:57:50 +0200
From:   Peter Zijlstra <>
To:     Sami Tolvanen <>
Cc:, Kees Cook <>,
        Josh Poimboeuf <>,,
        Catalin Marinas <>,
        Will Deacon <>,
        Mark Rutland <>,
        Nathan Chancellor <>,
        Nick Desaulniers <>,
        Joao Moreira <>,
        Sedat Dilek <>,
        Steven Rostedt <>,,,
Subject: Re: [RFC PATCH v2 00/21] KCFI support

On Fri, May 13, 2022 at 01:21:38PM -0700, Sami Tolvanen wrote:
> KCFI is a proposed forward-edge control-flow integrity scheme for
> Clang, which is more suitable for kernel use than the existing CFI
> scheme used by CONFIG_CFI_CLANG. KCFI doesn't require LTO, doesn't
> alter function references to point to a jump table, and won't break
> function address equality. The latest LLVM patch is here:
> This RFC series replaces the current arm64 CFI implementation with
> KCFI and adds support for x86_64.

You have some weird behaviour vs weak functions (I so hate those)...

100: 0000000000000980     9 FUNC    LOCAL  DEFAULT    2 __cfi_free_initmem
233: 0000000000000989    35 FUNC    WEAK   DEFAULT    2 free_initmem

With the result that on the final link:

   179: 00000000000009b0     9 FUNC    LOCAL  DEFAULT    1 __cfi_free_initmem
  8689: 00000000000007f0     9 FUNC    LOCAL  DEFAULT   65 __cfi_free_initmem
173283: 00000000000007f9   198 FUNC    GLOBAL DEFAULT   65 free_initmem

This is getting me objtool issues (I'll fix them) but perhaps it's
something you can do something about as well.

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