linux-kernel - Re: [PATCH 0/2] Fix CFI failures with GCOV_PROFILE

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Date:   Fri, 23 Jun 2023 11:13:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Fix CFI failures with GCOV_PROFILE_ALL

On Fri, Jun 23, 2023 at 12:11:41AM +0000, Sami Tolvanen wrote:
> Hi folks,
> 
> The following two patches fix CFI failures with GCOV_PROFILE_ALL,
> where the compiler injects indirectly called functions to object
> files that otherwise contain no executable code, and are not
> processed by objtool or don't have CFI enabled. This results in
> missing or incorrect type hashes during boot and when modules are
> loaded.
> 
> Sami Tolvanen (2):
>   kbuild: Fix CFI failures with GCOV
>   kbuild: Disable GCOV for *.mod.o
> 
>  init/Makefile             | 1 +
>  scripts/Makefile.modfinal | 2 +-
>  scripts/Makefile.vmlinux  | 1 +
>  3 files changed, 3 insertions(+), 1 deletion(-)
> 

Urgh, tricky stuff this.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

And yes, objtool essentially assumes vmlinux.o is complete and does LTO
like passes. Is there something kbuild can do to ensure noting else gets
linked in after this?