linux-kernel - Re: [PATCH v3] kbuild: Fix TRIM_UNUSED_KSYMS with LTO

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CABCJKucbKVFvOmo6AsJBQfxL0zO3N9R2ydoCvZKpTwPSbOvbkA@mail.gmail.com>
Date:   Mon, 16 Aug 2021 11:06:56 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Alexander Lobakin <alobakin@...me>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] kbuild: Fix TRIM_UNUSED_KSYMS with LTO_CLANG

On Sat, Aug 14, 2021 at 4:27 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Fri, Aug 13, 2021 at 6:46 AM 'Sami Tolvanen' via Clang Built Linux
> <clang-built-linux@...glegroups.com> wrote:
> >
> > With CONFIG_LTO_CLANG, we currently link modules into native
> > code just before modpost, which means with TRIM_UNUSED_KSYMS
> > enabled, we still look at the LLVM bitcode in the .o files when
> > generating the list of used symbols. As the bitcode doesn't
> > yet have calls to compiler intrinsics and llvm-nm doesn't see
> > function references that only exist in function-level inline
> > assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to
> > work with LTO.
> >
> > This change moves module LTO linking to happen earlier, and
> > thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS
> > entirely, allowing us to also drop the whitelist from
> > gen_autoksyms.sh.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1369
> > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> > Reviewed-by: Alexander Lobakin <alobakin@...me>
> > Tested-by: Alexander Lobakin <alobakin@...me>
> > ---
> > Changes in v3:
> > - Added missing FORCE.
>
>
>
> All the modules are recompiled every time.

Oops, .lto.o is missing from targets still, which breaks if_changed.
Fixed in v4. Thanks for testing!

Sami