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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Mon, 23 May 2022 01:09:11 +0900
Message-ID: <CAK7LNATr6gpR1TUBp+wxn_JfeQr+cfxwztwupVui1nrWO-8Osg@mail.gmail.com>
Subject: Re: [PATCH v6 00/10] kbuild: yet another series of cleanups (modpost,
 LTO, MODULE_REL_CRCS, export.h)
To:     Sedat Dilek <sedat.dilek@gmail.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-modules <linux-modules@vger.kernel.org>,
        clang-built-linux <llvm@lists.linux.dev>,
        Ard Biesheuvel <ardb@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>
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Precedence: bulk

On Sun, May 22, 2022 at 11:16 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Sun, May 22, 2022 at 11:45 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Sun, May 22, 2022 at 8:50 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > On Sun, May 22, 2022 at 10:45 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > > >
> > > > On Fri, May 13, 2022 at 4:31 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > > >
> > > > > On Fri, May 13, 2022 at 8:42 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > > > >
> > > > > >
> > > > > > This is the third batch of cleanups in this development cycle.
> > > > > >
> > > > >
> > > > >
> > > > > This series is available at
> > > > > git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
> > > > >  lto-cleanup-v6
> > > > >
> > > >
> > > > Hi Masahiro,
> > > >
> > > > I cloned the repository on top of latest Linus Git.
> > > >
> > > > Not able to boot in Quemu - Not able to boot on bare metal.
> > > >
> > > > $ grep module_layout log_quemu-5.18.0-rc7-2-amd64-clang14-lto.txt
> > > > 366:[    2.173265] floppy: disagrees about version of symbol module_layout
> > > > 367:[    2.198746] scsi_common: disagrees about version of symbol module_layout
> > > > 368:[    2.205573] i2c_piix4: disagrees about version of symbol module_layout
> > > > 369:[    2.210610] psmouse: disagrees about version of symbol module_layout
> > > > 370:[    2.225138] scsi_common: disagrees about version of symbol module_layout
> > > > 371:[    2.235536] scsi_common: disagrees about version of symbol module_layout
> > > > 375:Begin: Running /scripts/local-premount ... [    2.298555]
> > > > crc32c_intel: disagrees about version of symbol module_layout
> > > > 376:[    2.303335] crc32c_generic: disagrees about version of symbol
> > > > module_layout
> > > > 377:[    2.306667] libcrc32c: disagrees about version of symbol module_layout
> > > >
> > > > Infos: LLVM-14 + CONFIG_LTO_CLANG_THIN=y
> > > >
> > > > My linux-config and qemu-log are attached.
> > > >
> > >
> > >
> > > Thanks for your testing.
> > >
> > > I was also able to reproduce this issue.
> > >
> > >
> > > The problematic parts are:
> > >
> > > [    2.298555] crc32c_intel: disagrees about version of symbol module_layout
> > > [    2.303335] crc32c_generic: disagrees about version of symbol module_layout
> > > [    2.306667] libcrc32c: disagrees about version of symbol module_layout
> > >
> > >
> > >
> > > When CONFIG_LTO_CLANG_THIN=y,
> > > I cannot see any __crc_* symbols in "nm  vmlinux".
> > >
> > > Perhaps, LTO might have discarded all the __crc_* symbols
> > > from vmlinux, but I am still checking the details...
> > >
> >
> > Thanks for taking care.
> >
> > Just for the records:
> >
> > $ grep CONFIG_MODVERSIONS /boot/config-5.18.0-rc7-2-amd64-clang14-lto
> > CONFIG_MODVERSIONS=y
> >
>
> Did not try CONFIG_MODVERSIONS=n.
>
> We have a new file:
>
> [ include/linux/export-internal.h ]
> /* SPDX-License-Identifier: GPL-2.0-only */
> /*
> * Please do not include this explicitly.
> * This is used by C files generated by modpost.
> */
>
> #ifndef __LINUX_EXPORT_INTERNAL_H__
> #define __LINUX_EXPORT_INTERNAL_H__
>
> #include <linux/compiler.h>
> #include <linux/types.h>
>
> #define SYMBOL_CRC(sym, crc, sec)   \
>        u32 __section("___kcrctab" sec "+" #sym) __crc_##sym = crc
>
> #endif /* __LINUX_EXPORT_INTERNAL_H__ */
>
> But we discard __kcrctab in scripts/module.lds.S file.


No.
scripts/module.lds.S keeps __kcrctab.


The discarded sections are specified a few lines above:

/DISCARD/ : {
         *(.discard)
         *(.discard.*)
         SANITIZER_DISCARDS
}


> Maybe we need:


No.

The problem is __crc_* symbols are dropped from vmlinux
when CONFIG_LTO_CLANG=y.


Please try this fixup:
https://lore.kernel.org/linux-kbuild/20220522160117.599023-1-masahiroy@kernel.org/T/#u


>
> $ git diff scripts/module.lds.S
> diff --git a/scripts/module.lds.S b/scripts/module.lds.S
> index 1d0e1e4dc3d2..c04b596c364b 100644
> --- a/scripts/module.lds.S
> +++ b/scripts/module.lds.S
> @@ -21,8 +21,6 @@ SECTIONS {
>
>        __ksymtab               0 : { *(SORT(___ksymtab+*)) }
>        __ksymtab_gpl           0 : { *(SORT(___ksymtab_gpl+*)) }
> -       __kcrctab               0 : { *(SORT(___kcrctab+*)) }
> -       __kcrctab_gpl           0 : { *(SORT(___kcrctab_gpl+*)) }
>
>        .ctors                  0 : ALIGN(8) { *(SORT(.ctors.*)) *(.ctors) }
>        .init_array             0 : ALIGN(8) { *(SORT(.init_array.*))
> *(.init_array) }
>
> Or even?
>
> $ git diff scripts/kallsyms.c
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 8caabddf817c..fb3601fe8aa3 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -109,7 +109,6 @@ static bool is_ignored_symbol(const char *name, char type)
>        static const char * const ignored_prefixes[] = {
>                "$",                    /* local symbols for ARM, MIPS, etc. */
>                ".L",                   /* local labels,
> .LBB,.Ltmpxxx,.L__unnamed_xx,.LASANPC, etc. */
> -               "__crc_",               /* modversions */
>                "__efistub_",           /* arm64 EFI stub namespace */
>                "__kvm_nvhe_",          /* arm64 non-VHE KVM namespace */
>                "__AArch64ADRPThunk_",  /* arm64 lld */
>
> - Sedat -


-- 
Best Regards
Masahiro Yamada