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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Fri, 21 Jul 2023 23:19:21 +0900
Message-ID: <CAK7LNATKCNitdcWKmvJEWxq5YWq8RpFS+K=Xzji0Zx8wQikq_Q@mail.gmail.com>
Subject: Re: [PATCH -next] modpost: move some defines to the file head
To:     Palmer Dabbelt <palmer@rivosinc.com>
Cc:     wangkefeng.wang@huawei.com, mcgrof@kernel.org, nathan@kernel.org,
        ndesaulniers@google.com, nicolas@fjasle.eu,
        linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org
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On Fri, Jul 21, 2023 at 11:01=E2=80=AFPM Palmer Dabbelt <palmer@rivosinc.co=
m> wrote:
>
> On Fri, 21 Jul 2023 04:58:20 PDT (-0700), masahiroy@kernel.org wrote:
> > On Thu, Jul 13, 2023 at 1:28=E2=80=AFAM Palmer Dabbelt <palmer@rivosinc=
.com> wrote:
> >>
> >> On Wed, 12 Jul 2023 08:55:23 PDT (-0700), masahiroy@kernel.org wrote:
> >> > +To: Luis Chamberlain, the commiter of the breakage
> >> >
> >> >
> >> >
> >> > On Wed, Jul 12, 2023 at 10:44=E2=80=AFAM Kefeng Wang <wangkefeng.wan=
g@huawei.com> wrote:
> >> >>
> >> >> with "module: Ignore RISC-V mapping symbols too", build error occur=
s,
> >> >>
> >> >> scripts/mod/modpost.c: In function =E2=80=98is_valid_name=E2=80=99:
> >> >> scripts/mod/modpost.c:1055:57: error: =E2=80=98EM_RISCV=E2=80=99 un=
declared (first use in this function)
> >> >>   return !is_mapping_symbol(name, elf->hdr->e_machine =3D=3D EM_RIS=
CV);
> >> >>
> >> >> Fix it by moving the EM_RISCV to the file head, also some other
> >> >> defines in case of similar problem in the future.
> >> >
> >> >
> >> >
> >> > BTW, why is the flag 'is_riscv' needed?
> >> >
> >> >
> >> > All symbols starting with '$' look special to me.
> >> >
> >> >
> >> >
> >> > Why not like this?
> >> >
> >> >
> >> >        if (str[0] =3D=3D '$')
> >> >                  return true;
> >> >
> >> >        return false;
> >>
> >> There's a bit of commentary in the v1
> >> <https://lore.kernel.org/all/20230707054007.32591-1-palmer@rivosinc.co=
m/>,
> >> but essentially it's not necessary.  I just wanted to play things safe
> >> and avoid changing the mapping symbol detection elsewhere in order to
> >> deal with RISC-V.
> >>
> >> IIRC we decided $ was special in RISC-V because there were some other
> >> ports that behaved that way, but it wasn't universal.  If folks are OK
> >> treating $-prefixed symbols as special everywhere that's fine with me,=
 I
> >> just wasn't sure what the right answer was.
> >>
> >> There's also some similar arch-specific-ness with the labels and such =
in
> >> here.
> >
> > Hi Palmer,
> >
> > I am not a toolchain expert, but my gut feeling is
> > that the code was safer than needed.
> >
> >
> > I'd like to remove the 'is_riscv' switch rather than
> > applying this patch.
> >
> > Will you send a patch, or do you want me to do so?
>
> I've pretty much got it already.  Do you want it on top of the original
> patch, or just squashed in so you can drop it?


It is up to Luis Chamberlain.

The original patch does not exist in my kbuild tree.
(and I was not even not CC'ed, so I had not noticed it
before I saw this report)


commit c05780ef3c190c2dafbf0be8e65d4f01103ad577
Author:     Palmer Dabbelt <palmer@rivosinc.com>
AuthorDate: Fri Jul 7 09:00:51 2023 -0700
Commit:     Luis Chamberlain <mcgrof@kernel.org>
CommitDate: Mon Jul 10 12:45:23 2023 -0700

    module: Ignore RISC-V mapping symbols too

    RISC-V has an extended form of mapping symbols that we use to encode
    the ISA when it changes in the middle of an ELF.  This trips up modpost
    as a build failure, I haven't yet verified it yet but I believe the
    kallsyms difference should result in stacks looking sane again.

    Reported-by: Randy Dunlap <rdunlap@infradead.org>
    Closes: https://lore.kernel.org/all/9d9e2902-5489-4bf0-d9cb-556c8e5d71c=
2@infradead.org/
    Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
    Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
    Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
    Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>


--
Best Regards
Masahiro Yamada