linux-kernel - Re: [PATCH] scripts/kallsyms: skip ppc compiler stub *.long_branch.* / *.plt

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Date:   Fri, 25 Sep 2020 00:33:49 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scripts/kallsyms: skip ppc compiler stub *.long_branch.*
 / *.plt_branch.*

On Wed, Sep 23, 2020 at 5:43 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On Wed, Sep 23, 2020 at 02:48:56AM +0900, Masahiro Yamada wrote:
> > PowerPC allmodconfig often fails to build as follows:
> >
> >     LD      .tmp_vmlinux.kallsyms1
> >     KSYM    .tmp_vmlinux.kallsyms1.o
> >     LD      .tmp_vmlinux.kallsyms2
> >     KSYM    .tmp_vmlinux.kallsyms2.o
> >     LD      .tmp_vmlinux.kallsyms3
> >     KSYM    .tmp_vmlinux.kallsyms3.o
> >     LD      vmlinux
> >     SORTTAB vmlinux
> >     SYSMAP  System.map
> >   Inconsistent kallsyms data
> >   Try make KALLSYMS_EXTRA_PASS=1 as a workaround
> >   make[2]: *** [../Makefile:1162: vmlinux] Error 1
> >
> > Setting KALLSYMS_EXTRA_PASS=1 does not help.
> >
> > This is caused by the compiler inserting stubs such as *.long_branch.*
> > and *.plt_branch.*
> >
> >   $ powerpc-linux-nm -n .tmp_vmlinux.kallsyms2
> >    [ snip ]
> >   c00000000210c000 T __init_begin
> >   c00000000210c000 T _sinittext
> >   c00000000210c010 t 00000075.plt_branch.da9:19
> >   c00000000210c020 t 00000075.plt_branch.1677:5
> >   c00000000210c030 t 00000075.long_branch.memmove
> >   c00000000210c034 t 00000075.plt_branch.9e0:5
> >   c00000000210c044 t 00000075.plt_branch.free_initrd_mem
> >     ...
> >
> > Actually, the problem mentioned in scripts/link-vmlinux.sh comments;
> > "In theory it's possible this results in even more stubs, but unlikely"
> > is happening here, and ends up with another kallsyms step required.
> >
> > scripts/kallsyms.c already ignores various compiler stubs. Let's do
> > similar to make kallsysms for PowerPC always succeed in 2 steps.
> >
> > Reported-by: Guenter Roeck <linux@...ck-us.net>
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
>
> Tested-by: Guenter Roeck <linux@...ck-us.net>
>
> Thanks,
> Guenter
>
> > ---
> >
> >  scripts/kallsyms.c | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> > index 0096cd965332..306b9b38150f 100644
> > --- a/scripts/kallsyms.c
> > +++ b/scripts/kallsyms.c
> > @@ -120,17 +120,25 @@ static bool is_ignored_symbol(const char *name, char type)
> >               NULL
> >       };
> >
> > +     static const char * const ignored_matches[] = {
> > +             ".long_branch.",        /* ppc stub */
> > +             ".plt_branch.",         /* ppc stub */
> > +             NULL
> > +     };
> > +
> >       const char * const *p;
> >
> > -     /* Exclude symbols which vary between passes. */
> > +     /* ignore symbol names that exactly match to a particular string. */
> >       for (p = ignored_symbols; *p; p++)
> >               if (!strcmp(name, *p))
> >                       return true;
> >
> > +     /* ignore symbol names that start with a particular string. */
> >       for (p = ignored_prefixes; *p; p++)
> >               if (!strncmp(name, *p, strlen(*p)))
> >                       return true;
> >
> > +     /* ignore symbol names that end with a particular string. */
> >       for (p = ignored_suffixes; *p; p++) {
> >               int l = strlen(name) - strlen(*p);
> >
> > @@ -138,6 +146,12 @@ static bool is_ignored_symbol(const char *name, char type)
> >                       return true;
> >       }
> >
> > +     /* ignore symbol names that contain a particular string. */
> > +     for (p = ignored_matches; *p; p++) {
> > +             if (strstr(name, *p))
> > +                     return true;
> > +     }
> > +
> >       if (type == 'U' || type == 'u')
> >               return true;
> >       /* exclude debugging symbols */
> > --
> > 2.25.1
> >

Applied to linux-kbuild/fixes.



-- 
Best Regards
Masahiro Yamada