linux-kernel - Re: [PATCH v3] modpost: check for static EXPORT

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Date:   Wed, 31 Jul 2019 01:29:27 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Denis Efremov <efremov@...ux.com>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Michal Marek <michal.lkml@...kovi.net>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] modpost: check for static EXPORT_SYMBOL* functions

On Tue, Jul 30, 2019 at 4:00 PM Denis Efremov <efremov@...ux.com> wrote:
>
> On 30.07.2019 01:26, Stephen Rothwell wrote:
> > Hi Denis,
> >
> > On Mon, 29 Jul 2019 17:18:01 +0300 Denis Efremov <efremov@...ux.com> wrote:
> >>
> >> This patch adds a check to warn about static EXPORT_SYMBOL* functions
> >> during the modpost. In most of the cases, a static symbol marked for
> >> exporting is an odd combination that should be fixed either by deleting
> >> the exporting mark or by removing the static attribute and adding the
> >> appropriate declaration to headers.
> >
> > OK, this is now in linux-next and I am getting what look like false
> > positives :-(
> >
> > My powerpc builds produce these:
> >
> > WARNING: "ahci_em_messages" [vmlinux] is the static EXPORT_SYMBOL_GPL
> > WARNING: "ftrace_set_clr_event" [vmlinux] is the static EXPORT_SYMBOL_GPL
> > WARNING: "empty_zero_page" [vmlinux] is the static EXPORT_SYMBOL
> > WARNING: "jiffies" [vmlinux] is the static EXPORT_SYMBOL
> >
> > empty_zero_page (at least) is not static.  It is defined in assembler ...
>
> This could be fixed either by adding the type, for example:
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -478,6 +478,7 @@ EXPORT_SYMBOL(phys_base)
>
>          __PAGE_ALIGNED_BSS
>   NEXT_PAGE(empty_zero_page)
> +.type empty_zero_page, STT_OBJECT
>          .skip PAGE_SIZE
>   EXPORT_SYMBOL(empty_zero_page)

This would require us to fix-up
all assembly files, wouldn't it?


> Or by updating the check in the patch:
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1988,7 +1988,9 @@ static void read_symbols(const char *modname)
>                  unsigned char bind = ELF_ST_BIND(sym->st_info);
>                  unsigned char type = ELF_ST_TYPE(sym->st_info);
>
> -               if (type == STT_OBJECT || type == STT_FUNC) {
> +               if (type == STT_OBJECT ||
> +                   type == STT_FUNC ||
> +                   type == STT_NOTYPE) {
>
> Do I need to resend the whole patch or create new "patch-on-patch"?

I prefer this, but why do you need to check type?

Doesn't this work?

for (sym = info.symtab_start; sym < info.symtab_stop; sym++) {
        unsigned char bind = ELF_ST_BIND(sym->st_info);

        struct symbol *s = find_symbol(remove_dot(info.strtab +
                                                  sym->st_name));

        if (s && (bind == STB_GLOBAL || bind == STB_WEAK))
                s->is_static = 0;
}




-- 
Best Regards
Masahiro Yamada