Re: [PATCH v3] modpost: check for static EXPORT_SYMBOL* functions

Masahiro Yamada
2019-07-30T16:30:21Z

On Tue, Jul 30, 2019 at 4:00 PM Denis Efremov <efremov@linux.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@linux.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