Re: [PATCH] modpost: Get proper section index by get_secindex() instead of st_shndx

[Xiao Yang]

On 2020/3/18 17:49, Masahiro Yamada wrote:
> On Tue, Mar 17, 2020 at 10:05 AM Xiao Yang<yangx.jy@xxxxxxxxxxxxxx>  wrote:
> > On 2020/3/16 20:28, Xiao Yang wrote:
>
> Thanks for catching this bug.
>
>
> > > (uint16_t) st_shndx is limited to 65535(i.e. SHN_XINDEX) so sym_get_data() gets
> > > wrong section index by st_shndx if object file(e.g. vmlinux.o) has more than
> > Hi,
> >
> > It seems better to say that sym_get_data() gets wrong section index by
> > st_shndx if requested symbol contains extended section index that is
> > more than 65535.
>
>
> Sounds good to me.
>
>
> > Thanks,
> > Xiao Yang
> > > 65535 sessions.  In this case, we need to get proper section index by .symtab_shndx
> > > section.
> > >
> > > Module.symvers generated by building kernel with "-ffunction-sections -fdata-sections"
> > > shows the issue(i.e. cannot get 89902 by st_shndx):
> > > -------------------------------------------------------------------
> > > [root@Fedora-30 linux]# file Module.symvers
> > > Module.symvers: data
> > > [root@Fedora-30 linux]# head -n1 Module.symvers
> > > 0x5caf3011      ipv6_chk_custom_prefix  ââââââââ        vmlinux EXPORT_SYMBOL
>
>
> Could you delete this dump?
> I'd like to avoid garbling where possible.
Hi Masahiro,

Sure, it is OK to delete it.

> > > ...
> > > [root@Fedora-30 linux]# readelf -s -W vmlinux.o | grep __kstrtabns_ipv6_chk_custom_prefix
> > > 199174: 0000000000032578     1 OBJECT  LOCAL  DEFAULT 89902 __kstrtabns_ipv6_chk_custom_prefix
> > > [root@Fedora-30 linux]# readelf -S -W vmlinux.o | grep 89902
> > >     [89902] __ksymtab_strings PROGBITS        0000000000000000 a94e00 0345a2 00   A  0   0  1
> > > -------------------------------------------------------------------
> > >
> > > Fixes: afa0459daa7b ("modpost: add a helper to get data pointed by a symbol")
>
> Strictly speaking, this commit does not introduce any bug.
>
> The CRC bug for MODVERSIONS exists since
> 56067812d5b0 ("kbuild: modversions: add infrastructure for emitting
> relative CRCs")

Will replace it with your suggested commit.

> > > Fixes: 5545322c86d9 ("modpost: refactor namespace_from_kstrtabns() to not hard-code section name")
>
> This commit hash is wrong.
> The correct one is
>
> Fixes: e84f9fbbece1 ("modpost: refactor namespace_from_kstrtabns() to
> not hard-code section name")

Sorry for the wrong commit hash.

Thanks a lot for your quick review.
I will send v2 patch soon.

Best Regards,
Xiao Yang

> > > Signed-off-by: Xiao Yang<yangx.jy@xxxxxxxxxxxxxx>
> > > ---
> > >    scripts/mod/modpost.c | 3 ++-
> > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > > index d9418c58a8c0..c1fec8cac257 100644
> > > --- a/scripts/mod/modpost.c
> > > +++ b/scripts/mod/modpost.c
> > > @@ -310,7 +310,8 @@ static const char *sec_name(struct elf_info *elf, int secindex)
> > >
> > >    static void *sym_get_data(const struct elf_info *info, const Elf_Sym *sym)
> > >    {
> > > -     Elf_Shdr *sechdr =&info->sechdrs[sym->st_shndx];
> > > +     unsigned int secindex = get_secindex(info, sym);
> > > +     Elf_Shdr *sechdr =&info->sechdrs[secindex];
> > >        unsigned long offset;
> > >
> > >        offset = sym->st_value;
>
>
> --
> Best Regards
> Masahiro Yamada
>
>
> .