linux-kernel - Re: [PATCH] modpost: Get proper section index by get_secindex() instead of st

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Date:   Wed, 18 Mar 2020 18:08:46 +0800
From:   Xiao Yang <yangx.jy@...fujitsu.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
CC:     Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] modpost: Get proper section index by get_secindex() instead
 of st_shndx

On 2020/3/18 17:49, Masahiro Yamada wrote:
> On Tue, Mar 17, 2020 at 10:05 AM Xiao Yang<yangx.jy@...fujitsu.com>  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@...ora-30 linux]# file Module.symvers
>>> Module.symvers: data
>>> [root@...ora-30 linux]# head -n1 Module.symvers
>>> 0x5caf3011      ipv6_chk_custom_prefix  ▒▒▒▒▒▒▒▒        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@...ora-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@...ora-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@...fujitsu.com>
>>> ---
>>>    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
>
>
> .
>