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

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Date:   Tue, 17 Mar 2020 09:04:54 +0800
From:   Xiao Yang <yangx.jy@...fujitsu.com>
To:     <yamada.masahiro@...ionext.com>, <michal.lkml@...kovi.net>
CC:     Xiao Yang <yangx.jy@...fujitsu.com>,
        <linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] modpost: Get proper section index by get_secindex() instead
 of st_shndx

On 2020/3/16 20:28, Xiao Yang wrote:
> (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.

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
> ...
> [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")
> Fixes: 5545322c86d9 ("modpost: refactor namespace_from_kstrtabns() to not hard-code section name")
> 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;