hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5GB28
CVE: NA

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If ARCH_HAS_MC_EXTABLE is not set then the _mc_ex_table is empty.

There is a logic error in do_sort(). _mc_ex_table is different from
_ex_table. _ex_table is always not empty, while _mc_ex_table may be empty.
If _mc_ex_table is empty, there is a issue with setting the initial value
of mc_extable_index to 0.

Fixes: 8bb071c9 ("arm64: extable: add new extable type "__mc_ex_table"")
Signed-off-by: NTong Tiangen <tongtiangen@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>