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Re: IFUNCs used by libc.so.6 internally on x86-64
On Wed, Jun 7, 2017 at 6:08 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Jun 6, 2017 at 10:50 PM, Florian Weimer <fweimer@redhat.com> wrote:
>> On 06/07/2017 04:11 AM, H.J. Lu wrote:
>>> On Wed, May 31, 2017 at 8:26 AM, Andreas Schwab <schwab@suse.de> wrote:
>>>> On Feb 06 2017, Florian Weimer <fweimer@redhat.com> wrote:
>>>>
>>>>> The selection of string functions is rather curious. Were these choices
>>>>> deliberate?
>>>>
>>>> They probably just happen, because check-localplt doesn't fail.
>>>>
>>>
>>> I believe all internal calls within libc.so can use IFUNC on x86-64 since
>>> unlike x86, x86-64 doesn't need to reserve a register to make a PLT call.
>>> For libc,a, we can't use IFUNC for functions which are called before IFUNC
>>> has been initialized.
>>
>> I see IFUNC relocations on i386 as well:
>>
>> Relocation section [10] '.rel.plt' for section [33] '.got.plt' at offset
>> 0x17678 contains 3 entries:
>> Offset Type Value Name
>> 0x001d7014 386_IRELATIVE 0000000000
>> 0x001d7010 386_IRELATIVE 0000000000
>> 0x001d700c 386_IRELATIVE 0000000000
>>
>> Unfortunately, it's really hard to figure out what they are.
>>
>
> Please try -z print-local-ifuncs:
>
> https://sourceware.org/ml/binutils/2017-06/msg00066.html
>
There are
/tmp/libc.so: local IFUNC function `__wcslen' in
`/export/build/gnu/glibc-32bit/build-i686-linux/libc_pic.os'
/tmp/libc.so: local IFUNC function `__memrchr' in
`/export/build/gnu/glibc-32bit/build-i686-linux/libc_pic.os'
/tmp/libc.so: local IFUNC function `__strncasecmp' in
`/export/build/gnu/glibc-32bit/build-i686-linux/libc_pic.os'
Should they be marked as hidden?
--
H.J.