IFUNCs used by libc.so.6 internally on x86-64

[Florian Weimer]

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.

Thanks,
Florian