[Bug c/83782] New: Inconsistent address for hidden ifunc in a shared library

[rafael.espindola at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83782

            Bug ID: 83782
           Summary: Inconsistent address for hidden ifunc in a shared
                    library
           Product: gcc
           Version: 7.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rafael.espindola at gmail dot com
  Target Milestone: ---

Created attachment 43092
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43092&action=edit
testcase

If a function with hidden visibility is implemented with an ifunc, different
translation units have different opinions as to what its address is.

The translation unit implementing the function gets its address with

movq    foo@GOTPCREL(%rip), %rax

That is, it finds the address of the actual function after it is selected.

Any translation unit will use

leaq    foo(%rip), %rax

which the linker translates to the address of the plt.

The net result is that the attached program finds two addresses for the same
function:

$ ./t
0x7fc5f331360a 0x7fc5f3313510

Gives the desire to allow ifuncs to be used by changing just the implementation
(not the declaration), I think the only solution is to use the plt address in
both translation units.