pthread sem_open : private glibc functions (__libc*

[Florian Weimer]

* Carlos O'Donell:

> On 2/19/19 8:26 AM, Tone Kastlunger wrote:
>> Hi;
>> the sem_open implementation in the pthread library seems to refer to
>> privately defined aliases of some functions of the glibc
>> (__libc_open/cloe, __libc_write for instance).
>> 
>> On the other hand, in the same implementation
>> other glibc function calls are addressed via the (usual) public counterparts
>> (for example unlink).
>> 
>> I'm puzzled about this "dissonance". Any reason behind int?
>
> It's complicated.
>
> https://www.sourceware.org/glibc/wiki/Style_and_Conventions#Double-underscore_names_for_public_API_functions
>
> In this case it's libpthread calling to libc for unlink and munmap.
>
> So it's easiest to call the public symbol because we know in the
> given standard, POSIX, which defines sem_open, we must also have
> a working unlink and munmap.
>
> So there is no namespace issue, and there is no PLT avoidance needed.

But that's true for open and write as well.  I don't know for certain,
but I suspect it's related to the interceptors for open and write in
libpthread (which are still there today, but are not actually needed).

Thanks,
Florian