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Re: pthread sem_open : private glibc functions (__libc*

* Tone Kastlunger:

> Pardon my blatant ignorance;
> libpthread has interceptors?

Yes, it interposes many I/O-related functions:

Compare this (not linked with libpthread):

$ LD_DEBUG=bindings /usr/bin/applydeltarpm |& grep pwrite64
     16014:	binding file /usr/bin/applydeltarpm [0] to /lib64/libc.so.6 [0]: normal symbol `pwrite64' [GLIBC_2.2.5]

To this (linked with libpthread):

$ LD_DEBUG=bindings /usr/bin/perf |& grep pwrite64
     16031:	binding file /usr/bin/perf [0] to /lib64/libpthread.so.0 [0]: normal symbol `pwrite64' [GLIBC_2.2.5]

Depending on how these indirections are implemented, there is an
overhead at each call (IFUNCs are not supported on all targets, after
all).  Calling the libc implementation under a different name avoids the
indirection overhead.

Thanks,
Florian
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