__libc_xxx functions: what are they?

[Carmelo Amoroso]

Denys Vlasenko wrote:
> Hi,
> 
> We have the following aliases witj __libc prefix:
> 
> # grep -rh $'[ \t]__libc_[a-z_0-9]*;$' . | sort | uniq | grep __typeof
> extern __typeof(accept) __libc_accept;
> extern __typeof(close) __libc_close;
> extern __typeof(connect) __libc_connect;
> extern __typeof(creat) __libc_creat;
> extern __typeof(creat64) __libc_creat64;
> extern __typeof(fcntl) __libc_fcntl;
> extern __typeof(fcntl64) __libc_fcntl64;
> extern __typeof(fork) __libc_fork;
> extern __typeof(fstatfs) __libc_fstatfs;
> extern __typeof(fsync) __libc_fsync;
> extern __typeof(getdomainname) __libc_getdomainname;
> extern __typeof(getpid) __libc_getpid;
> extern __typeof(lseek) __libc_lseek;
> extern __typeof(lseek64) __libc_lseek64;
> extern __typeof(msync) __libc_msync;
> extern __typeof(nanosleep) __libc_nanosleep;
> extern __typeof(open) __libc_open;
> extern __typeof(open64) __libc_open64;
> extern __typeof(pause) __libc_pause;
> extern __typeof(poll) __libc_poll;
> extern __typeof(pread) __libc_pread;
> extern __typeof(pread64) __libc_pread64;
> extern __typeof(pselect) __libc_pselect;
> extern __typeof(pwrite) __libc_pwrite;
> extern __typeof(pwrite64) __libc_pwrite64;
> extern __typeof(read) __libc_read;
> extern __typeof(readv) __libc_readv;
> extern __typeof(recv) __libc_recv;
> extern __typeof(recvfrom) __libc_recvfrom;
> extern __typeof(recvmsg) __libc_recvmsg;
> extern __typeof(select) __libc_select;
> extern __typeof(send) __libc_send;
> extern __typeof(sendmsg) __libc_sendmsg;
> extern __typeof(sendto) __libc_sendto;
> extern __typeof(sigaction) __libc_sigaction;
> extern __typeof(sigsuspend) __libc_sigsuspend;
> extern __typeof(statfs) __libc_statfs;
> extern __typeof(system) __libc_system;
> extern __typeof(tcdrain) __libc_tcdrain;
> extern __typeof(wait) __libc_wait;
> extern __typeof(waitpid) __libc_waitpid;
> extern __typeof(write) __libc_write;
> extern __typeof(writev) __libc_writev;
> 
> I do not see any explanation what are these?
> 
> I do see that some of them are used from libpthread, but
> many are not (__libc_accept, __libc_getdomainname...).
> 
> One purpose I might imagine if to make sure you are using
> libc implementation of a function, not something from
> another library...
> 
IIRC, this is one of the reason.

> Anyone knows better?

probably these were intended to be used with
libc_hidden_proto/defs for avoing PLT entries
when called from within libc itself... but now
it should be the case any more.
> --
> vda
carmelo
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