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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Modified 2005-01-09 by aeb
.\"
.TH USELIB 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
uselib \- load shared library
.SH SYNOPSIS
.B #include <unistd.h>
.PP
.BI "int uselib(const char *" library );
.PP
.IR Note :
No declaration of this system call is provided in glibc headers; see NOTES.
.SH DESCRIPTION
The system call
.BR uselib ()
serves to load
a shared library to be used by the calling process.
It is given a pathname.
The address where to load is found
in the library itself.
The library can have any recognized
binary format.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
In addition to all of the error codes returned by
.BR open (2)
and
.BR mmap (2),
the following may also be returned:
.TP
.B EACCES
The library specified by
.I library
does not have read or execute permission, or the caller does not have
search permission for one of the directories in the path prefix.
(See also
.BR path_resolution (7).)
.TP
.B ENFILE
The system-wide limit on the total number of open files has been reached.
.TP
.B ENOEXEC
The file specified by
.I library
is not an executable of a known type;
for example, it does not have the correct magic numbers.
.SH CONFORMING TO
.BR uselib ()
is Linux-specific, and should not be used in programs
intended to be portable.
.SH NOTES
This obsolete system call is not supported by glibc.
No declaration is provided in glibc headers, but, through a quirk of history,
glibc versions before 2.23 did export an ABI for this system call.
Therefore, in order to employ this system call,
it was sufficient to manually declare the interface in your code;
alternatively, you could invoke the system call using
.BR syscall (2).
.PP
In ancient libc versions,
.BR uselib ()
was used to load
the shared libraries with names found in an array of names
in the binary.
.PP
.\" libc 4.3.1f - changelog 1993-03-02
Since libc 4.3.2, startup code tries to prefix these names
with "/usr/lib", "/lib" and "" before giving up.
.\" libc 4.3.4 - changelog 1993-04-21
In libc 4.3.4 and later these names are looked for in the directories
found in
.BR LD_LIBRARY_PATH ,
and if not found there,
prefixes "/usr/lib", "/lib" and "/" are tried.
.PP
From libc 4.4.4 on only the library "/lib/ld.so" is loaded,
so that this dynamic library can load the remaining libraries needed
(again using this call).
This is also the state of affairs in libc5.
.PP
glibc2 does not use this call.
.PP
Since Linux 3.15,
.\" commit 69369a7003735d0d8ef22097e27a55a8bad9557a
this system call is available only when the kernel is configured with the
.B CONFIG_USELIB
option.
.SH SEE ALSO
.BR ar (1),
.BR gcc (1),
.BR ld (1),
.BR ldd (1),
.BR mmap (2),
.BR open (2),
.BR dlopen (3),
.BR capabilities (7),
.BR ld.so (8)