.\" $OpenBSD: library-specs.7,v 1.13 2018/07/09 15:34:10 jmc Exp $
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.Dd $Mdocdate: July 9 2018 $
.Dt LIBRARY-SPECS 7
.Os
.Sh NAME
.Nm library-specs
.Nd shared library name specifications
.Sh DESCRIPTION
Each
.Ev WANTLIB
item in the ports tree conforms to
.Bd -literal -offset indent
[path/]libname[=major[.minor]]
.Ed
.Pp
or
.Bd -literal -offset indent
[path/]libname[>=major[.minor]]
.Ed
.Pp
All libraries that a package needs must be mentioned in that list.
Except for system and X11 libraries, they all must be reachable through
.Ev LIB_DEPENDS
and
.Ev RUN_DEPENDS ,
directly, or indirectly through recursive dependencies.
.Pp
Conversely, the ports tree
uses
.Ev WANTLIB
to check whether a given
.Ev LIB_DEPENDS
will be required at runtime for shared libraries, and thus turn it into a
.Cm @depend
line
.Po
see
.Xr pkg_create 1
.Pc .
.Pp
The package system will embed correct dependency checks in the built
package in the form of
.Cm @wantlib
lines, according to the normal shared library semantics: any library with
the same major number, and a greater or equal minor number will do.
.Pp
Note that static libraries can only satisfy a library specification if
no shared library has been found.
Thus, if WANTLIB = foo>=5, and both libfoo.so.4.0 and libfoo.a are present,
the check will fail.
.Pp
Therefore, porters must strive to respect correct shared library semantics
in their own ports: by bumping the minor number each time the interface is
augmented, and by bumping the major number each time the interface changes.
Note that adding functions to a library is an interface augmentation.
Removing functions is an interface change.
.Pp
The major.minor components of the library specification are used only as a
build-time check, the run-time checks are computed by
.Xr port-resolve-lib-helper 1 .
For
.Sq libname>=major[.minor] ,
any library which is more recent than the given major.minor version will
do.
If a specific major number is needed, use the form
.Sq libname=major[.minor] .
If the minor component is left empty, any minor will do.
If both components are left empty, any version will do.
.Pp
Most specifications won't mention a
.Pa path :
.Xr port-resolve-lib-helper 1
will look in the default
.Xr ldconfig 8
path automatically, namely
.Pa /usr/local/lib ,
.Pa /usr/X11R6/lib ,
.Pa /usr/lib .
It is generally a bad idea to put libraries elsewhere as they won't be
reached directly.
.Pp
However, distinct ports may install different major versions of the same
library in
.Pa /usr/local/lib ,
and disambiguate the build by creating a link in a separate directory,
and specifying the right options to the linker.
.Pp
These libraries will require a
.Pa path
component in the corresponding
.Ev WANTLIB
to make sure the right library is resolved.
This path is rooted under
.Pa /usr/local .
For instance, to refer to
.Pa /usr/local/lib/qt3/libqt-mt.so.33.0 ,
one would use
.Sq lib/qt3/qt-mt>=33 .
.Sh SEE ALSO
.Xr check-lib-depends 1 ,
.Xr ld 1 ,
.Xr ld.so 1 ,
.Xr pkg_add 1 ,
.Xr port-resolve-lib-helper 1 ,
.Xr bsd.port.mk 5 ,
.Xr packages 7 ,
.Xr packages-specs 7 ,
.Xr ports 7 ,
.Xr ldconfig 8
.Sh HISTORY
Full support for library specifications first appeared in
.Ox 3.1 .
The format of specifications changed slightly to include
.Sq >=
before
.Ox 4.0 .
The interactions between
.Ev LIB_DEPENDS
and
.Ev WANTLIB
were modified and clarified for
.Ox 4.8 .
The format of specifications changed again before
.Ox 4.9
to remove extra noise.