[MacPorts] #41918: R-3.0.2_1: +atlas variant fails to build

[MacPorts]

#41918: R-3.0.2_1: +atlas variant fails to build
-------------------------+--------------------------------
 Reporter:  drjesacco@…  |      Owner:  macports-tickets@…
     Type:  defect       |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:  2.2.1
 Keywords:               |       Port:  R-3.0.2_1
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 The +atlas variant of R-3.0.2_1 fails to build because of a library search
 path issue.  A patch is attached to this ticket.

 -Joseph

 Discussion
 ----------
 So... You have been passing flags to linkers for years. Altering the
 linker search path using the -L option has been a favorite:

 Search paths
    ld maintains a list of directories to search for a library or framework
 to use.  The default library search path
    is /usr/lib then /usr/local/lib. The -L option will add a new library
 search path. The default framework search path is /Library/Frameworks then
 /System/Library/Frameworks. (Note: previously, /Network/Library/Frame-
 works was at the end of the default path.  If you need that functionality,
 you need to explicitly add -F/Net-work/Library/Frameworks). The -F option
 will add a new framework search path.  The -Z option will remove the
 standard search paths.  The -syslibroot option will prepend a prefix to
 all search paths.


 Use the -L option and the linker will do your bidding. Add some -Lpath
 statements  to the compile line and the linker will search for libraries
 in the order of your choosing. Right?

 Well... Not quite. The linker prefers shared libraries over static
 libraries.  If you ask it to find

         -lMyLib

 the linker will first search the *entire* search path for a shared library
 version of MyLib. If none is found, it will then search through the entire
 search path for the static version of MyLib.


 Why is this a bad thing and what can you do about it?


 Suppose you create a static version of libatlas and install it in

         /opt/local/lib/libatlas.a

 When you want to link against this library, you would might use something
 like

         -L/opt/local/lib -latlas

 This works provided libatlas.dylib does not exist elsewhere in the ld
 search path. Suppose libatlas.dylib exists in /usr/lib.  Even though you
 have altered the ld search path with a -Lpath statement,  the linker will
 choose the shared version in /usr/lib over the static version in
 /opt/local/lib

 What to do?

 The linker has yet another flag that will alter the search procedure to do
 what you really had in mind:

  -search_paths_first

 By default the -lx and -weak-lx options first search for a file of the
 form 'libx.dylib' in each directory in the library search path, then a
 file of the form 'libx.a' is searched for in the library search paths.
 This option changes it so that in each path `libx.dylib' is searched for
 then'libx.a' before the next path in the library search path is searched.

-- 
Ticket URL: <https://trac.macports.org/ticket/41918>
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