[CMake] Magical transformation of /path/to/libmylib.so to -lmylib

[Jens Mueller]

Michael Hertling wrote:
> On 07/14/2011 12:54 AM, Jens Mueller wrote:
> > Michael Hertling wrote:
> >> On 07/11/2011 11:34 PM, Jens Mueller wrote:
> >>> Hi,
> >>>
> >>> I'm trying to figure out where the path for a found library is changed.
> >>> In my case Curses is found at /usr/lib/libcurses.so. When linking with
> >>> gcc "/usr/lib/libcurses.so" is replaced by "-lcurses" as it is specified
> >>> at http://www.cmake.org/Wiki/CMake_2.6_Notes#Linking_to_System_Libraries.
> >>> Where can I find the code that causes these changes? I looked into
> >>> share/Modules/ at various CMake* files but I'm unable find the code.
> >>>
> >>> Jens
> >>
> >> The system directories are identified during the initial detection
> >> of the compiler ABI ("Detecting <LANG> compiler ABI info"), see
> >>
> >> Modules/CMakeDetermineCompilerABI.cmake
> >> Modules/CMakeParseImplicitLinkInfo.cmake
> >>
> >> w.r.t. the CMAKE_<LANG>_IMPLICIT_LINK_DIRECTORIES variables.
> >>
> >> AFAIK, the actual conversion of the full path to a -l option
> >> is performed in Source/cmComputeLinkInformation.cxx by:
> >>
> >> cmComputeLinkInformation::AddFullItem()
> >> cmComputeLinkInformation::CheckImplicitDirItem()
> >> cmComputeLinkInformation::AddUserItem()
> >>
> >> Previously, the underlying cmComputeLinkInformation::ImplicitLinkDirs
> >> set is populated by cmComputeLinkInformation::LoadImplicitLinkInfo()
> >> from the CMAKE_<LANG>_IMPLICIT_LINK_DIRECTORIES variables' contents.
> > 
> > Thanks very much. This helped a lot. I see much clearer now. The
> > compiler I'm using uses gcc for linking. I made sure that the implicit
> > link directories are properly extracted. But somehow I need to
> > trigger/allow the conversion of full path to -l. It does not work
> > automatically. Do I have to configure this for a new language/new
> > compiler?
> > 
> > Jens
> 
> Although I don't get your drift, you might use imported targets to
> force linking against full paths as well as against -l switches:
> 
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
> PROJECT(IMPORTED C)
> SET(CMAKE_VERBOSE_MAKEFILE ON)
> LINK_DIRECTORIES($ENV{HOME}/lib)
> ADD_LIBRARY(f SHARED IMPORTED)
> ADD_LIBRARY(g SHARED IMPORTED)
> SET_TARGET_PROPERTIES(f PROPERTIES
>     IMPORTED_LOCATION /usr/lib/libncurses.so)
> SET_TARGET_PROPERTIES(g PROPERTIES
>     IMPORTED_LOCATION -lncurses)
> FILE(WRITE ${CMAKE_BINARY_DIR}/main.c "int main(void){return 0;}\n")
> ADD_EXECUTABLE(main main.c)
> TARGET_LINK_LIBRARIES(main f -L/usr/lib g)
> 
> The -L switches can be placed immediately in TARGET_LINK_LIBRARIES() or
> enabled by LINK_DIRECTORIES(), but be aware that -L may be dangerous in
> a subtle manner, see [1].

Sorry. I wasn't specific. With the above I can manually force either
full path or -l behavior. My problem is that I have basic support for a
language that is not yet supported by CMake. Its reference compiler
uses gcc for linking. But I haven't found a way to enable this full path
library conversion and I need it because gcc needs it. Linking a path
like /usr/lib/libcurses.so won't link. Right now I can extract the
implicit link paths. But now I need to trigger this process of
conversion for the compiler. As you say I can do it manually but how do
I enable it for another compiler?

Jens