pnoltes opened a new pull request, #524:
URL: https://github.com/apache/celix/pull/524
This PR adds the generation and usage of an export header and its macros to
the libraries etcdlib, dfi, utils and framework.
For the updated libraries the default (C) symbol visibility is also set to
hidden.
As result almost all headers for the libraries etcdlib, dfi, utils and
framework are updated to ensure the correct symbol visibility.
This is the first step for the issue #442.
The export headers are generated using the CMake function
`generate_export_header` and for dfi, utils and framework the header filename
is configured as `celix_<lib>_export.h` and the base macro name as
`CELIX_<LIB>`.
The utils and framework libraries also have an `OBJECT` library variant
(needed for error injection). For now I updated the CMakelists.txt file to
configure the `SHARED` / `OBJECT` libs in 2 different ways:
- The current way of configuring the _obj `OBJECT` library and having the
`SHARED` library depending (link PUBLIC) on the _obj library.
- Using a cmake function to configure both the `OBJECT` and `SHARED`
libraries and generating a export header for both library (with the same
filename and macro names).
The different ways can be toggled using the CMake variables
`CELIX_UTILS_CMAKE_CONFIGURE_ALT_OPTION` and
`CELIX_FRAMEWORK_CMAKE_CONFIGURE_ALT_OPTION`, but before merging the PR I would
like to choice one way and remove the other.
The reason I added an other way of configuring the `SHARED` and `OBJECT`
library for utils and framework is that the generated export header use a
`#ifdef` to distinguish against building and using a library and IMO to let
this work as intended both the `OBJECT` and `SHARED` library should have their
own export header.
See the following snippets from the utils and utils_obj generated export
header:
```C
# ifdef utils_EXPORTS
/* We are building this library */
# define CELIX_UTILS_EXPORT __attribute__((visibility("default")))
# else
/* We are using this library */
# define CELIX_UTILS_EXPORT __attribute__((visibility("default")))
# endif
```
```C
# ifdef utils_obj_EXPORTS
/* We are building this library */
# define CELIX_UTILS_EXPORT __attribute__((visibility("default")))
# else
/* We are using this library */
# define CELIX_UTILS_EXPORT __attribute__((visibility("default")))
# endif
```
For both Linux and OSX the visibility attribute is always "default", so for
Linux/OSX only 1 export header will also work.
Although I think generating 2 export headers for the `OBJECT` and `SHARED`
libraries is more correct, I am not sure if we
should do this because it is more confusion.
Also note that only 1 export header will be installed (the `SHARED` export
header).
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