Difference between revisions of "Documentation/Snapshot/Developers/Overlinking Underlinking"
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= Questions = | = Questions = | ||
| − | + | == Should we use the --as-needed linker flags ? (see [1], [2], [3], [4]) ? == | |
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| + | * References: | ||
[1] http://linux.die.net/man/1/ld | [1] http://linux.die.net/man/1/ld | ||
[2] http://blog.flameeyes.eu/2009/07/01/does-as-needed-link-make-software-faster | [2] http://blog.flameeyes.eu/2009/07/01/does-as-needed-link-make-software-faster | ||
[3] http://www.gentoo.org/proj/en/qa/asneeded.xml | [3] http://www.gentoo.org/proj/en/qa/asneeded.xml | ||
[4] http://wiki.mandriva.com/en/Overlinking#Problems_introduced_by_--as-needed | [4] http://wiki.mandriva.com/en/Overlinking#Problems_introduced_by_--as-needed | ||
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| + | == Should we avoid the use of {VTK,ITK}_LIBRARIES and specify dependency explicitly when developing libraries depending on these toolkit ? == | ||
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| + | * Reply from Ben Boeckel: | ||
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| + | This would be the way I'd go. It reduces the amount of work the linker | ||
| + | needs to do and if dependencies grow, and it triggers a linker error | ||
| + | instead of passing silently. | ||
| + | |||
| + | To fully do this, the libraries in VTK and ITK should specify | ||
| + | target_link_libraries(lib LINK_INTERFACE_LIBRARIES ...) correctly so | ||
| + | that transitive dependencies don't silently supply dependency growth as | ||
| + | well. Newer versions of gcc and binutils are moving towards doing this | ||
| + | by default, so running a dashboard on something with at least gcc 4.6 | ||
| + | should help. | ||
| + | |||
| + | There's some slight differences between static and shared libraries on | ||
| + | both *nix and Win32 (not that familiar with Mac) as well that dashboards | ||
| + | should test. | ||
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| + | == Should we update VTK, ITK, ... build system to understand the COMPONENT parameters of find_package ? == | ||
| + | |||
| + | == Would it speed up the "fixup" of libraries when generating packages on Mac ? == | ||
Revision as of 17:37, 3 March 2012
Home < Documentation < Snapshot < Developers < Overlinking UnderlinkingContents
- 1 Hypothesis
- 2 Background
- 3 Questions
- 3.1 Should we use the --as-needed linker flags ? (see [1], [2], [3], [4]) ?
- 3.2 Should we avoid the use of {VTK,ITK}_LIBRARIES and specify dependency explicitly when developing libraries depending on these toolkit ?
- 3.3 Should we update VTK, ITK, ... build system to understand the COMPONENT parameters of find_package ?
- 3.4 Would it speed up the "fixup" of libraries when generating packages on Mac ?
Hypothesis
When building application on the top of our toolkits: VTK, ITK, etc ..
.... we usually rely on the CMake variable named: VTK_LIBRARIES, ITK_LIBRARIES, ...
This implies that every targets linked using these variables will be linked against the complete list of libraries.
Background
- While working on issue associated with ITK_AUTOLOAD_FACTORY, I noticed that using tool like ldd was systematically listing all VTK and ITK libraries to list dependency of a custom factory. Using the "-u" flag helps to find out which library are not direct dependency ... doing so just doesn't "feel" right and make the all process tedious and time consuming.
- Then, instead of trying to work around the "issue", I decided to communicate with the rest of the team to get a better understanding of what we should be doing and, by extension, what we should be recommending to developers outside Kitware.
Questions
Should we use the --as-needed linker flags ? (see [1], [2], [3], [4]) ?
- References:
[1] http://linux.die.net/man/1/ld [2] http://blog.flameeyes.eu/2009/07/01/does-as-needed-link-make-software-faster [3] http://www.gentoo.org/proj/en/qa/asneeded.xml [4] http://wiki.mandriva.com/en/Overlinking#Problems_introduced_by_--as-needed
Should we avoid the use of {VTK,ITK}_LIBRARIES and specify dependency explicitly when developing libraries depending on these toolkit ?
- Reply from Ben Boeckel:
This would be the way I'd go. It reduces the amount of work the linker needs to do and if dependencies grow, and it triggers a linker error instead of passing silently.
To fully do this, the libraries in VTK and ITK should specify target_link_libraries(lib LINK_INTERFACE_LIBRARIES ...) correctly so that transitive dependencies don't silently supply dependency growth as well. Newer versions of gcc and binutils are moving towards doing this by default, so running a dashboard on something with at least gcc 4.6 should help.
There's some slight differences between static and shared libraries on both *nix and Win32 (not that familiar with Mac) as well that dashboards should test.
