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CMP0156.rst

CMP0156.rst 2.2 KB
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  1. CMP0156
    2. 

  2. -------
    3. 

  3. 

  4. .. versionadded:: 3.29
    5. 

  5. 

  6. De-duplicate libraries on link lines based on linker capabilities.
    7. 

  7. 

  8. Traditional linkers maintain a set of undefined symbols during linking. The
    9. 

  9. linker processes each file in the order in which it appears on the command
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  10. line, until the set of undefined symbols becomes empty. An object file is
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  11. linked into the output object when it is encountered, with its undefined
    12. 

  12. symbols added to the set. Upon encountering an archive file a traditional
    13. 

  13. linker searches the objects contained therein, and processes those that satisfy
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  14. symbols in the unresolved set.
    15. 

  15. 

  16. Handling mutually dependent archives may be awkward when using a traditional
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  17. linker. Archive files may have to be specified multiple times.
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  18. 

  19. Some linkers (for instance Apple or Windows linkers, as well as ``LLVM LLD``)
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  20. record all symbols found in objects and archives as they iterate over command
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  21. line arguments. When one of these linkers encounters an undefined symbol that
    22. 

  22. can be resolved by an object file contained in a previously processed archive
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  23. file, it immediately extracts and links it into the output object.
    24. 

  24. 

  25. CMake 3.28 and below may generate link lines that repeat static libraries as
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  26. a traditional linker would need, even when using a linker that does not need it.
    27. 

  27. They may also de-duplicate shared libraries by keeping their last occurrence,
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  28. which on Windows platforms can change DLL load order.
    29. 

  29. 

  30. CMake 3.29 and above prefer to apply different strategies based on linker
    31. 

  31. capabilities.  So, when targeting Apple and Windows platforms, all
    32. 

  32. libraries are de-duplicated.  Moreover, on Windows platforms, libraries
    33. 

  33. are de-duplicated by keeping their first occurrence, thus respecting the
    34. 

  34. project-specified order.  This policy provides compatibility with projects
    35. 

  35. that have not been updated to expect the latter behavior.
    36. 

  36. 

  37. The ``OLD`` behavior for this policy is to always repeat static libraries
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  38. as if using a traditional linker, and always de-duplicate shared libraries
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  39. by keeping the last occurrence of each.  The ``NEW`` behavior for this policy
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  40. is to apply different strategies based on linker capabilities.
    41. 

  41. 

  42. .. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.29
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  43. .. |WARNS_OR_DOES_NOT_WARN| replace:: does *not* warn
    44. 

  44. .. include:: STANDARD_ADVICE.txt
    45. 

  45. 

  46. .. include:: DEPRECATED.txt
    47.