Build fixes #176
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Build fixes #176
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VPATH is a mechanism used to allow out-of-tree build, not to use source code from a different directory. For this purpose, one should simply use the "subdir-objects" AUTOMAKE_OPTIONS, and reference the source code of the sub-directory in the <prog>_SOURCES variable. Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Using AC_CHECK_LIB() doesn't work properly for static linking, because it doesn't return information on transitive dependencies of libraries. For example, if library A internally uses library B, then with dynamic linking, doing -lA is sufficient. However, with static linking, one must do -lA -lB, and AC_CHECK_LIB() will only give the -lA information. This for example causes a build failure when building sngrep statically with openssl enabled: checking for SSL_new in -lssl... no configure: error: You need to have libssl installed to compile sngrep due to undefined symbols in the OpenSSL library. The proper solution for this is to discover the library using pkg-config, because pkg-config properly returns the list of necessary libraries, as it understands the concept of "list of libraries needed when dynamic linking" and "list of libraries needed for static linking". Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
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Hi @tpetazzoni Thanks for the PR and the awesome explanation of the changes. Thanks again as this PR not only improves the code; I have learnt something so It also improves myself! |
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Yes, whenever pkg-config files are provided by libraries, I believe using pkg-config is better. Sadly, one library that causes a problem when static linking is libpcap, but it doesn't install a .pc file, so pkg-config cannot be used. |
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Ok, I'll give it a try tomorrow replacing some of the other libraries and test under a couple of different distributions :-) |
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Kaian
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Apr 3, 2017
PKG_CHECK_MODULES macro is installed in pkg-config package which is not present in all installations. While it has its advantes, we must check if it's available to support legacy configurations.
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