build/separate.md: explain rpath vs runpath #371
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- Explain that LD_LIBRARY_PATH can override runpath but not rpath. .. because using runpath solved some in-tree curl testing problems I had with libtool, so I figure other users may benefit from knowing about it. Ref: curl/curl#432 (comment) Closes #xxxx
| since then libtool can use `LD_LIBRARY_PATH`. To use an rpath as a runpath add | ||
| the linker flag `-Wl,--enable-new-dtags` like this: | ||
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| LDFLAGS="-Wl,-rpath,$HOME/install/lib -Wl,--enable-new-dtags" ./configure ... |
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Jeffrey Walton pointed out this interesting link on the mailing list:
https://stackoverflow.com/a/55283740
It highlights the fact that gcc's -Wl,-rpath= option already in fact sets the runpath property if you use a new gcc/ld. i verified this with gcc 13.2.0 on Debian.
Somewhat more explained here: https://rohgarg.github.io/notes/2020/02/20/library-search-order.html.
Thus, this section should probably emphasize that this is only valid for "old" linkers. I have not managed to figure out exactly when this change was done.
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I don't think there's enough info to say that for certain that only older linkers set RPATH by default. I pushed a change that says newer linkers may use it:
Newer linkers may use the runpath form of rpath by default when rpath is specified but others need an additional linker flag -Wl,--enable-new-dtags like this:
LDFLAGS="-Wl,-rpath,$HOME/install/lib -Wl,--enable-new-dtags" ./configure ...
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The way you phrase this makes it sound as if this is the preferred way to do it with current toolchains, while in reality it is a way to do it only with old compilers/linkers. I think this should rather stress that part. The already document way sets runpath with current toolsets.
.. because using runpath solved some in-tree curl testing problems I had with libtool, so I figure other users may benefit from knowing about it.
Ref: curl/curl#432 (comment)
Closes #xxxx