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Ulrich Drepper

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The Evils of pkgconfig and libtool [Nov. 12th, 2007|06:02 pm]
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If you need more proof that this insane just look at some of the packages using it. I recently was looking at krb5-auth-dialog. The output of ldd -u -r on the original binary shows 26 unused DSOs.

This can be changed quite easily: add -Wl,--as-needed to link line. Do this in case of this package all but one of the unused dependencies is going away. This has several benefits:

The binary size is actually measurably reduced.

   text    data     bss     dec     hex filename
  35944    6512      64   42520    a618 src/krb5-auth-dialog-old
  35517    6112      64   41693    a2dd src/krb5-auth-dialog

That’s a 2% improvement. Note that all the saved dependencies are all recursive dependencies. The runtime is therefore not much effected (only a little). The saved data is pure overhead. Multiply the number by the thousands of binaries and DSOs which are shipped and the savings are significant.

The second problem to mention here is that not all unused dependencies are gone because somebody thought s/he is clever and uses -pthread in one of the pkgconfig files instead of linking with -lpthread. That’s just stupid when combined with the insanity called libtool. The result is that the -Wl,--as-needed is not applied to the thread library.

Just avoid libtool and pkgconfig. At the very least fix up the pkgconfig files to use -Wl,--as-needed.

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