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flameeyes 08/07/31 09:41:56 |
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|
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Modified: asneeded.xml |
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Log: |
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Improve the section about ./configure failure. |
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Name and note problems related to using LDFLAGS variable to pass libraries during tests. |
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|
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Revision Changes Path |
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1.16 xml/htdocs/proj/en/qa/asneeded.xml |
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|
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file : http://sources.gentoo.org/viewcvs.py/gentoo/xml/htdocs/proj/en/qa/asneeded.xml?rev=1.16&view=markup |
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plain: http://sources.gentoo.org/viewcvs.py/gentoo/xml/htdocs/proj/en/qa/asneeded.xml?rev=1.16&content-type=text/plain |
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diff : http://sources.gentoo.org/viewcvs.py/gentoo/xml/htdocs/proj/en/qa/asneeded.xml?r1=1.15&r2=1.16 |
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|
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Index: asneeded.xml |
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=================================================================== |
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RCS file: /var/cvsroot/gentoo/xml/htdocs/proj/en/qa/asneeded.xml,v |
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retrieving revision 1.15 |
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retrieving revision 1.16 |
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diff -u -r1.15 -r1.16 |
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--- asneeded.xml 31 Jul 2008 08:45:47 -0000 1.15 |
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+++ asneeded.xml 31 Jul 2008 09:41:56 -0000 1.16 |
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@@ -1,6 +1,6 @@ |
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<?xml version="1.0" encoding="UTF-8"?> |
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<!DOCTYPE guide SYSTEM "http://www.gentoo.org/dtd/guide.dtd"> |
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-<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/proj/en/qa/asneeded.xml,v 1.15 2008/07/31 08:45:47 flameeyes Exp $ --> |
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+<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/proj/en/qa/asneeded.xml,v 1.16 2008/07/31 09:41:56 flameeyes Exp $ --> |
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|
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<guide link="/proj/en/qa/asneeded.xml" lang="en"> |
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<title>--as-needed introduction and fixing guide</title> |
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@@ -18,7 +18,7 @@ |
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<!-- See http://creativecommons.org/licenses/by-sa/2.5 --> |
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<license/> |
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|
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-<version>0.9</version> |
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+<version>0.11</version> |
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<date>2008-07-31</date> |
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|
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<chapter> <!-- Introduction --> |
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@@ -304,30 +304,37 @@ |
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<body> |
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|
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<p> |
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-This is hopefully the less frequent failure but it's also one of the most |
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-impractical to find, although is no different to fix than other failures. |
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-Basically the <c>./configure</c> script of an autotooled package can fail to |
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-find a given library (and thus abort if the support is a strict requirement, or |
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-simply ignore the presence of a library) if that library does not link against |
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-its right dependencies. |
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+Albeit less common than other kind of failures, <c>./configure</c> |
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+execution can fail because of <c>--as-needed</c> too. With this kind |
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+of failures, though, it's difficult to give a single and simple |
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+solution, as there are multiple reasons that might make the script |
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+fail. |
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</p> |
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|
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<p> |
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-The quickest way to find possible failures because of the above is to look into |
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-<path>AC_CHECK_LIB</path> calls inside the configure script; when the fifth |
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-parameter is used (<e>other-libraries</e>) it often means that those libraries |
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-need to be linked in the same binary with the one to check, as they are not |
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-linked in automatically. While this works in a normal situation, when using the |
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-<c>--as-needed</c> flag, they are probably dropped because they are not used by |
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-the test program. |
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+The most common option between those that we have now is that a |
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+library is checked for, but that library wasn't linked to all its |
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+prerequisites (and thus required them to be passed afterward). As |
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+<c>--as-needed</c> makes the linker ignore all the libraries not |
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+needed by the current target, the prerequisites will result missing. |
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</p> |
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|
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<p> |
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-The fixes are the usual ones explained above, but instead of being applied to |
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-the failing package they have to be applied to the library that's failing to be |
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-detected. |
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+To check a <path>configure.ac</path> or <path>configure.in</path> file |
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+for this kind of failures, you can look for the <c>AC_CHECK_LIB</c> |
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+macro, and see whether the fifth parameter is used |
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+(<e>other-libraries</e>). When it is, it often means that those |
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+libraries need to be linked in the final binary to satisfy the |
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+dependencies of the library to check for. At that point, the library |
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+need to be fixed. |
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</p> |
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|
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+<pre caption="example of AC_CHECK_LIB call with fifth-parameter"> |
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+AC_CHECK_LIB([foo], [foo_something], |
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+ [have_foo=yes], [have_foo=no], |
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+ [-ldl -lnsl]) |
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+</pre> |
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+ |
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<note> |
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While applying patches to libraries to fix <c>--as-needed</c> support, it is |
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usually not the case to apply a revision bump: those who don't want to use the |
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@@ -336,6 +343,33 @@ |
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libraries are rebuilt. |
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</note> |
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|
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+<p> |
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+Another possible failure during <c>./configure</c> execution happens |
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+when the code is going to check for functions or other particular |
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+items (symbols, behaviour) and mistakenly pass the dependency |
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+libraries through the <path>LDFLAGS</path> variable. |
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+</p> |
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+ |
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+<pre caption="example of mistake in library checks"> |
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+PKG_CHECK_MODULES([FOO], [foo]) |
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+ |
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+... |
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+ |
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+save_LDFLAGS=$LDFLAGS |
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+LDFLAGS="$LDFLAGS $FOO_LIBS" |
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+ |
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+AC_CHECK_FUNCS([foo_choice1 foo_choice2 foo_choice3]) |
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+ |
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+LDFLAGS=$save_LDFLAGS |
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+</pre> |
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+ |
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+<p> |
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+In this case the solution is very quick: just replace LDFLAGS with |
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+LIBS in both saving and restoring. This way the libraries will be |
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+passed in the correct order (see the following section for more |
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+insight about this kind of problem). |
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+</p> |
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+ |
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</body> |
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</section> |
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<section> <!-- Importance of linking order --> |
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