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--- developingpld:advanceddeveloping:fixingasneeded [2006-08-07 02:52]
SamChi - shorter examplex (removed my cflags)
+++ developingpld:advanceddeveloping:fixingasneeded [2007-05-27 20:51]
arekm
@@ Line 1: / Line 1: @@
-====== Fixing --as-needed problems ======
-==== Quick Workaround ====
-Put in spec file this line:
-<file>%devine filterout_ld -Wl,--as-needed
-</file>
-But **don't use it** unless you really need.
-Why ? Because it's very stupid. If something fails to build normally it's a sign ''--as-needed'' did well it's job and disabled unneeded libraries.
-===== How --as-needed works =====
-With ''--as-needed'' enabled only libraries which contain symbols required by __object files__ are linked.
-== About positions ==
-Linker options are positional, and position is very important. Because it looks for missing symbols only in libraries coming after object file.
-Correct ones are:
-<file>$ gcc $(LDFLAGS) -o $@ $(OBJECTS) $(LIBS)
-</file>
-and this generally works well.
-If there is something like that:
-<file>$ gcc -Wl,--as-needed -l<library> <objects.o>
-</file>
-the library will __never__ be linked, because it's not required at the time it's checked.
-And with something like that:
-<file>$ gcc -l<library> -Wl,--as-needed <objects.o>
-</file>
-library will allways be linked, even if it's not required.
-==== Short examples ====
-Most of problems are with readline/ncurses and tinfo, and it's nice example: tinfo is required by both readline and ncurses, and both are linked with this library (now, when I've [[http://cvs.pld-linux.org/cgi-bin/cvsweb/SOURCES/readline-shared.patch?r1=1.6&amp;r2=1.7|fixed readline]];).
-But some packages link with readline or ncurses while they use __only__ symbols from tinfo.  //Without// ''--as-needed'' those executables work because they are linked with tinfo from readline/ncurses library.  //With// ''--as-needed'' it will not work, because readline/ncurses contain no symbols required by executable so they are not linked, it's dependencies naturally are neither linked. Thats why there is a need to pass ''-ltinfo''. If it requires only symbols from tinfo it's ok to ''s/ncurses/tinfo/''. But if it really requires readline/ncurses but there is some executable (or ./configure) which requires only tinfo both ''-lreadline''/''-lncurses'' and ''-ltinfo'' should be passed.
-For a longer example take a look at real example nr. 1.
-Other common problem is when package produces some shared libraries without linking them with all required libraries, and everything is linked at the end to one binary. So we have:
-<file>$ gcc -Wl,--as-needed -o executable <objects.o> -l2 -l1
-</file>
-it's usual when object files require only library 2, and -l1 is required by -l2. As I said linker only checks for symbols from objects, so -l1 is not linked. Normally it is easy to fix it, simply make sure while linking -l2 it is linked to -l1 (take a look at the second real example).
-===== Real examples =====
-==== 1. unresolved symbols in executable ====
-Very common situation, [[http://cvs.pld-linux.org/cgi-bin/cvsweb/SPECS/xmoto.spec?rev=HEAD|xmoto.spec]]. Actually, it's nothing new. Every linking behaves this way if some library is missing.
-With ''-Wl,--as-needed'' enabled it stops on something like this:
-<file>x86_64-pld-linux-g++ -DNOMMGR -Wall -DGAMEDATADIR=\"/usr/share/xmoto\"  -ggdb -O2 -Wl,--as-needed -o xmoto-edit  BuiltInFont.o [...object files...] Packager.o -lGL -lcurl -lode -llualib50 -llua50 -lSDL_mixer -lbz2 -lz -lpng -ljpeg
-VApp.o: In function `vapp::App::getRealTime()':
-src/VApp.cpp:287: undefined reference to `SDL_GetTicks'
-VApp.o: In function `vapp::App::getTime()':
-src/VApp.cpp:284: undefined reference to `SDL_GetTicks'
-[... bunch of missing SDL functions ...]
-Editor.o: In function `vapp::EditorApp::viewDrawGrid()':
-src/Editor.cpp:777: undefined reference to `SDL_GetMouseState'
-Editor.o:src/Editor.cpp:46: more undefined references to `SDL_GetMouseState' follow
-EditorMain.o: In function `main':
-src/EditorMain.cpp:59: undefined reference to `SDL_Quit'
-collect2: ld returned 1 exit status
-make[1]: *** [xmoto-edit] Error 1
-</file>
-So let's try to find some of missing symbols:
-<file>$ grep SDL_GetMouseState /usr/lib64/libSDL*.so
-Binary file /usr/lib64/libSDL.so matches
-</file>
-they are in ''-lSDL'', but binary does not link with ''-lSDL''; edit Makefile by hand and add ''-lSDL'' at the same place ''-lSDL_mixer'' is: ''LIBS = -lcurl -lode -llualib50 -llua50 -lSDL_mixer -lSDL -lbz2 -lz -lpng -ljpeg''
-What we get after running make in build tree:
-<file>x86_64-pld-linux-g++ -DNOMMGR -Wall -DGAMEDATADIR=\"/usr/share/xmoto\" -ggdb -O2 -Wl,--as-needed -o xmoto-edit BuiltInFont.o [...object files...] Packager.o  -lcurl -lode -llualib50 -llua50 -lSDL_mixer -lSDL -lbz2 -lz -lpng -ljpeg
-VApp.o: In function `vapp::App::grabScreen()':
-src/VApp.cpp:667: undefined reference to `glReadBuffer'
-src/VApp.cpp:671: undefined reference to `glReadPixels'
-[...more missing gl functions...]
-src/Editor.cpp:1280: undefined reference to `glEnable'
-src/Editor.cpp:1288: undefined reference to `glDisable'
-collect2: ld returned 1 exit status
-</file>
-Same story:
-<file>$ grep glEnableClientState /usr/lib64/lib*.so
-Binary file /usr/lib64/libGL.so matches
-</file>
-''LIBS = -lcurl -lode -llualib50 -llua50 -lSDL_mixer -lSDL -lGL -lbz2 -lz -lpng -ljpeg''
-But [[http://cvs.pld-linux.org/cgi-bin/cvsweb/SPECS/xmoto.spec?rev=1.21|take a look at spec file]], ''-lGL'' thing was fixed there already:
-<file>%{__make} \
-        GL_LIBS="-lGL"
-</file>
-Anyway, lets run make, and what we get ?
-<file>x86_64-pld-linux-g++ -DNOMMGR -Wall -DGAMEDATADIR=\"/usr/share/xmoto\"  -ggdb -O2 -Wl,--as-needed -o xmoto-edit  BuiltInFont.o [...object files...] Packager.o  -lcurl -lode -llualib50 -llua50 -lSDL_mixer -lSDL -lGL -lbz2 -lz -lpng -ljpeg
-make[1]: Leaving directory `/home/users/sparky/rpm/BUILD/xmoto-0.2.0'
-</file>
-//It worked !//
-== Why was it working without --as-needed ? ==
-Answer is really easy: libSDL is required by SDL_mixer:
-<file>$ ldd /usr/lib64/libSDL_mixer-1.2.so.0.2.4 | grep SDL
-        libSDL-1.2.so.0 => /usr/lib64/libSDL-1.2.so.0 (0x00002ab425307000)
-</file>
-but xmoto-edit contains no SDL_mixer symbols, that's why it wasn't linked with SDL_mixer, and there was nothing providing SDL library.
-Can you see now why was it stupid to disable ''--as-needed'' ? It worked just perfectly disabling unneeded library !
- Finally, fix for this may be:
-<file>%configure \
-        LIBS="-lSDL -lGL"
-</file>
-or patching configure.in, and the result is:
-''Wrote: /home/users/sparky/rpm/RPMS/xmoto-0.2.0-2.x86_64.rpm''
-==== 2. unresolved symbols in library while linking executable ====
-That's the most common and a little more difficult case, [[http://cvs.pld-linux.org/cgi-bin/cvsweb/SPECS/evolution-data-server.spec?rev=HEAD|evolution-data-server]]:
-Compilation stops at this place:
-<file>/bin/sh ../libtool --tag=CC --mode=link x86_64-pld-linux-gcc -ggdb -O2 -Wall  -Wl,--as-needed -o test-source-selector  test-source-selector.o libedataserverui-1.2.la ../libedataserver/libedataserver-1.2.la -pthread -lglade-2.0 [...many -l libraries...]
--lgnome-keyring -lpthread
-x86_64-pld-linux-gcc -ggdb -O2 -Wall -Wl,--as-needed -o .libs/test-source-selector test-source-selector.o -pthread ./.libs/libedataserverui-1.2.so [many, many .so and -l libraries] -lpthread
-./.libs/libedataserverui-1.2.so: undefined reference to `glade_xml_new'
-./.libs/libedataserverui-1.2.so: undefined reference to `gnome_keyring_find_items_sync'
-./.libs/libedataserverui-1.2.so: undefined reference to `gnome_keyring_get_default_keyring_sync'
-./.libs/libedataserverui-1.2.so: undefined reference to `gnome_keyring_attribute_list_free'
-./.libs/libedataserverui-1.2.so: undefined reference to `glade_xml_get_widget'
-./.libs/libedataserverui-1.2.so: undefined reference to `gnome_keyring_create_sync'
-./.libs/libedataserverui-1.2.so: undefined reference to `gnome_keyring_item_delete_sync'
-./.libs/libedataserverui-1.2.so: undefined reference to `gnome_keyring_item_create_sync'
-collect2: ld returned 1 exit status
-make[2]: *** [test-source-selector] Error 1
-</file>
-It's different case, now it isn't problem with binary file, but with shared library. And the difficulty is it shows up at executable-linking time, because undefined symbols in libraries are permited.
-OK, lets try to fix that library:
-<file>$ grep gnome_keyring_item_delete_sync /usr/lib64/lib*.so
-Binary file /usr/lib64/libgnome-keyring.so matches
-$ grep glade_xml_new /usr/lib64/lib*.so
-Binary file /usr/lib64/libglade-2.0.so matches
-</file>
-Editing Makefile we find:
-''GNOME_KEYRING_LIBS = -lgnome-keyring -lglib-2.0''
-So add this one and glade to that library deps:
-<file>libedataserverui_1_2_la_LIBADD = \
-        $(top_builddir)/addressbook/libebook/libebook-1.2.la    \
-        $(GNOME_KEYRING_LIBS) -lglade-2.0 \
-        $(E_DATA_SERVER_LIBS)
-</file>
-As it uses libtool, remove .la to force regeneration: ''$ rm libedataserverui-1.2.la'' and try to build ''$ make'' passes without problems.
-Now we only need to fix it correcly, after looking at configure.in and Makefile.am one can see it was only a typo:
-<file>libedataserverui_1_2_la_LIBADD = \
-        $(top_builddir)/addressbook/libebook/libebook-1.2.la    \
-        $(E_DATA_SERVER_UI_LIBS)
-                        ^^^
-</file>
-== Why was it working without --as-needed ? ==
-test-source-selector binary was linked with all libraries needed by libedataserverui-1.2.so, and the binary was the one who provided missing symbols to libedataserverui-1.2.so
-==== 3. unresolved symbols caused by incorrect order ====
-Two of most difficult of common problems at once,  [[http://cvs.pld-linux.org/cgi-bin/cvsweb/SPECS/evolution.spec?rev=HEAD|evolution.spec]]:
-The difficulties are:
-  - it appears in configure, what may be difficult to fix and difficult to find what the real problem is
-  - the problem is not a missing library, but arguments order
-configure stops with such message, which says nothing:
-<file>checking if pilot-link handles UTF-8 conversions... no
-configure: error: evolution requires pilot-link to have working UTF-8 conversion routines
-</file>
-let's look at config.log:
-<file>x86_64-pld-linux-gcc -o conftest -ggdb -O2 -DORBIT2=1 -pthread -I/usr/include/libgnome-2.0 [...many -I...] -I/usr/include/libxml2 -Wl,--as-needed -pthread -lgpilotd [...many -l...] -lglib-2.0 conftest.c >&5
-/home/users/sparky/tmp/ccgrL9ll.o: In function `main':
-/home/users/sparky/rpm/BUILD/evolution-2.7.90/conftest.c:64: undefined reference to `convert_ToPilotChar'
-collect2: ld returned 1 exit status
-</file>
-function '''convert_ToPilotChar''', may be found in passed library, but take a look at section about positions, arguments order is incorrect: libraries go before objects (conftest.c) it's very common when someone puts ''-l<>'' in ''LDFLAGS'' instead of ''LIBS'', that was the case too
-just take a look at my fix:
-<file>-       LDFLAGS_save="$LDFLAGS"
--       LDFLAGS="$LDFLAGS $GNOME_PILOT_LIBS"
-+       LIBS_save="$LIBS"
-+       LIBS="$LIBS $GNOME_PILOT_LIBS"
-[...]
--       LDFLAGS="$LDFLAGS_save"
-+       LIBS="$LIBS_save"
-</file>
-with this simple change everything works perfectly.

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