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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] (current)
arekm
@@ Line 4: / Line 4: @@
-==== Quick Workaround ====
+===== Quick and ugly workaround (DON'T USE IT!) =====
-Put in spec file this line:
+Put this line in ''spec'' file:
-<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.
+<file>%define filterout_ld -Wl,--as-needed
+</file>
+But **don't use it** unless you really need to quickly build a package. Never ever try to commit such a change. It might be tempting to do so but if you think about it ''--as-needed'' did it's job well and disabled unneeded libraries. If building fails, it's the package that needs to get fixed, not the linker flags.
 ===== How --as-needed works =====
-With ''--as-needed'' enabled only libraries which contain symbols required by __object files__ are linked.
+With ''--as-needed'' enabled, only libraries containing symbols required by __object files__ are linked.
-== About positions ==
+==== Why it fails for some packages ====
-Linker options are positional, and position is very important. Because it looks for missing symbols only in libraries coming after object file.
+In other words, if you list 10 libraries and only 3 of them contain referenced symbols, others are silently discarded. This is a good thing but unfortunately some projects fail to list all their dependencies properly.
-Correct ones are:
+This normally works because if project requires libraries //A// and //B// and //A// itself lists //B// as a dependency, both //A// and //B// get pulled in even if the project itself only lists //A//.
+Now assume that //A// is a superfluous (unneeded) dependency which gets dropped (or //A// requiring //B// is superfluous and //B// gets dropped from //A//). The symbols are no longer available.
+==== About positions ====
+Linker options are positional, and position is very important. It looks for missing symbols only in libraries coming after object file.
+Correct positions are:
 <file>$ gcc $(LDFLAGS) -o $@ $(OBJECTS) $(LIBS)
@@ Line 29: / Line 38: @@
 and this generally works well.
-If there is something like that:
+ If there is something like that:
 <file>$ gcc -Wl,--as-needed -l<library> <objects.o>
@@ Line 35: / Line 45: @@
 the library will __never__ be linked, because it's not required at the time it's checked.
-And with something like that:
+ 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.
+library will __allways__ be linked, even if it isn't 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]];).
+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 [[http://cvs.pld-linux.org/cgi-bin/cvsweb/SOURCES/readline-shared.patch?r1=1.6&amp;r2=1.7|fixed readline]] is fixed).
-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.
+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'' linking 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.
@@ Line 59: / Line 70: @@
 <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).
+It's usual situation 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).
@@ Line 73: / Line 84: @@
-<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
+<file>g++ -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()':
@@ Line 98: / Line 109: @@
 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''
+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:
@@ Line 104: / Line 115: @@
-<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
+<file>g++ -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()':
@@ Line 137: / Line 148: @@
-<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
+<file>g++ -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 !//
+**It worked !**
@@ Line 178: / Line 189: @@
-<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...]
+<file>/bin/sh ../libtool --tag=CC --mode=link gcc -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
+gcc -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'
@@ Line 210: / Line 221: @@
 ''GNOME_KEYRING_LIBS = -lgnome-keyring -lglib-2.0''
-So add this one and glade to that library deps:
+So add this one and ''-lglade-2.0'' to that library deps:
@@ Line 233: / Line 244: @@
 == 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
+''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
+=== What if broken library comes from other package ? ===
+You can check manually does library has all required symbols, simply running ' gcc //library// ', like this:
+This is an example of correctly linked library:
+<file>$ gcc /usr/lib64/liblftp-tasks.so.0.0.0
+/usr/lib64/gcc/x86_64-pld-linux/4.1.2/../../../../lib64/crt1.o: In function `_start':
+(.text+0x20): undefined reference to `main'
+collect2: ld returned 1 exit status
+</file>
+And incorrectly linked one:
+<file>$ gcc /usr/lib64/liblftp-jobs.so.0.0.0
+/usr/lib64/gcc/x86_64-pld-linux/4.1.2/../../../../lib64/crt1.o: In function `_start':
+(.text+0x20): undefined reference to `main'
+/usr/lib64/liblftp-jobs.so.0.0.0: undefined reference to `StringSet::Remove(int)'
+/usr/lib64/liblftp-jobs.so.0.0.0: undefined reference to `Buffer::Format(char const*, ...)'
+[...]
+/usr/lib64/liblftp-jobs.so.0.0.0: undefined reference to `SMTask::SuspendSlave()'
+collect2: ld returned 1 exit status
+</file>
+**Warning:** some libraries may require to have unresolved symbols.
 ==== 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]]:
+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:
@@ Line 256: / Line 292: @@
-<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
+<file>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':
@@ Line 263: / Line 299: @@
 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
+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:
+Just take a look at my fix:
@@ Line 277: / Line 313: @@
 +       LIBS="$LIBS_save"
 </file>
-with this simple change everything works perfectly.
+With this simple change everything works perfectly.

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