Differences

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--- developingpld:advanceddeveloping:fixingasneeded [2006-08-07 16:27] – - some fixes, gcc <library> trick SamChi
+++ 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.
@@ Line 20: / Line 20: @@
-== About positions ==
+==== Why it fails for some packages ====
+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.
+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.
@@ Line 41: / Line 50: @@
 <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 75: / Line 84: @@
-<file>x86_64-pld-linux-g++ -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 106: / Line 115: @@
-<file>x86_64-pld-linux-g++ -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 139: / Line 148: @@
-<file>x86_64-pld-linux-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
+<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'
@@ Line 180: / Line 189: @@
-<file>/bin/sh ../libtool --tag=CC --mode=link x86_64-pld-linux-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...]
+<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 -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 240: / Line 249: @@
 === What if broken library comes from other package ? ===
-You can check manually does library has all required symbols, simply running 'gcc //library// ', like this:
+You can check manually does library has all required symbols, simply running ' gcc //library// ', like this:
 This is an example of correctly linked library:
@@ Line 249: / Line 258: @@
 collect2: ld returned 1 exit status
 </file>
-And inclrrectly linked:
+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'
@@ Line 260: / Line 269: @@
 collect2: ld returned 1 exit status
 </file>
+**Warning:** some libraries may require to have unresolved symbols.
@@ Line 281: / 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 288: / 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 302: / Line 313: @@
 +       LIBS="$LIBS_save"
 </file>
-with this simple change everything works perfectly.
+With this simple change everything works perfectly.