> According to notting and the experimentation that I did after the FESCo > meeting, the shared libraries bring in any libraries that they depend on. > However, if the application linking to the shared library also requires the > third shared library but doesn't explicitly link it then the link will fail. That's right. > ie: > > Given: > libfoo requires libbar. > This is used to link: gcc -o libfoo.so -lbar foo.o > libfoo.so contains the dependency on libbar. > > Scenario 1: > /usr/bin/baz depends on symbols in libfoo but not libbar. > This can be used to link: gcc -o baz -lfoo baz.o > The link succeeds and the resulting /usr/bin/baz links to both libfoo.so and > libbar.so as expected. > > Scenario 2: > /usr/bin/baz depends on symbols in both libfoo and llibbar > This fails to link because of missing libbar: gcc -o baz -lfoo baz.o > This succeeds: gcc -o baz -lfoo -lbar baz.o > > Roland, can you clarify that this is indeed how things are supposed to work? Yes, that's correct. A common example seems to be -lm. If you use 'pow' (or whatever), then you should pass -lm. If some other library you use happens to use -lm at the moment, that doesn't mean you shouldn't pass -lm when you are using some API symbols from -lm. > Also... it took me quite a while to come up with the command line flags on > F12 that would allow me to test this (I think I had to get gcc to show me > the linker invokation it used and then run those linker lines with my > modifications), can you tell us what command line flags let us test out the > differences in behaviour on F12? You can always pass extra linker flags through gcc with -Wl,--foo. You can give as many of these as you like, and -Wl,a,b is the same as -Wl,a -Wl,b (both mean to pass "a" and "b" arguments on to ld). On F12 (or F11) you can use 'gcc -Wl,--no-add-needed' to get the new linking semantics. e.g., .../configure LDFLAGS=-Wl,--no-add-needed probably works on many packages if you want to try a manual build of something this way. Thanks, Roland -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
