"H.J. Lu" <hjl.to...@gmail.com> writes: > On Thu, Dec 2, 2010 at 11:37 AM, Ian Lance Taylor <i...@google.com> wrote: >> "H.J. Lu" <hjl.to...@gmail.com> writes: >> >>> g++ adds -lm since libstdc++ uses libm. If we do it in gcc, we may >>> add run-time dependency on libm.so to all C programs even if they >>> don't use libm at all. >> >> No. All the gcc driver has to do is: *if* -lm is used on the link line, >> also add it after the use of --plugin-callback. > > How many libraries specified at command line do we have to check?
We only have to check the ones for which LTO can potentially generate a reference which did not exist in the original object file. Or, more precisely, for which LTO can generate a reference which the plugin did not report when the original object file was seen. As far as I can tell at this point, the complete set of libraries we need to check is: -lc -lm -lgcc -lgcc_s. We could remove -lm from that list if we arranged for the plugin to report a potential reference to sin even if the object file does not list it for whatever reason. I saw your earlier test case but I don't actually know why the reference to sin in the source code disappeared from the object file and was reinserted by LTO. > How do we handle -Wl, -Wl,-Bstatic/-Wl,-Bdynamic,-Wl,--start-group, .... > and other linker switches? A fair point. Ideally we would want to recreate the state of those options for all libraries explicitly mentioned by the user. Ian
