On Thu, Dec 2, 2010 at 11:53 AM, Ian Lance Taylor <i...@google.com> wrote: > "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.
It isn't a complete list. At least, we need -lgcov and may be others. > > 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. It can get quite complex. You start turning GCC driver into a linker :-). What do we do when a new switch is added to linker? -- H.J.
