Hi On Wed, Nov 26, 2014 at 6:40 PM, Gustavo Sverzut Barbieri <gustavo.barbi...@intel.com> wrote: > On Wed, Nov 26, 2014 at 06:33:31PM +0100, Lennart Poettering wrote: >> On Wed, 26.11.14 15:16, Gustavo Sverzut Barbieri >> (gustavo.barbi...@intel.com) wrote: >> >> > I'm okay with the change to remove gc-sections. >> > >> > systemd is pretty good at not leaving crap in its code, then results >> > are pretty small as we saw. >> > >> > My only comment is that we should also remove: >> > -ffunction-sections >> > -fdata-sections >> > those are only useful to enable gc-sections. >> > >> > From time to time someone should run a build with >> > -ffunction-sections >> > -fdata-sections >> > -Wl,--gc-sections >> > -Wl,--print-gc-sections >> > so we print out sections that are dangling and then we could remove >> > them from source code if needed. >> >> This is not that simple. We have a large set of shared functions in >> src/shared/*.c, and we link that into pretty much any binary we build, >> even though each binary only needs a small subset of them. We rely on >> the GC logic to deal with this and remove the functions that are >> unused by the specific program. Howver, that is not an indication that >> we can remove the function, that's simply an indication that that one >> binary of the 90 or so we build doesn't need it. Other binaries might >> need it still, but print-gc-sections won't tell you about that. > > For shared libraries it won't remove exported (visible) symbols. Only > stuff (functions, variables) that have not reference are removed. > > Of course those local to a file (ie: static) are always eliminated, > that's why we see minor benefit with gc-sections as the major bulk are > marked as "static". As I said, if the functions are exported > (visibility=default), then they are not GC, what leaves us to "extern" > symbols, those that are visible across files but not exported in the elf.
We _really_ depend on --gc-sections. We link a lot of stuff from src/shared/ statically into all binaries and expect the linker to drop any unused symbols. Note that none of the symbols from src/shared/ are exported, so the linker can drop them safely. I don't get why we work around linker bugs in systemd? The bug was fixed upstream, so make them backport it, if it's a critical bug. If they refuse to do so, blacklist the given version. But I dislike carrying fixes for other software in systemd-git. Thanks David _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel