Hi On Thu, Nov 27, 2014 at 4:42 PM, Gustavo Sverzut Barbieri <gustavo.barbi...@intel.com> wrote: > On Thu, Nov 27, 2014 at 03:42:37PM +0100, David Herrmann wrote: >> 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. > > Did you confirm what you said or is it a supposition? > > I'm asking because from Peter Wu's email we're 26384 - 26380 = 4Kb > heavier in the whole installed set of binaries. If this is correct I > doubt the gc-sections is making any difference in the linkage of > static libraries (src/shared). In this case my *assumption* (as I have > no deep knowledge about the linker) is that it's selectively picking > the symbols it uses and leaving the other stuff out of it.
-ffunction-section -fdata-section make the binaries slightly bigger, but with --gc-sections I get a difference of >1MB for each of the shared library objects (libudev.so.1.6.1, libsystemd.so.0.5.0, ...). Thanks David _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel