On Mon, Nov 27, 2017 at 09:21:16AM +0100, Dridi Boukelmoune wrote: > On Mon, Nov 13, 2017 at 11:01 PM, Tomasz Kłoczko > <kloczko.tomasz@xxxxxxxxx> wrote: > > On 13 November 2017 at 10:52, Björn 'besser82' Esser > > <besser82@xxxxxxxxxxxxxxxxx> wrote: > <snip> > > However AFAIK only reason of any issues related to use -Wl,--as-needed > > is using WRONG list -l<foo> parameters (lack of some -l<foo>) and this > > needs to be not treated by apply some workaround but but by apply > > necessary fixes in -l<foo> linking parameters. > > Off the top of my head I can see glibc leading to "over" linking: if > upstream is not GNU/Linux-only it may need -lm, -lrt, -lsocket, -lnls > etc for other platforms. For autotools-based projects depending on how > you do the functions detection it may or may not add the -l* flags to > $LIBS if provided by the libc. There are several problems with forceful --as-needed: 1) forcing it everywhere is a workaround to broken tools that add -l* options just in case (like auto*, libtool, pkg-config) 2) until recently, there was no way to enable the option for just one library and restore it afterwards, so many spots, including, but not limited to, gcc driver itself, do --as-needed -lgcc_s --no-as-needed, which if somebody forces --as-needed at the start of the linker command line has the effect that everything up to the -lgcc_s on the command line behaves --as-needed, and everything after it doesn't. Since 3 years ago ld offers the --push-state/--pop-state options, so one can use --push-state --as-needed -lgcc_s --pop-state instead and that at the end restores the previous --as-needed behavior. So, before turning it by default, you'd need to check everywhere where --no-as-needed is used and see if it is something where --push-state/--pop-state should be used. 3) forcing --as-needed breaks some legitimate uses where some work is done e.g. in the constructors of some library, but there is no need to use any symbols, or if you know some library needs to be initialized early but will be used only from dlopened libraries (e.g. AddressSanitizer and ThreadSanitizer can be examples of this), or the library extends the binary and provides necessary symbols for a plugin that will be dlopened. Jakub _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx
