On Sun, Sep 2, 2012 at 8:56 AM, Georg-Johann Lay <a...@gjlay.de> wrote: > Weddington, Eric schrieb: >>> >>> On Behalf Of Georg-Johann Lay >>> >>> for historical reasons, AVR-Libc implements functions that >>> GCC expects to live in libgcc, namely float functions like >>> __fixsfsi. >>> >>> Currently, avr-gcc is not configurable to accommodate that >>> situation which leads to performance problems if the float >>> support functions from libgcc are used. >>> >>> This happens at least in the following situations: >>> >>> * The user does not specify -lm. -lm should only be needed >>> if function from math.h are used, not for language core >>> features like int i = (int) float. >>> >>> * The application is LTO compiled, i.e. linked with -flto. >>> The plugin machinery passes lgcc -lc lgcc through to the >>> linker by means of -plugin-opt=-pass-through=-lgcc etc. >>> so that -lgcc is linked prior to -lm. >>> >>> * The user uses fixed <-> float conversion routines from >>> libgcc. These routines refer float functions, and the linker >>> resolves these function in libgcc if they are there. >>> >>> * avr-g++ is used as linker driver. >> >> >> Yes, we definitely want to make sure all the above are working. >> >>> >>> In order to fix all of these cases, at least two changes >>> are needed in the compiler. >>> >>> 1) Remove respective functions from libgcc >>> >>> 2) libm.a is not a "math library", it is a "libgcc supplement". >>> Thus, -lm has to be treated like libgcc. >> >> >> Joerg Wunsch and I have talked for years about the idea of >> integrating libm into libc, so that way there was only one library >> to deal with. Would this be a good point to do that as well? >> Would that make all the linker flag stuff easier to deal with? > > > If there are plans to integrate libm into libc then this should > be done *before* GCC supports --with-avrlibc configure option. > > Otherwise, AVR-Libc would knock out itself making the linker throw > a "cannot find -lm" or similar linker error which would make that > configure option obsolete... > > The preferred way would be *not* to move libm to libc so > that the library layout is stable and the configure option > works across various versions of AVR-Libc, even older ones. > > The intersection between libgcc and AVR-Libc is stable and > did not change often, if I see correctly. Changing the layout > just now might be not helpful; except in the case there is > a dummy libm.a that prevents "cannot find -lm" link error. > > Johann
How about just having the driver add -lm (unless specifically instructed not to) systematically? -- Gaby _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org https://lists.nongnu.org/mailman/listinfo/avr-gcc-list
