http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47571
--- Comment #30 from dave at hiauly1 dot hia.nrc.ca 2011-03-09 00:10:22 UTC --- > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47571 > > --- Comment #29 from Janne Blomqvist <jb at gcc dot gnu.org> 2011-03-08 > 22:38:49 UTC --- > (In reply to comment #28) > > (In reply to comment #26) > > > Tru64 UNIX doesn't support weak undefined symbols, which seems to be > > > what weakrefs are. > > > > Hmm, I think it is going to be difficult. What we want to have: > > > > a) If libc has clock_gettime, use it unconditionally > > b) If librt has clock_gettime and weak refs are supported, use it if > > available > > c) If librt has it, but no weak refs are supported, don't use it. > > d) If it not available at all, don't use it. > > Yes, sounds like a good plan. > > > (b) and (d) work; also (a) works - albeit with a warning. Now one needs to > > support (c). > > Indeed; the patch was developed based on the understanding that only Linux has > clock_gettime in librt, and Linux supports weakrefs, so (c) does not need to > be > considered. Oh well. > > > I think the best would be to set (effectively) HAVE_CLOCK_GETTIME > > to false. > > > > One possibility would be to replace: > > > > #ifdef HAVE_CLOCK_GETTIME > > # ifdef SUPPORTS_WEAK > > ... > > # else > > > > by > > > > #if define(HAVE_CLOCK_GETTIME) && define(SUPPORTS_WEAK) > > > > That would exclude platforms, where libc supports clock_gettime but which do > > not have weak refs. Another possibility is a link-time check which does not > > work well for some cross-compilations. > > > > What do you think? > > I think the easiest way would be to change the test in configure.ac where we > check for clock_gettime in librt, so that we set, say, > HAVE_CLOCK_GETTIME_LIBRT > instead of HAVE_CLOCK_GETTIME, thus allowing us to distinguish whether the > function a) exists at all b) is in libc or librt. I think it is unnecessary to check whether clock_gettime is in librt as we don't want libgfortran to depend on librt in general. This reduces the accuracy when weak references are not supported and clock_gettime is only in librt. The case where weak references are supported and clock_gettime isn't available at all seems remote. If weak references are supported, always define weak_gettime as __attribute__((__weakref__("clock_gettime"))). Probably, the extra overhead of the runtime check is acceptable. If weak references are not supported and clock_gettime is in libc, define weak_gettime as we currently do: static inline int weak_gettime (clockid_t clk_id, struct timespec *res) { return clock_gettime (clk_id, res); } Condition the code that uses weak_gettime on either having clock_gettime in libc or weak references. This could be tweaked to eliminate the `if' when clock_gettime is in libc. Dave
