* Florian Weimer: > * Mark Kralj-Taylor: > >> The wording of Linux docs suggests that clock_gettime(CLOCK_REALTIME) >> should be supported if the clock_gettime() API exists. But other clock >> sources are not mandatory. > > Really old glibc emulates clock_gettime (CLOCK_REALTIME) using > gettimeofday, yes. > > clock_gettime was already in Linux 2.12 (and possibly quite a bit
That should have been Linux 2.6.12, sorry. > earlier, I did not check), so that is not likely to be a limitation. > > A tricky question is whether it's possible to avoid loading librt. > The present code already uses dlopen, but I think it could try a > little bit harder (try resolving clock_gettime first, and then load > librt, and try again). For distribution builds that do not need to be > compatible with glibc versions before 2.17, directly calling > clock_gettime would also be an option. (clock_gettime moved to > libc.so.6 in glibc 2.17, but a lot of software keeps linking against > librt for the definition of clock_gettime, something that we are > finally tackling on the glibc side.) > > Making a direct system call instead is a bit tricky because it's > absolutely required to use the vDSO if possible, for performance > reasons. But it's possible to obtain the address of the vDSO function > using dlvsym, so that might be an option as well.
