> Date: Mon, 22 Jun 2020 02:06:39 +0300 > From: Paul Irofti <p...@irofti.net> > > În 22 iunie 2020 00:15:59 EEST, Christian Weisgerber <na...@mips.inka.de> a > scris: > >Paul Irofti: > > > >[Unrelated, just to mark where we're at] > >> Right. Just reproduced it here. This moves the check at the top so > >that > >> each CPU checks its own skew and disables tc_user if necessary. > > > >I tweaked the patch locally to make _timekeep a visible global > >symbol in libc. > > > >Printing its value has revealed two issues: > > > >* The timekeep page is mapped to the same address for every process. > > It changes across reboots, but once running, it's always the same. > > kettenis suggested > > - vaddr_t va; > > + vaddr_t va = 0; > > in exec_timekeep_map(), but that doesn't make a difference. > > The va is set a few lines down the line. No point in > initialization. This is identical behavior to the emul mapping > before timekeep.
Well, uvm_map() picks a virtual address based on the value of va that is passed in. If it is zero, it picks a random address. If not, it uses the value as a hint and tries to pick something nearby. So passing in stack garbage is a bad thing. > > >* I'm indeed seeing init(8) with _timekeep == NULL. > > Probably because it is the first process? If you want to follow this > read the kernel init bits and the syscall exec bits. Possible. The way process 1 is created is a bit of a hack. Anyway, _timekeep = NULL should not be a problem; the code should fall back on using system calls in that case.
