On Mon, 2025-09-22 at 16:01 +0200, Thomas Weißschuh wrote: > Right now it does not provide any advantage over a regular syscall. > Essentially it is just overhead. That said, if you do want to make a > real vDSO out of it, I'd be happy to help in that.
I don't know if I'd say "just overhead" - depends on which path is more optimised in a typical libc implementation? I'd basically think it's identical, no? You either link to the vDSO, or a __weak same function in the libc? > > I mean ... on the one hand, sure, it doesn't really do much after this, > > but OTOH it lets userspace actually use that path? So might be useful. > > What advantage does userspace have from it? Right now, none? But it's easier to play with if you have the infrastructure, and I'm not convinced there's a _disadvantage_? > > > Also the functionality to map the host vDSO and vsyscall page into UML > > > userspace looks very weird and error-prone. Maybe it can also go away. > > > > Surely host vDSO etc. is never mapped into UML userspace and never is, > > not sure what you're thinking of, but clearly that's wrong as written. > > This is how I understand the 32bit implementation using > ARCH_REUSE_HOST_VSYSCALL_AREA and NEW_AUX_ENT(AT_SYSINFO_EHDR, vsyscall_ehdr) > where vsyscall_ehdr comes from the hosts getauxval(AT_SYSINFO_EHDR). Huh, hm, yeah I forgot about that ... 32-bit. Yeah, agree we should just kill that. I'm not even sure it works with the host kernel trapping there? Oh well. johannes
