Messages in this thread |  | | | Date | Sat, 28 May 2011 17:35:36 +0200 | | From | Ingo Molnar <> | | Subject | Re: [GIT pull] x86 vdso updates |
| |
* Andrew Lutomirski <luto@mit.edu> wrote:
> On Fri, May 27, 2011 at 7:36 AM, Andrew Lutomirski <luto@mit.edu> wrote: > > 3. Add int 0xcc and use it from vgettimeofday. It will SIGSEGV if > > called from a user address (so it has no risk of ever becoming ABI) > > and it will do gettimeofday if called from the right address. (I like > > 0xcc better than 0x81 because then I don't have to wonder whether any > > syscall-like instructions start with 0x81.) I'm not convinced that > > the existing syscall entries are usable, because syscall itself has a > > different calling convention and int 0x80 is a compat syscall. > > > > I started looking at what needs to be done and I wanted to get your > opinion before I wrote a bunch of code that you'd reject. Here are > three ideas for how the int 0xcc / int 0x81 entry could work: > > *** Idea 1 *** > > Make it a real syscall but with extra constraints. It would have the > same calling convention as the syscall instruction, but it would turn > into SIGKILL if the calling address isn't in the VSYSCALL page or if > the syscall number isn't __NR_clock_gettimeofday. It would BUG() if > called from kernel mode. There are two ways to implement this: > > 1. Have the interrupt entry check constraints, twiddle its stack frame > to look like a syscall instruction, and jump to the syscall entry. > This way there's little code duplication. (Is it safe to sysret back > to userspace from an interrupt gate? I don't see why not, but it > seems to violate the spirit of the thing.)
Yeah, i think it should be safe. Lets try this? It looks like the simplest variant.
Thanks,
Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |