[uml-devel] skas3 (almost) works on amd64?

[Antoine Martin <antoine@nagafix.co.uk>]

(..)
> > I can't speak to how stable it was. I'm pretty sure I wasn't using Skas,
> It isn't skas as the skas3 code hasn't been ported to x86_64 yet.
Or has it?
I've just removed mode=skas0 from the command line during testing and I
was surprised to see this:
Checking that ptrace can change system call numbers...OK
Checking syscall emulation patch for ptrace...missing
Checking PROT_EXEC mmap in /dev/shm/...OK
Checking if syscall restart handling in host can be skipped...OK
Checking for the skas3 patch in the host:
  - /proc/mm...found
  - PTRACE_FAULTINFO...found
  - PTRACE_LDT...found
UML running in SKAS3 mode
??????
The host was patched with the skas patch (even though it is a 64bit
kernel) as the patch does not seem to interfere and it clearly provides
something useful!

Now it doesn't quite work for me, but it is close enough that I feel it
is well worth investigating (skas3 being much faster - even though skas0
is pretty good - skas3 stills has the advantage)

Here are some test results:
* with kernel32-2.6.15-rc5:
it gets stuck right after printing "SKAS3 mode", here is the full strace
(not big 16KB):
http://uml.nagafix.co.uk/logs/2.6.15-rc5-skas3.strace
the last few lines are:
sigaltstack({ss_sp=0xa0464000, ss_flags=0x3ffc,
ss_size=11548988665867022973}, NULL) = 0
rt_sigaction(SIGUSR1, {0x8000000a0023390, [], 0}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [USR1], NULL, 8) = 0
getpid()                                = 22917
kill(22917, SIGUSR1)                    = 0
--- SIGUSR1 (User defined signal 1) @ 0 (0) ---
rt_sigprocmask(SIG_UNBLOCK, [USR1], [USR1], 8) = 0
sigaltstack({ss_sp=0x200000000, ss_flags=0, ss_size=6979621237}, NULL) =
0
getpid()                                = 22917
pause(
--- It hangs there until I ^C it.

* with kernel32-2.6.14.4-bs3 and kernel32-2.6.13-bs3 (and others):
as above but the strace is different!?, here it is (76KB)
http://uml.nagafix.co.uk/logs/2.6.14.4-bs3.strace
difference is that this is similar to what was reported a while back:
lots of these:
rt_sigprocmask(SIG_BLOCK, [ALRM VTALRM IO], NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [], [ALRM VTALRM IO], 8) = 0
rt_sigprocmask(SIG_BLOCK, [ALRM VTALRM IO], NULL, 8) = 0
rt_sigprocmask(SIG_SETMASK, NULL, [ALRM VTALRM IO], 8) = 0
And at the end:
kill(23087, SIGKILL)                    = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
ptrace(PTRACE_KILL, 23087, 0x8000, 0xa001ab33) = 0
Segmentation fault

* with 2.4.32-bs2:
Apart from this warning near the top:
Checking for /dev/anon on the host...Not available (open failed with
errno 2)
It spins (consuming CPU) after mounting root (or mounting devfs if
enabled) with:
rt_sigprocmask(SIG_BLOCK, [ALRM VTALRM IO], NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [ALRM VTALRM IO], [ALRM VTALRM IO], 8) = 0
Interestingly similar to 2.6.14/2.6.13 above, log here (a lot bigger:
260MB uncompressed / 220KB compressed):
http://uml.nagafix.co.uk/logs/2.4.32-bs2.strace.bz2

* with 2.6.15-rc1:
As with 2.4.32, it spins after mounting root, but seems to be on this:
--- SIGCHLD (Child exited) @ 0 (0) ---
waitpid(23866, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSEGV}], WSTOPPED) =
23866
ptrace(PTRACE_GETREGS, 23866, 0, 0xa07af9d4) = 0
ptrace(PTRACE_GETFPXREGS, 23866, 0, 0xa07afbcc) = 0
ptrace(0x34 /* PTRACE_??? */, 23866, 0, 0xa07afdcc) = 0
gettimeofday({1021846869037274, 11531684934252935416}, NULL) = 0
write(4, "137333\t 1134874842.237917  Alloc"..., 49) = 49
ptrace(PTRACE_SETREGS, 23866, 0, 0xa07af9d4) = 0
ptrace(PTRACE_SETFPXREGS, 23866, 0, 0xa07afbcc) = 0
ptrace(PTRACE_SYSCALL, 23866, 0, SIG_0) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
full log here (700MB/840KB)


The kernels were built using vanilla gcc-3.4.4, and the tests were
repeated on 2 separate platforms (gentoo 2005.1 and FC4) - selinux was
disabled for the tests.

Antoine



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