Bodo Stroesser wrote:
If we talk about using a new ptrace code for the new API, old UML
binaries running
on a host supporting the new API will recognize that there is no SYSEMU
they can
use. So /proc/sysemu will not allow to switch on or off anything (IIRC,
the file
will not even be created). That means, that an old binary will run safe
but slow
in this case. One could argue, that this is a changed behaviour of the
old binary.
OTOH, if the new API would reuse the same ptrace code, check_sysemu of
the old
binaries will fail on i386 (and I hope on x86_64, too). That means,
sysemu again
will be disabled. AFAICS, it will not refuse to run at all. (Not tested,
taken from
the code only)
On s390 the check even might succeed accidentally, but that's no
problem, as s390
isn't mainline yet, we can change check_sysemu() to avoid problems.
There will
never be an old binary for s390.
Resume: it doesn't matter if a new ptrace code is used or the old one is
reused.
Usage of sysemu will be restricted to "new UML on new host" or "old UML
on old host"
as long as host doesn't support _both_ APIs (selectable by two separate
ptrace codes
or by a new flag to PTRACE_SETOPTIONS). AFAICS, there is no reason to
change
/proc/sysemu at all, right?
Some more points:
The new API must have PTRACE_SYSEMU _and_ PTRACE_SYSEMU_SINGLESTEP.
While with the old API SYSEMU_SINGLESTEP was inserted to improve security,
with the new one it will be necessary to allow singlestepping of processes
in UML-SKAS at all. Suppose a singlestepped userspace is stopped at a
syscall interception. Now UML needs to restart it with SYSEMU for syscall
emulation, but also wants to proceed with singlestepping. PTRACE_SYSEMU wouldn't
do the job, as it starts userspace in "normal" mode, no singlestepping.
Also, in tt new API's PTRACE_SYSEMU behaves as PTRACE_SYSCALL does, because
tracer
uses PTRACE_CONT after syscall interception. So tt (do_syscall(), ...) needs to
be
changed. PTRACE_SYSEMU_SINGLESTEP still should be used, as if it's name were
PTRACE_SYSCALL_SINGLESTEP.
Bodo
-------------------------------------------------------
SF.Net email is sponsored by:
Tame your development challenges with Apache's Geronimo App Server. Download
it for free - -and be entered to win a 42" plasma tv or your very own
Sony(tm)PSP. Click here to play: http://sourceforge.net/geronimo.php
_______________________________________________
User-mode-linux-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
