This is the mail archive of the systemtap@sourceware.org mailing list for the systemtap project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: systemtap ARM port status


Roland McGrath <roland@redhat.com> writes:

> [...]  In almost all cases, they could check [for kernel- vs
> user-space pointers].  But in the general case, there is not
> necessarily any such check that can be made.  (The actual instance
> of that case is the "4G/4G" kernel, which exists in RHEL4 for i386.)

I suspect that we will care little about preserving full function on
4G/4G if in exchange we can make systemtap more robust everywhere
else.  For one thing, I expect not to see utrace and uprobes on RHEL4,
so it will fall behind anyway.

> I would have thought that user address access in the runtime would
> just use the vanilla uaccess.h calls (get_user et al), but perhaps
> there is some __might_sleep issue in kprobes handlers.

That's exactly it.  General kprobe handlers need to be atomic.

> [...]  What it must do is gracefully goto deref_fault for any kind
> address access that does not work.  [...]

This includes detection of problems such as unaligned, unmapped,
I/O-sensitive pointer values.  Assume only that the pointer fits into
64 bits, but otherwise it might be random.

- FChE


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]