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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