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Re: probes that access userspace
- From: Roland McGrath <roland at redhat dot com>
- To: Jim Keniston <jkenisto at us dot ibm dot com>
- Cc: "Frank Ch. Eigler" <fche at redhat dot com>,Kevin Stafford <kevinrs at us dot ibm dot com>,SystemTAP <systemtap at sources dot redhat dot com>
- Date: Fri, 14 Oct 2005 15:14:56 -0700 (PDT)
- Subject: Re: probes that access userspace
> > No, there appears to be no such qualification data in the debuginfo at
> > all. IIRC, the preprocessor makes __user go away before the compiler
> > ever sees it.
>
> That's my understanding as well.
It's certainly possible to do a compiler extension to express __user in the
DWARF type info. I've considered it, and can discuss it further with the
compiler folks. That solution is a long-term prospect--it would be
unlikely to happen by GCC 4.1, and might never be backported to compilers
like RHEL4's.
However, we've also gotten the opinion from at least one kernel developer
that relying on __user annotations is still insufficiently paranoid. That
is, they might be missing from some kernel source, and so any time you
access a pointer you are taking your fate in your own hands since it might
be an unannotated user-mode pointer. I'm not sure there is anything more
to be done about that concern than state the caveat.
Thanks,
Roland