[Bug runtime/14883] New: let probefunc() not fail - or fail more informatively, on non-uprobes kernels

["fche at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14883

             Bug #: 14883
           Summary: let probefunc() not fail - or fail more informatively,
                    on non-uprobes kernels
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap@sourceware.org
        ReportedBy: fche@redhat.com
    Classification: Unclassified


Bug #13693 rewrote probefunc() to go to usymname(uaddr()) if user_mode, which
in turn activates the whole task-finder mechanism.  If the kernel is not up to
that, the user gets a bewildering error message:

user-space facilities not available without kernel CONFIG_UTRACE or
CONFIG_TRACEPOINTS/CONFIG_ARCH_SUPPORTS_UPROBES/CONFIG_UPROBES

Running with --compatible=1.8 makes things work.

We should improve this; some options:
- change usym*() to tolerate absence of the utrace/uprobes goo, and return
empty or hex strings
- or one level down: change the runtime for pragma:vma without utrace/uprobes
to succeed with a stub dummy
- improve the error message in its own right (probably don't list CONFIG*
literals)

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