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[Bug uprobes/5273] New: x86 arch_validate_probed_insn(): lighten up?

In uprobes_i386.c and uprobes_x86_64.c, we spend quite a bit of code on refusing
to probe certain types of instructions, such as undefined opcodes and other
instructions that are likely to yield SIGILL when single-stepped in user mode. 
There's also some paranoia about how instruction prefixes and such might affect
our decisions about which instructions need to be treated specially when
single-stepping them out of line.

We could probably lighten up here.  One disadvantage of the paranoia is that
tests that try to probe (say) EVERY instruction in a .o file will choke on
things like hlt.

For illegal instructions, if the SIGILL kills the task before the SIGTRAP from
the single-step is reported to us -- we need to test this -- then we should be
OK.  Testing suggests that we know how to handle tasks that die of other causes
during probepoint processing.

And I think we've successfully identified instructions that need special
attention during SSOL.  It's probably just a matter of testing each currently
banned instruction type to verify that it doesn't present an unforeseen problem.

           Summary: x86 arch_validate_probed_insn(): lighten up?
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: minor
          Priority: P3
         Component: uprobes
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: jkenisto at us dot ibm dot com

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