HowToDebugLinuxExceptions < DULG

%SECTION0{name=HowToDebugLinuxExceptions}% How to Debug Linux Exceptions

   Question:: I am trying to single step into a Linux exception handler.
    This does not seem to work. Setting a breakpoint does not work either.

   Answer:: The problem is bit complex on a MPC8xx target.
    Debug mode entry is like an exception and therefore
    only safe at locations in the code where an exception
    does not lead to an unrecoverable state.
    Another exception can only be accepted if SRR0 and
    SRR1 are saved. The MSR[RI] should indicate if
    currently an exception is safe. MSR[RI] is cleared
    automatically at exception entry.
    <p></p>
    The MPC8xx hardware breakpoints do only trigger if
    MSR[RI] is set in order to prevent non-recoverable state.
    <p></p>
    The problem is that the Linux exception handler does not
    take all this into account. First priority has speed,
    therefore neither SRR0 nor SRR1 are saved immediately.
    Only after EXCEPTION_PROLOG this registers are saved.
    Also Linux does not handle the MSR[RI] bit.
    <p></p>
    %T% Hint: Use STEPMODE HWBP when debugging Linux.
    This allows the TLB Miss Exception handler to update
    the TLB while you are single stepping.

   Conclusion:: You cannot debug Linux exception entry and exit code.
    Because of speed, !DataStoreTLBMiss does not even make use
    of EXCEPTION_PROLOG, and SRR0/SRR1 are never saved.
    Therefore you cannot debug !DataStoreTLBMiss unless you
    change it's code (save SRR0/SRR1, set MSR[RI].
14.6.1. Where can I find BDI2000 Configuration Files?		1. Abstract		14.6.3. How to single step through "RFI" instruction
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