Re: Single-stepping with interrupts enabled.

[Richard J Moore <richardj_moore@uk.ibm.com>]

You can't do without post-handlers. SystemTap might not use them explicitly
but post-handling of the single-step (in kprobes) is required whether or
not a user handler is registered. For example for correcting the outcome of
an instructions execution (certain adjustments may have to be made - E49,
etc..); for handling exceptions from the single-stepped instruction
correctly; for giving the correct 'logical' view at a higher level of a
trace event following the generation of a recoverable page-fault on
single-step; for correcting IF manipulating instructions where the state of
the interrupt flag is not actually as the probed program logically thinks
it is; for correcting the TRAP Flag for the same reasons as IF.

There must be more.

- -
Richard J Moore
IBM Advanced Linux Response Team - Linux Technology Centre
MOBEX: 264807; Mobile (+44) (0)7739-875237
Office: (+44) (0)1962-817072


                                                                           
             fche@redhat.com                                               
             (Frank Ch.                                                    
             Eigler)                                                    To 
             Sent by:                  Richard J Moore/UK/IBM@IBMGB        
             fche@redhat.com                                            cc 
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             27/02/2006                                                    
             13:51                                                 Subject 
                                       Re: Single-stepping with interrupts 
                                       enabled.                            
                                                                           
                                                                           





richardj_moore wrote:

> [...]  The problem is down to the need to save state over the
> single-step, so that pre- and post-processing either side of the
> single-step can be correctly associated with each other. [...]

How much of this would be simplified if we did away with support for
post_handlers (which we don't use in systemtap)?

- FChE