Hmm, with Pentium Pro and more recent processors there is actually a
nasty hack that will let you get away with POPF/RET and TF set. ;) You
can try it if you like and can arrange for an appropriate scenario.
Yes, if you return to elsewhere, then that's actually quite desirable
IMHO.
This RF flag is quite complicated to handle and there are some errata
involved too. If I understand it correctly, all fault-class exception
handlers are expected to set it manually in the image to be restored if
they return to the original faulting instruction (that includes the debug
exception handler if it was invoked as a fault, i.e. in response to an
instruction breakpoint). Then all trap-class exception handlers are
expected to clear the flag (and that includes the debug exception handler
if it was invoked as a trap, e.g. in response to a data breakpoint or a
single step). I haven't checked if Linux gets these bits right, but it
may be worth doing so.
For the record -- GDB hardly cares, because it removes any instruction
breakpoints before it is asked to resume execution of an instruction that
has a breakpoint set at, single-steps the instruction with all the other
threads locked out and then reinserts the breakpoints so that they can hit
again. Then it proceeds with whatever should be done next to fulfil the
execution request.
Maciej
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