Am 15.09.2014 um 18:10 schrieb Peter Maydell: > On 15 September 2014 09:02, Martin Galvan > <martin.gal...@tallertechnologies.com> wrote: >> I did a bit more research on how Cortex-M handles nested interrupts. >> In particular, I noticed if we were to have an invalid instruction >> inside the exception handler itself, trying to single-step it would >> again cause Qemu not to return control back to gdb. Reading up a bit I >> found out that when the CPU is handling an exception, all other >> exceptions with the same or lower priority will be blocked. >> >> Qemu seems to implement this by setting the exception as pending, yet >> not changing cpu->interrupt_request so that we modify the PC in the >> second call to do_interrupt. That seems fine to me, but since the >> translation block is the same as before (and if that one contained an >> exception_with_syndrome ending in a call to cpu_loop_exit) we'll be >> stuck in the loop and we'll never return control to Gdb. >> >> Therefore I have two questions: >> 1) Is this a bug? >> 2) If it is, what should the behaviour be? I think we should return >> control back to gdb, but we shouldn't try to translate that >> instruction again. How could we handle this in a clean way? > > Our handling of exceptions and exception priorities for > Cortex-M CPUs is totally wrong. We attempt to reuse the > GIC priority handling code for interrupts, which then leaves > the exceptions without the correct priority handling. Ideally > we should rewrite this completely to give the M profile > cores the architecturally mandated exception priority > handling and masking, and stop trying to reuse the > A/R profile core code at all. The two profiles are just > too different for that to make sense.
Are you saying we should dump the inheritence completely? Andreas > > Any bugs or weirdness in the current code are likely > symptoms of attempting to shoehorn M profile into the > A/R profile handling. > > -- PMM > -- SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
