Messages in this thread | | | Subject | Re: [PATCH v3 0/5] ARM64: disable irq between breakpoint and step exception | From | Pratyush Anand <> | Date | Tue, 1 Aug 2017 14:02:02 +0530 |
| |
Hi Takahiro,
On Tuesday 01 August 2017 01:44 PM, AKASHI Takahiro wrote: > Hi Pratyush, > > On Mon, Jul 31, 2017 at 04:10:28PM +0530, Pratyush Anand wrote: >> v2 -> v3 >> - Moved step_needed from uapi structure to kernel only structure >> - Re-enable interrupt if stepped instruction faults >> - Modified register_wide_hw_breakpoint() to accept step_needed arg >> v2 was here: http://marc.info/?l=linux-arm-kernel&m=149942910730496&w=2 >> >> v1 -> v2: >> - patch 1 of v1 has been modified to patch 1-3 of v2. >> - Introduced a new event attribute step_needed and implemented >> hw_breakpoint_needs_single_step() (patch 1) >> - Replaced usage of is_default_overflow_handler() with >> hw_breakpoint_needs_single_step(). (patch 2) >> - Modified sample test to set set step_needed bit field (patch 3) >> v1 was here: http://marc.info/?l=linux-arm-kernel&m=149910958418708&w=2 >> >> samples/hw_breakpoint/data_breakpoint.c passes with x86_64 but fails with >> ARM64. Even though it has been NAKed previously on upstream [1, 2], I have >> tried to come up with patches which can resolve it for ARM64 as well. >> >> I noticed that even perf step exception can go into an infinite loop if CPU >> receives an interrupt while executing breakpoint/watchpoint handler. So, >> event though we are not concerned about above test, we will have to find a >> solution for the perf issue. >> >> This patchset attempts to resolve both the issue. Please review. >> Since, it also takes care of SW breakpoint, so I hope kgdb should also be >> fine. However, I have not tested that. >> @Takahiro: Will it be possible to test these patches for kgdb. > > I have not yet understood the details of your patch, but > I gave it a try and didn't see any difference around the behavior > of kgdb's single stepping. > > I also gave a try to James' patch, but again nothing different > as long as kgdb is concerned. > (I'm tackling some issue in single stepping at irq's kernel_exit, > in particular, 'eret'.)
You mean that you were expecting an step exception after eret (and this eret was being called from kgdb breakpoint exception handler), but you got irq exception? This is what I understood from your previous patch [0].
If that was the case, then I was expecting that this patch series should help. See, patch 4/5: - kgdb breakpoint handler kgdb_brk_fn() will be called from arch/arm64/kernel/debug-monitors.c: brk_handler(). - If we are expecting a step exception after servicing this breakpoint handler, then kgdb code would have called kernel_enable_single_step(). So, we should see kernel_active_single_step() true in brk_handler(). - If above happens then do_debug_exception() will make sure that PSR I bit is set before eret is called and we should not see an IRQ exception after eret.
Can you please help me with your reproducer test case?
[0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-May/508066.html
-- Regards Pratyush
| |