Messages in this thread | | | Date | Tue, 21 Apr 2020 08:10:45 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: hw_breakpoint: don't clear debug registers in halt mode |
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On Tue, Apr 21, 2020 at 11:49:11AM +0800, tingwei@codeaurora.org wrote: > 在 2020-03-31 19:45,Will Deacon 写道: > > On Tue, Mar 31, 2020 at 07:33:38PM +0800, tingwei@codeaurora.org wrote: > > > 在 2020-03-31 15:41,Will Deacon 写道: > > > > On Tue, Mar 31, 2020 at 10:39:42AM +0800, tingwei@codeaurora.org wrote: > > > > > For reset the registers after "debug_enabled" is toggled, I'm > > > > > thinking if > > > > > we are adding unnecessary complexity here.If we take that approach, we > > > > > will > > > > > hook "debug_enabled" interface and use smp_call_function_single() to > > > > > call > > > > > hw_breakpoint_reset() on each CPU. Wait for all CPUs' execution done > > > > > and > > > > > change "debug_enabled". External debugger would clear the > > > > > breakpoints when > > > > > it detaches the device and restores its breakpoints when attaches the > > > > > device. > > > > > Assume debug_enabled is changed to one after external debugger > > > > > detaches > > > > > the > > > > > device. Debugger would already clear the breakpoint registers. If > > > > > debgger > > > > > is > > > > > still attached, there's nothing Kernel can do to stop it > > > > > restores/programs > > > > > the breakpoint registers. > > > > > > > > > > What do you think of this? > > > > > > > > It's all a bit of a mess. Looking at it some more, why can't the > > > > external > > > > debugger simply trap access to the debug registers using EDSCR.TDA? That > > > > way, we don't have to change anything in the kernel. > > > > > > > > > > External debugger has the function to trap access to debug registers > > > now. > > > What do we expect debugger to do after core is stopped? Skip that msr > > > instruction and continue to run? > > > > The nicest thing to do would probably be to record all the accesses made > > by the OS so that it can emulate reads and replay writes when external > > debugging is over. Given that you'd still be expecting to pass > > "nodebugmon", > > the emulation should be pretty straightforward, I think. > > > > To provide an update on this, I've worked with external debugger vendor on > this. > Now external debugger can trap the write to debug registers and ignore the > write. > This is the first step.
Thanks for the update! Please let us know if you run into any unforeseen problems.
Will
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