Messages in this thread | | | Date | Mon, 30 Mar 2020 14:42:18 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: hw_breakpoint: don't clear debug registers in halt mode |
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On Mon, Mar 30, 2020 at 01:39:46PM +0100, Mark Rutland wrote: > On Sat, Mar 28, 2020 at 04:32:09PM +0800, Tingwei Zhang wrote: > > If external debugger sets a breakpoint for one Kernel function > > when device is in bootloader mode and loads Kernel, this breakpoint > > will be wiped out in hw_breakpoint_reset(). To fix this, check > > MDSCR_EL1.HDE in hw_breakpoint_reset(). When MDSCR_EL1.HDE is > > 0b1, halting debug is enabled. Don't reset debug registers in this case. > > I don't think this is sufficient, because the kernel can still > subsequently mess with breakpoints, and the HW debugger might not be > attached at this point in time anyhow. > > I reckon this should hang off the existing "nodebumon" command line > option, and we shouldn't use HW breakpoints at all when that is passed. > Then you can pass that to prevent the kernel stomping on the external > debugger. > > Will, thoughts?
I was going to suggest the same thing, although we will also need to take care to reset the registers if "nodebugmon" is toggled at runtime via the "debug_enabled" file in debugfs.
Will
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