[Lldb-commits] [PATCH] D21164: Improve watchpoint error reporting specially for arm/aarch64 targets

Muhammad Omair Javaid via lldb-commits lldb-commits at lists.llvm.org
Mon Jun 27 05:33:27 PDT 2016

omjavaid added inline comments.

Comment at: source/Target/Target.cpp:714
@@ -713,2 +713,3 @@
         uint32_t num_current_watchpoints = target->GetWatchpointList().GetSize();
+        if (num_supported_hardware_watchpoints == 0)
clayborg wrote:
> This logic isn't necessarily correct. If we have the ability to watch N bytes at a time with a single hardware watchpoint, we might have 1 hardware watchpoint that is able to watch multiple things. So for code like:
> ```
> char buffer[8] = ...;
> ```
> then we watch "buffer[1]" and "buffer[7]", we could actually have 2 watchpoints but only use 1 hardware watchpoint. We really should be allowing each process plug-in to try and set the watchpoint and return the correct error instead of generically trying to catch _anything_ at the target level. So it seems like this code should be removed and moved into RegisterContext and allow each register context plug-in to respond correctly as only the it will know what can be done.
I am seeing this a little different. GetWatchpointSupportInfo has to provide information on number of watchpoint resources a target supports.
We should only fail a watchpoint on the basis of GetWatchpointSupportInfo if it returns zero that is for a particular hardware we have no watchpoint support.

For the case where we want to utilize same hardware resource to watch multiple watchpoints, we should try to manage that in register context where we can keep track of watchpoints previously installed without getting the target backend involved. First we can attempt to intall a watchpoint using an existing resource and if that fails we can use a new hardware resource. Return failure if watchpoint resources are used up. This way you can put multiple watchpoint on same address without having to use up hardware watchpoint resources. I will post this solution of arm and aarch64 soon.

Comment at: source/Target/Target.cpp:721
@@ +720,3 @@
+        }
+        else if (num_current_watchpoints >= num_supported_hardware_watchpoints)
+        {
I am going to remove this case from final commit as we may have more watchpoints utilizing one or more hardware watchpoint resources.


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