Fix universal symbol conversion for overlapping mappings

[Copilot]

This PR fixes a critical issue where overlapping memory mappings in universal traces (nettrace files) cause a NullReferenceException during symbol processing.

Problem

When loading nettrace files with overlapping mappings, PerfView would crash with a NullReferenceException. The issue occurred when:

1. Multiple mappings share the same start address but have different end addresses
2. The first mapping creates a TraceModuleFile with a smaller image size
3. The second mapping reuses the existing TraceModuleFile without updating its size
4. Later, symbol processing tries to resolve addresses within the larger range but fails because the cached module file has the wrong size

Example scenario from the issue:

Mapping 1: Start=0x0000738e0b840000, End=0x0000738e0b8a2fff (length=0x62fff)
Mapping 2: Start=0x0000738e0b840000, End=0x0000738e0b8a3fff (length=0x63fff) 

Solution

1. Enhanced UniversalMapping method:

• Calculate the new image size from mapping data
• Expand existing ModuleFile.imageSize when new mappings have larger ranges
• Handle both new and existing loaded modules properly

2. Added defensive null checks in AddUniversalDynamicSymbol:

• Check if loadedModule is null before using it
• Only create managed modules when a valid loaded module is found
• Prevent NullReferenceException when symbol addresses fall outside known mappings

Changes

• TraceLoadedModules.UniversalMapping(): Now properly expands ModuleFile size for overlapping mappings
• TraceLoadedModules.UniversalMapping(): Adds a new LoadedModuleFile when the necessary
• TraceCodeAddresses.AddUniversalDynamicSymbol(): Added null checks to handle missing modules gracefully
• TraceCodeAddresses.AddUniversalDynamicSymbol(): Adds an assert to ensure that all dynamic symbols have a corresponding LoadedModule.

Coverage

This fix handles all overlapping mapping scenarios:
✅ Complete replacement of existing mapping
✅ Mapping that overlaps and extends beyond existing mapping
✅ Mapping contained within existing mapping
✅ Partial overlaps with shared start addresses

The changes are minimal and surgical, maintaining backward compatibility while resolving the crash in user_events scenarios.

Fixes #2250.

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[brianrob]

GetOrCreateModule will only return a TraceModuleFile whose ImageBase matches the incoming mapping, so if the mapping happens to have the same name, as does the mappings for jitted code on Linux, then GetOrCreateModule will just create a new module.

FindModuleAndIndexContainingAddress will return a TraceLoadedModule that contains data.StartAddress, but doesn't necessarily start with it. If it doesn't start with it, then we need to create a new TraceLooadedModule and insert it - this is needed to handle the overlapping mapping case.

[Copilot]

Fixed in 6caab6b. Now checking if loadedModule.ImageBase != data.StartAddress and creating a new TraceLoadedModule when they don't match, ensuring proper handling of overlapping mappings where the module containing the address doesn't start at the mapping's start address.

[brianrob]

This else clause is valid if the ImageBase of loadedModule matches the StartAddress of the new mapping. But, in this case, we still should update loadTimeQPC to match the new mapping timestamp. We also need to determine if overlaps needs to be set because we're not re-inserting it. If we can't do this here, we will need to just create a new TraceLoadedModule and insert it so that the underlying code can properly set overlaps if necessary.

[Copilot]

Fixed in 6caab6b. The else clause now properly updates loadTimeQPC to match the new mapping timestamp with loadedModule.loadTimeQPC = data.TimeStampQPC. The InsertAndSetOverlap call in the creation path will handle the overlaps flag correctly.

[brianrob]

On line 7130, we set the timestamp to the start of the trace because mappings are enumerated at the start of the trace. This doesn't always happen - we should set the timestamp properly.

[Copilot]

Fixed in 6caab6b. Changed from process.Log.sessionStartTimeQPC to data.TimeStampQPC to use the proper timestamp from the mapping data.

[brianrob]

Copilot Post-Mortem:

• Helped me to not "over-code" a solution since there is already support in TraceLoadedModules for overlapping mappings.
• It would be nice to for copilot to update the PR description automatically in response to comments that cause it to diverge the PR from the original description.

[brianrob]

@noahfalk, this change is a bit more involved than just the repro case that you hit, but FWIW, I did confirm that your trace works, and that there are no symbols that don't have a corresponding loaded module.

[noahfalk]

Looks fine to me!

[noahfalk]

Is there anything blocking this PR from getting merged?

[brianrob]

This one just needs a review from someone in the CODEOWNERS file. I have a request out on that, and I will see if I can get traction on it tomorrow.

[mconnew]

Why not Debug.Assert(loadedModule != null, "loadedModule is missing for symbol") before the if statement?

[brianrob]

You're right. I can't remember why I went with this, but I've updated to use your suggestion.

[mconnew]

[mconnew]

[brianrob]

/azp run

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