[LLDB] SBMemoryRegionInfoListExtensions re-uses reference and then mutates it.

[Jlalond]

In SBMemoryRegionInfoListExtensions, the __iter__ function always yields the same SBMemoryRegionInfo reference, but each loop the content of the info will be updated.

Using the example that I wrote in the docs:

        readable_regions = []
        for region in exe_ctx.GetProcess().GetMemoryRegions():
            if region.IsReadable():
                readable_regions.append(region)

We end up with a list all to the same region

This is because in the iter:

    def __iter__(self):
      '''Iterate over all the memory regions in a lldb.SBMemoryRegionInfoList object.'''
      import lldb
      size = self.GetSize()
      region = lldb.SBMemoryRegionInfo()
      for i in range(size):
        self.GetMemoryRegionAtIndex(i, region)
        yield region

Region is a reference and if you assign it to anything, that new variable will be mutated in the next loop.

I filed this as an issue to communicate the bug because I assume a user has encountered this without realizing (because it's not very apparent).

[Jlalond]

@satyajanga could you fix this?

[llvmbot]

@llvm/issue-subscribers-lldb

Author: Jacob Lalonde (Jlalond)

In [SBMemoryRegionInfoListExtensions](https://github.com/llvm/llvm-project/blob/main/lldb/bindings/interface/SBMemoryRegionInfoListExtensions.i#L8), the `__iter__` function always yields the same `SBMemoryRegionInfo` reference, but each loop the content of the info will be updated.

Using the example that I wrote in the docs:

        readable_regions = []
        for region in exe_ctx.GetProcess().GetMemoryRegions():
            if region.IsReadable():
                readable_regions.append(region)

We end up with a list all to the same region

This is because in the iter:

    def __iter__(self):
      '''Iterate over all the memory regions in a lldb.SBMemoryRegionInfoList object.'''
      import lldb
      size = self.GetSize()
      region = lldb.SBMemoryRegionInfo()
      for i in range(size):
        self.GetMemoryRegionAtIndex(i, region)
        yield region

Region is a reference, and we will in the contents every loop, but if you assign anything to this reference, it will then be mutated next loop.

I filed this as an issue to communicate the bug because I assume a user has encountered this without realizing (because it's not very apparent).

[Jlalond]

@JDevlieghere & @DavidSpickett as an FYI.

[zyn-li]

@Jlalond I can fix this, assign to me

[Jlalond]

@Jlalond I can fix this, assign to me

Sounds good, as @aperez mentioned to me offline, we should also update the test to assert about the elements after we've iterated

https://github.com/llvm/llvm-project/blob/main/lldb/test/API/python_api/find_in_memory/TestFindInMemory.py#L165