🍒 [lldb] Cherry pick patches for MultiMemoryRead packet p2 (21.x) #11674
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This commit introduces a base-class implementation for a method that
reads memory from multiple ranges at once. This implementation simply
calls the underlying `ReadMemoryFromInferior` method on each requested
range, intentionally bypassing the memory caching mechanism (though this
may be easily changed in the future).
`Process` implementations that can be perform this operation more
efficiently - e.g. with the MultiMemPacket described in [1] - are
expected to override this method.
As an example, this commit changes AppleObjCClassDescriptorV2 to use the
new API.
Note about the API
------------------
In the RFC, we discussed having the API return some kind of class
`ReadMemoryRangesResult`. However, while writing such a class, it became
clear that it was merely wrapping a vector, without providing anything
useful. For example, this class:
```
struct ReadMemoryRangesResult {
ReadMemoryRangesResult(
llvm::SmallVector<llvm::MutableArrayRef<uint8_t>> ranges)
: ranges(std::move(ranges)) {}
llvm::ArrayRef<llvm::MutableArrayRef<uint8_t>> getRanges() const {
return ranges;
}
private:
llvm::SmallVector<llvm::MutableArrayRef<uint8_t>> ranges;
};
```
As can be seen in the added test and in the added use-case
(AppleObjCClassDescriptorV2), users of this API will just iterate over
the vector of memory buffers. So they want a return type that can be
iterated over, and the vector seems more natural than creating a new
class and defining iterators for it.
Likewise, in the RFC, we discussed wrapping the result into an
`Expected`. Upon experimenting with the code, this feels like it limits
what the API is able to do as the base class implementation never needs
to fail the entire result, it's the individual reads that may fail and
this is expressed through a zero-length result. Any derived classes
overriding `ReadMemoryRanges` should also never produce a top level
failure: if they did, they can just fall back to the base class
implementation, which would produce a better result.
The choice of having the caller allocate a buffer and pass it to
`Process::ReadMemoryRanges` is done mostly to follow conventions already
done in the Process class.
[1]:
https://discourse.llvm.org/t/rfc-a-new-vectorized-memory-read-packet/
(cherry picked from commit f2cb997)
…164311) This commit makes use of the newly created MultiMemRead packet to provide an efficient implementation of MultiMemRead inside ProcessGDBRemote. Testing is tricky, but it is accomplished two ways: 1. Some Objective-C tests would fail if this were implemented incorrectly, as there is already an in-tree use of the base class implementation of MultiMemRead, which is now getting replaced by the derived class. 2. One Objective-C test is modified so that we ensure the packet is being sent by looking at the packet logs. While not the most elegant solution, it is a strategy adopted in other tests as well. This gets around the fact that we cannot instantiate / unittest a mock ProcessGDBRemote. Depends on llvm#163651 (cherry picked from commit 276bccd)
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@swift-ci smoke test |
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@swift-ci test |
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@swift-ci please smoke test macOS platform |
|
@swift-ci test macos platform |
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