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jkotas committed Dec 7, 2023
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2 changes: 1 addition & 1 deletion .config/dotnet-tools.json
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]
},
"microsoft.dotnet.xharness.cli": {
"version": "9.0.0-prerelease.23577.1",
"version": "9.0.0-prerelease.23605.1",
"commands": [
"xharness"
]
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2 changes: 2 additions & 0 deletions .github/CODEOWNERS
Validating CODEOWNERS rules …
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/src/native/public/mono @marek-safar @lambdageek

/src/libraries/sendtohelix-browser.targets @radical
/src/libraries/sendtohelix-wasm.targets @radical
/src/libraries/sendtohelix-wasi.targets @radical
/src/mono/wasm @lewing @pavelsavara @kg
/src/mono/wasm/debugger @thaystg @radical
/src/mono/wasm/build @radical
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8 changes: 2 additions & 6 deletions docs/design/coreclr/botr/clr-abi.md
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Expand Up @@ -195,9 +195,7 @@ JIT32 does not implement finally cloning.

In order to have proper forward progress and `Thread.Abort` semantics, there are restrictions on where a call-to-finally can be, and what the call site must look like. The return address can **NOT** be in the corresponding try body (otherwise the VM would think the finally protects itself). The return address **MUST** be within any outer protected region (so exceptions from the finally body are properly handled).

JIT64, and RyuJIT for AMD64 and ARM64, creates something similar to a jump island: a block of code outside the try body that calls the finally and then branches to the final target of the leave/non-local-exit. This jump island is then marked in the EH tables as if it were a cloned finally. The cloned finally clause prevents a Thread.Abort from firing before entering the handler. By having the return address outside of the try body we satisfy the other constraint.

Note that ARM solves this by not using a call (bl) instruction and instead explicitly places a return address in `LR` and then jumps to the finally. We have not yet implemented this for AMD64 because it might mess up the call-return predictor on the CPU. (So far performance data on ARM indicates they don't have an issue).
JIT64, and RyuJIT for non-x86, creates something similar to a jump island: a block of code outside the try body that calls the finally and then branches to the final target of the leave/non-local-exit. This jump island is then marked in the EH tables as if it were a cloned finally. The cloned finally clause prevents a Thread.Abort from firing before entering the handler. By having the return address outside of the try body we satisfy the other constraint.

## ThreadAbortException considerations

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The unwind callbacks don't know if the current frame is a leaf or a return address. Consequently, the JIT must ensure that the return address of a call is in the same region as the call. Specifically, the JIT must add a NOP (or some other instruction) after any call that otherwise would directly precede the start of a try body, the end of a try body, or the end of a method.

The OS has an optimization in the unwinder such that if an unwind results in a PC being within (or at the start of) an epilog, it assumes that frame is unimportant and unwinds again. Since the CLR considers every frame important, it does not want this double-unwind behavior and requires the JIT to place a NOP (or other instruction) between the any call and any epilog.
The OS has an optimization in the unwinder such that if an unwind results in a PC being within (or at the start of) an epilog, it assumes that frame is unimportant and unwinds again. Since the CLR considers every frame important, it does not want this double-unwind behavior and requires the JIT to place a NOP (or other instruction) between any call and any epilog.

### ARM and ARM64 padding info

The OS unwinder uses the `RUNTIME_FUNCTION` extents to determine which function or funclet to unwind out of. The net result is that a call (bl opcode) to `IL_Throw` cannot be the last thing. So similar to AMD64 the JIT must inject an opcode (a breakpoint in this case) when the `bl IL_Throw` would otherwise be the last opcode of a function or funclet, the last opcode before the end of the hot section, or (this might be an x86-ism leaking into ARM) the last before a "special throw block".

The CLR unwinder assumes any non-leaf frame was unwound as a result of a call. This is mostly (always?) true except for non-exceptional finally invocations. For those cases, the JIT must place a 2 byte NOP **before** the address set as the finally return address (in the LR register, before jumping to the finally). I believe this is only needed if the preceding 2 bytes would have otherwise been in a different region (i.e. the end or start of a try body, etc.), but currently the JIT always emits the NOP. This is because the stack walker looks at the return address, subtracts 2, and uses that as the PC for the next step of stack walking. Note that the inserted NOP must have correct GC information.

# Profiler Hooks

If the JIT gets passed `CORJIT_FLG_PROF_ENTERLEAVE`, then the JIT might need to insert native entry/exit/tail call probes. To determine for sure, the JIT must call GetProfilingHandle. This API returns as out parameters, the true dynamic boolean indicating if the JIT should actually insert the probes and a parameter to pass to the callbacks (typed as void*), with an optional indirection (used for NGEN). This parameter is always the first argument to all of the call-outs (thus placed in the usual first argument register `RCX` (AMD64) or `R0` (ARM, ARM64)).
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8 changes: 4 additions & 4 deletions docs/design/features/NonGC-Heap.md
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Expand Up @@ -9,8 +9,8 @@ flowchart
nongcheap("NonGC Heap\n(Not managed by GC)")
subgraph gcheap[GC Heaps]
soh("Small Object Heap (SOH)")
poh("Pinned Object Heap (SOH)")
loh("Large Object Heap (SOH)")
poh("Pinned Object Heap (POH)")
loh("Large Object Heap (LOH)")
end
style nongcheap stroke:green
```
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## Limitations: which objects cannot be allocated on NonGC heaps
The NonGC Heap, while powerful and beneficial, comes with certain inherent limitations, both obvious and specific to the current design used by CoreCLR and NativeAOT:
* **Non-immortal objects:** Only immortal objects should be allocated on NonGC heap to avoid "dead weight" in that heap.
* **Objects from unloadble contexts:** NonGC heap should never be used for objects belonging to unloadable contexts. Doing so could lead to potential memory leaks. As a consequence, all string literals associated with **unloadable** Assembly Load Contexts (ALCs) won't be placed in the NonGC Heap.
* **Objects from unloadable contexts:** NonGC heap should never be used for objects belonging to unloadable contexts. Doing so could lead to potential memory leaks. As a consequence, all string literals associated with **unloadable** Assembly Load Contexts (ALCs) won't be placed in the NonGC Heap.
* **No References to GC Heap's objects:** NonGC heap **must** never contain references to GC heaps' objects. However, it may contain references to other NonGC objects and GC heaps are allowed to reference NonGC objects.
* The current design of CoreCLR's `FrozenObjectHeapManager` has certain design limitations such as:
* Large objects are not supported.
Expand Down Expand Up @@ -118,4 +118,4 @@ but with the help of NonGC heap, it's now:
* Certain kinds of `static readonly` fields which can be pre-initialized on NativeAOT or recognized by CoreCLR e.g., `Array<>.Empty`.

## Diagnostics and visible changes in .NET 8.0
The most visible change that now `GC.GetGeneration(object)` API returns `int.MaxValue` for such objects. This change serves to emphasize that these objects are not managed by the garbage collector. Similiarly, corresponding `ICorProfiler` APIs may return the same value as a generation. A full inventory of new APIs and alterations related to diagnostic support for the NonGC Heap can be found in the ["Diagnostic support for NonGC heap"](https://github.com/dotnet/runtime/issues/75836) issue. An important detail to keep in mind is that these objects should never be considered as "dead" if no one references them since it's possible that they're actually kept alive by unmanaged data structures in VM itself.
The most visible change that now `GC.GetGeneration(object)` API returns `int.MaxValue` for such objects. This change serves to emphasize that these objects are not managed by the garbage collector. Similarly, corresponding `ICorProfiler` APIs may return the same value as a generation. A full inventory of new APIs and alterations related to diagnostic support for the NonGC Heap can be found in the ["Diagnostic support for NonGC heap"](https://github.com/dotnet/runtime/issues/75836) issue. An important detail to keep in mind is that these objects should never be considered as "dead" if no one references them since it's possible that they're actually kept alive by unmanaged data structures in VM itself.
4 changes: 3 additions & 1 deletion docs/design/features/globalization-hybrid-mode.md
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Expand Up @@ -463,7 +463,9 @@ Affected public APIs:
- CompareInfo.GetSortKeyLength
- CompareInfo.GetHashCode

Apple Native API does not have an equivalent, so they throw `PlatformNotSupportedException`.
Implemeneted using [stringByFoldingWithOptions:locale:](https://developer.apple.com/documentation/foundation/nsstring/1413779-stringbyfoldingwithoptions)

Note: This implementation does not construct SortKeys like ICU ucol_getSortKey does, and might not adhere to the specifications specifications of SortKey such as SortKeys from different collators not being comparable and merging sortkeys.


## Case change
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