Mono Method Body Replacement #44806

lambdageek · 2020-11-17T16:13:28Z

Contributes to dotnet/xamarin#13 and dotnet/aspnetcore#5456

Overview

The goal of Mono method body replacement is to improve the inner dev loop experience for customers using Xamarin to create mobile apps and those using Blazor to create WebAssembly projects.

Method body replacement is a subset of a more general hot reload experience with a restricted subset of allowed edits. Non-supported ("rude") edits will generally be rejected by the tooling outside the runtime, however the runtime
itself should be transactional in that a change is either committed by the runtime in total or else it is rejected and the runtime state is unchanged.

The changes are delivered to the runtime using the EnC "dmeta" and "DIL" (and "DPDB") delta files. If the changes are accepted, then future invocations of methods affected by the delta will use the new method bodies. Currently executing versions of the methods will use the previous versions.

Multiple versions of changes can be applied in succession. Once a change is applied, it cannot be unapplied (but of course a new change can be used to undo the previous change). For collectible ALCs unloading the assembly will unload all its changes.

Method body replacement will only be supported with the Mono interpreter with inlining turned off. The DOTNET_MODIFIABLE_ASSEMBLIES environment variable must be set to the (case-insensitive) value debug. The assemblies that are eligible for modifications must be compiled with the /debug option.

Method body replacement will not interfere with debugging.

Metadata deltas will be injected either using the debugger or using a managed API. If the debugger is not involved, the runtime will pause the executing user threads at critical points during the update.

End to end scenarios

CLI (dotnet-watch)
- Blazor WebAssembly
- ~~MAUI~~ postponed to .net7
Visual Studio "Apply Changes" during debugging
- Android
- iOS
  - Depends on [dotnet] Support interpreter-only mode in the simulator xamarin/xamarin-macios#11421
- ~~WebAssembly~~ postponed to .net7

Tasks

Priority 0

Priority 1

Future (.net7 +)

Moved to #57365

Bugs

[mono] ApplyDelta results in BadImageFormatException #49227 -> PR [metadata_update] Fix bounds check error #49328
- This was previously reported as:
  
  Most changes to a protected override void BuildRenderTree (Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder builder); method on a component class ends up producing a kind of change that the runtime can't apply and crashes with errors like "BadImageFormatException: Image with invalid assemblyref token 0000000f".
PR [mbr] Return -1 if relative index is not in given generation #49795
- This was previously reported as:
  
  Changing logic in basic ways usually does not work fine. For example, changing return "my string"; to var other = "test"; return "my string" + other; leads to a crash with error "TypeLoadException: Could not resolve type with token 0100004c from typeref".
- and as Blazor Wasm rendering incorrect components (ie multiple <Counter/> components would render as another previously added component)
WebAssembly hot reload reverts to old version of a type #50190 - editing type 'B' (referenced from A) then editing 'A' causes changes to 'B' to be reverted - PR [mbr] Fix encmap boundary and method RVA lookup. #50248 (also backported to 6.0 preview3 branch - [release/6.0-preview3] [mbr] Fix encmap boundary and method RVA lookup. #50254)
[metadata-update] Make a copy of the DIL when applying updates #52344 - A GC after applying an update can collect the updated method bodies (!!). This manifests in a variety of ways but is usually a BadImageFormatException thrown from the caller of an updated method.
[mono] Allow CustomAttribute table modifications if Parent stays unchanged #55097

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ghost · 2020-11-17T16:13:30Z

Tagging subscribers to this area: @CoffeeFlux
See info in area-owners.md if you want to be subscribed.

Issue Details

Description:	Method Body Replacement Contributes to dotnet/xamarin#13 and dotnet/aspnetcore#5456 Overview The goal of Mono method body replacement is to improve the inner dev loop experience for customers using Xamarin to create mobile apps and those using Blazor to create WebAssembly projects. Method body replacement is a subset of a more general hot reload experience with a restricted subset of allowed edits. Non-supported ("rude") edits will generally be rejected by the tooling outside the runtime, however the runtime itself should be transactional in that a change is either committed by the runtime in total or else it is rejected and the runtime state is unchanged. The changes are delivered to the runtime using the EnC "dmeta" and "DIL" (and "DPDB") delta files. If the changes are accepted, then future invocations of methods affected by the delta will use the new method bodies. Currently executing versions of the methods will use the previous versions. Method body replacement will only be supported with the Mono interpreter with inlining turned off. Method body replacement will not interfere with debugging. Metadata deltas will be injected either using the debugger or using another API. If the debugger is not involved, the runtime will pause the executing user threads at critical points during the update. Tasks Priority 0 Put the metadata update work-in-progress under a compile-time feature flag and merge to dotnet/runtime master Investigate what happens with debugger attached Add support for consuming "dpdb" debugger file deltas What should happen if there is a breakpoint in an old version of a method - migrate breakpoint to new version or keep both? How should a breakpoint hit in a previous version of a method be reported to the debugger frontend? Properly detect cases we don't support, backout metadata updates and raise a managed exception Investiage MonoImage refcount mistake - fix the shutdown hack (`exe_image`) set compile time feature flag to on by default (in debug builds?), put under runtime feature flag set up testing infrastructure and run CI publish external testing artifact that our CI will depend on msbuild task for working with pre-canned deltas Publish wasm, android and ios Debug runtime packs with MBR support Priority 1 Support mixed AOT/interp hybrid mode Support adding nested classes, lambdas and async methods Propose and implement an API event that can be used to notify frameworks that a change was applied. Implement additional Future Type system additions (static fields, static methods, virtual method overrides, etc) Out of scope Type system modifications Active statements / On-stack replacement Object migration JIT support
Author:	lambdageek
Assignees:	-
Labels:	`Team Epic`, `area-VM-meta-mono`, `hard problem`, `tracking`
Milestone:	-

srxqds · 2020-11-17T17:44:22Z

why not support for jit?

srxqds · 2020-12-05T03:54:53Z

hope you can support it in jit mode

lambdageek · 2020-12-05T15:53:25Z

@srxqds The reason we're initially focusing on the interpreter is both for practical implementation reasons and due to the use-case that we're targeting. The use-case is Blazor WebAssembly and Xamarin mobile developers who are iterating on their code. This functionality is intended to be an improvement to the developer experience, not something that we expect developers to ship in production to end-users. For this use-case, it made sense to focus on the interpreter - because that's all that is available for WebAssembly, and it can also be supported on mobile.

The practical engineering reason is because this is going to involve a lot of changes at a foundational level in Mono. There are basically three places where we will need to make changes: in the low-level code that deals with .NET IL metadata; in the type system representation (MonoClass etc); and in the compilation stage and the execution engine. The advantage of doing interpreter first is that it has a relatively isolated compilation (inter/transform.c) and there is a single place where the code to be executed is looked up. So we can make a small change that we are pretty sure won't lead to a ton of bugs.

So we can focus on making changes to the metadata and the type system without also having to deal with the compilation and execution engine at the same time.

Once the metadata and typesystem changes are stable, it might make sense to look at the JIT, but right now it would just be a distraction.

srxqds · 2020-12-07T13:09:50Z

@srxqds The reason we're initially focusing on the interpreter is both for practical implementation reasons and due to the use-case that we're targeting. The use-case is Blazor WebAssembly and Xamarin mobile developers who are iterating on their code. This functionality is intended to be an improvement to the developer experience, not something that we expect developers to ship in production to end-users. For this use-case, it made sense to focus on the interpreter - because that's all that is available for WebAssembly, and it can also be supported on mobile.

The practical engineering reason is because this is going to involve a lot of changes at a foundational level in Mono. There are basically three places where we will need to make changes: in the low-level code that deals with .NET IL metadata; in the type system representation (MonoClass etc); and in the compilation stage and the execution engine. The advantage of doing interpreter first is that it has a relatively isolated compilation (inter/transform.c) and there is a single place where the code to be executed is looked up. So we can make a small change that we are pretty sure won't lead to a ton of bugs.

So we can focus on making changes to the metadata and the type system without also having to deal with the compilation and execution engine at the same time.

Once the metadata and typesystem changes are stable, it might make sense to look at the JIT, but right now it would just be a distraction.

ok, thank you for reply.

First part of support for metadata updates. Contributes to dotnet/runtime#44806 The feature is off by default. To enable, build with `/p:MonoMetadataUpdate=true` (e.g. `./build.sh --os browser /p:MonoMetadataUpdate=true`). There are samples in `src/mono/netcore/sample/mbr` (see the README - the samples aren't completely standalone and need some external tooling to build) for console (only tested on Mac and Linux) and wasm. There's a demo at https://lambdageek.dev/dl0/

First part of support for metadata updates. Contributes to dotnet/runtime#44806 The feature is off by default. To enable, build with `/p:MonoMetadataUpdate=true` (e.g. `./build.sh --os browser /p:MonoMetadataUpdate=true`). There are samples in `src/mono/netcore/sample/mbr` (see the README - the samples aren't completely standalone and need some external tooling to build) for console (only tested on Mac and Linux) and wasm. There's a demo at https://lambdageek.dev/dl0/ * Initial metadata-update prototype Co-Authored-By: Bernhard Urban-Forster <lewurm@gmail.com> * Add metadata-update.{c,h} to CMakeLists.txt * Add icall to corelib * Add console and browser metadata update samples Both samples depend on the roslynildiff tool which should be specified with a RoslynILDiffFullPath property in the .csproj files for the projects. * Add README for mbr samples * [build] Add initial runtime support for MonoMetadataUpdate property In the runtime defines cmake ENABLE_METADATA_UPDATE option and sets a preprocessor flag. In System.Private.CoreLib, defines FEATURE_METADATA_UPDATE and uses it to throw a NotSupportedException from LoadMetadataUpdate * [runtime] ifdef out metadata updates if not enabled Also move execution engine initialization into the main update function and use a MonoError to signal failures (such as if interp inlining is not turned off) instead of asserting at startup. * [wasm] set log mask to metadata-update * [mbr] Add InjectUpdate fn to sample * [metadata-update] don't merge heaps * Don't make entrypoint public yet * Add LoadMetadataUpdate to linker descriptor * [wasm] add default Makefile variable value * fix mono/mono CI don't try to run enc tests yet since they depend on roslynildiff * remove mono/mono/tests/enc Will add as runtime tests in a future PR * [metadata-update] Add per-thread exposed generation A thread has to voluntarily roll up to the latest published generation in order to see updates. - Roll up to the latest published generation when attaching a thread - The updater thread sees the allocated unpublished generation * [mbr] Fixup console sample Use a single changing testfile * [metadata-update] delete unused method * [mbr] Use 2 threads in console sample * [metadata-update] Respect exposed generation in MethdDef RVA lookups * [interp] Expose latest metadata update before transforming methods * [mbr] Update samples after rebase Use the WasmApp.targets * [metadata-update] Don't fail after the first unsupported edit Log all the unsupported edits, then cancel the update * [metadata_update] Keep track of logical table sizes for deltas Keep track of inserted/modified rows for each table in each delta. This will help to use a simpler algorithm to locate effective table rows by keeping track of the logical number of rows in the appended tables * [metadata-update] Use a GList for MonoImage:delta_image We're going to need to walk backwards from the latest published delta * [metadata-update] add effective table lookup debug output * Address review feedback * [interp] Save top interp frame at MINT_SAFEPOINT to ThreadContext Give metadata updates a peek at the interp frames since the LMF so that it can copy the InterpMethods that are currently executing This only works with hybrid and full coop suspend. Preemptive suspend will need another mechanism. * [mbr] Extend console sample Add a busy thread to demonstrate that interp frames since the last managed frame are visible to the metadata update mechanism and the active method bodies are copied before being invalidated. * [interp] Check mono_polling_required at safepoint Co-authored-by: Bernhard Urban-Forster <lewurm@gmail.com> Co-authored-by: lambdageek <lambdageek@users.noreply.github.com>

…wser (#47785) Contributes to #44806

[Mono.Debugger.Soft] add ModuleMirror.ApplyChanges [Mono.Debugging.Soft] add SoftDebuggerSession.ApplyChanges Related mono/mono Mono.Debugger.Soft PR: mono/mono#20889 Related dotnet/runtime PR: dotnet/runtime#49043 Contributes to dotnet/runtime#44806

srxqds · 2021-06-22T15:04:31Z

hi, when can you begin to support add static fields and methods to existing classes work?

lambdageek · 2021-08-13T20:08:16Z

Pushed the future work to a separate tracking issue. This one is done. #57365

lambdageek added hard-problem area-VM-meta-mono tracking This issue is tracking the completion of other related issues. Team Epic labels Nov 17, 2020

Dotnet-GitSync-Bot added the untriaged New issue has not been triaged by the area owner label Nov 17, 2020

lambdageek removed the untriaged New issue has not been triaged by the area owner label Nov 17, 2020

lambdageek self-assigned this Nov 17, 2020

This was referenced Nov 17, 2020

Xamarin developers can use C# Hot Reload while their app is running dotnet/xamarin#13

Open

Hot Reload for Blazor dotnet/aspnetcore#5456

Closed

lambdageek added this to the 6.0.0 milestone Nov 17, 2020

lambdageek mentioned this issue Dec 4, 2020

[Mono] Initial metadata update support #45612

Merged

tommcdon mentioned this issue Dec 5, 2020

Support Dev inner loop improvements in CoreCLR VM #45629

Closed

monojenkins mentioned this issue Dec 6, 2020

[Mono] Initial metadata update support mono/mono#20629

Merged

lambdageek mentioned this issue Dec 7, 2020

Add runtime API to load Hot Reload deltas #45689

Closed

lambdageek mentioned this issue Jan 12, 2021

[mono] Set thread suspend default in mono.proj; default to hybrid #46873

Merged

This was referenced Jan 21, 2021

Hosting API to enable hot reload at startup #47274

Closed

Add support for host startup hooks to Mono #47462

Closed

marek-safar removed the Team Epic label Jan 29, 2021

lambdageek added a commit that referenced this issue Feb 4, 2021

[mono] Compile runtime with MBR support by default on Android and Bro…

9f31242

…wser (#47785) Contributes to #44806

lambdageek mentioned this issue Feb 18, 2021

[mono] Add debugger-agent command to apply hot reload update #48458

Closed

This was referenced Mar 3, 2021

[sdb] Add MODULE_APPLY_CHANGES command for hot reload #49043

Merged

Add Module.ApplyChanges mono/debugger-libs#342

Merged

[sdb] Add Module.ApplyChanges mono/mono#20889

Merged

This was referenced Mar 17, 2021

[metadata] Don't access MonoTableInfo:rows, use table_info_get_rows() #49738

Merged

[mbr] Return -1 if relative index is not in given generation #49795

Merged

internal runtime API to return hot reload capabilities #50111

Closed

This was referenced Apr 5, 2021

[mbr] Add Apple sample #50740

Merged

Use MetadataUpdateHandlerAttribute to clear Mono's reflection cache #50978

Closed

[mbr] Add support for editing property getters/setters #51011

Merged

lambdageek added area-EnC-mono Hot Reload for WebAssembly, iOS/Android, etc and removed area-VM-meta-mono labels Apr 23, 2021

lambdageek mentioned this issue May 19, 2021

[metadata-update] Add support for deltas with CustomAttributes modifications #52993

Closed

lambdageek mentioned this issue Jul 2, 2021

[mono] Allow CustomAttribute table modifications if Parent stays unchanged #55097

Closed

lambdageek mentioned this issue Jul 15, 2021

[mono] Disable unsupported apply update scenarios #55698

Merged

This was referenced Jul 29, 2021

[hot_reload] Mono should ignore Param table row updates #56574

Closed

[EnC] Implement the UpdateParameters capability #56626

Closed

[hot_reload] Allow benign Param table updates #56800

Merged

lambdageek mentioned this issue Aug 13, 2021

Continued improvements to Mono Method Body Replacement #57365

Closed

27 tasks

lambdageek closed this as completed Aug 13, 2021

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Mono Method Body Replacement #44806

Mono Method Body Replacement #44806

lambdageek commented Nov 17, 2020 •

edited

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ghost commented Nov 17, 2020

Overview

Tasks

Priority 0

Priority 1

Future

Out of scope

srxqds commented Nov 17, 2020

srxqds commented Dec 5, 2020

lambdageek commented Dec 5, 2020

srxqds commented Dec 7, 2020

srxqds commented Jun 22, 2021

lambdageek commented Aug 13, 2021

Mono Method Body Replacement #44806

Mono Method Body Replacement #44806

Comments

lambdageek commented Nov 17, 2020 • edited Loading

Overview

End to end scenarios

Tasks

Priority 0

Priority 1

Future (.net7 +)

Bugs

ghost commented Nov 17, 2020

Overview

Tasks

Priority 0

Priority 1

Future

Out of scope

srxqds commented Nov 17, 2020

srxqds commented Dec 5, 2020

lambdageek commented Dec 5, 2020

srxqds commented Dec 7, 2020

srxqds commented Jun 22, 2021

lambdageek commented Aug 13, 2021

lambdageek commented Nov 17, 2020 •

edited

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