[browser][coreCLR] Loading WebCIL 1.0

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904

[pavelsavara]

Enable WebCIL support for CoreCLR on Browser/WASM

Fixes#120248

WebCIL format v1.0 with 16-byte section alignment and IMAGE_SECTION_HEADER format

Bumps WebCIL version from 0.0 to 1.0.

• The WebcilConverter now emits section data at 16-byte-aligned offsets, ensuring RVA static fields backing ReadOnlySpan<T> over types up to Vector128<T> retain their natural alignment.
• The section headers are full IMAGE_SECTION_HEADER that makes the code of reading much simpler.

CoreCLR PEDecoder: native WebCIL parsing

New src/coreclr/inc/webcil.h defines WebcilHeader and WebcilSectionHeader C structs with static_assert size checks. PEDecoder gains:

• FLAG_WEBCIL flag; HasWebcilHeaders() validates magic, version, section count/bounds/ordering and synthesizes IMAGE_SECTION_HEADER[] from WebCIL sections so RvaToSection()/RvaToOffset() work uniformly.
• HasHeaders() / CheckHeaders() as unified entry points that dispatch to WebCIL or NT paths.
• WebCIL-aware HasDirectoryEntry(), GetDirectoryEntryData() (handles COMHEADER and DEBUG entries via WebcilHeader fields with explicit range validation against section data).
• CheckCorHeader() and CheckILOnly() WebCIL branches (WebCIL images are always IL-only by definition).
• GetPEKindAndMachine() reports peILonly / IMAGE_FILE_MACHINE_I386 for WebCIL.
• GetNumberOfRvaAndSizes() moved from public to private API; GetNumberOfSections() / FindFirstSection() delegate to synthesized headers for WebCIL.
• Preconditions across the file generalized from CheckNTHeaders() to CheckHeaders() / HasHeaders().

PEImage / PEAssembly integration

PEImage exposes HasHeaders() forwarding to PEDecoder::HasHeaders(). PEAssembly uses HasHeaders() instead of HasNTHeaders() for metadata access.

Browser host loader: WebCIL module instantiation

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable
• Enabling WebCIL by default for CoreCLR-on-WASM via WasmEnableWebcil.

DAC support gap

All WebCIL code paths in PEDecoder are gated behind #ifdef TARGET_BROWSER, which is mutually exclusive with DACCESS_COMPILE.
Should we drop #ifdef TARGET_BROWSER ? Or build target specific DAC binaries ?
Follow up in #124467

(func$getWebcilPayload(;1;) (export"getWebcilPayload") (param$d(;0;)i32) (param$n(;1;)i32)
local.get$di32.const0local.get$nmemory.init1
)

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds support for loading WebCIL version 1.0 assemblies in CoreCLR on browser/WASM targets. WebCIL is an alternative container format for ECMA-335 assemblies that strips PE headers and packages assemblies as WebAssembly modules with a .wasm extension, helping avoid issues with firewalls/antivirus software that block .dll files.

Changes:

• Added WebCILImageLayout C++ class that extends PEImageLayout to handle WebCIL format, parsing WebCIL headers and mapping RVAs to file offsets
• Implemented instantiateWebCILModule in TypeScript that instantiates WebCIL .wasm modules and extracts assembly payloads into aligned memory
• Enabled WebCIL support for CoreCLR by removing WasmEnableWebcil=false restrictions and updating test configurations

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil1" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added instantiateWebCILModule to BrowserHost exports
src/native/libs/Common/JavaScript/cross-module/index.ts	Updated export table to include instantiateWebCILModule
src/native/corehost/browserhost/loader/dotnet.d.ts	Added "webcil1" type definition
src/native/corehost/browserhost/loader/assets.ts	Added WebCIL detection and loading logic, mapping .wasm to .dll paths
src/native/corehost/browserhost/host/index.ts	Exported instantiateWebCILModule function
src/native/corehost/browserhost/host/host.ts	Updated assembly path mapping to replace .wasm with .dll
src/native/corehost/browserhost/host/assets.ts	Implemented instantiateWebCILModule to extract WebCIL payload and register assemblies
src/mono/wasm/Wasm.Build.Tests/Common/BuildEnvironment.cs	Removed CoreCLR restriction for WebCIL in tests
src/mono/browser/build/WasmApp.InTree.props	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment
src/coreclr/vm/webcildecoder.cpp	New file implementing WebCILImageLayout class for parsing and validating WebCIL format
src/coreclr/vm/peimagelayout.h	Added WebCIL header structures and WebCILImageLayout class declaration
src/coreclr/vm/peimagelayout.cpp	Added WebCIL format detection in LoadFlat
src/coreclr/vm/peassembly.cpp	Excluded 32-bit NT headers check for TARGET_BROWSER, added braces for consistency
src/coreclr/vm/coreassemblyspec.cpp	Added braces around single-statement if bodies
src/coreclr/vm/CMakeLists.txt	Added webcildecoder.cpp to browser build
src/coreclr/inc/pedecoder.h	Made specific PEDecoder methods virtual for browser target to enable WebCILImageLayout overrides
eng/testing/tests.browser.targets	Removed WasmEnableWebcil=false for CoreCLR, updated TODO comment

[davidwrighton]

Please have @elinor-fung look at this

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 7 comments.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 19 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[adamperlin]

In corerun, we don't have the implementation of external_assembly_probe yet and for loading R2R it would be necessary. Because it needs to be loaded by the "JS host into JS VM" rather than by "dotnet process into WASM linear memory". I think should do it, but it is out of scope of this PR, which only matches the Mono functionality.

That said, is there more feedback for this PR ?

Definitely agreed that it is out of scope for this PR! I was mostly just wanting to understand what direction we are heading in on the host loading side and what work is still required, so I appreciate the clarification here. I don't have any more feedback, and I think this looks good for now as a start! Since I have limited expertise in this area though, it would be great if @elinor-fung could take a look before this goes in.

[Copilot]

Pull request overview

Copilot reviewed 37 out of 38 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 35 out of 36 changed files in this pull request and generated no new comments.

[pavelsavara]

it would be great if @elinor-fung could take a look before this goes in.

As we are waiting for more feedback on native part, I split of JS part, for which I'm pretty confident into #124758 and will merge that first.

[elinor-fung]

This feels a bit like PEDecoder has been hijacked to also handle Webcil. There are a number of things on it that simply don't apply or make sense for Webcil. While they can share some logic around reading, they are not fundamentally the same format. I would prefer something like:

• Separate PEDecoder and WebcilDecoder
• Helper functions the decoders can use for shared logic like reading the IMAGE_SECTION_HEADER
• PEImageLayout stops inheriting from PEDecoder and instead contains either a PEDecoder or WebcilDecoder (exposing what is needed for callers that were directly calling into PEDecoder)

I know that may be a significant amount of refactoring, but hopefully somewhat mechanical and something copilot would be good at.

[jkotas]

Also, we won't need to artificially inflate the section headers if we go with Elinor's suggestion.

[pavelsavara]

The new PEImageLayout will forward about 80 methods to a particular assembly decoder.
About 50 of them are PE only members (some of them would be shared when we add R2R to webcil later).

It will be massive change, are you sure ?
I will do it into separate branch, so that we could compare it

I think we would like to avoid C++ virtual methods, so that DAC is easier, right ?
Probably via on discriminated union.

[pavelsavara]

Closing in favor of #124904