[r8-obfuscation] Add PE metadata rebuild substrate by simonrozsival · Pull Request #12629 · dotnet/android

simonrozsival · 2026-09-01T14:29:23Z

Summary

This is layer 2 of 6 in the replacement stack for PR #12575. It adds the internal PE and metadata reconstruction substrate required by later JNI name-rewriting layers, without enabling any build behavior.

Rebuilds managed PE images while preserving existing metadata tokens and supported table row ordering.
Re-emits method bodies, embedded resources, debug-directory data, native resources, and FieldRVA mapped data, including ranges from different PE sections.
Preserves overlapping/aliased FieldRVA backing data by relocating rewritten fields instead of modifying shared storage.
Validates malformed IL, resource offsets/directories, and strong-name signature directories through controlled rewrite errors.
Emits event/property method semantics explicitly in HasSemantics coded-index order.
Rejects unsupported field-backed ImplMap rows instead of silently dropping metadata.
Adds low-level metadata encoding, raw-column, IL operand-scanning, and rewrite-plan primitives.
Covers longer and shorter UTF-8 FieldRVA replacements, aliased mapped fields, event/property accessor preservation, per-use #US splitting, and strong-name signature preservation directly through AssemblyRebuilder.
Uses the executing runtime's core assembly version in generated fixtures so rebuilt images load across target frameworks.

Scope

This layer intentionally does not add JNI-specific planning or attribute/ldstr orchestration, the assembly-rewriter facade, the RewriteJniNamesForR8 MSBuild task, typemap rewrite behavior, CoreCLR/NativeAOT target integration, or documentation. Those surfaces belong to later stack layers.

Validation

./dotnet-local.sh build src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Xamarin.Android.Build.Tests.csproj -c Debug -v:minimal --no-restore
./dotnet-local.sh test bin/TestDebug/net10.0/Xamarin.Android.Build.Tests.dll --filter 'FullyQualifiedName~NativeResourceSectionCopierTests|FullyQualifiedName~AssemblyRebuilderTests'
Direct layer-2 result: 18 passed, 0 failed.
Cumulative layer-3 RewrittenAssemblyLoadsAndRunsInTheRuntime result: 1 passed, 0 failed.

Related to #12535

Depends on #12628

simonrozsival · 2026-09-01T22:49:38Z

/azp run

azure-pipelines · 2026-09-01T22:50:01Z

Azure Pipelines: Successfully started running 1 pipeline(s).

simonrozsival · 2026-09-02T05:04:48Z

/azp run

azure-pipelines · 2026-09-02T05:05:11Z

Azure Pipelines: Successfully started running 1 pipeline(s).

simonrozsival · 2026-09-02T09:27:57Z

/azp run

azure-pipelines · 2026-09-02T09:28:10Z

Azure Pipelines: Successfully started running 1 pipeline(s).

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Use the executing runtime version in metadata fixtures so rebuilt images load across target frameworks. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot

Copilot review overview

🟡 Changes recommended

MetadataEncoding.ReadCompressedInteger does not guard against negative offsets, causing unintended IndexOutOfRangeException instead of a controlled rewrite failure.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review tier: Lite
Findings: 1 · 1

New issues introduced by this change (2)

Severity	Finding
	`src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/MetadataEncoding.cs` — ❌ error Bug — ReadCompressedInteger allows a negative offset, which will throw…
	`src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/AssemblyRebuilder.cs` — 💡 suggestion Formatting / Conventions — Prefer `[]` over `Array.Empty<T>()` in this repo to…

What changed in this PR

Adds the internal PE + ECMA-335 metadata rebuild substrate under Xamarin.Android.Build.Tasks to support later R8/JNI name-rewriting layers, while keeping this layer behaviorally inert (no build integration yet). The new utilities focus on rebuilding managed assemblies without moving metadata tokens, while re-emitting method bodies, resources, debug directory data, native resources, and FieldRVA mapped data, plus adding targeted validation against malformed inputs.

Changes:

Introduces AssemblyRebuilder and supporting primitives for token-preserving PE/metadata reconstruction, IL scanning, and selective heap/value rewrites.
Adds low-level helpers for raw metadata column access, compressed integer encoding/decoding, FieldRVA decoding/relayout, and Win32 resource section relocation.
Adds focused NUnit coverage with a fixture generator to validate native resources, FieldRVA behaviors, IL scanning validation, and strong-name signature handling.

File	Description
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/AssemblyRebuilder.cs	Core token-preserving managed PE rebuild implementation (IL, resources, debug/native resources, FieldRVA).
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/FieldRvaTable.cs	Reads and interprets `FieldRVA` rows and mapped data, including typemap-style UTF-8 payload detection.
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/NativeResourceSectionCopier.cs	Copies and relocates `.rsrc` directory data for rebuilt PEs with validation.
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/MetadataRawColumns.cs	Reads metadata table columns not exposed by `MetadataReader` (e.g., `ImplMap.MemberForwarded`).
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/MetadataEncoding.cs	ECMA-335 compressed integer encode/decode helper used for manual blob rewriting.
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/JniRewritePlan.cs	Holds per-use-site rewrite decisions for attributes, `ldstr`, and UTF-8 FieldRVA data.
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/JniRewriteException.cs	Dedicated exception type for rewrite failures and validation errors.
src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/IlOpcodeTable.cs	Minimal operand-size table enabling IL walks without a full IL parser.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/JniRemapping/AssemblyRebuilderTests.cs	End-to-end tests for rebuild invariants (FieldRVA/resources, IL, strong-name space, validation).
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/JniRemapping/NativeResourceSectionCopierTests.cs	Validates `.rsrc` copying/relocation and malformed directory rejection.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/JniRemapping/JniFixtureBuilder.cs	Produces minimal managed PE fixtures to exercise the rebuilder without external binaries.

Detach rewritten mapped fields from overlapping source storage so shorter replacements cannot corrupt aliased fields. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Validate negative compressed-integer offsets and use the repository empty-array convention when rebuilding method bodies. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Validate malformed resource and strong-name directory values through the rewrite error contract, and emit MethodSemantics rows in HasSemantics coded-index order. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-09-02T14:43:12Z

/review

github-actions · 2026-09-02T14:43:58Z

✅ Android PR Reviewer completed successfully!

Generated by Android PR Reviewer for #12629

github-actions

⚠️ Needs Changes — 1 error, 2 warnings.

The table-by-table token preservation and malformed-metadata coverage are strong, and all 44 CI checks are green. Before merge, the rebuild needs to reject or preserve non-MethodDef entry points; I also called out two validation gaps that can silently produce altered or inconsistent output for malformed metadata.

Generated by Android PR Reviewer for #12629 · gpt56 · 227.7 AIC · ⌖ 9.02 AIC · ⊞ 25.7K
_{Comment /review to run again}

Validate colliding synthetic UTF-8 types before reuse and reject half-populated native resource directories. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-09-02T16:03:11Z

/azp run

azure-pipelines · 2026-09-02T16:03:24Z

Azure Pipelines: Successfully started running 1 pipeline(s).

simonrozsival · 2026-09-02T17:38:39Z

/azp run

azure-pipelines · 2026-09-02T17:39:01Z

Azure Pipelines: Successfully started running 1 pipeline(s).

Related to #12535 Depends on #12629 Layer 3 of 6 in the replacement stack for #12575. This layer rewrites standard managed JNI metadata from R8 mappings. Trimmable typemap and FieldRVA handling follows in layer 4.

simonrozsival changed the title ~~Add PE metadata rebuild substrate~~ [r8-obfuscation] Add PE metadata rebuild substrate Sep 1, 2026

simonrozsival mentioned this pull request Sep 1, 2026

[r8-obfuscation] Rewrite managed JNI metadata from R8 mappings #12630

Merged

simonrozsival force-pushed the simonrozsival-pe-metadata-rebuild-substrate branch 3 times, most recently from e83dcaa to 58ac474 Compare September 1, 2026 18:36

simonrozsival force-pushed the simonrozsival-pe-metadata-rebuild-substrate branch 2 times, most recently from fdb7393 to 311a3bf Compare September 2, 2026 08:52

Base automatically changed from simonrozsival-r8-mapping-primitives to main September 2, 2026 11:23

simonrozsival and others added 3 commits September 2, 2026 13:23

Add PE metadata rebuild substrate

f55937e

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Address PE rebuild review findings

9188705

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Cover PE rebuild plan mutations

cc7f216

Use the executing runtime version in metadata fixtures so rebuilt images load across target frameworks. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

simonrozsival force-pushed the simonrozsival-pe-metadata-rebuild-substrate branch from 311a3bf to cc7f216 Compare September 2, 2026 11:23

simonrozsival marked this pull request as ready for review September 2, 2026 11:27

simonrozsival requested a review from jonathanpeppers as a code owner September 2, 2026 11:27

Copilot AI lite review requested due to automatic review settings September 2, 2026 11:27

Copilot started reviewing on behalf of simonrozsival September 2, 2026 11:27 View session

Copilot AI reviewed Sep 2, 2026

View reviewed changes

Comment thread src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/MetadataEncoding.cs Outdated

Comment thread src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/AssemblyRebuilder.cs Outdated

simonrozsival and others added 3 commits September 2, 2026 13:34

Preserve aliased FieldRVA data during rewrites

7278ba7

Detach rewritten mapped fields from overlapping source storage so shorter replacements cannot corrupt aliased fields. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Address PE metadata review feedback

e1289ad

Validate negative compressed-integer offsets and use the repository empty-array convention when rebuilding method bodies. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Harden PE metadata preservation

645cdda

Validate malformed resource and strong-name directory values through the rewrite error contract, and emit MethodSemantics rows in HasSemantics coded-index order. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

simonrozsival added the ready-to-review This PR is ready to review/merge, I think any CI failures are just flaky (ignorable). label Sep 2, 2026

github-actions Bot reviewed Sep 2, 2026

View reviewed changes

Comment thread src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/AssemblyRebuilder.cs

Comment thread src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/AssemblyRebuilder.cs

Comment thread src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/NativeResourceSectionCopier.cs Outdated

Address PE metadata validation review

b89f204

Validate colliding synthetic UTF-8 types before reuse and reject half-populated native resource directories. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

jonathanpeppers approved these changes Sep 2, 2026

View reviewed changes

simonrozsival merged commit 0267ea6 into main Sep 3, 2026
44 checks passed

simonrozsival deleted the simonrozsival-pe-metadata-rebuild-substrate branch September 3, 2026 05:00

This was referenced Sep 3, 2026

CI: MAUI R2R Helix device-lab failures across Android queues #12658

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Helix Android queues repeatedly assign unhealthy devices to MAUI R2R work items dotnet/arcade#17483

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