Arm64: don't fold ldr page offset (PAGEOFFSET_12L) for NativeAOT by EgorBo · Pull Request #129966 · dotnet/runtime

EgorBo · 2026-06-29T06:02:03Z

PR #129589 added an Arm64 fold of adrp+add+ldr into adrp+ldr[#:lo12:] via a 64-bit PAGEOFFSET_12L reloc (R_AARCH64_LDST64_ABS_LO12_NC). That reloc encodes the offset scaled by 8, so the target must be 8-byte aligned. In R2R the relocatable loads always go through pointer-aligned indirection cells, but NativeAOT can fold a direct 64-bit load of byte-packed frozen data (4-byte aligned), which ld.lld rejects:

ld.lld : error : improper alignment for relocation R_AARCH64_LDST64_ABS_LO12_NC: 0x74A52C is not aligned to 8 bytes

The fold is purely a size optimization, so this restricts it to non-NativeAOT and falls back to the always-safe adrp+add+ldr.

Validation (SPMI, linux-arm64):

benchmarks.run (R2R, ~427K contexts): 0 asm diffs — the win is preserved.
smoke_tests.nativeaot (18891 ctx): clean replay, no diffs.

The adrp+add+ldr to adrp+ldr[#:lo12:] fold uses a 64-bit PAGEOFFSET_12L reloc (R_AARCH64_LDST64_ABS_LO12_NC), whose scaled offset requires the target to be 8-byte aligned. R2R loads always go through pointer-aligned indirection cells, but NativeAOT can fold a direct 64-bit load of byte-packed frozen data (4-byte aligned), which the linker rejects with 'improper alignment for relocation'. Restrict the fold to non-NativeAOT. Fixes dotnet#129936 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-06-29T06:03:19Z

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Copilot

Pull request overview

This PR adjusts the Arm64 emitter’s TryFoldPageOffsetIntoLdr peephole optimization to avoid emitting PAGEOFFSET_12L relocations when targeting the NativeAOT ABI, preventing generation of linker-invalid R_AARCH64_LDST64_ABS_LO12_NC relocations in scenarios where the referenced symbol may not be 8-byte aligned.

Changes:

Disable adrp+add+ldr → adrp+ldr[#:lo12:] folding for NativeAOT by early-returning in TryFoldPageOffsetIntoLdr.
Add an in-code rationale describing the alignment requirement of PAGEOFFSET_12L / R_AARCH64_LDST64_ABS_LO12_NC and why NativeAOT differs.

jakobbotsch

LGTM

Co-authored-by: Jakob Botsch Nielsen <Jakob.botsch.nielsen@gmail.com>

Copilot

Pull request overview

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

The adrp+add+ldr -> adrp+ldr[#:lo12:] fold uses R_AARCH64_LDST64_ABS_LO12_NC, which encodes the :lo12: page offset scaled by 8, so the reloc target must be 8-byte aligned. Replace the blanket NativeAOT opt-out with a new JIT-EE API, getAddressAlignment(void*), and only fold when the VM guarantees the target is at least 8-byte aligned. - VM (CoreCLR/NGen): reports the alignment of the absolute address. - crossgen2 (R2R): reports pointer size; direct relocatable loads only target pointer-aligned data. - NativeAOT: reports the exact alignment of non-GC statics (the failing case) and pointer size for GC-statics/RVA data, and fails closed otherwise so an unaligned relocation can never be emitted. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

MichalStrehovsky

Thank you for making it work for native AOT!

…Alignment Replace the duplicated per-node alignment logic in getAddressAlignment with a new IObjectNodeWithAlignment interface implemented by NonGCStaticsNode, GCStaticsNode and FieldRvaDataNode. Each node's GetData/GetDehydratableData now uses GetAlignment(factory) so the value reported to the JIT can never drift from the alignment actually baked into the node's data. Also move getAddressAlignment out of the shared CorInfoImpl.cs (dropping the #if READYTORUN split) into CorInfoImpl.ReadyToRun.cs and CorInfoImpl.RyuJit.cs. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 26 out of 26 changed files in this pull request and generated 1 comment.

…tion) Address review feedback: instead of R2R's blanket `return PointerSize`, resolve the reloc target node and report its real alignment, mirroring the NativeAOT implementation. Adds a parallel R2R IObjectNodeWithAlignment interface (R2R has a separate node/NodeFactory system, so it can't share the NAOT one) implemented on Import (returns the pointer-sized import-section EntrySize) and CopiedFieldRvaNode. Unknown targets fall back to 1 so the JIT never emits an alignment-sensitive reloc it can't prove is legal. Validated: full System.Private.CoreLib arm64 R2R crossgen compiles cleanly; every LDST64 fold candidate is an Import subclass reporting align=8 (no MISS, no align<8), so the adrp+add+ldr -> adrp+ldr[:lo12:] fold is preserved. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The R2R and NAOT bodies are now identical, so host it once in the shared partial. Each compiler still binds its own IObjectNodeWithAlignment and NodeFactory (only one is visible per compilation), so it resolves correctly. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…naot # Conflicts: # src/coreclr/inc/jiteeversionguid.h

Copilot

Pull request overview

Copilot reviewed 29 out of 29 changed files in this pull request and generated no new comments.

EgorBo · 2026-07-07T23:28:23Z

@jkotas @MichalStrehovsky anything else here?

MichalStrehovsky

We now have two IObjectNodeWithAlignment.cs files with slightly different comments. But I really just want to unblock the CI. I would have preferred we revert the change that broke ARM64 testing the moment we found out it's not quite right and then do it properly at leisure.

MichalStrehovsky · 2026-07-08T00:29:30Z

RyuJIT assert == build break and we cannot test anything.

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Disable System.Text.Json polymorphic source-gen tests on NativeAOT #129965

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Update src/coreclr/jit/emitarm64.cpp

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Co-authored-by: Jakob Botsch Nielsen <Jakob.botsch.nielsen@gmail.com>

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github-actions Bot mentioned this pull request Jul 2, 2026

[aw] No-Op Runs #129501

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EgorBo requested a review from MichalStrehovsky as a code owner July 3, 2026 16:05

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[ci-scan] Test failure: System.Formats.Tar.Tests.TarFile_ExtractToDirectory_File_Tests.ExtractToDirectory_RejectsChainedSymlinkDirectoryTraversal_WithNestedFile #130177

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MichalStrehovsky mentioned this pull request Jul 7, 2026

Arm64: [PAC-RET] NativeAOT changes #128950

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EgorBo and others added 2 commits July 7, 2026 11:57

Merge remote-tracking branch 'origin/main' into fix-129936-arm64-12l-…

4ab787b

…naot # Conflicts: # src/coreclr/inc/jiteeversionguid.h

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MichalStrehovsky merged commit a526847 into dotnet:main Jul 8, 2026
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Copilot AI mentioned this pull request Jul 8, 2026

Deduplicate IObjectNodeWithAlignment into shared Common dependency analysis #130325

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[main] Source code updates from dotnet/runtime dotnet/dotnet#7592

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