[cDAC] Add Apple to RuntimeInfoOperatingSystem

[max-charlamb]

Note

This PR description was drafted with AI (Copilot CLI) assistance.

Summary

Adds a dedicated Apple value to RuntimeInfoOperatingSystem so the cDAC can distinguish Apple platforms (macOS / iOS / tvOS / MacCatalyst) from other Unix targets. The native data descriptor emits the new Apple string whenever TARGET_APPLE is defined, checked before the generic TARGET_UNIX arm.

Fixes #127282.

Motivation

CallingConventionInfo in #126408 needs to set IsAppleArm64ABI only on Apple platforms, because Apple ARM64 uses different stack-argument alignment than Linux ARM64 (natural alignment for primitives, 4-byte alignment for float HFAs, vs. Linux's uniform 8-byte slots). With today's enum collapsing everything non-Windows/non-Browser into Unix, that check cannot be expressed and IsAppleArm64ABI is effectively hardcoded.

Changes

• src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeInfo.cs — add Apple to the enum.
• src/coreclr/vm/datadescriptor/datadescriptor.inc — emit CDAC_GLOBAL_STRING(OperatingSystem, Apple) when TARGET_APPLE is defined, before the TARGET_UNIX arm. Follows the existing #ifdef guard pattern.
• docs/design/datacontracts/RuntimeInfo.md — document the new value and clarify that Apple is still POSIX for != Windows checks.
• src/native/managed/cdac/tests/DumpTests/RuntimeInfoDumpTests.cs — map dump metadata "osx" to Apple (was Unix); "linux"/"freebsd" stay Unix.

Compatibility

The enum is parsed via Enum.TryParse(ignoreCase: true):

• Old runtime + new cDAC: old runtimes still emit "Unix" on macOS, so dumps look identical to today.
• New runtime + old cDAC: old cDACs fail to parse "Apple" and return Unknown; every production check is == Windows / != Windows, which is unaffected.

No RuntimeInfo contract version bump is needed — V1 is defined in terms of parsing, not the specific token set.

Where the enum is used

All usages are inside src/native/managed/cdac; an org-wide GitHub search found no references outside dotnet/runtime and the dotnet/dotnet VMR mirror, and dotnet/diagnostics has zero references.

Definition

• Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeInfo.cs — enum + IRuntimeInfo.GetTargetOperatingSystem().

Production (parser + consumers)

• Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeInfo_1.cs — Enum.TryParse(ignoreCase: true) of the OperatingSystem global, fallback to Unknown.
• Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs — != Windows.
• …/StackWalk/Context/AMD64/AMD64Unwinder.cs (2 sites) — != Windows → _unixAMD64ABI, and a Debug.Assert(... == Windows) on the Windows-only path.
• …/StackWalk/Context/X86/X86Unwinder.cs — != Windows.

Tests

• tests/RuntimeInfoTests.cs — theory data auto-generated from the enum; picks up Apple automatically.
• tests/DumpTests/RuntimeInfoDumpTests.cs — dump-metadata → enum map (updated by this PR).

Call-site audit

All current GetTargetOperatingSystem() consumers compare against Windows, not Unix, so adding Apple changes no runtime behavior:

Site	Check
AMD64Unwinder.cs:34	!= Windows → sets _unixAMD64ABI. Apple x64 is Unix AMD64 ABI ✓
AMD64Unwinder.cs:853	Debug.Assert(... == Windows) on Windows path ✓
X86Unwinder.cs:37	!= Windows (x86 has no Apple target) ✓
SOSDacImpl.cs:745	!= Windows ✓

Follow-up in #126408 will flip IsAppleArm64ABI = os == Unix to os == Apple.

Testing

• Microsoft.Diagnostics.DataContractReader.Tests — all 1751 tests pass, including the auto-generated "apple" round-trip case in RuntimeInfoTests.GetTargetOperatingSystemTest.
• Dump test mapping updated so existing macOS dump configs validate against Apple.
• The native datadescriptor.inc change is a preprocessor-only addition following the existing pattern and is inert on non-Apple builds.

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[Copilot]

Pull request overview

Adds an Apple operating system discriminator to the cDAC RuntimeInfo contract so consumers can reliably distinguish Apple targets (macOS/iOS/tvOS/MacCatalyst) from other Unix platforms.

Changes:

• Added RuntimeInfoOperatingSystem.Apple to the managed contract enum.
• Updated the CoreCLR data descriptor to emit OperatingSystem = "Apple" when TARGET_APPLE is defined (checked before TARGET_UNIX).
• Updated dump-based tests and contract documentation to account for the new OS value.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/native/managed/cdac/tests/DumpTests/RuntimeInfoDumpTests.cs	Maps dump metadata "osx" to the new RuntimeInfoOperatingSystem.Apple.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeInfo.cs	Adds the Apple enum value for RuntimeInfoOperatingSystem.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Emits OperatingSystem=Apple under TARGET_APPLE before the TARGET_UNIX arm.
docs/design/datacontracts/RuntimeInfo.md	Documents the new Apple value and intended semantics.

[max-charlamb]

/ba-g cDAC only change and cDAC legs pass