Deduplicate minipal thread ID TLS cache.

[lateralusX]

Summary

Deduplicate the TLS cache used by minipal_get_current_thread_id.

Fixes #131954.

Root cause

minipal_get_current_thread_id previously declared its cached thread ID as a function-local static thread_local variable in thread.h.

Because the function has internal linkage, each translation unit using it could emit a separate 8-byte TLS slot. Enabling the in-process crash reporter added another consumer, increasing libcoreclr.so's TLS footprint enough to exceed glibc's optional static TLS allocation on Linux ARM64.

This caused glibc to resolve CoreCLR TLS accesses through _dl_tlsdesc_dynamic instead of _dl_tlsdesc_return, adding overhead to allocation, thread-static access, and other common runtime paths.

Changes

• Move the cached thread ID into a single minipal compilation unit.
• Externally declare the shared TLS variable from thread.h.
• Use a common macro for the C and C++ TLS storage-class spellings.

Validation

A test with two independent C and C++ translation units showed:

• Before: two local 8-byte TLS slots and a 16-byte TLS segment.
• After: one shared 8-byte TLS slot.
• GCC C++ emits no TLS dynamic-initialization relocation for the shared variable.

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[dotnet-policy-service]

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[Copilot]

Pull request overview

Deduplicates the TLS-backed cache used by minipal_get_current_thread_id() by moving the cached thread ID out of a function-local TLS and into a single TLS variable defined in a dedicated minipal compilation unit.

Changes:

• Introduces MINIPAL_THREAD_LOCAL and uses it to declare a shared TLS variable minipal_cached_thread_id in thread.h.
• Adds thread.c to define minipal_cached_thread_id (under the same WASM/reentrancy guards).
• Updates minipal’s CMake source list to compile thread.c on Unix hosts.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/native/minipal/thread.h	Switches the cache from a function-local TLS static to an extern TLS variable and adds a TLS macro.
src/native/minipal/thread.c	Defines the shared TLS variable so all translation units refer to the same TLS slot.
src/native/minipal/CMakeLists.txt	Ensures thread.c is built into minipal on Unix.

[EgorBo]

@EgorBot -linux_arm64 --filter "System.Tests.Perf_UInt16.Parse*"

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[AndyAyersMS]

For some reason egorbot failed on main, but passed on the PR

Method	Toolchain	value	Mean	Error	Ratio	Allocated	Alloc Ratio
Parse	/main/corerun	0	NA	NA	?	NA	?
Parse	/PR_131991/corerun	0	5.631 ns	0.0008 ns	1.00	-	NA
Parse	/main/corerun	12345	NA	NA	?	NA	?
Parse	/PR_131991/corerun	12345	8.717 ns	0.0013 ns	1.00	-	NA
Parse	/main/corerun	65535	NA	NA	?	NA	?
Parse	/PR_131991/corerun	65535	8.852 ns	0.0014 ns	1.00	-	NA

PR results look similar to the fast "before" results we have from the lab

[mdh1418]

@EgorBot -linux_arm64

using BenchmarkDotNet.Attributes;
 
public class Perf_Enum
{
    [Benchmark]
    [Arguments(DayOfWeek.Wednesday, "x")]
    public string ToString_Format_NonFlags(DayOfWeek value, string format) =>
        value.ToString(format);
}