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@jkotas jkotas commented Nov 13, 2025

Fixes #121596

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jkotas commented Nov 13, 2025

With this fix, we should see the following error message on unpatched Windows 10 machines:

Fatal error.
Your Windows doesn't fully support CET. Please install all available Windows updates.

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Pull Request Overview

This PR fixes an access violation that occurs when ThreadStore::HoldingThreadStore() is called during early startup from HandleFatalError, before the thread store has been initialized.

Key changes:

  • Added a null check for s_pThreadStore in HoldingThreadStore() to prevent dereferencing a null pointer during early startup error handling

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jkotas commented Nov 14, 2025

/backport to release/10.0

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Started backporting to release/10.0 (link to workflow run)

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jkotas commented Nov 14, 2025

/ba-g timeouts

@jkotas jkotas merged commit 39d4138 into dotnet:main Nov 14, 2025
102 of 105 checks passed
@jkotas jkotas deleted the issue-121596 branch November 18, 2025 17:31
steveisok pushed a commit that referenced this pull request Nov 21, 2025
…g startup (#121605)

Backport of #121602 to release/10.0

/cc @jkotas

## Customer Impact

Allow customers to self-diagnose fail fasts encountered early during
startup, such as running on unpatched Windows 10 machine that does not
support CET correctly.

This change fixes crash during printing of the fail fast error message
early during startup.

- [x] Customer reported
- [ ] Found internally

## Regression

- [ ] Yes
- [x] No

## Testing

Manual simulated test

## Risk

Low

Co-authored-by: Jan Kotas <[email protected]>
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csc.exe crashes with exit code -1073741819 (0xC0000005) with .NET SDK 10.0.100 on Windows 10 (VS 2026)

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