[release/6.0] Fix Unix ARM64 RtlRestoreContext implementation #59849
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The RtlRestoreContext sets SP before reading out PC from the context. That can lead to a corruption of the PC in the context if an async signal is delivered to the thread or the thread is interrupted by any other mean after the SP is set and before the value of PC is extracted from the context. This change fixes it by setting the SP after both PC and SP values are read from the context data structure.
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jkotas
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Oct 1, 2021
jeffschwMSFT
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Oct 1, 2021
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Backport of #59831 to release/6.0
/cc @jkotas @janvorli
Customer Impact
Linux ARM64 reliability. Hard to diagnose crash (jump to a random IP read from overwritten memory) triggered by specific interleaving of exception thrown on one thread and GC suspension executing on a second thread.
The bug was tracked to a crash that is observed in dotnet/runtime CI in System.Text.Json tests every few days (#57198). There are likely other crashes caused by this bug.
Testing
Standard dotnet/runtime CI pass.
Risk
Minimal. One-liner fix. Code path is exercised on every exception thrown.