[ruby-core:112458] [Ruby master Bug#19444] YJIT String#+@ miscompilations

16 Feb 2023

      Issue #19444 has been reported by alanwu (Alan Wu).

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Bug #19444: YJIT String#+@ miscompilations
https://bugs.ruby-lang.org/issues/19444

* Author: alanwu (Alan Wu)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: REQUIRED
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We noticed two issues with YJIT's `String#+@` (String unary plus) implementation.

1. It has issues with GC allocation tracing. We saw it SEGV with the `Stackprof` gem
2. It has a type confusion issue from assuming that the method always return an `::String` instance. It can return subclass instances

The YJIT override does not exist on the 3.1 series.

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