[release/6.0] Port #58410: Fix zero initialization use of "initReg" #62207
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…Reg" If the only local is an enregistered must-init struct, we were setting `initReg` to its register (in this case, `xmm0`). However, `initReg` is expected to be an integer register. In the test case, with GS cookie stress, the GS cookie code asserted that `initReg` was an integer register, but it wasn't. The fix is the change the condition to use the actual register assigned to the variable (in this case, `xmm0`), not the variable type (here, `TYP_STRUCT`). No spmi asm diffs. Fixes dotnet#57911
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Tagging subscribers to this area: @JulieLeeMSFT Issue DetailsBackport #58410 to release/6.0 Customer ImpactSilent bad codegen: in certain rare cases, a variable is not correctly zero initialized, possibly leading to incorrect results or crashes. The issue was originally found with internal "stress" testing, but was reported by an external F# customer on the 6.0 release. TestingThe fix has been in 'main' for 3 months, but wasn't ported to release/6.0 before release. RiskLow
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@jakobbotsch @dotnet/jit-contrib PTAL: back-port of fix to .NET 6 |
AndyAyersMS
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jakobbotsch
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jeffschwMSFT
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Backport #58410 to release/6.0
Fixes #62103
Customer Impact
Silent bad codegen: in certain rare cases, a variable is not correctly zero initialized, possibly leading to incorrect results or crashes. Typically, this requires a single local variable that is a register-sized struct, marked as requiring zero initialization by the JIT.
The issue was originally found with internal "stress" testing late in .NET 6 product development, but the fix was not ported to the .NET 6 release branch. However, it was subsequently reported by an external F# customer on the 6.0 release.
This was a regression between .NET 5 and .NET 6 due to extensive struct optimization work in the JIT.
Testing
The fix has been in 'main' for 3 months, but wasn't ported to release/6.0 before release.
Risk
Low