Fix argument passing of structs with padding on x86 #108867
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When passing a struct by value on x86, we copy its value to the stack. Sometimes this is done one field at a time, if the struct has been promoted. If there is padding between the fields (to create appropriate field alignment), then that padding needs to be zeroed. The bug is a case where there is padding between an earlier `double` field and a later, larger, SIMD field. We push 4-byte zeros but the code thinks it is pushing 8-byte zeros. The fix is simply to correctly calculate the number of zeros to push. Fixes dotnet#106140
ghost
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area-CodeGen-coreclr
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Based on #106516. I saw no x86 asm diffs locally. |
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@AndyAyersMS @dotnet/jit-contrib PTAL |
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should this be backported given the simple repro? what happens in release mode? |
IMO, it's too late. The assert is a noway_assert, so it fails in release mode (the JIT crashes). Also, apparently this failure existed in .NET 8 according to Will. |
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When passing a struct by value on x86, we copy its value to the stack. Sometimes this is done one field at a time, if the struct has been promoted. If there is padding between the fields (to create appropriate field alignment), then that padding needs to be zeroed.
The bug is a case where there is padding between an earlier
doublefield and a later, larger, SIMD field. We push 4-byte zeros but the code thinks it is pushing 8-byte zeros. The fix is simply to correctly calculate the number of zeros to push.Fixes #106140