Fix potential BitCast bug for platforms without unaligned reads (#89364)

MichalPetryka · web-flow · commit 65536eb2f01e · 2023-07-23T11:20:38.000-07:00
BitCast could potentially make an invalid read when reinterpreting a type to another that requires higher alignment, which could possibly cause a fault on Mono ARMv6.
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/Unsafe.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/Unsafe.cs
@@ -253,7 +253,7 @@ public static TTo BitCast<TFrom, TTo>(TFrom source)
             {
                 ThrowHelper.ThrowNotSupportedException();
             }
-            return As<TFrom, TTo>(ref source);
+            return ReadUnaligned<TTo>(ref As<TFrom, byte>(ref source));
         }
 
         /// <summary>

Original file line number	Diff line number	Diff line change
`@@ -253,7 +253,7 @@ public static TTo BitCast<TFrom, TTo>(TFrom source)`
`253`	`253`	`{`
`254`	`254`	`ThrowHelper.ThrowNotSupportedException();`
`255`	`255`	`}`
`256`		`- return As<TFrom, TTo>(ref source);`
	`256`	`+ return ReadUnaligned<TTo>(ref As<TFrom, byte>(ref source));`
`257`	`257`	`}`
`258`	`258`
`259`	`259`	`/// <summary>`