[release/6.0] [mono] Use unsigned char when computing UTF8 string has…

…hes (#83303)

* [mono] Use `unsigned char` when computing UTF8 string hashes

The C standard does not specify whether `char` is signed or unsigned,
it is implementation defined.

Apparently Android aarch64 makes a different choice than other
platforms (at least macOS arm64 and Windows x64 give different
results).

Mono uses `mono_metadata_str_hash` in the AOT compiler and AOT runtime
to optimize class name lookup.  As a result, classes whose names
include UTF-8 continuation bytes (with the high bit = 1) will hash
differently in the AOT compiler and on the device.

Fixes #82187
Fixes #78638

* Add regression test

---------

Co-authored-by: Aleksey Kliger <alklig@microsoft.com>

src/mono/mono/eglib/ghashtable.c

@@ -673,7 +673,7 @@ guint
 g_str_hash (gconstpointer v1)
 {
 	guint hash = 0;
-	char *p = (char *) v1;
+	unsigned char *p = (unsigned char *) v1;
 
 	while (*p++)
 		hash = (hash << 5) - (hash + *p);

src/mono/mono/metadata/metadata.c

@@ -5386,7 +5386,8 @@ guint
 mono_metadata_str_hash (gconstpointer v1)
 {
 	/* Same as g_str_hash () in glib */
-	char *p = (char *) v1;
+	/* note: signed/unsigned char matters - we feed UTF-8 to this function, so the high bit will give diferent results if we don't match. */
+	unsigned char *p = (unsigned char *) v1;
 	guint hash = *p;
 
 	while (*p++) {

src/tests/Loader/classloader/regressions/GitHub_82187/GitHub_82187.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="repro.cs" />
+  </ItemGroup>
+</Project>

src/tests/Loader/classloader/regressions/GitHub_82187/repro.cs

@@ -0,0 +1,31 @@
+using System;
+
+/* Regression test for https://github.com/dotnet/runtime/issues/78638
+ * and https://github.com/dotnet/runtime/issues/82187 ensure AOT
+ * cross-compiler and AOT runtime use the same name hashing for names
+ * that include UTF-8 continuation bytes.
+ */
+
+[MySpecial(typeof(MeineTüre))]
+public class Program
+{
+    public static int Main()
+    {
+        var attr = (MySpecialAttribute)Attribute.GetCustomAttribute(typeof (Program), typeof(MySpecialAttribute), false);
+        if (attr == null)
+            return 101;
+        if (attr.Type == null)
+            return 102;
+        if (attr.Type.FullName != "MeineTüre")
+            return 103;
+        return 100;
+    }
+}
+
+public class MySpecialAttribute : Attribute
+{
+    public Type Type {get; private set; }
+    public MySpecialAttribute(Type t) { Type = t; }
+}
+
+public class MeineTüre {}