Don't modify MonoImageStorage:raw_data

instead just keep track of the webcil offset in the MonoImageStorage.

This introduces a situation where MonoImage:raw_data is different from
MonoImageStorage:raw_data.  The one to use for accessing IL and
metadata is MonoImage:raw_data.

The storage pointer is just used by the image loading machinery

src/mono/mono/metadata/metadata-internals.h

@@ -282,6 +282,12 @@ typedef struct {
 	/* Module entry point is _CorDllMain. */
 	guint8 has_entry_point : 1;
 #endif
+#ifdef ENABLE_WEBCIL
+	/* set to a non-zero value when we load a webcil-in-wasm image.
+	 * Note that in that case MonoImage:raw_data is not equal to MonoImageStorage:raw_data
+	 */
+	int32_t webcil_section_adjustment;
+#endif
 } MonoImageStorage;
 
 struct _MonoImage {
@@ -297,7 +303,7 @@ struct _MonoImage {
 
 	MonoImageStorage *storage;
 
-	/* Aliases storage->raw_data when storage is non-NULL. Otherwise NULL. */
+	/* Points into storage->raw_data when storage is non-NULL. Otherwise NULL. */
 	char *raw_data;
 	guint32 raw_data_len;
 

src/mono/mono/metadata/webcil-loader.c

@@ -137,12 +137,16 @@ webcil_image_load_pe_data (MonoImage *image)
 		goto invalid_image;
 	/* HACK! RVAs and debug table entry pointers are from the beginning of the webcil payload. adjust MonoImage:raw_data to point to it */
 	g_assert (image->ref_count == 1);
-	g_assert (image->storage->ref.ref == 1);
+	// NOTE: image->storage->raw_data could be shared if we loaded this image multiple times (for different ALCs, for example)
+	// Do not adjust image->storage->raw_data.
+#ifdef ENABLE_WEBCIL
+	int32_t old_adjustment;
+	old_adjustment = mono_atomic_cas_i32 ((volatile gint32*)&image->storage->webcil_section_adjustment, webcil_section_adjustment, 0);
+	g_assert (old_adjustment == 0 || old_adjustment == webcil_section_adjustment);
+#endif
 	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_ASSEMBLY, "Adjusting offset image %s [%p].", image->name, image);
-	image->storage->raw_data += webcil_section_adjustment;
-	image->storage->raw_data_len -= webcil_section_adjustment;
-	image->raw_data = image->storage->raw_data;
-	image->raw_data_len = image->storage->raw_data_len;
+	image->raw_data += webcil_section_adjustment;
+	image->raw_data_len -= webcil_section_adjustment;
 	offset -= webcil_section_adjustment;
 	// parts of ecma-335 loading depend on 4-byte alignment of the image
 	g_assertf (((intptr_t)image->raw_data) % 4 == 0, "webcil image %s [%p] raw data %p not 4 byte aligned\n", image->name, image, image->raw_data);