Fix find_last_non_zero_bit, and align metadata address before convert…

…ing to data address. (#1188)

This PR fixes some bugs in finding base references for internal
references. Prominently two bugs:
1. The way we find the last non zero bit was wrong. We used to to use
`trailing_zeroes` and compare the result with the given range of the
starting and ending bits. This was simply wrong. Now we do a mask first
to extract the value between the starting and the ending bits, and then
use `leading_zeroes`. Performance-wise, the new code has similar
performnace.
2. When we convert a metadata bit (address + bit offset) back to the
data address, the metadata bit needs to be the start of the metadata
value. If it is the middle of the metadata value, then the computed data
address will be incorrect. This PR adds `align_metadata_address`.

This PR skips some tests for LOS in plans that do not use LOS.

src/util/metadata/side_metadata/global.rs

@@ -991,6 +991,7 @@ impl SideMetadataSpec {
     ///
     /// This function uses non-atomic load for the side metadata. The user needs to make sure
     /// that there is no other thread that is mutating the side metadata.
+    #[allow(clippy::let_and_return)]
     pub unsafe fn find_prev_non_zero_value<T: MetadataValue>(
         &self,
         data_addr: Address,
@@ -1000,7 +1001,15 @@ impl SideMetadataSpec {
 
         if self.uses_contiguous_side_metadata() {
             // Contiguous side metadata
-            self.find_prev_non_zero_value_fast::<T>(data_addr, search_limit_bytes)
+            let result = self.find_prev_non_zero_value_fast::<T>(data_addr, search_limit_bytes);
+            #[cfg(debug_assertions)]
+            {
+                // Double check if the implementation is correct
+                let result2 =
+                    self.find_prev_non_zero_value_simple::<T>(data_addr, search_limit_bytes);
+                assert_eq!(result, result2, "find_prev_non_zero_value_fast returned a diffrent result from the naive implementation.");
+            }
+            result
         } else {
             // TODO: We should be able to optimize further for this case. However, we need to be careful that the side metadata
             // is not contiguous, and we need to skip to the next chunk's side metadata when we search to a different chunk.
@@ -1018,12 +1027,10 @@ impl SideMetadataSpec {
         let region_bytes = 1 << self.log_bytes_in_region;
         // Figure out the range that we need to search.
         let start_addr = data_addr.align_down(region_bytes);
-        let end_addr = data_addr
-            .saturating_sub(search_limit_bytes)
-            .align_down(region_bytes);
+        let end_addr = data_addr.saturating_sub(search_limit_bytes) + 1usize;
 
         let mut cursor = start_addr;
-        while cursor > end_addr {
+        while cursor >= end_addr {
             // We encounter an unmapped address. Just return None.
             if !cursor.is_mapped() {
                 return None;
@@ -1073,6 +1080,7 @@ impl SideMetadataSpec {
                 BitByteRange::Bytes { start, end } => {
                     match helpers::find_last_non_zero_bit_in_metadata_bytes(start, end) {
                         helpers::FindMetaBitResult::Found { addr, bit } => {
+                            let (addr, bit) = align_metadata_address(self, addr, bit);
                             res = Some(contiguous_meta_address_to_address(self, addr, bit));
                             // Return true to abort the search. We found the bit.
                             true
@@ -1091,6 +1099,7 @@ impl SideMetadataSpec {
                     match helpers::find_last_non_zero_bit_in_metadata_bits(addr, bit_start, bit_end)
                     {
                         helpers::FindMetaBitResult::Found { addr, bit } => {
+                            let (addr, bit) = align_metadata_address(self, addr, bit);
                             res = Some(contiguous_meta_address_to_address(self, addr, bit));
                             // Return true to abort the search. We found the bit.
                             true