Zero alloc BMC!

hbvm/src/vm/mem/mod.rs

@@ -220,40 +220,28 @@ impl Memory {
     ///     - Addr-san claims it's fine but who knows is she isn't lying :ferrisSus:
     pub unsafe fn block_copy(
         &mut self,
-        src: u64,
-        dst: u64,
+        mut src: u64,
+        mut dst: u64,
         count: usize,
         traph: &mut impl HandlePageFault,
     ) -> Result<(), BlkCopyError> {
         // Yea, i know it is possible to do this more efficiently, but I am too lazy.
 
-        const STACK_BUFFER_SIZE: usize = 512;
-
-        // Decide if to use stack-allocated buffer or to heap allocate
-        // Deallocation is again decided on size at the end of the function
-        let mut buf = MaybeUninit::<[u8; STACK_BUFFER_SIZE]>::uninit();
-        let buf = if count <= STACK_BUFFER_SIZE {
-            buf.as_mut_ptr().cast()
-        } else {
-            unsafe {
-                let layout = core::alloc::Layout::from_size_align_unchecked(count, 1);
-                let ptr = alloc::alloc::alloc(layout);
-                if ptr.is_null() {
-                    alloc::alloc::handle_alloc_error(layout);
-                }
-
-                ptr
-            }
-        };
-
-        // Perform memory block transfer
-        let status = (|| {
-            // Load to buffer
+        impl Memory {
+            #[inline]
+            unsafe fn act(
+                &mut self,
+                src: u64,
+                dst: u64,
+                buf: *mut u8,
+                count: usize,
+                traph: &mut impl HandlePageFault,
+            ) -> Result<(), BlkCopyError> {
                 self.memory_access(
                     MemoryAccessReason::Load,
                     src,
                     buf,
-                count,
+                    STACK_BUFFER_SIZE,
                     |perm| {
                         matches!(
                             perm,
@@ -268,7 +256,6 @@ impl Memory {
                     addr,
                 })?;
 
-            // Store from buffer
                 self.memory_access(
                     MemoryAccessReason::Store,
                     dst,
@@ -283,18 +270,26 @@ impl Memory {
                     addr,
                 })?;
 
-            Ok::<_, BlkCopyError>(())
-        })();
-
-        // Deallocate if used heap-allocated array
-        if count > STACK_BUFFER_SIZE {
-            alloc::alloc::dealloc(
-                buf,
-                core::alloc::Layout::from_size_align_unchecked(count, 1),
-            );
+                Ok(())
+            }
         }
 
-        status
+        const STACK_BUFFER_SIZE: usize = 4096;
+
+        // Decide if to use stack-allocated buffer or to heap allocate
+        // Deallocation is again decided on size at the end of the function
+        let mut buf = MaybeUninit::<[u8; STACK_BUFFER_SIZE]>::uninit();
+
+        let n_buffers = count / STACK_BUFFER_SIZE;
+        let rem = count % STACK_BUFFER_SIZE;
+
+        for _ in 0..n_buffers {
+            self.act(src, dst, buf.as_mut_ptr().cast(), STACK_BUFFER_SIZE, traph)?;
+            src += STACK_BUFFER_SIZE as u64;
+            dst += STACK_BUFFER_SIZE as u64;
+        }
+
+        self.act(src, dst, buf.as_mut_ptr().cast(), rem, traph)
     }
 
     /// Split address to pages, check their permissions and feed pointers with offset