debug(mm): 转储 memmap 描述符 + buddy 初始化循环进度

mm.init 报 start=0x400000 size=4292411392（≈4GB）后挂起——256MB 内存不该有
4GB 可用区，怀疑 memmap 描述符读到垃圾。新增：1) init 内转储全部描述符
（type/start/pages）；2) buddy __init__ 循环打印前 6 次迭代与 loop done 标记，
定位挂起点。

VKernel/Kernel/mm/mm.vp

@@ -104,6 +104,10 @@ class _BuddySystemObject:
         self.buddy.end_addr = t.CVoid(t.CUInt64T(start_addr) + size, t.CPtr)
         remaining: t.CUInt64T = size
         cur_addr: t.CUInt64T = t.CUInt64T(start_addr)
+        # [DBG] buddy 初始化循环进度（用后移除）
+        import drivers.serial.uart.serial as _sdbg
+        _dbp: t.CArray[t.CChar, 80]
+        _itc: t.CInt = 0
         while remaining >= MIN_BLOCK_SIZE:
             order: t.CInt = 0
             tmp: t.CUInt64T = remaining
@@ -115,6 +119,11 @@ class _BuddySystemObject:
                 order -= 1
                 block_size = get_block_size(order)
             if block_size > remaining: break
+            _itc += 1
+            if _itc <= 6:
+                viperlib.snprintf(c.Addr(_dbp), 80, "[mm] it=%d order=%d bs=0x%lx addr=0x%lx rem=%lu\n",
+                                  _itc, order, block_size, cur_addr, remaining)
+                _sdbg.puts(c.Addr(_dbp))
             block: memory_block | t.CPtr = cur_addr
             block.size = block_size
             block.state = BLOCK_FREE
@@ -128,6 +137,7 @@ class _BuddySystemObject:
                 self.buddy.free_lists[order] = block
             cur_addr += block_size
             remaining -= block_size
+        _sdbg.puts("[mm] buddy loop done\n")
         # DEBUG: print free_lists status after init
         import drivers.serial.uart.serial as serial
         _dmsg: t.CArray[t.CChar, 40]
@@ -506,6 +516,13 @@ def init(MemmapAddr: t.CUInt64T, MemmapSize: t.CUInt64T, MemmapDescSize: t.CUInt
                 best_ld_size: t.CUInt64T = 0
                 best_ld_start: t.CUInt64T = 0
                 i: t.CUInt64T
+                # [DBG] 转储全部 memmap 描述符，定位 4GB 伪可用区的来源（用后移除）
+                for i in range(num_entries):
+                    entry: bootinfo.memory_map_entry | t.CPtr = t.CVoid(MemmapAddr + i * MemmapDescSize, t.CPtr)
+                    _dbgd: t.CArray[t.CChar, 100]
+                    viperlib.snprintf(c.Addr(_dbgd), 100, "[mm] d[%lu] t=%lu start=0x%lx np=%lu\n",
+                                      i, t.CUInt64T(entry.type), entry.physical_start, entry.num_pages)
+                    serial.puts(c.Addr(_dbgd))
                 for i in range(num_entries):
                     entry: bootinfo.memory_map_entry | t.CPtr = t.CVoid(MemmapAddr + i * MemmapDescSize, t.CPtr)
                     etype: t.CUInt64T = entry.type