[Lldb-commits] [lldb] [lldb] Fix and speedup the `memory find` command (PR #104193)

[David Spickett via lldb-commits]

================
@@ -3367,21 +3340,48 @@ lldb::addr_t Process::FindInMemory(lldb::addr_t low, lldb::addr_t high,
   if (region_size < size)
     return LLDB_INVALID_ADDRESS;
 
+  // See "Boyer-Moore string search algorithm".
   std::vector<size_t> bad_char_heuristic(256, size);
-  ProcessMemoryIterator iterator(*this, low);
-
   for (size_t idx = 0; idx < size - 1; idx++) {
     decltype(bad_char_heuristic)::size_type bcu_idx = buf[idx];
     bad_char_heuristic[bcu_idx] = size - idx - 1;
   }
-  for (size_t s = 0; s <= (region_size - size);) {
+
+  // Memory we're currently searching through.
+  llvm::SmallVector<uint8_t, 0> mem;
+  // Position of the memory buffer.
+  addr_t mem_pos = low;
+  // Maximum number of bytes read (and buffered). We need to read at least
+  // `size` bytes for a successful match.
+  const size_t max_read_size = std::max<size_t>(size, 0x10000);
+
+  for (addr_t s = low; s <= (high - size);) {
+    if (s + size > mem.size() + mem_pos) {
+      // We need to read more data. We don't attempt to reuse the data we've
+      // already read (up to `size-1` bytes from `s` to `mem_pos+mem.size()`).
+      // This is fine for patterns much smaller than max_read_size. For very
+      // long patterns we may need to do something more elaborate.
+      mem.resize_for_overwrite(max_read_size);
+      Status error;
+      mem.resize(
+          ReadMemory(s, mem.data(), std::min(mem.size(), high - s), error));
+      mem_pos = s;
+      if (error.Fail() || size > mem.size()) {
+        // We didn't read enough data. Skip to the next memory region.
+        MemoryRegionInfo info;
+        error = GetMemoryRegionInfo(mem_pos + mem.size(), info);
+        if (error.Fail())
+          break;
+        s = info.GetRange().GetRangeEnd();
----------------
DavidSpickett wrote:

It is intentional that `mem_pos` is not updated here, correct?

https://github.com/llvm/llvm-project/pull/104193