[Lldb-commits] [lldb] [lldb] Respect max packet size limits for MultiMemRead in ProcessGDBRemote (PR #172022)

[David Spickett via lldb-commits]

================
@@ -2790,29 +2790,62 @@ size_t ProcessGDBRemote::DoReadMemory(addr_t addr, void *buf, size_t size,
   return 0;
 }
 
+/// Returns the number of ranges that is safe to request using MultiMemRead
+/// while respecting max_packet_size.
+static uint64_t ComputeNumRangesMultiMemRead(
+    uint64_t max_packet_size,
+    llvm::ArrayRef<Range<lldb::addr_t, size_t>> ranges) {
+  // Each range is specified by two numbers (~16 ASCII characters) and one
+  // comma.
+  constexpr uint64_t range_overhead = 33;
+  uint64_t current_size = 0;
+  for (auto [idx, range] : llvm::enumerate(ranges)) {
+    uint64_t potential_size = current_size + range.size + range_overhead;
+    if (potential_size > max_packet_size)
+      return idx;
+  }
+  return ranges.size();
+}
+
 llvm::SmallVector<llvm::MutableArrayRef<uint8_t>>
 ProcessGDBRemote::ReadMemoryRanges(
     llvm::ArrayRef<Range<lldb::addr_t, size_t>> ranges,
     llvm::MutableArrayRef<uint8_t> buffer) {
   if (!m_gdb_comm.GetMultiMemReadSupported())
     return Process::ReadMemoryRanges(ranges, buffer);
 
-  llvm::Expected<StringExtractorGDBRemote> response =
-      SendMultiMemReadPacket(ranges);
-  if (!response) {
-    LLDB_LOG_ERROR(GetLog(GDBRLog::Process), response.takeError(),
-                   "MultiMemRead error response: {0}");
-    return Process::ReadMemoryRanges(ranges, buffer);
-  }
-
-  llvm::StringRef response_str = response->GetStringRef();
-  const unsigned expected_num_ranges = ranges.size();
+  const llvm::ArrayRef<Range<lldb::addr_t, size_t>> original_ranges = ranges;
   llvm::SmallVector<llvm::MutableArrayRef<uint8_t>> memory_regions;
-  if (llvm::Error error = ParseMultiMemReadPacket(
-          response_str, buffer, expected_num_ranges, memory_regions)) {
-    LLDB_LOG_ERROR(GetLog(GDBRLog::Process), std::move(error),
-                   "MultiMemRead error parsing response: {0}");
-    return Process::ReadMemoryRanges(ranges, buffer);
+
+  while (!ranges.empty()) {
+    uint64_t num_ranges =
+        ComputeNumRangesMultiMemRead(m_max_memory_size, ranges);
+    if (num_ranges == 0) {
+      LLDB_LOG(
+          GetLog(GDBRLog::Process),
+          "MultiMemRead has a range bigger than maximum allowed by remote");
----------------
DavidSpickett wrote:

If you could log the range itself, that would be great. I think it's easiest to move the log call into the helper.

https://github.com/llvm/llvm-project/pull/172022