[Lldb-commits] [lldb] [lldb][Windows] Return EOF from PipeWindows::Read on a closed write end (PR #207017)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Charles Zablit (charles-zablit)

<details>
<summary>Changes</summary>

A closed pipe write end is EOF, not an error. On POSIX, `read()` returns 0, but on Windows `ReadFile` fails with `ERROR_BROKEN_PIPE`. The lldb-server `gdbserver/platform` pipe synchronization in `GDBRemoteCommunication::StartDebugserverProcess` reads the pipe until EOF, so without this it sees an error instead of EOF and reports the sync as failed.

Translate both broken-pipe conditions to a zero-length read so cross-platform callers can detect EOF uniformly.

rdar://180736036

---
Full diff: https://github.com/llvm/llvm-project/pull/207017.diff


1 Files Affected:

- (modified) lldb/source/Host/windows/PipeWindows.cpp (+15-3) 


``````````diff
diff --git a/lldb/source/Host/windows/PipeWindows.cpp b/lldb/source/Host/windows/PipeWindows.cpp
index e2a64e65cee00..abf608750e61a 100644
--- a/lldb/source/Host/windows/PipeWindows.cpp
+++ b/lldb/source/Host/windows/PipeWindows.cpp
@@ -291,8 +291,15 @@ llvm::Expected<size_t> PipeWindows::Read(void *buf, size_t size,
     return bytes_read;
 
   DWORD failure_error = ::GetLastError();
-  if (failure_error != ERROR_IO_PENDING)
+  switch (failure_error) {
+  case ERROR_BROKEN_PIPE:
+  case ERROR_HANDLE_EOF:
+    return 0;
+  case ERROR_IO_PENDING:
+    break;
+  default:
     return Status(failure_error, eErrorTypeWin32).takeError();
+  }
 
   DWORD timeout_msec =
       timeout ? std::chrono::ceil<std::chrono::milliseconds>(*timeout).count()
@@ -319,8 +326,13 @@ llvm::Expected<size_t> PipeWindows::Read(void *buf, size_t size,
 
   // Now we call GetOverlappedResult setting bWait to false, since we've
   // already waited as long as we're willing to.
-  if (!::GetOverlappedResult(m_read, &m_read_overlapped, &bytes_read, FALSE))
-    return Status(::GetLastError(), eErrorTypeWin32).takeError();
+  if (!::GetOverlappedResult(m_read, &m_read_overlapped, &bytes_read, FALSE)) {
+    DWORD overlapped_error = ::GetLastError();
+    if (overlapped_error == ERROR_BROKEN_PIPE ||
+        overlapped_error == ERROR_HANDLE_EOF)
+      return 0;
+    return Status(overlapped_error, eErrorTypeWin32).takeError();
+  }
 
   return bytes_read;
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/207017