[Lldb-commits] [lldb] 75e0516 - [lldb][Windows] Return EOF from PipeWindows::Read on a closed write end (#207017)

[via lldb-commits]

Author: Charles Zablit
Date: 2026-07-02T10:05:10+01:00
New Revision: 75e0516da874501d7bb3417b7364a452827dea93

URL: https://github.com/llvm/llvm-project/commit/75e0516da874501d7bb3417b7364a452827dea93
DIFF: https://github.com/llvm/llvm-project/commit/75e0516da874501d7bb3417b7364a452827dea93.diff

LOG: [lldb][Windows] Return EOF from PipeWindows::Read on a closed write end (#207017)

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

Added: 
    

Modified: 
    lldb/source/Host/windows/PipeWindows.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/Host/windows/PipeWindows.cpp b/lldb/source/Host/windows/PipeWindows.cpp
index e2a64e65cee00..d69a28cd69324 100644
--- a/lldb/source/Host/windows/PipeWindows.cpp
+++ b/lldb/source/Host/windows/PipeWindows.cpp
@@ -291,8 +291,18 @@ 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) {
+  // A closed write end is EOF, not an error. POSIX read() returns 0
+  // in this case. Mirror that so cross-platform callers can detect EOF
+  // uniformly.
+  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 +329,14 @@ 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();
+    // See above: a closed write end is end-of-file, not an error.
+    if (overlapped_error == ERROR_BROKEN_PIPE ||
+        overlapped_error == ERROR_HANDLE_EOF)
+      return 0;
+    return Status(overlapped_error, eErrorTypeWin32).takeError();
+  }
 
   return bytes_read;
 }