Prevent Stockfish from exiting if DTZ table is not present

During TB initialisation, Stockfish checks for the presence of WDL
tables but not for the presence of DTZ tables. When attempting to probe
a DTZ table, it is therefore possible that the table is not present.
In that case, Stockfish should neither exit nor report an error.

To verify the bug:
$ ./stockfish
setoption name SyzygyTable value <path_to_WDL_dir>
position fen 8/8/4r3/4k3/8/1K2P3/3P4/6R1 w - -
go infinite
Could not mmap() /opt/tb/regular/KRPPvKR.rtbz
$

(On my system, the WDL tables are in one directory and the DTZ tables
in another. If they are in the same directory, it will be difficult
to trigger the bug.)

The fix is trivial: check the file descriptor/handle after opening
the file.

No functional change.

diff --git a/src/syzygy/tbprobe.cpp b/src/syzygy/tbprobe.cpp
index 8b87c250662ef60d013331911f41adafd0fc815e..4aff3b2da4bfe4d3b5f4f74c57be09d7b614647c 100644 (file)
--- a/src/syzygy/tbprobe.cpp
+++ b/src/syzygy/tbprobe.cpp
@@ -341,6 +341,10 @@ public:
 #ifndef _WIN32
         struct stat statbuf;
         int fd = ::open(fname.c_str(), O_RDONLY);
+
+        if (fd == -1)
+            return *baseAddress = nullptr, nullptr;
+
         fstat(fd, &statbuf);
         *mapping = statbuf.st_size;
         *baseAddress = mmap(nullptr, statbuf.st_size, PROT_READ, MAP_SHARED, fd, 0);
@@ -353,6 +357,10 @@ public:
 #else
         HANDLE fd = CreateFile(fname.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr,
                                OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+
+        if (fd == INVALID_HANDLE_VALUE)
+            return *baseAddress = nullptr, nullptr;
+
         DWORD size_high;
         DWORD size_low = GetFileSize(fd, &size_high);
         HANDLE mmap = CreateFileMapping(fd, nullptr, PAGE_READONLY, size_high, size_low, nullptr);
@@ -380,8 +388,7 @@ public:
             || *data++ != *TB_MAGIC) {
             std::cerr << "Corrupted table in file " << fname << std::endl;
             unmap(*baseAddress, *mapping);
-            *baseAddress = nullptr;
-            return nullptr;
+            return *baseAddress = nullptr, nullptr;
         }
 
         return data;
@@ -482,7 +489,7 @@ void HashTable::insert(const std::vector<PieceType>& pieces) {
 
     TBFile file(code.insert(code.find('K', 1), "v") + ".rtbw"); // KRK -> KRvK
 
-    if (!file.is_open())
+    if (!file.is_open()) // Only WDL file is checked
         return;
 
     file.close();