Merge pull request #10814 from MarcZX10/marc/fix-ctime-fallback-buffer-race

fix(libc): give ctime's unrepresentable-time text a buffer per thread

core/libs/prx/libc/src/Time.cpp

@@ -604,7 +604,7 @@ char* APS5_VABI asctime_nid_postfix(const GuestTm* timeptr) {
 
 char* APS5_VABI ctime_nid_postfix(const int64_t* timer) {
     if (const GuestTm* local = localtime_nid_postfix(timer)) return asctime_nid_postfix(local);
-    static char unknown[26];
+    static thread_local char unknown[26];
     std::memcpy(unknown, "??? ??? ?? ??:??:?? ????\n", sizeof(unknown));
     errno = EINVAL;
     return unknown;

core/libs/tests/GuestTimeConversion.cpp

@@ -496,6 +496,21 @@ int main() {
     *__error_nid_postfix() = 0;
     Require(std::strcmp(ctime_nid_postfix(&underflow), "??? ??? ?? ??:??:?? ????\n") == 0 && *__error_nid_postfix() == 22,
         "ctime of an unrepresentable time did not report it");
+    {
+        std::barrier finish(3);
+        std::array<const char*, 2> texts{};
+        std::array<std::thread, 2> readers;
+        for (std::size_t index = 0; index < readers.size(); ++index) {
+            readers[index] = std::thread([&, index] {
+                texts[index] = ctime_nid_postfix(&underflow);
+                finish.arrive_and_wait();
+            });
+        }
+        const char* own = ctime_nid_postfix(&underflow);
+        finish.arrive_and_wait();
+        Require(texts[0] != texts[1] && texts[0] != own && texts[1] != own, "ctime of an unrepresentable time shared one buffer between threads");
+        for (auto& reader : readers) reader.join();
+    }
 
     constexpr std::int64_t latest = std::numeric_limits<std::int64_t>::max();
     constexpr std::int64_t earliest = std::numeric_limits<std::int64_t>::min();