[clang][analyzer] Support fflush in the StreamChecker

clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp

@@ -266,6 +266,8 @@ class StreamChecker : public Checker<check::PreCall, eval::Call,
        {&StreamChecker::preFseek, &StreamChecker::evalFseek, 0}},
       {{{"ftell"}, 1},
        {&StreamChecker::preDefault, &StreamChecker::evalFtell, 0}},
+      {{{"fflush"}, 1},
+       {&StreamChecker::preFflush, &StreamChecker::evalFflush, 0}},
       {{{"rewind"}, 1},
        {&StreamChecker::preDefault, &StreamChecker::evalRewind, 0}},
       {{{"fgetpos"}, 2},
@@ -360,6 +362,12 @@ class StreamChecker : public Checker<check::PreCall, eval::Call,
                          CheckerContext &C,
                          const StreamErrorState &ErrorKind) const;
 
+  void preFflush(const FnDescription *Desc, const CallEvent &Call,
+                 CheckerContext &C) const;
+
+  void evalFflush(const FnDescription *Desc, const CallEvent &Call,
+                  CheckerContext &C) const;
+
   /// Check that the stream (in StreamVal) is not NULL.
   /// If it can only be NULL a fatal error is emitted and nullptr returned.
   /// Otherwise the return value is a new state where the stream is constrained
@@ -1191,6 +1199,83 @@ void StreamChecker::evalSetFeofFerror(const FnDescription *Desc,
   C.addTransition(State);
 }
 
+void StreamChecker::preFflush(const FnDescription *Desc, const CallEvent &Call,
+                              CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  SVal StreamVal = getStreamArg(Desc, Call);
+  std::optional<DefinedSVal> Stream = StreamVal.getAs<DefinedSVal>();
+  if (!Stream)
+    return;
+
+  ProgramStateRef StateNotNull, StateNull;
+  std::tie(StateNotNull, StateNull) =
+      C.getConstraintManager().assumeDual(State, *Stream);
+  if (StateNotNull && !StateNull)
+    ensureStreamOpened(StreamVal, C, StateNotNull);
+}
+
+void StreamChecker::evalFflush(const FnDescription *Desc, const CallEvent &Call,
+                               CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  SVal StreamVal = getStreamArg(Desc, Call);
+  std::optional<DefinedSVal> Stream = StreamVal.getAs<DefinedSVal>();
+  if (!Stream)
+    return;
+
+  // Skip if the stream can be both NULL and non-NULL.
+  ProgramStateRef StateNotNull, StateNull;
+  std::tie(StateNotNull, StateNull) =
+      C.getConstraintManager().assumeDual(State, *Stream);
+  if (StateNotNull && StateNull)
+    return;
+  if (StateNotNull && !StateNull)
+    State = StateNotNull;
+  else
+    State = StateNull;
+
+  const CallExpr *CE = dyn_cast_or_null<CallExpr>(Call.getOriginExpr());
+  if (!CE)
+    return;
+
+  // `fflush` returns EOF on failure, otherwise returns 0.
+  ProgramStateRef StateFailed = bindInt(*EofVal, State, C, CE);
+  ProgramStateRef StateNotFailed = bindInt(0, State, C, CE);
+
+  // Clear error states if `fflush` returns 0, but retain their EOF flags.
+  auto ClearErrorInNotFailed = [&StateNotFailed, Desc](SymbolRef Sym,
+                                                       const StreamState *SS) {
+    if (SS->ErrorState & ErrorFError) {
+      StreamErrorState NewES =
+          (SS->ErrorState & ErrorFEof) ? ErrorFEof : ErrorNone;
+      StreamState NewSS = StreamState::getOpened(Desc, NewES, false);
+      StateNotFailed = StateNotFailed->set<StreamMap>(Sym, NewSS);
+    }
+  };
+
+  if (StateNotNull && !StateNull) {
+    // Skip if the input stream's state is unknown, open-failed or closed.
+    if (SymbolRef StreamSym = StreamVal.getAsSymbol()) {
+      const StreamState *SS = State->get<StreamMap>(StreamSym);
+      if (SS) {
+        assert(SS->isOpened() && "Stream is expected to be opened");
+        ClearErrorInNotFailed(StreamSym, SS);
+      }
+    }
+  } else {
+    // Clear error states for all streams.
+    const StreamMapTy &Map = StateNotFailed->get<StreamMap>();
+    for (const auto &I : Map) {
+      SymbolRef Sym = I.first;
+      const StreamState &SS = I.second;
+      if (SS.isOpened())
+        ClearErrorInNotFailed(Sym, &SS);
+    }
+  }
+
+  C.addTransition(StateNotFailed);
+  C.addTransition(StateFailed);
+}
+
 ProgramStateRef
 StreamChecker::ensureStreamNonNull(SVal StreamVal, const Expr *StreamE,
                                    CheckerContext &C,

clang/test/Analysis/Inputs/system-header-simulator.h

@@ -61,6 +61,7 @@ void clearerr(FILE *stream);
 int feof(FILE *stream);
 int ferror(FILE *stream);
 int fileno(FILE *stream);
+int fflush(FILE *stream);
 
 size_t strlen(const char *);
 

clang/test/Analysis/stream-error.c

@@ -299,6 +299,73 @@ void error_fseek_0(void) {
   fclose(F);
 }
 
+void error_fflush_after_fclose(void) {
+  FILE *F = tmpfile();
+  int Ret;
+  fflush(NULL);                      // no-warning
+  if (!F)
+    return;
+  if ((Ret = fflush(F)) != 0)
+    clang_analyzer_eval(Ret == EOF); // expected-warning {{TRUE}}
+  fclose(F);
+  fflush(F);                         // expected-warning {{Stream might be already closed}}
+}
+
+void error_fflush_on_open_failed_stream(void) {
+  FILE *F = tmpfile();
+  if (!F) {
+    fflush(F); // no-warning
+    return;
+  }
+  fclose(F);
+}
+
+void error_fflush_on_unknown_stream(FILE *F) {
+  fflush(F);   // no-warning
+  fclose(F);   // no-warning
+}
+
+void error_fflush_on_non_null_stream_clear_error_states(void) {
+  FILE *F0 = tmpfile(), *F1 = tmpfile();
+  // `fflush` clears a non-EOF stream's error state.
+  if (F0) {
+    StreamTesterChecker_make_ferror_stream(F0);
+    if (fflush(F0) == 0) {             // no-warning
+      clang_analyzer_eval(ferror(F0)); // expected-warning {{FALSE}}
+      clang_analyzer_eval(feof(F0));   // expected-warning {{FALSE}}
+    }
+    fclose(F0);
+  }
+  // `fflush` clears an EOF stream's error state.
+  if (F1) {
+    StreamTesterChecker_make_feof_stream(F1);
+    if (fflush(F1) == 0) {             // no-warning
+      clang_analyzer_eval(ferror(F1)); // expected-warning {{FALSE}}
+      clang_analyzer_eval(feof(F1));   // expected-warning {{TRUE}}
+    }
+    fclose(F1);
+  }
+}
+
+void error_fflush_on_null_stream_clear_error_states(void) {
+  FILE *F0 = tmpfile(), *F1 = tmpfile();
+  // `fflush` clears all stream's error states, while retains their EOF states.
+  if (F0 && F1) {
+    StreamTesterChecker_make_ferror_stream(F0);
+    StreamTesterChecker_make_feof_stream(F1);
+    if (fflush(NULL) == 0) {           // no-warning
+      clang_analyzer_eval(ferror(F0)); // expected-warning {{FALSE}}
+      clang_analyzer_eval(feof(F0));   // expected-warning {{FALSE}}
+      clang_analyzer_eval(ferror(F1)); // expected-warning {{FALSE}}
+      clang_analyzer_eval(feof(F1));   // expected-warning {{TRUE}}
+    }
+  }
+  if (F0)
+    fclose(F0);
+  if (F1)
+    fclose(F1);
+}
+
 void error_indeterminate(void) {
   FILE *F = fopen("file", "r+");
   if (!F)