[clang] [clang][analyzer] Support 'fflush' in the StdLibraryFunctionsChecker (PR #76557)

[Balazs Benics via cfe-commits]

https://github.com/steakhal updated https://github.com/llvm/llvm-project/pull/76557

>From 2eebb462b8a7865684d3baaffbad7560eed10e57 Mon Sep 17 00:00:00 2001
From: Ben Shi <bennshi at tencent.com>
Date: Fri, 29 Dec 2023 16:44:47 +0800
Subject: [PATCH 1/2] [clang][analyzer] Support 'fflush' in the
 StdLibraryFunctionsChecker

---
 .../Checkers/StdLibraryFunctionsChecker.cpp   |  8 ++++++
 clang/test/Analysis/stream-errno.c            | 26 +++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
index fffcaf7ed18fb7..4ca49b9c0546d9 100644
--- a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
@@ -2244,6 +2244,14 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
             .ArgConstraint(NotNull(ArgNo(0)))
             .ArgConstraint(NotNull(ArgNo(1))));
 
+    // int fflush(FILE *stream);
+    addToFunctionSummaryMap(
+        "fflush", Signature(ArgTypes{FilePtrTy}, RetType{IntTy}),
+        Summary(NoEvalCall)
+            .Case(ReturnsZero, ErrnoMustNotBeChecked, GenericSuccessMsg)
+            .Case({ReturnValueCondition(WithinRange, SingleValue(EOFv))},
+                  ErrnoNEZeroIrrelevant, GenericFailureMsg));
+
     // long ftell(FILE *stream);
     // From 'The Open Group Base Specifications Issue 7, 2018 edition':
     // "The ftell() function shall not change the setting of errno if
diff --git a/clang/test/Analysis/stream-errno.c b/clang/test/Analysis/stream-errno.c
index bf0a61db2424f9..d52480741d4cd1 100644
--- a/clang/test/Analysis/stream-errno.c
+++ b/clang/test/Analysis/stream-errno.c
@@ -222,3 +222,29 @@ void check_fileno(void) {
   }
   if (errno) {} // expected-warning{{An undefined value may be read from 'errno'}}
 }
+
+void check_fflush_0(void) {
+  FILE *F = tmpfile();
+  if (!F)
+    return;
+  int N = fflush(F);
+  if (N == EOF) {
+    clang_analyzer_eval(errno != 0); // expected-warning{{TRUE}}
+    if (errno) {}                    // no-warning
+  } else {
+    clang_analyzer_eval(N == 0);     // expected-warning{{TRUE}}
+    if (errno) {}                    // expected-warning{{An undefined value may be read from 'errno'}}
+  }
+  fclose(F);
+}
+
+void check_fflush_1(void) {
+  int N = fflush(NULL);
+  if (N == 0) {
+    if (errno) {}                    // expected-warning{{An undefined value may be read from 'errno'}}
+  } else {
+    clang_analyzer_eval(N == EOF);   // expected-warning{{TRUE}}
+    clang_analyzer_eval(errno != 0); // expected-warning{{TRUE}}
+    if (errno) {}                    // no-warning
+  }
+}

>From 3c0f61c3d317e2c4bcff77532677b68c9bc0e01a Mon Sep 17 00:00:00 2001
From: Balazs Benics <benicsbalazs at gmail.com>
Date: Fri, 29 Dec 2023 11:01:01 +0100
Subject: [PATCH 2/2] Update the release notes

---
 clang/docs/ReleaseNotes.rst | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3c08d1808b0e7f..2d5391702385a7 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1126,9 +1126,11 @@ Improvements
 ^^^^^^^^^^^^
 
 - Improved the ``unix.StdCLibraryFunctions`` checker by modeling more
-  functions like ``send``, ``recv``, ``readlink`` and ``errno`` behavior.
+  functions like ``send``, ``recv``, ``readlink``, ``fflush`` and
+  ``errno`` behavior.
   (`52ac71f92d38 <https://github.com/llvm/llvm-project/commit/52ac71f92d38f75df5cb88e9c090ac5fd5a71548>`_,
   `#71373 <https://github.com/llvm/llvm-project/pull/71373>`_,
+  `#76557 <https://github.com/llvm/llvm-project/pull/76557>`_,
   `#71392 <https://github.com/llvm/llvm-project/pull/71392>`_)
 
 - Fixed a false negative for when accessing a nonnull property (ObjC).