[analyzer] [MallocChecker] Assume functions with ownership_returns return unknown memory

[pskrgag]

There is no good way to tell CSA if function with ownership_returns attribute returns initialized or not initialized memory. To make FP rate lower, let's assume that memory returned from such functions is unknown and do not reason about it.

In future it would be great to add a way to annotate such behavior

[llvmbot]

@llvm/pr-subscribers-clang-static-analyzer-1

@llvm/pr-subscribers-clang

Author: Pavel Skripkin (pskrgag)

Changes

There is no good way to tell CSA if function with ownership_returns attribute returns initialized or not initialized memory. To make FP rate lower, let's assume that memory returned from such functions is unknown and do not reason about it.

In future it would be great to add a way to annotate such behavior

---

Full diff: https://github.com/llvm/llvm-project/pull/110115.diff

2 Files Affected:

• (modified) clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp (+2-2)
• (modified) clang/test/Analysis/malloc-annotations.c (+14)

diff --git a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
index 81ec8e1b516986..3e95db7e97fac8 100644
--- a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
@@ -1811,9 +1811,9 @@ MallocChecker::MallocMemReturnsAttr(CheckerContext &C, const CallEvent &Call,
   if (!Att->args().empty()) {
     return MallocMemAux(C, Call,
                         Call.getArgExpr(Att->args_begin()->getASTIndex()),
-                        UndefinedVal(), State, Family);
+                        UnknownVal(), State, Family);
   }
-  return MallocMemAux(C, Call, UnknownVal(), UndefinedVal(), State, Family);
+  return MallocMemAux(C, Call, UnknownVal(), UnknownVal(), State, Family);
 }
 
 ProgramStateRef MallocChecker::MallocBindRetVal(CheckerContext &C,
diff --git a/clang/test/Analysis/malloc-annotations.c b/clang/test/Analysis/malloc-annotations.c
index c2fdf8a5641ae4..c601a0383d2210 100644
--- a/clang/test/Analysis/malloc-annotations.c
+++ b/clang/test/Analysis/malloc-annotations.c
@@ -3,6 +3,7 @@
 // RUN:   -analyzer-checker=alpha.deadcode.UnreachableCode \
 // RUN:   -analyzer-checker=alpha.core.CastSize \
 // RUN:   -analyzer-checker=unix.Malloc \
+// RUN:   -analyzer-checker=debug.ExprInspection \
 // RUN:   -analyzer-config unix.DynamicMemoryModeling:Optimistic=true %s
 
 typedef __typeof(sizeof(int)) size_t;
@@ -23,6 +24,12 @@ void __attribute((ownership_holds(malloc, 1))) my_hold(void *);
 void __attribute((ownership_holds(malloc, 1)))
 __attribute((ownership_holds(malloc, 1)))
 __attribute((ownership_holds(malloc, 3))) my_hold2(void *, void *, void *);
+
+__attribute((ownership_returns(user_malloc, 1))) void *user_malloc(size_t);
+__attribute((ownership_takes(user_malloc, 1))) void user_free(void *);
+
+void clang_analyzer_dump(int);
+
 void *my_malloc3(size_t);
 void *myglobalpointer;
 struct stuff {
@@ -273,3 +280,10 @@ void testMultipleFreeAnnotations(void) {
   my_freeBoth(p, q);
 }
 
+void testNoUninitAttr(void) {
+  int *p = user_malloc(sizeof(int));
+  int read = p[0]; // no-warning
+  clang_analyzer_dump(p[0]); // expected-warning{{Unknown}}
+  user_free(p);
+}
+

[NagyDonat]

Good catch, thanks for the fix.