[clang] [clang][analyzer] Improve modeling of 'realpath' in StdLibraryFunctionsChecker (PR #79939)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ben Shi (benshi001)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/79939.diff


2 Files Affected:

- (modified) clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp (+4-2) 
- (modified) clang/test/Analysis/errno-stdlibraryfunctions.c (+10) 


``````````diff
diff --git a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
index be26f5521c8d7..3bcde86c9e66f 100644
--- a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
@@ -2992,12 +2992,14 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
 
     // char *realpath(const char *restrict file_name,
     //                char *restrict resolved_name);
-    // FIXME: Improve for errno modeling.
     addToFunctionSummaryMap(
         "realpath",
         Signature(ArgTypes{ConstCharPtrRestrictTy, CharPtrRestrictTy},
                   RetType{CharPtrTy}),
-        Summary(NoEvalCall).ArgConstraint(NotNull(ArgNo(0))));
+        Summary(NoEvalCall)
+            .Case({NotNull(Ret)}, ErrnoMustNotBeChecked, GenericSuccessMsg)
+            .Case({IsNull(Ret)}, ErrnoNEZeroIrrelevant, GenericFailureMsg)
+            .ArgConstraint(NotNull(ArgNo(0))));
 
     QualType CharPtrConstPtr = getPointerTy(getConstTy(CharPtrTy));
 
diff --git a/clang/test/Analysis/errno-stdlibraryfunctions.c b/clang/test/Analysis/errno-stdlibraryfunctions.c
index 9b487fed0a2eb..a28efb764edfd 100644
--- a/clang/test/Analysis/errno-stdlibraryfunctions.c
+++ b/clang/test/Analysis/errno-stdlibraryfunctions.c
@@ -128,3 +128,13 @@ void errno_pclose(void) {
     if (errno) {} // expected-warning{{An undefined value may be read from 'errno'}}
   }
 }
+
+void errno_realpath(char *Path, char *Buf) {
+  char *Ret = realpath(Path, Buf);
+  if (!Ret) {
+    clang_analyzer_eval(errno != 0);  // expected-warning{{TRUE}}
+    if (errno) {}                     // no-warning
+  } else {
+    if (errno) {} // expected-warning{{An undefined value may be read from 'errno'}}
+  }
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/79939