[clang] [clang][analyzer] Refine modeling of 'getcwd' in StdCLibraryFunctions checker (PR #141076)

[Balázs Kéri via cfe-commits]

https://github.com/balazske created https://github.com/llvm/llvm-project/pull/141076

Add extra branches for the case when the buffer argument is NULL.

>From a82a775585ea473d6c29457b260848436071d0ff Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bal=C3=A1zs=20K=C3=A9ri?= <balazs.keri at ericsson.com>
Date: Thu, 22 May 2025 16:41:46 +0200
Subject: [PATCH] [clang][analyzer] Refine modeling of 'getcwd' in
 StdCLibraryFunctions checker

Add extra branches for the case when the buffer argument is NULL.
---
 .../Checkers/StdLibraryFunctionsChecker.cpp       | 14 ++++++++++----
 clang/test/Analysis/errno-stdlibraryfunctions.c   | 15 ++++++++++++++-
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
index 3c6c3123f5cdd..6dae817fe89b5 100644
--- a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
@@ -2651,16 +2651,22 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
     addToFunctionSummaryMap(
         "getcwd", Signature(ArgTypes{CharPtrTy, SizeTy}, RetType{CharPtrTy}),
         Summary(NoEvalCall)
-            .Case({ArgumentCondition(1, WithinRange, Range(1, SizeMax)),
+            .Case({NotNull(0),
+                   ArgumentCondition(1, WithinRange, Range(1, SizeMax)),
                    ReturnValueCondition(BO_EQ, ArgNo(0))},
                   ErrnoMustNotBeChecked, GenericSuccessMsg)
-            .Case({ArgumentCondition(1, WithinRange, SingleValue(0)),
+            .Case({NotNull(0),
+                   ArgumentCondition(1, WithinRange, SingleValue(0)),
                    IsNull(Ret)},
                   ErrnoNEZeroIrrelevant, "Assuming that argument 'size' is 0")
-            .Case({ArgumentCondition(1, WithinRange, Range(1, SizeMax)),
+            .Case({NotNull(0),
+                   ArgumentCondition(1, WithinRange, Range(1, SizeMax)),
                    IsNull(Ret)},
                   ErrnoNEZeroIrrelevant, GenericFailureMsg)
-            .ArgConstraint(NotNull(ArgNo(0)))
+            .Case({IsNull(0), NotNull(Ret)}, ErrnoMustNotBeChecked,
+                  GenericSuccessMsg)
+            .Case({IsNull(0), IsNull(Ret)}, ErrnoNEZeroIrrelevant,
+                  GenericFailureMsg)
             .ArgConstraint(
                 BufferSize(/*Buffer*/ ArgNo(0), /*BufSize*/ ArgNo(1)))
             .ArgConstraint(
diff --git a/clang/test/Analysis/errno-stdlibraryfunctions.c b/clang/test/Analysis/errno-stdlibraryfunctions.c
index 657aa37a42670..72d167f68a1f4 100644
--- a/clang/test/Analysis/errno-stdlibraryfunctions.c
+++ b/clang/test/Analysis/errno-stdlibraryfunctions.c
@@ -99,7 +99,9 @@ void errno_mkdtemp3(CHAR_PTR template) {
   }
 }
 
-void errno_getcwd(char *Buf, size_t Sz) {
+void errno_getcwd_buf_nonnull(char *Buf, size_t Sz) {
+  if (Buf == NULL)
+    return;
   char *Path = getcwd(Buf, Sz);
   if (Sz == 0) {
     clang_analyzer_eval(errno != 0);   // expected-warning{{TRUE}}
@@ -114,6 +116,17 @@ void errno_getcwd(char *Buf, size_t Sz) {
   }
 }
 
+void errno_getcwd_buf_null() {
+  // POSIX does not mention this case but many implementations (Linux, FreeBSD) work this way.
+  char *Path = getcwd(NULL, 1);
+  if (Path == NULL) {
+    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'}}
+  }
+}
+
 void errno_execv(char *Path, char * Argv[]) {
   int Ret = execv(Path, Argv);
   clang_analyzer_eval(Ret == -1);  // expected-warning{{TRUE}}