[PATCH] D124659: [analyzer][docs] Document alpha.security.cert.pos.34c limitations

[Balázs Benics via Phabricator via cfe-commits]

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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124659

Files:
  clang/docs/analyzer/checkers.rst


Index: clang/docs/analyzer/checkers.rst
===================================================================
--- clang/docs/analyzer/checkers.rst
+++ clang/docs/analyzer/checkers.rst
@@ -2268,6 +2268,25 @@
     return putenv(env); // putenv function should not be called with auto variables
   }
 
+Limitations:
+
+   - Technically, one can pass automatic variables to ``putenv``,
+     but one needs to ensure that the given environment key stays
+     alive until it's removed or overwritten.
+     Since the analyzer cannot keep track of which envvars get overwritten
+     and when, it needs to be slightly more aggressive and warn for such
+     cases too, leading in some cases to false-positive reports like this:
+
+     .. code-block:: c
+
+        void baz() {
+          char env[] = "NAME=value";
+          putenv(env); // false-positive warning: putenv function should not be called...
+          // More code...
+          putenv((char *)"NAME=anothervalue");
+          // This putenv call overwrites the previous entry, thus that can no longer dangle.
+        } // 'env' array becomes dead only here.
+
 alpha.security.cert.env
 ^^^^^^^^^^^^^^^^^^^^^^^
 


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