================
@@ -934,6 +934,76 @@ Check calls to various UNIX/Posix functions: ``open,
pthread_once, calloc, mallo
.. literalinclude:: checkers/unix_api_example.c
:language: c
+.. _unix-Errno:
+
+unix.Errno (C)
+""""""""""""""
+
+Check for improper use of ``errno``.
+This checker implements partially CERT rule
+`ERR30-C. Set errno to zero before calling a library function known to set
errno,
+and check errno only after the function returns a value indicating failure
+<https://wiki.sei.cmu.edu/confluence/pages/viewpage.action?pageId=87152351>`_.
+The checker can find the first read of ``errno`` after successful standard
+function calls.
+
+The C and POSIX standards often do not define if a standard library function
+may change value of ``errno`` if the call does not fail.
+Therefore, ``errno`` should only be used if it is known from the return value
+of a function that the call has failed.
+There are exceptions to this rule (for example ``strtol``) but the affected
+functions are not yet supported by the checker.
+The return values for the failure cases are documented in the standard Linux
man
+pages of the functions and in the `POSIX standard
<https://pubs.opengroup.org/onlinepubs/9699919799/>`_.
+
+.. code-block:: c
+
+ int unsafe_errno_read(int sock, void *data, int data_size) {
+ if (send(sock, data, data_size, 0) != data_size) {
+ // 'send' can be successful even if not all data was sent
+ if (errno == 1) { // An undefined value may be read from 'errno'
+ return 0;
+ }
+ }
+ return 1;
+ }
+
+The checker :ref:`unix-StdCLibraryFunctions` must be turned on to get the
+warnings from this checker. The supported functions are the same as by
----------------
DonatNagyE wrote:
Thanks for the clarification. I think it'd be important to improve this
situation (it's very user-hostile to hide an "if you want to use this, you must
manually enable another checker" remark in the docs), but this is independent
of the currently reviewed commit.
https://github.com/llvm/llvm-project/pull/69469
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