posix.cfg: Improved configuration of readlinkat().

cfg/posix.cfg

@@ -3906,6 +3906,7 @@ The function 'mktemp' is considered to be dangerous due to race conditions and s
       <not-uninit/>
     </arg>
   </function>
+  <!-- https://man7.org/linux/man-pages/man2/readlink.2.html -->
   <!-- int readlinkat(int dirfd, const char *pathname, char *buf, size_t bufsiz); -->
   <function name="readlinkat">
     <returnValue type="int"/>
@@ -3914,6 +3915,7 @@ The function 'mktemp' is considered to be dangerous due to race conditions and s
     <arg nr="1" direction="in">
       <not-uninit/>
       <not-bool/>
+      <valid>0:</valid>
     </arg>
     <arg nr="2" direction="in">
       <not-null/>

test/cfg/posix.c

@@ -32,6 +32,15 @@
 #include <wchar.h>
 #include <string.h>
 
+int nullPointer_readlinkat(int dirfd, const char *pathname, char *buf, size_t bufsiz)
+{
+    // cppcheck-suppress nullPointer
+    (void) readlinkat(dirfd, NULL, buf, bufsiz);
+    // cppcheck-suppress nullPointer
+    (void) readlinkat(dirfd, pathname, NULL, bufsiz);
+    return readlinkat(dirfd, pathname, buf, bufsiz);
+}
+
 ssize_t nullPointer_recv(int sockfd, void *buf, size_t len, int flags)
 {
     // cppcheck-suppress nullPointer