Adding three new function attributes for static analysis of file descriptors

This patch adds three new function attributes to GCC that
are used for static analysis of usage of file descriptors:

1) __attribute__ ((fd_arg(N))): The attributes may be applied to a function that
takes an open file descriptor at refrenced argument N.

It indicates that the passed filedescriptor must not have been closed.
Therefore, when the analyzer is enabled with -fanalyzer, the
analyzer may emit a -Wanalyzer-fd-use-after-close diagnostic
if it detects a code path in which a function with this attribute is
called with a closed file descriptor.

The attribute also indicates that the file descriptor must have been checked for
validity before usage. Therefore, analyzer may emit
-Wanalyzer-fd-use-without-check diagnostic if it detects a code path in
which a function with this attribute is called with a file descriptor that has
not been checked for validity.

2) __attribute__((fd_arg_read(N))): The attribute is identical to
fd_arg, but with the additional requirement that it might read from
the file descriptor, and thus, the file descriptor must not have been opened
as write-only.

The analyzer may emit a -Wanalyzer-access-mode-mismatch
diagnostic if it detects a code path in which a function with this
attribute is called on a file descriptor opened with O_WRONLY.

3) __attribute__((fd_arg_write(N))): The attribute is identical to fd_arg_read
except that the analyzer may emit a -Wanalyzer-access-mode-mismatch diagnostic if
it detects a code path in which a function with this attribute is called on a
file descriptor opened with O_RDONLY.

gcc/analyzer/ChangeLog:
	* sm-fd.cc (fd_param_diagnostic): New diagnostic class.
	(fd_access_mode_mismatch): Change inheritance from fd_diagnostic
	to fd_param_diagnostic. Add new overloaded constructor.
	(fd_use_after_close): Likewise.
	(unchecked_use_of_fd): Likewise and also change name to fd_use_without_check.
	(double_close): Change name to fd_double_close.
	(enum access_directions): New.
	(fd_state_machine::on_stmt): Handle calls to function with the
	new three function attributes.
	(fd_state_machine::check_for_fd_attrs): New.
	(fd_state_machine::on_open): Use the new overloaded constructors
	of diagnostic classes.

gcc/c-family/ChangeLog:
	* c-attribs.cc: (c_common_attribute_table): add three new attributes
	namely: fd_arg, fd_arg_read and fd_arg_write.
	(handle_fd_arg_attribute): New.

gcc/ChangeLog:
	* doc/extend.texi: Add fd_arg, fd_arg_read and fd_arg_write under
	"Common Function Attributes" section.
	* doc/invoke.texi: Add docs to -Wanalyzer-fd-access-mode-mismatch,
	-Wanalyzer-use-after-close, -Wanalyzer-fd-use-without-check that these
	warnings may be emitted through usage of three function attributes used
	for static analysis of file descriptors namely fd_arg, fd_arg_read and
	fd_arg_write.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/fd-5.c: New test.
	* gcc.dg/analyzer/fd-4.c: Remove quotes around 'read-only' and
	'write-only'.
	* c-c++-common/attr-fd.c: New test.

Signed-off-by: Immad Mir <mirimmad17@gmail.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index c8d9672..e4f1d35 100644
--- a/gcc/c-family/c-attribs.cc
+++ b/gcc/c-family/c-attribs.cc
@@ -173,6 +173,7 @@ static tree handle_objc_nullability_attribute (tree *, tree, tree, int, bool *);
 static tree handle_signed_bool_precision_attribute (tree *, tree, tree, int,
 						    bool *);
 static tree handle_retain_attribute (tree *, tree, tree, int, bool *);
+static tree handle_fd_arg_attribute (tree *, tree, tree, int, bool *);
 
 /* Helper to define attribute exclusions.  */
 #define ATTR_EXCL(name, function, type, variable)	\
@@ -555,6 +556,12 @@ const struct attribute_spec c_common_attribute_table[] =
 			      handle_dealloc_attribute, NULL },
   { "tainted_args",	      0, 0, true,  false, false, false,
 			      handle_tainted_args_attribute, NULL },
+  { "fd_arg",             1, 1, false, true, true, false,
+            handle_fd_arg_attribute, NULL},      
+  { "fd_arg_read",        1, 1, false, true, true, false,
+            handle_fd_arg_attribute, NULL},
+  { "fd_arg_write",       1, 1, false, true, true, false,
+            handle_fd_arg_attribute, NULL},         
   { NULL,                     0, 0, false, false, false, false, NULL, NULL }
 };
 
@@ -4521,6 +4528,30 @@ handle_nonnull_attribute (tree *node, tree name,
   return NULL_TREE;
 }
 
+/* Handle the "fd_arg", "fd_arg_read" and "fd_arg_write" attributes */
+
+static tree
+handle_fd_arg_attribute (tree *node, tree name, tree args,
+                              int ARG_UNUSED (flags), bool *no_add_attrs)
+{
+  tree type = *node;
+  if (!args)
+    {
+      if (!prototype_p (type))
+        {
+          error ("%qE attribute without arguments on a non-prototype", name);
+          *no_add_attrs = true;
+        }
+      return NULL_TREE;
+    }
+
+  if (positional_argument (*node, name, TREE_VALUE (args), INTEGER_TYPE))
+      return NULL_TREE;
+
+  *no_add_attrs = true;  
+  return NULL_TREE;
+}
+
 /* Handle the "nonstring" variable attribute.  */
 
 static tree