[PATCH] Adding three new function attributes for static analysis of file descriptors

[Immad Mir <mirimmad@outlook.com>]

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 on 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.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/fd-5.c: New test.
	* c-c++-common/attr-fd.c: New test.

Signed-off-by: Immad Mir <mirimmad@outlook.com>
---
 gcc/analyzer/sm-fd.cc                | 323 +++++++++++++++++++++------
 gcc/c-family/c-attribs.cc            |  36 ++-
 gcc/doc/extend.texi                  |  34 +++
 gcc/testsuite/c-c++-common/attr-fd.c |  18 ++
 gcc/testsuite/gcc.dg/analyzer/fd-5.c |  53 +++++
 5 files changed, 398 insertions(+), 66 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/attr-fd.c
 create mode 100644 gcc/testsuite/gcc.dg/analyzer/fd-5.c

diff --git a/gcc/analyzer/sm-fd.cc b/gcc/analyzer/sm-fd.cc
index 8e4300b06e2..c577a7db7ea 100644
--- a/gcc/analyzer/sm-fd.cc
+++ b/gcc/analyzer/sm-fd.cc
@@ -39,10 +39,13 @@ along with GCC; see the file COPYING3.  If not see
 #include "analyzer/analyzer-selftests.h"
 #include "tristate.h"
 #include "selftest.h"
+#include "stringpool.h"
+#include "attribs.h"
 #include "analyzer/call-string.h"
 #include "analyzer/program-point.h"
 #include "analyzer/store.h"
 #include "analyzer/region-model.h"
+#include "bitmap.h"
 
 #if ENABLE_ANALYZER
 
@@ -59,6 +62,13 @@ enum access_mode
   WRITE_ONLY
 };
 
+enum access_directions
+{
+  DIRS_READ_WRITE,
+  DIRS_READ,
+  DIRS_WRITE
+};
+
 class fd_state_machine : public state_machine
 {
 public:
@@ -146,7 +156,7 @@ private:
   void check_for_open_fd (sm_context *sm_ctxt, const supernode *node,
                           const gimple *stmt, const gcall *call,
                           const tree callee_fndecl,
-                          enum access_direction access_fn) const;
+                          enum access_directions access_fn) const;
 
   void make_valid_transitions_on_condition (sm_context *sm_ctxt,
                                             const supernode *node,
@@ -156,12 +166,17 @@ private:
                                               const supernode *node,
                                               const gimple *stmt,
                                               const svalue *lhs) const;
+  void check_for_fd_attrs (sm_context *sm_ctxt, const supernode *node,
+                           const gimple *stmt, const tree callee_fndecl,
+                           const char *attr_name,
+                           access_directions fd_attr_access_dir) const;
+
 };
 
 /* Base diagnostic class relative to fd_state_machine. */
 class fd_diagnostic : public pending_diagnostic
 {
-public:
+public:  
   fd_diagnostic (const fd_state_machine &sm, tree arg) : m_sm (sm), m_arg (arg)
   {
   }
@@ -220,6 +235,65 @@ protected:
   tree m_arg;
 };
 
+class fd_param_diagnostic : public fd_diagnostic
+{
+public:
+  fd_param_diagnostic (const fd_state_machine &sm, tree arg, tree callee_fndecl,
+                       bool attr, int arg_idx)
+      : fd_diagnostic (sm, arg), m_callee_fndecl (callee_fndecl), m_attr (attr),
+        m_arg_idx (arg_idx)
+  {
+  }
+
+  fd_param_diagnostic (const fd_state_machine &sm, tree arg, tree callee_fndecl)
+      : fd_diagnostic (sm, arg), m_callee_fndecl (callee_fndecl),
+        m_attr (false), m_arg_idx (-1)
+  {
+  }
+ 
+  bool
+  subclass_equal_p (const pending_diagnostic &base_other) const override
+  {
+    const fd_param_diagnostic &sub_other
+        = (const fd_param_diagnostic &)base_other;
+    return (same_tree_p (m_arg, sub_other.m_arg)
+            && m_callee_fndecl == sub_other.m_callee_fndecl
+            && m_attr == sub_other.m_attr
+            && m_arg_idx == sub_other.m_arg_idx);
+  }
+
+  void
+  inform_filedescriptor_attribute (access_directions fd_dir)
+  {
+
+    if (m_attr)
+      switch (fd_dir)
+        {
+        case DIRS_READ_WRITE:
+          inform (DECL_SOURCE_LOCATION (m_callee_fndecl),
+                  "argument %d of %qD must be an open file descriptor",
+                  m_arg_idx + 1, m_callee_fndecl);
+          break;
+        case DIRS_WRITE:
+          inform (DECL_SOURCE_LOCATION (m_callee_fndecl),
+                  "argument %d of %qD must be a read-only file descriptor",
+                  m_arg_idx + 1, m_callee_fndecl);
+          break;
+        case DIRS_READ:
+          inform (DECL_SOURCE_LOCATION (m_callee_fndecl),
+                  "argument %d of %qD must be a write-only file descriptor",
+                  m_arg_idx + 1, m_callee_fndecl);
+          break;
+        }
+  }
+
+protected:
+  tree m_callee_fndecl;
+  bool m_attr;
+  /* ARG_IDX is 0-based. */
+  int m_arg_idx;
+};
+
 class fd_leak : public fd_diagnostic
 {
 public:
@@ -290,18 +364,25 @@ private:
   diagnostic_event_id_t m_open_event;
 };
 
-class fd_access_mode_mismatch : public fd_diagnostic
+class fd_access_mode_mismatch : public fd_param_diagnostic
 {
 public:
   fd_access_mode_mismatch (const fd_state_machine &sm, tree arg,
-                           enum access_direction fd_dir,
-                           const tree callee_fndecl)
-      : fd_diagnostic (sm, arg), m_fd_dir (fd_dir),
-        m_callee_fndecl (callee_fndecl)
+                           enum access_directions fd_dir,
+                           const tree callee_fndecl, bool attr, int arg_idx)
+      : fd_param_diagnostic (sm, arg, callee_fndecl, attr, arg_idx),
+        m_fd_dir (fd_dir)
 
   {
   }
 
+  fd_access_mode_mismatch (const fd_state_machine &sm, tree arg,
+                           enum access_directions fd_dir,
+                           const tree callee_fndecl)
+      : fd_param_diagnostic (sm, arg, callee_fndecl), m_fd_dir (fd_dir)
+  {
+  }
+  
   const char *
   get_kind () const final override
   {
@@ -317,29 +398,25 @@ public:
   bool
   emit (rich_location *rich_loc) final override
   {
+    bool warned;
     switch (m_fd_dir)
       {
-      case DIR_READ:
-        return warning_at (rich_loc, get_controlling_option (),
+      case DIRS_READ:
+        warned =  warning_at (rich_loc, get_controlling_option (),
                            "%qE on %<read-only%> file descriptor %qE",
                            m_callee_fndecl, m_arg);
-      case DIR_WRITE:
-        return warning_at (rich_loc, get_controlling_option (),
+        break;
+      case DIRS_WRITE:
+        warned = warning_at (rich_loc, get_controlling_option (),
                            "%qE on %<write-only%> file descriptor %qE",
                            m_callee_fndecl, m_arg);
+        break;
       default:
         gcc_unreachable ();
       }
-  }
-
-  bool
-  subclass_equal_p (const pending_diagnostic &base_other) const override
-  {
-    const fd_access_mode_mismatch &sub_other
-        = (const fd_access_mode_mismatch &)base_other;
-    return (same_tree_p (m_arg, sub_other.m_arg)
-            && m_callee_fndecl == sub_other.m_callee_fndecl
-            && m_fd_dir == sub_other.m_fd_dir);
+      if (warned)
+        inform_filedescriptor_attribute (m_fd_dir);
+      return warned;
   }
 
   label_text
@@ -347,10 +424,10 @@ public:
   {
     switch (m_fd_dir)
       {
-      case DIR_READ:
+      case DIRS_READ:
         return ev.formatted_print ("%qE on %<read-only%> file descriptor %qE",
                                    m_callee_fndecl, m_arg);
-      case DIR_WRITE:
+      case DIRS_WRITE:
         return ev.formatted_print ("%qE on %<write-only%> file descriptor %qE",
                                    m_callee_fndecl, m_arg);
       default:
@@ -359,21 +436,20 @@ public:
   }
 
 private:
-  enum access_direction m_fd_dir;
-  const tree m_callee_fndecl;
+  enum access_directions m_fd_dir;
 };
 
-class double_close : public fd_diagnostic
+class fd_double_close : public fd_diagnostic
 {
 public:
-  double_close (const fd_state_machine &sm, tree arg) : fd_diagnostic (sm, arg)
+  fd_double_close (const fd_state_machine &sm, tree arg) : fd_diagnostic (sm, arg)
   {
   }
 
   const char *
   get_kind () const final override
   {
-    return "double_close";
+    return "fd_double_close";
   }
 
   int
@@ -418,12 +494,18 @@ private:
   diagnostic_event_id_t m_first_close_event;
 };
 
-class fd_use_after_close : public fd_diagnostic
+class fd_use_after_close : public fd_param_diagnostic
 {
 public:
+  fd_use_after_close (const fd_state_machine &sm, tree arg,
+                      const tree callee_fndecl, bool attr, int arg_idx)
+      : fd_param_diagnostic(sm, arg, callee_fndecl, attr, arg_idx)
+  {
+  }
+
   fd_use_after_close (const fd_state_machine &sm, tree arg,
                       const tree callee_fndecl)
-      : fd_diagnostic (sm, arg), m_callee_fndecl (callee_fndecl)
+      : fd_param_diagnostic(sm, arg, callee_fndecl)
   {
   }
 
@@ -442,9 +524,13 @@ public:
   bool
   emit (rich_location *rich_loc) final override
   {
-    return warning_at (rich_loc, get_controlling_option (),
+    bool warned;
+    warned = warning_at (rich_loc, get_controlling_option (),
                        "%qE on closed file descriptor %qE", m_callee_fndecl,
                        m_arg);
+    if (warned)
+      inform_filedescriptor_attribute (DIRS_READ_WRITE);
+    return warned;
   }
 
   label_text
@@ -466,32 +552,37 @@ public:
   describe_final_event (const evdesc::final_event &ev) final override
   {
     if (m_first_close_event.known_p ())
-      return ev.formatted_print (
-          "%qE on closed file descriptor %qE; %qs was at %@", m_callee_fndecl,
-          m_arg, "close", &m_first_close_event);
-    else
-      return ev.formatted_print ("%qE on closed file descriptor %qE",
-                                 m_callee_fndecl, m_arg);
+        return ev.formatted_print (
+            "%qE on closed file descriptor %qE; %qs was at %@", m_callee_fndecl,
+            m_arg, "close", &m_first_close_event);
+      else
+        return ev.formatted_print ("%qE on closed file descriptor %qE",
+                                  m_callee_fndecl, m_arg);
   }
 
 private:
   diagnostic_event_id_t m_first_close_event;
-  const tree m_callee_fndecl;
 };
 
-class unchecked_use_of_fd : public fd_diagnostic
+class fd_use_without_check : public fd_param_diagnostic
 {
 public:
-  unchecked_use_of_fd (const fd_state_machine &sm, tree arg,
+  fd_use_without_check (const fd_state_machine &sm, tree arg,
+                       const tree callee_fndecl, bool attr, int arg_idx)
+      : fd_param_diagnostic(sm, arg, callee_fndecl, attr, arg_idx)
+  {
+  }
+
+  fd_use_without_check (const fd_state_machine &sm, tree arg,
                        const tree callee_fndecl)
-      : fd_diagnostic (sm, arg), m_callee_fndecl (callee_fndecl)
+      : fd_param_diagnostic(sm, arg, callee_fndecl)
   {
   }
 
   const char *
   get_kind () const final override
   {
-    return "unchecked_use_of_fd";
+    return "fd_use_without_check";
   }
 
   int
@@ -503,18 +594,12 @@ public:
   bool
   emit (rich_location *rich_loc) final override
   {
-    return warning_at (rich_loc, get_controlling_option (),
-                       "%qE on possibly invalid file descriptor %qE",
-                       m_callee_fndecl, m_arg);
-  }
-
-  bool
-  subclass_equal_p (const pending_diagnostic &base_other) const override
-  {
-    const unchecked_use_of_fd &sub_other
-        = (const unchecked_use_of_fd &)base_other;
-    return (same_tree_p (m_arg, sub_other.m_arg)
-            && m_callee_fndecl == sub_other.m_callee_fndecl);
+    bool warned;
+    warned = warning_at (rich_loc, get_controlling_option (),
+                        "%qE on possibly invalid file descriptor %qE",
+                        m_callee_fndecl, m_arg);
+    if (warned)
+     inform_filedescriptor_attribute (DIRS_READ_WRITE);
   }
 
   label_text
@@ -542,7 +627,7 @@ public:
 
 private:
   diagnostic_event_id_t m_first_open_event;
-  const tree m_callee_fndecl;
+  
 };
 
 fd_state_machine::fd_state_machine (logger *logger)
@@ -647,11 +732,119 @@ fd_state_machine::on_stmt (sm_context *sm_ctxt, const supernode *node,
             on_read (sm_ctxt, node, stmt, call, callee_fndecl);
             return true;
           } // "read"
+
+          
+          {
+            // Handle __attribute__((fd_arg))
+            
+            check_for_fd_attrs (sm_ctxt, node, stmt, callee_fndecl, "fd_arg", DIRS_READ_WRITE);
+    
+            // Handle __attribute__((fd_arg_read))
+           
+            check_for_fd_attrs (sm_ctxt, node, stmt, callee_fndecl, "fd_arg_read", DIRS_READ);
+            
+            // Handle __attribute__((fd_arg_write))
+           
+            check_for_fd_attrs (sm_ctxt, node, stmt, callee_fndecl, "fd_arg_write", DIRS_WRITE);
+            
+            return true;
+          }
+          
       }
 
   return false;
 }
 
+void
+fd_state_machine::check_for_fd_attrs (
+    sm_context *sm_ctxt, const supernode *node, const gimple *stmt,
+    const tree callee_fndecl, const char *attr_name,
+    access_directions fd_attr_access_dir) const
+{
+
+  tree attrs = TYPE_ATTRIBUTES (TREE_TYPE (callee_fndecl));
+  attrs = lookup_attribute (attr_name, attrs);
+  if (!attrs)
+    return;
+
+  if (!TREE_VALUE (attrs))
+    return;
+
+  auto_bitmap argmap;
+
+  for (tree idx = TREE_VALUE (attrs); idx; idx = TREE_CHAIN (idx))
+    {
+      unsigned int val = TREE_INT_CST_LOW (TREE_VALUE (idx)) - 1;
+      bitmap_set_bit (argmap, val);
+    }
+  if (bitmap_empty_p (argmap))
+    return;
+
+  for (unsigned i = 0; i < gimple_call_num_args (stmt); i++)
+    {
+
+      unsigned int arg_idx = i;
+      tree arg = gimple_call_arg (stmt, arg_idx);
+      tree diag_arg = sm_ctxt->get_diagnostic_tree (arg);
+      state_t state = sm_ctxt->get_state (stmt, arg);
+      bool bit_set = bitmap_bit_p (argmap, arg_idx);
+      if (TREE_CODE (TREE_TYPE (arg)) != INTEGER_TYPE)
+        continue;
+      if (bit_set) // Check if arg_idx is marked by any of the file descriptor
+                   // attributes
+        {
+
+          if (is_closed_fd_p (state))
+            {
+
+              sm_ctxt->warn (node, stmt, arg,
+                             new fd_use_after_close (*this, diag_arg,
+                                                     callee_fndecl, true,
+                                                     arg_idx));
+              continue;
+            }
+
+          if (!(is_valid_fd_p (state) || (state == m_stop)))
+            {
+              if (!is_constant_fd_p (state))
+                sm_ctxt->warn (node, stmt, arg,
+                               new fd_use_without_check (*this, diag_arg,
+                                                        callee_fndecl, true,
+                                                        arg_idx));
+            }
+
+          switch (fd_attr_access_dir)
+            {
+            case DIRS_READ_WRITE:
+              break;
+            case DIRS_READ:
+
+              if (is_writeonly_fd_p (state))
+                {
+                  sm_ctxt->warn (
+                      node, stmt, arg,
+                      new fd_access_mode_mismatch (*this, diag_arg, DIRS_WRITE,
+                                                   callee_fndecl, true, i));
+                }
+
+              break;
+            case DIRS_WRITE:
+
+              if (is_readonly_fd_p (state))
+                {
+                  sm_ctxt->warn (
+                      node, stmt, arg,
+                      new fd_access_mode_mismatch (*this, diag_arg, DIRS_READ,
+                                                   callee_fndecl, true, i));
+                }
+
+              break;
+            }
+        }
+    }
+}
+
+
 void
 fd_state_machine::on_open (sm_context *sm_ctxt, const supernode *node,
                            const gimple *stmt, const gcall *call) const
@@ -706,7 +899,7 @@ fd_state_machine::on_close (sm_context *sm_ctxt, const supernode *node,
 
   if (is_closed_fd_p (state))
     {
-      sm_ctxt->warn (node, stmt, arg, new double_close (*this, diag_arg));
+      sm_ctxt->warn (node, stmt, arg, new fd_double_close (*this, diag_arg));
       sm_ctxt->set_next_state (stmt, arg, m_stop);
     }
 }
@@ -715,21 +908,21 @@ fd_state_machine::on_read (sm_context *sm_ctxt, const supernode *node,
                            const gimple *stmt, const gcall *call,
                            const tree callee_fndecl) const
 {
-  check_for_open_fd (sm_ctxt, node, stmt, call, callee_fndecl, DIR_READ);
+  check_for_open_fd (sm_ctxt, node, stmt, call, callee_fndecl, DIRS_READ);
 }
 void
 fd_state_machine::on_write (sm_context *sm_ctxt, const supernode *node,
                             const gimple *stmt, const gcall *call,
                             const tree callee_fndecl) const
 {
-  check_for_open_fd (sm_ctxt, node, stmt, call, callee_fndecl, DIR_WRITE);
+  check_for_open_fd (sm_ctxt, node, stmt, call, callee_fndecl, DIRS_WRITE);
 }
 
 void
 fd_state_machine::check_for_open_fd (
     sm_context *sm_ctxt, const supernode *node, const gimple *stmt,
     const gcall *call, const tree callee_fndecl,
-    enum access_direction callee_fndecl_dir) const
+    enum access_directions callee_fndecl_dir) const
 {
   tree arg = gimple_call_arg (call, 0);
   tree diag_arg = sm_ctxt->get_diagnostic_tree (arg);
@@ -748,30 +941,32 @@ fd_state_machine::check_for_open_fd (
           if (!is_constant_fd_p (state))
             sm_ctxt->warn (
                 node, stmt, arg,
-                new unchecked_use_of_fd (*this, diag_arg, callee_fndecl));
+                new fd_use_without_check (*this, diag_arg, callee_fndecl));
         }
       switch (callee_fndecl_dir)
         {
-        case DIR_READ:
+        case DIRS_READ:
           if (is_writeonly_fd_p (state))
             {
               tree diag_arg = sm_ctxt->get_diagnostic_tree (arg);
               sm_ctxt->warn (node, stmt, arg,
                              new fd_access_mode_mismatch (
-                                 *this, diag_arg, DIR_WRITE, callee_fndecl));
+                                 *this, diag_arg, DIRS_WRITE, callee_fndecl));
             }
 
           break;
-        case DIR_WRITE:
+        case DIRS_WRITE:
 
           if (is_readonly_fd_p (state))
             {
               tree diag_arg = sm_ctxt->get_diagnostic_tree (arg);
               sm_ctxt->warn (node, stmt, arg,
                              new fd_access_mode_mismatch (
-                                 *this, diag_arg, DIR_READ, callee_fndecl));
+                                 *this, diag_arg, DIRS_READ, callee_fndecl));
             }
           break;
+        default:
+          gcc_unreachable ();
         }
     }
 }
diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index c8d96723f4c..a04cc541f95 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)	\
@@ -426,7 +427,7 @@ const struct attribute_spec c_common_attribute_table[] =
   { "tls_model",	      1, 1, true,  false, false, false,
 			      handle_tls_model_attribute, NULL },
   { "nonnull",                0, -1, false, true, true, false,
-			      handle_nonnull_attribute, NULL },
+			      handle_nonnull_attribute, NULL },         
   { "nonstring",              0, 0, true, false, false, false,
 			      handle_nonstring_attribute, NULL },
   { "nothrow",                0, 0, true,  false, false, false,
@@ -555,7 +556,13 @@ 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 },
-  { NULL,                     0, 0, false, false, false, false, NULL, NULL }
+  { NULL,                     0, 0, false, false, false, false, NULL, 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},
 };
 
 /* Give the specifications for the format attributes, used by C and all
@@ -4521,6 +4528,31 @@ 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 (tree val = 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
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index dfbe33ac652..7945d769e23 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -3007,6 +3007,40 @@ produced by @command{gold}.
 For other linkers that cannot generate resolution file,
 explicit @code{externally_visible} attributes are still necessary.
 
+@item fd_arg
+@cindex @code{fd_arg} function attribute
+The @code{fd_arg} attribute may be applied to a function that takes an open 
+file descriptor at referenced argument @var{N}.
+
+It indicates that the passed filedescriptor must not have been closed.
+Therefore, when the analyzer is enabled with @option{-fanalyzer}, the 
+analyzer may emit a @option{-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
+@option{-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.
+
+@item fd_arg_read
+@cindex @code{fd_arg_read} function attribute
+The @code{fd_arg_read} is identical to @code{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 @option{-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 @code{O_WRONLY}.
+
+@item fd_arg_write
+@cindex @code{fd_arg_write} function attribute
+The @code{fd_arg_write} is identical to @code{fd_arg_read} except that the
+analyzer may emit a @option{-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 @code{O_RDONLY}.
+
 @item flatten
 @cindex @code{flatten} function attribute
 Generally, inlining into a function is limited.  For a function marked with
diff --git a/gcc/testsuite/c-c++-common/attr-fd.c b/gcc/testsuite/c-c++-common/attr-fd.c
new file mode 100644
index 00000000000..292c329856e
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-fd.c
@@ -0,0 +1,18 @@
+
+int not_a_fn __attribute__ ((fd_arg(1))); /* { dg-warning "'fd_arg' attribute only applies to function types" } */
+
+void f (char *p) __attribute__ ((fd_arg(1))); /* { dg-warning "'fd_arg' attribute argument value '1' refers to parameter type 'char \\\*'" } */
+
+
+int not_a_fn_b __attribute__ ((fd_arg_read(1))); /* { dg-warning "'fd_arg_read' attribute only applies to function types" } */
+
+void g (char *p) __attribute__ ((fd_arg_read(1))); /* { dg-warning "'fd_arg_read' attribute argument value '1' refers to parameter type 'char \\\*'" } */
+
+
+int not_a_fn_c __attribute__ ((fd_arg_write(1))); /* { dg-warning "'fd_arg_write' attribute only applies to function types" } */
+
+void f (char *p) __attribute__ ((fd_arg_write(1))); /* { dg-warning "'fd_arg_write' attribute argument value '1' refers to parameter type 'char \\\*'" } */
+
+
+void fn_a (int fd) __attribute__ ((fd_arg(0))); /* { dg-warning "'fd_arg' attribute argument value '0' does not refer to a function parameter" } */
+void fd_a_1 (int fd) __attribute__ ((fd_arg("notint"))); /* { dg-warning "'fd_arg' attribute argument has type 'char\\\[7\\\]'" } */
diff --git a/gcc/testsuite/gcc.dg/analyzer/fd-5.c b/gcc/testsuite/gcc.dg/analyzer/fd-5.c
new file mode 100644
index 00000000000..6287ddd38fc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/fd-5.c
@@ -0,0 +1,53 @@
+int open(const char *, int mode);
+void close(int fd);
+int write (int fd, void *buf, int nbytes);
+int read (int fd, void *buf, int nbytes);
+
+#define O_RDONLY 0
+#define O_WRONLY 1
+#define O_RDWR 2
+
+void f (int fd) __attribute__((fd_arg(1))); /* { dg-message "argument 1 of 'f' must be an open file descriptor" } */
+
+void
+test_1 (const char *path)
+{
+    int fd = open (path, O_RDWR);
+    close(fd);
+    f(fd); /* { dg-warning "'f' on closed file descriptor 'fd'" } */
+      /* { dg-message "\\(3\\) 'f' on closed file descriptor 'fd'; 'close' was at \\(2\\)" "" { target *-*-* } .-1 } */
+}
+
+void g (int fd) __attribute__((fd_arg_read(1))); /* { dg-message "argument 1 of 'g' must be a read-only file descriptor" } */
+
+void
+test_2 (const char *path)
+{
+  int fd = open (path, O_WRONLY);
+  if (fd != -1)
+  {
+    g (fd); /* { dg-warning "'g' on 'write-only' file descriptor 'fd'" } */
+  }
+  close (fd);
+}
+
+void h (int fd) __attribute__((fd_arg_write(1))); /* { dg-message "argument 1 of 'h' must be a write-only file descriptor" } */
+void
+test_3 (const char *path)
+{
+  int fd = open (path, O_RDONLY);
+  if (fd != -1)
+  {
+    h (fd); /* { dg-warning "'h' on 'read-only' file descriptor 'fd'" } */
+  }
+  close(fd);
+}
+
+void ff (int fd) __attribute__((fd_arg(1))); /* { dg-message "argument 1 of 'ff' must be an open file descriptor" } */
+
+void test_4 (const char *path)
+{
+  int fd = open (path, O_RDWR);
+  ff (fd); /* { dg-warning "'ff' on possibly invalid file descriptor 'fd'" } */
+  close(fd);
+}
\ No newline at end of file
-- 
2.25.1