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

[Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org>]

On Wed, 20 Jul 2022 at 23:31, Immad Mir via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> 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.
>         * 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.
>         * c-c++-common/attr-fd.c: New test.
>
> Signed-off-by: Immad Mir <mirimmad@outlook.com>
> ---
>  gcc/analyzer/sm-fd.cc                | 335 +++++++++++++++++++++------
>  gcc/c-family/c-attribs.cc            |  32 +++
>  gcc/doc/extend.texi                  |  37 +++
>  gcc/doc/invoke.texi                  |  17 +-
>  gcc/testsuite/c-c++-common/attr-fd.c |  18 ++
>  gcc/testsuite/gcc.dg/analyzer/fd-5.c |  53 +++++
>  6 files changed, 422 insertions(+), 70 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..bb89c471f7e 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,
> @@ -156,6 +166,10 @@ 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,
Hi Immad,
Sorry to nitpick -- I assume stmt here refers to a call stmt ?
In that case, I suppose it'd be better to use const gcall *stmt ?

Thanks,
Prathamesh
> +                           const char *attr_name,
> +                           access_directions fd_attr_access_dir) const;
>  };
>
>  /* Base diagnostic class relative to fd_state_machine. */
> @@ -220,6 +234,68 @@ 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,
> +                       const char *attr_name, int arg_idx)
> +      : fd_diagnostic (sm, arg), m_callee_fndecl (callee_fndecl),
> +        m_attr_name (attr_name), 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_name (NULL), 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)
> +            && same_tree_p (m_callee_fndecl, sub_other.m_callee_fndecl)
> +            && m_arg_idx == sub_other.m_arg_idx
> +            && ((m_attr_name) ? (m_attr_name == sub_other.m_attr_name) : true));
> +  }
> +
> +  void
> +  inform_filedescriptor_attribute (access_directions fd_dir)
> +  {
> +
> +    if (m_attr_name)
> +      switch (fd_dir)
> +        {
> +        case DIRS_READ_WRITE:
> +          inform (DECL_SOURCE_LOCATION (m_callee_fndecl),
> +                  "argument %d of %qD must be an open file descriptor, due to "
> +                  "%<__attribute__((%s(%d)))%>",
> +                  m_arg_idx + 1, m_callee_fndecl, m_attr_name, m_arg_idx + 1);
> +          break;
> +        case DIRS_WRITE:
> +          inform (DECL_SOURCE_LOCATION (m_callee_fndecl),
> +                  "argument %d of %qD must be a readable file descriptor, due "
> +                  "to %<__attribute__((%s(%d)))%>",
> +                  m_arg_idx + 1, m_callee_fndecl, m_attr_name, m_arg_idx + 1);
> +          break;
> +        case DIRS_READ:
> +          inform (DECL_SOURCE_LOCATION (m_callee_fndecl),
> +                  "argument %d of %qD must be a writable file descriptor, due "
> +                  "to %<__attribute__((%s(%d)))%>",
> +                  m_arg_idx + 1, m_callee_fndecl, m_attr_name, m_arg_idx + 1);
> +          break;
> +        }
> +  }
> +
> +protected:
> +  tree m_callee_fndecl;
> +  const char *m_attr_name;
> +  /* ARG_IDX is 0-based. */
> +  int m_arg_idx;
> +};
> +
>  class fd_leak : public fd_diagnostic
>  {
>  public:
> @@ -290,18 +366,26 @@ 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, const char *attr_name,
> +                           int arg_idx)
> +      : fd_param_diagnostic (sm, arg, callee_fndecl, attr_name, 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 +401,25 @@ 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 (),
> -                           "%qE on %<read-only%> file descriptor %qE",
> +      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 (),
> -                           "%qE on %<write-only%> file descriptor %qE",
> +        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
> @@ -347,11 +427,11 @@ public:
>    {
>      switch (m_fd_dir)
>        {
> -      case DIR_READ:
> -        return ev.formatted_print ("%qE on %<read-only%> file descriptor %qE",
> +      case DIRS_READ:
> +        return ev.formatted_print ("%qE on read-only file descriptor %qE",
>                                     m_callee_fndecl, m_arg);
> -      case DIR_WRITE:
> -        return ev.formatted_print ("%qE on %<write-only%> file descriptor %qE",
> +      case DIRS_WRITE:
> +        return ev.formatted_print ("%qE on write-only file descriptor %qE",
>                                     m_callee_fndecl, m_arg);
>        default:
>          gcc_unreachable ();
> @@ -359,21 +439,20 @@ 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 +497,19 @@ 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, const char *attr_name,
> +                      int arg_idx)
> +      : fd_param_diagnostic (sm, arg, callee_fndecl, attr_name, 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 +528,13 @@ 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 +556,38 @@ 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,
> -                       const tree callee_fndecl)
> -      : fd_diagnostic (sm, arg), m_callee_fndecl (callee_fndecl)
> +  fd_use_without_check (const fd_state_machine &sm, tree arg,
> +                        const tree callee_fndecl, const char *attr_name,
> +                        int arg_idx)
> +      : fd_param_diagnostic (sm, arg, callee_fndecl, attr_name, arg_idx)
> +  {
> +  }
> +
> +  fd_use_without_check (const fd_state_machine &sm, tree arg,
> +                        const tree 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 +599,12 @@ 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
> @@ -541,8 +631,7 @@ public:
>    }
>
>  private:
> -  diagnostic_event_id_t m_first_open_event;
> -  const tree m_callee_fndecl;
> +  diagnostic_event_id_t m_first_open_event;
>  };
>
>  fd_state_machine::fd_state_machine (logger *logger)
> @@ -647,11 +736,117 @@ 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 arg_idx = 0; arg_idx < gimple_call_num_args (stmt); arg_idx++)
> +    {
> +      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, attr_name,
> +                                                     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, attr_name,
> +                                                        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, attr_name, arg_idx));
> +                }
> +
> +              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, attr_name, arg_idx));
> +                }
> +
> +              break;
> +            }
> +        }
> +    }
> +}
> +
> +
>  void
>  fd_state_machine::on_open (sm_context *sm_ctxt, const supernode *node,
>                             const gimple *stmt, const gcall *call) const
> @@ -706,7 +901,7 @@ 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 +910,21 @@ 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 +943,32 @@ 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..0ad3a1a7040 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 +4528,31 @@ 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..1d08324a70c 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -3007,6 +3007,43 @@ produced by @command{gold}.
>  For other linkers that cannot generate resolution file,
>  explicit @code{externally_visible} attributes are still necessary.
>
> +@item fd_arg
> +@itemx fd_arg (@var{N})
> +@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
> +@itemx fd_arg_read (@var{N})
> +@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
> +@itemx fd_arg_write (@var{N})
> +@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/doc/invoke.texi b/gcc/doc/invoke.texi
> index d5ff1018372..9234275ca6d 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -9843,7 +9843,12 @@ This warning requires @option{-fanalyzer}, which enables it; use
>  to disable it.
>
>  This diagnostic warns for paths through code in which a
> -@code{read} on a write-only file descriptor is attempted, or vice versa
> +@code{read} on a write-only file descriptor is attempted, or vice versa.
> +
> +This diagnostic also warns for code paths in a which a function with attribute
> +@code{fd_arg_read (N)} is called with a file descriptor opened with @code{O_WRONLY}
> +at refrenced argument @code{N} or a function with attribute @code{fd_arg_write (N)}
> +is called with a file descriptor opened with @code{O_RDONLY} at refrenced argument @var{N},
>
>  @item -Wno-analyzer-fd-double-close
>  @opindex Wanalyzer-fd-double-close
> @@ -9875,6 +9880,11 @@ to disable it.
>  This diagnostic warns for paths through code in which a
>  read or write is called on a closed file descriptor.
>
> +This diagnostic also warns for paths through code in which
> +a function with attribute @code{fd_arg (N)} or @code{fd_arg_read (N)}
> +or @code{fd_arg_write (N)} is called with a closed file descriptor at
> +refrenced argument @code{N}.
> +
>  @item -Wno-analyzer-fd-use-without-check
>  @opindex Wanalyzer-fd-use-without-check
>  @opindex Wno-analyzer-fd-use-without-check
> @@ -9885,6 +9895,11 @@ to disable it.
>  This diagnostic warns for paths through code in which a
>  file descriptor is used without being checked for validity.
>
> +This diagnostic also warns for paths through code in which
> +a function with attribute @code{fd_arg (N)} or @code{fd_arg_read (N)}
> +or @code{fd_arg_write (N)} is called with a file descriptor, at refrenced
> +argument @code{N}, without being checked for validity.
> +
>  @item -Wno-analyzer-file-leak
>  @opindex Wanalyzer-file-leak
>  @opindex Wno-analyzer-file-leak
> 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..9805f7f79c5
> --- /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, due to '__attribute__\\(\\(fd_arg\\(1\\)\\)\\)'" } */
> +
> +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 readable file descriptor, due to '__attribute__\\(\\(fd_arg_read\\(1\\)\\)\\)'" } */
> +
> +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 writable file descriptor, due to '__attribute__\\(\\(fd_arg_write\\(1\\)\\)\\)'" } */
> +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, due to '__attribute__\\(\\(fd_arg\\(1\\)\\)\\)'" } */
> +
> +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
>