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 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
  

On Wed, 2022-07-20 at 23:29 +0530, Immad Mir wrote:


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

Thanks for the updated patch.

Some very minor spelling/grammar/whitespace nits...

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

"on open" -> "an open"

"refrenced" -> "referenced"

[...snip...]

> 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)}

"refrenced" -> "referenced"

> +is called with a file descriptor opened with @code{O_RDONLY} at refrenced argument @var{N},

"refrenced" -> "referenced".

Please wrap these lines to avoid going over 80 columns.

>  
>  @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}.

"refrenced" -> "referenced".


> +
>  @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.

"refrenced" -> "referenced".

> +
>  @item -Wno-analyzer-file-leak
>  @opindex Wanalyzer-file-leak
>  @opindex Wno-analyzer-file-leak

[...snip...]

...but with those fixed, this patch is OK for trunk, assuming it
bootstraps and passes regression tests.

Thanks!
Dave
  

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
>
  

> 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 for the catch, Prathamesh.

Immad.


On Wed, Jul 20, 2022 at 11:59 PM Prathamesh Kulkarni <
prathamesh.kulkarni@linaro.org> wrote:

> 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
> >
>