[PATCH] fortran: Ignore use statements on error [PR107426]

[Mikael Morin <mikael@gcc.gnu.org>]

Hello,

here is a fix for an ICE caused by dangling pointers to ISO_C_BINDING's
C_PTR symbol in the global intrinsic symbol for C_LOC.
I tried to fix it by making the intrinsic symbol use its own copy of
C_PTR, but it regressed heavily.

Instead, I propose this which is based on a patch I attached to the PR
one year ago.  It's sufficient to remove the access to freed memory.

However, an underlying problem remains that successive use-associations
of ISO_C_BINDING's symbols in different scopes cause the return type
of the C_LOC global intrinsic symbol to be set to the C_PTR from each
scope successively, with the last one "winning".  Not very pretty.

Anyway, there are two changed messages in the testsuite as a side-effect
of the proposed change.  I regard them as acceptable, albeit slightly worse.
No regression otherwise on x86_64-pc-linux-gnu.
Ok for 14 master?

Mikael

-- >8 --

This fixes an access to freed memory on the testcase from the PR.
The problem comes from an invalid subroutine statement in an interface,
which is ignored and causes the following statements forming the procedure
body to be rejected.  One of them use-associates the intrinsic ISO_C_BINDING
module, which imports new symbols in a namespace that is freed at the time
the statement is rejected.  However, this creates dangling pointers as
ISO_C_BINDING is special and its import creates a reference to the imported
C_PTR symbol in the return type of the global intrinsic symbol for C_LOC
(see the function create_intrinsic_function).

This change saves and restores the list of use statements, so that rejected
use statements are removed before they have a chance to be applied to the
current namespace and create dangling pointers.

	PR fortran/107426

gcc/fortran/ChangeLog:

	* gfortran.h (gfc_save_module_list, gfc_restore_old_module_list):
	New declarations.
	* module.cc (old_module_list_tail): New global variable.
	(gfc_save_module_list, gfc_restore_old_module_list): New functions.
	(gfc_use_modules): Set module_list and old_module_list_tail.
	* parse.cc (next_statement): Save module_list before doing any work.
	(reject_statement): Restore module_list to its saved value.

gcc/testsuite/ChangeLog:

	* gfortran.dg/pr89943_3.f90: Update error pattern.
	* gfortran.dg/pr89943_4.f90: Likewise.
	* gfortran.dg/use_31.f90: New test.
---
 gcc/fortran/gfortran.h                  |  2 ++
 gcc/fortran/module.cc                   | 31 +++++++++++++++++++++++++
 gcc/fortran/parse.cc                    |  4 ++++
 gcc/testsuite/gfortran.dg/pr89943_3.f90 |  2 +-
 gcc/testsuite/gfortran.dg/pr89943_4.f90 |  2 +-
 gcc/testsuite/gfortran.dg/use_31.f90    | 25 ++++++++++++++++++++
 6 files changed, 64 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/use_31.f90

diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index c7039730fad..fec7b53ff1a 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -3926,6 +3926,8 @@ void gfc_module_done_2 (void);
 void gfc_dump_module (const char *, int);
 bool gfc_check_symbol_access (gfc_symbol *);
 void gfc_free_use_stmts (gfc_use_list *);
+void gfc_save_module_list ();
+void gfc_restore_old_module_list ();
 const char *gfc_dt_lower_string (const char *);
 const char *gfc_dt_upper_string (const char *);
 
diff --git a/gcc/fortran/module.cc b/gcc/fortran/module.cc
index d1de53cbdb4..c565b84d61b 100644
--- a/gcc/fortran/module.cc
+++ b/gcc/fortran/module.cc
@@ -195,7 +195,12 @@ static const char *module_name;
 /* The name of the .smod file that the submodule will write to.  */
 static const char *submodule_name;
 
+/* The list of use statements to apply to the current namespace
+   before parsing the non-use statements.  */
 static gfc_use_list *module_list;
+/* The end of the MODULE_LIST list above at the time the recognition
+   of the current statement started.  */
+static gfc_use_list **old_module_list_tail;
 
 /* If we're reading an intrinsic module, this is its ID.  */
 static intmod_id current_intmod;
@@ -7561,6 +7566,8 @@ gfc_use_modules (void)
       gfc_use_module (module_list);
       free (module_list);
     }
+  module_list = NULL;
+  old_module_list_tail = &module_list;
   gfc_rename_list = NULL;
 }
 
@@ -7584,6 +7591,30 @@ gfc_free_use_stmts (gfc_use_list *use_stmts)
 }
 
 
+/* Remember the end of the MODULE_LIST list, so that the list can be restored
+   to its previous state if the current statement is erroneous.  */
+
+void
+gfc_save_module_list ()
+{
+  gfc_use_list **tail = &module_list;
+  while (*tail != NULL)
+    tail = &(*tail)->next;
+  old_module_list_tail = tail;
+}
+
+
+/* Restore the MODULE_LIST list to its previous value and free the use
+   statements that are no longer part of the list.  */
+
+void
+gfc_restore_old_module_list ()
+{
+  gfc_free_use_stmts (*old_module_list_tail);
+  *old_module_list_tail = NULL;
+}
+
+
 void
 gfc_module_init_2 (void)
 {
diff --git a/gcc/fortran/parse.cc b/gcc/fortran/parse.cc
index a2bf328f681..79c810c86ba 100644
--- a/gcc/fortran/parse.cc
+++ b/gcc/fortran/parse.cc
@@ -1800,6 +1800,7 @@ next_statement (void)
   locus old_locus;
 
   gfc_enforce_clean_symbol_state ();
+  gfc_save_module_list ();
 
   gfc_new_block = NULL;
 
@@ -3104,6 +3105,9 @@ reject_statement (void)
 
   gfc_reject_data (gfc_current_ns);
 
+  /* Don't queue use-association of a module if we reject the use statement.  */
+  gfc_restore_old_module_list ();
+
   gfc_new_block = NULL;
   gfc_undo_symbols ();
   gfc_clear_warning ();
diff --git a/gcc/testsuite/gfortran.dg/pr89943_3.f90 b/gcc/testsuite/gfortran.dg/pr89943_3.f90
index 38b723e2458..84a9fb74741 100644
--- a/gcc/testsuite/gfortran.dg/pr89943_3.f90
+++ b/gcc/testsuite/gfortran.dg/pr89943_3.f90
@@ -22,7 +22,7 @@ submodule(Foo_mod) Foo_smod
       module subroutine runFoo4C(ndim) bind(C, name="runFu")   ! { dg-error "Mismatch in BIND" }
          use, intrinsic :: iso_c_binding                 ! { dg-error "Unexpected USE statement" }
          implicit none                                   ! { dg-error "Unexpected IMPLICIT NONE statement" }
-         integer(c_int32_t) , intent(in) :: ndim         ! { dg-error "Unexpected data declaration" }
+         integer(c_int32_t) , intent(in) :: ndim         ! { dg-error "Symbol 'c_int32_t' at .1. has no IMPLICIT type" }
       end subroutine runFoo4C                            ! { dg-error " Expecting END SUBMODULE" }
 
 end submodule Foo_smod
diff --git a/gcc/testsuite/gfortran.dg/pr89943_4.f90 b/gcc/testsuite/gfortran.dg/pr89943_4.f90
index 8eba2eda171..cb955d01c88 100644
--- a/gcc/testsuite/gfortran.dg/pr89943_4.f90
+++ b/gcc/testsuite/gfortran.dg/pr89943_4.f90
@@ -23,7 +23,7 @@ submodule(Foo_mod) Foo_smod
       module function runFoo4C(ndim) bind(C, name="runFu")  ! { dg-error "Mismatch in BIND" }
          use, intrinsic :: iso_c_binding     ! { dg-error "Unexpected USE statement in" }
          implicit none                       ! { dg-error "Unexpected IMPLICIT NONE statement" }
-         integer(c_int32_t) , intent(in) :: ndim   ! { dg-error "Unexpected data declaration" }
+         integer(c_int32_t) , intent(in) :: ndim   ! { dg-error "Symbol 'c_int32_t' at .1. has no IMPLICIT type" }
       end function runFoo4C                  ! { dg-error "Expecting END SUBMODULE" }
 
 end submodule Foo_smod
diff --git a/gcc/testsuite/gfortran.dg/use_31.f90 b/gcc/testsuite/gfortran.dg/use_31.f90
new file mode 100644
index 00000000000..818f2e30b09
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/use_31.f90
@@ -0,0 +1,25 @@
+! { dg-do compile }
+!
+! PR fortran/107426
+! This example used to generate an ICE, caused by the use stmt from the nested
+! procedure declaration wrongly applying to the host procedure and overwriting
+! the symbols there.
+!
+! Contributed by Gerhard Steinmetz <gscfq@t-online.de>
+
+module m
+contains
+   subroutine p() bind(c)
+      use, intrinsic :: iso_c_binding
+      integer, target :: a = 1
+      type(c_ptr) :: z
+      interface
+         subroutine s(x) bind(cc)            ! { dg-error "Missing closing paren" }
+            use, intrinsic :: iso_c_binding  ! { dg-error "Unexpected USE statement in INTERFACE block" }
+            integer(c_int), value :: x       ! { dg-error "Parameter 'c_int' at .1. has not been declared" }
+         end                                 ! { dg-error "END INTERFACE statement expected" }
+      end interface
+      z = c_loc(a)
+      call s(z)
+   end
+end
-- 
2.43.0