Fix crash in Fortran code

PR fortran/28801 points out a gdb crash that can be provoked by
certain Fortran code.  The bug is that f77_get_upperbound assumes the
property is either a constant or undefined, but in this case it is
PROP_LOCEXPR.

This patch fixes the crash by making this function (and the
lower-bound one as well) do the correct check before calling
'const_val'.

Thanks to Andrew for writing the test case.

Co-authored-by: Andrew Burgess <aburgess@redhat.com>
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28801

gdb/f-valprint.c

@@ -43,7 +43,7 @@ static void f77_get_dynamic_length_of_aggregate (struct type *);
 LONGEST
 f77_get_lowerbound (struct type *type)
 {
-  if (type->bounds ()->low.kind () == PROP_UNDEFINED)
+  if (type->bounds ()->low.kind () != PROP_CONST)
     error (_("Lower bound may not be '*' in F77"));
 
   return type->bounds ()->low.const_val ();
@@ -52,7 +52,7 @@ f77_get_lowerbound (struct type *type)
 LONGEST
 f77_get_upperbound (struct type *type)
 {
-  if (type->bounds ()->high.kind () == PROP_UNDEFINED)
+  if (type->bounds ()->high.kind () != PROP_CONST)
     {
       /* We have an assumed size array on our hands.  Assume that
 	 upper_bound == lower_bound so that we show at least 1 element.

gdb/testsuite/gdb.dwarf2/fortran-var-string.c

@@ -0,0 +1,31 @@
+/* Copyright 2022 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* In the generated DWARF, we'll pretend that ARG is a string with dynamic
+   length.  */
+int
+main_helper (void *arg)
+{
+  asm ("main_helper_label: .globl main_helper_label");
+  return 0;
+}
+
+int
+main (void)
+{
+  asm ("main_label: .globl main_label");
+  main_helper (0);
+  return 0;
+}

gdb/testsuite/gdb.dwarf2/fortran-var-string.exp

@@ -0,0 +1,175 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile .c -dw.S
+
+# We need to know the size of integer and address types in order
+# to write some of the debugging info we'd like to generate.
+#
+# For that, we ask GDB by debugging our dynarr-ptr.c program.
+# Any program would do, but since we already have dynarr-ptr.c
+# specifically for this testcase, might as well use that.
+
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
+    return -1
+}
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    set int_size [get_sizeof "int" 4]
+
+    get_func_info main
+    get_func_info main_helper
+
+    cu {} {
+	DW_TAG_compile_unit {
+                {DW_AT_language @DW_LANG_Fortran90}
+                {DW_AT_name     fortran-var-string.f90}
+                {DW_AT_comp_dir /tmp}
+        } {
+	    declare_labels integer_label string_label array_lb_label \
+		array_ub_label
+
+	    DW_TAG_subprogram {
+		{name main}
+		{low_pc $main_helper_start addr}
+		{high_pc $main_helper_len data8}
+		{DW_AT_type :$integer_label}
+		{DW_AT_decl_file 1 data1}
+		{DW_AT_decl_line 1 data1}
+	    }
+
+	    DW_TAG_subprogram {
+		{name test_1_func}
+		{low_pc $main_start addr}
+		{high_pc $main_len data8}
+		{DW_AT_type :$integer_label}
+		{DW_AT_decl_file 1 data1}
+		{DW_AT_decl_line 2 data1}
+	    } {
+		formal_parameter {
+		    {name arg1}
+		    {type :$string_label}
+		}
+	    }
+
+	    DW_TAG_subprogram {
+		{name test_2_func}
+		{low_pc $main_start addr}
+		{high_pc $main_len data8}
+		{DW_AT_type :$integer_label}
+		{DW_AT_decl_file 1 data1}
+		{DW_AT_decl_line 3 data1}
+	    } {
+		formal_parameter {
+		    {name arg1}
+		    {type :$array_ub_label}
+		}
+	    }
+
+	    DW_TAG_subprogram {
+		{name test_3_func}
+		{low_pc $main_start addr}
+		{high_pc $main_len data8}
+		{DW_AT_type :$integer_label}
+		{DW_AT_decl_file 1 data1}
+		{DW_AT_decl_line 4 data1}
+	    } {
+		formal_parameter {
+		    {name arg1}
+		    {type :$array_lb_label}
+		}
+	    }
+
+	    integer_label: DW_TAG_base_type {
+		{DW_AT_byte_size $int_size DW_FORM_sdata}
+		{DW_AT_encoding  @DW_ATE_signed}
+		{DW_AT_name      integer}
+	    }
+
+	    string_label: DW_TAG_string_type {
+		{DW_AT_byte_size $int_size DW_FORM_sdata}
+		{DW_AT_name      .str.arg}
+		{DW_AT_string_length {} DW_FORM_block1}
+	    }
+
+	    array_lb_label: DW_TAG_array_type {
+		{DW_AT_ordering 1 data1}
+		{DW_AT_type :$integer_label}
+	    } {
+		DW_TAG_subrange_type {
+		    {DW_AT_lower_bound {} DW_FORM_block1}
+		    {DW_AT_upper_bound 10 DW_FORM_data1}
+		}
+	    }
+
+	    array_ub_label: DW_TAG_array_type {
+		{DW_AT_ordering 1 data1}
+		{DW_AT_type :$integer_label}
+	    } {
+		DW_TAG_subrange_type {
+		    {DW_AT_upper_bound {} DW_FORM_block1}
+		}
+	    }
+	}
+    }
+}
+
+# Now that we've generated the DWARF debugging info, rebuild our
+# program using our debug info instead of the info generated by
+# the compiler.
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_test_no_output "set language fortran"
+
+gdb_test "info functions test_1_func" \
+    "2:\\s+integer test_1_func\\(character\\*\\(\\*\\)\\);"
+
+# We print `1` here as the bound because GDB treats this as an assumed
+# size array, and just reports the lower bound value for the upper
+# bound.
+#
+# We might, in the future, decide that there's a better way we could
+# tell the user about the type of this array argument, when that
+# happens it's OK to change the expected results here.
+gdb_test "info functions test_2_func" \
+    "3:\\s+integer test_2_func\\(integer \\(1\\)\\);"
+
+# It's not completely clear that this error is correct here.  Why
+# can't the lower bound be a dynamic expression?
+#
+# This test was initially added to guard against the case where GDB
+# was crashing if/when it saw this situation.
+#
+# If later on, GDB's handling of array types with a dynamic loewr
+# bound changes, then it is possible that the expected result here
+# should change.
+gdb_test "info functions test_3_func" \
+    "4:\\s+Lower bound may not be '\\*' in F77"