[PATCH v3 1/1] gdb: Fix assertion in 'value_primitive_field'

[Stephan Rohr <stephan.rohr@intel.com>]

From: "Rohr, Stephan" <stephan.rohr@intel.com>

GDB asserts that the data location of a value's field with a dynamic
data location is resolved when fetching the field's value in
'value_primitive_field'.  This assertion was hit because of bogus DWARF
generated by the Intel Fortran compiler.  While that compiler should fix
the DWARF, we prefer GDB to error out here instead, e.g. to allow the
user to continue debugging other parts of the program.
---
 .../locexpr-data-member-dynamic-location.c    |  32 +++++
 .../locexpr-data-member-dynamic-location.exp  | 129 ++++++++++++++++++
 gdb/value.c                                   |   4 +-
 3 files changed, 164 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.c
 create mode 100644 gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.exp

diff --git a/gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.c b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.c
new file mode 100644
index 00000000000..dbe591ab884
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.c
@@ -0,0 +1,32 @@
+/* Copyright 2024 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+struct container
+{
+  int *data;
+};
+
+int size = 5;
+
+int var_a_data[] = {5, 8, 13, 21, 34};
+struct container var_a = {var_a_data};
+
+int
+main (void)
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.exp b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.exp
new file mode 100644
index 00000000000..1dd2e91ffdd
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-dynamic-location.exp
@@ -0,0 +1,129 @@
+# Copyright 2024 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/>.
+#
+# Tests that GDB prints an error when fetching a value's (dynamic) field
+# with unresolved data location.  For a reproducer, we setup the following
+# struct type:
+#
+#   struct container
+#     {
+#       int *data;
+#     };
+#
+# We use a variable 'size' to define the upper bound 'DW_AT_upper_bound' for
+# the non-static field 'data'.  The error reproduces with invalid DWARF, i.e.
+# when pushing the memory location of an instance 'var_a' of struct
+# 'container' on the DWARF stack:
+#
+#   DW_AT_location {
+#     DW_OP_addr [gdb_target_symbol var_a]
+#     DW_OP_deref
+#     DW_OP_stack_value
+#   } SPECIAL_expr}
+
+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
+
+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 {
+    cu {} {
+	DW_TAG_compile_unit {} {
+	    declare_labels integer_label array_label struct_label var_a_label
+	    set int_size [get_sizeof "int" 4]
+	    set addr_size [get_sizeof "void *" 8]
+
+	    integer_label: DW_TAG_base_type {
+		{DW_AT_byte_size $int_size DW_FORM_sdata}
+		{DW_AT_encoding  @DW_ATE_signed}
+	    }
+
+	    array_label: DW_TAG_array_type {
+		{DW_AT_type :$integer_label}
+		{DW_AT_data_location {
+		    DW_OP_push_object_address
+		    DW_OP_deref
+		} SPECIAL_expr}
+	    } {
+		DW_TAG_subrange_type {
+		    {DW_AT_type :$integer_label}
+		    {DW_AT_upper_bound {
+			DW_OP_addr [gdb_target_symbol size]
+			DW_OP_deref
+			DW_OP_lit1
+			DW_OP_minus
+		    } SPECIAL_expr}
+		}
+	    }
+
+	    struct_label: DW_TAG_structure_type {
+		{DW_AT_byte_size 8 DW_FORM_udata}
+	    } {
+		DW_TAG_member {
+		    {DW_AT_name "data"}
+		    {DW_AT_type :${array_label}}
+		    {DW_AT_data_member_location 0 DW_FORM_udata}
+		}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name var_a_valid_location}
+		{DW_AT_type :$struct_label}
+		{DW_AT_location {
+		    DW_OP_addr [gdb_target_symbol var_a]
+		} SPECIAL_expr}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name var_a_invalid_location}
+		{DW_AT_type :$struct_label}
+		{DW_AT_location {
+		    DW_OP_addr [gdb_target_symbol var_a]
+		    DW_OP_deref
+		    DW_OP_stack_value
+		} SPECIAL_expr}
+	    }
+	}
+    }
+}
+
+# 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 "print var_a_valid_location" \
+	 " = \\{data = \\{5, 8, 13, 21, 34\\}\\}"
+
+gdb_test "print var_a_invalid_location" \
+	 " = \\{data = <error reading variable: cannot read data.*"
diff --git a/gdb/value.c b/gdb/value.c
index a2b2721d183..145e70074a9 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -3060,7 +3060,9 @@ value::primitive_field (LONGEST offset, int fieldno, struct type *arg_type)
 
       gdb_assert (0 == offset);
       /* We expect an already resolved data location.  */
-      gdb_assert (TYPE_DATA_LOCATION (type)->is_constant ());
+      if (!TYPE_DATA_LOCATION (type)->is_constant ())
+	error (_("cannot read %s, expected an already resolved data "
+		 "location."), arg_type->field (fieldno).name ());
       /* For dynamic data types defer memory allocation
 	 until we actual access the value.  */
       v = value::allocate_lazy (type);
-- 
2.34.1

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