Fix dynamic type resolution for LOC_CONST and LOC_CONST_BYTES symbols

PR rust/31005 points out that dynamic type resolution of a LOC_CONST
or LOC_CONST_BYTES symbol will fail, leading to output like:

    from_index=<error reading variable: Cannot access memory at address 0x0>

This patch fixes the problem by using the constant value or bytes when
performing type resolution.

Thanks to tpzker@thepuzzlemaker.info for a first version of this
patch.

I also tested this on a big-endian PPC system (cfarm203).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31005

diff --git a/gdb/findvar.c b/gdb/findvar.c
index 952ec20c0b73b6eef56d9204d2531506935a0702..02b4a12970b3d3176655051b702418d62b6714f6 100644 (file)
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -534,8 +534,16 @@ language_defn::read_var_value (struct symbol *var,
     case LOC_CONST:
       if (is_dynamic_type (type))
        {
-         /* Value is a constant byte-sequence and needs no memory access.  */
-         type = resolve_dynamic_type (type, {}, /* Unused address.  */ 0);
+         gdb_byte bytes[sizeof (LONGEST)];
+
+         size_t len = std::min (sizeof (LONGEST), (size_t) type->length ());
+         store_unsigned_integer (bytes, len,
+                                 type_byte_order (type),
+                                 var->value_longest ());
+         gdb::array_view<const gdb_byte> view (bytes, len);
+
+         /* Value is a constant byte-sequence.  */
+         type = resolve_dynamic_type (type, view, /* Unused address.  */ 0);
        }
       /* Put the constant back in target format. */
       v = value::allocate (type);
@@ -575,8 +583,11 @@ language_defn::read_var_value (struct symbol *var,
     case LOC_CONST_BYTES:
       if (is_dynamic_type (type))
        {
-         /* Value is a constant byte-sequence and needs no memory access.  */
-         type = resolve_dynamic_type (type, {}, /* Unused address.  */ 0);
+         gdb::array_view<const gdb_byte> view (var->value_bytes (),
+                                               type->length ());
+
+         /* Value is a constant byte-sequence.  */
+         type = resolve_dynamic_type (type, view, /* Unused address.  */ 0);
        }
       v = value::allocate (type);
       memcpy (v->contents_raw ().data (), var->value_bytes (),

diff --git a/gdb/testsuite/gdb.dwarf2/rust-enum.exp b/gdb/testsuite/gdb.dwarf2/rust-enum.exp
new file mode 100644 (file)
index 0000000..a052c11
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/rust-enum.exp
@@ -0,0 +1,120 @@
+# Copyright 2023 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.
+require dwarf2_support
+
+standard_testfile main.c -dw.S
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    upvar cu_lang cu_lang
+
+    declare_labels uinteger_label discr_1_label
+    declare_labels one_label two_label simple_label
+
+    cu { addr_size 4 } {
+       compile_unit {
+           {name file1.txt}
+           {language @DW_LANG_Rust}
+       } {
+           uinteger_label: DW_TAG_base_type {
+               {DW_AT_byte_size 1 DW_FORM_sdata}
+               {DW_AT_encoding  @DW_ATE_unsigned}
+               {DW_AT_name      {unsigned integer}}
+           }
+
+           one_label: structure_type {
+               {name One}
+               {byte_size 1 DW_FORM_sdata}
+           } {
+               member {
+                   {name __0}
+                   {type :$uinteger_label}
+                   {data_member_location 0 data1}
+               }
+           }
+
+           two_label: structure_type {
+               {name Two}
+               {byte_size 1 DW_FORM_sdata}
+           } {
+               member {
+                   {name __0}
+                   {type :$uinteger_label}
+                   {data_member_location 0 data1}
+               }
+           }
+
+           simple_label: structure_type {
+               {name Simple}
+               {byte_size 2 DW_FORM_sdata}
+           } {
+               variant_part {
+                   {discr :$discr_1_label DW_FORM_ref4}
+               } {
+                   discr_1_label: member {
+                       {type :$uinteger_label}
+                       {data_member_location 0 data1}
+                       {artificial 1 DW_FORM_flag_present}
+                   }
+
+                   variant {
+                       {discr_value 65 udata}
+                   } {
+                       member {
+                           {type :$one_label}
+                           {data_member_location 1 data1}
+                       }
+                   }
+
+                   variant {
+                   } {
+                       member {
+                           {type :$two_label}
+                           {data_member_location 1 data1}
+                       }
+                   }
+               }
+           }
+
+           # In PR rust/31005, a constant Rust enum value could not
+           # be correctly resolved.
+           DW_TAG_variable {
+               {name constant_variable}
+               {const_value 0x4141 udata}
+               {type :$simple_label}
+           }
+           DW_TAG_variable {
+               {name constant_variable2}
+               {const_value "AA" DW_FORM_block1}
+               {type :$simple_label}
+           }
+       }
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+         [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+gdb_test_no_output "set language rust"
+
+gdb_test "print constant_variable" [string_to_regexp "One(65)"]
+gdb_test "print constant_variable2" [string_to_regexp "One(65)"]