[PATCH] gdb: Preserve the operand type in DW_OP_plus_uconst

[PATCH] gdb: Preserve the operand type in DW_OP_plus_uconst

[Jielun Wu]

DWARF v5 requires DW_OP_plus_uconst to interpret its unsigned LEB128
constant as the type of the popped stack entry and push a result of that
same type.  GDB instead reconstructs the result using address_type,
discarding an explicit base type.

Construct the result using the popped value's type.

Add a DWARF assembler test that uses a typed value after
DW_OP_plus_uconst in another typed arithmetic operation.  Without the
fix, the expression fails with incompatible DWARF stack types.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34315
Signed-off-by: Jielun Wu <firmiana402@gmail.com>
---
 gdb/dwarf2/expr.c                             |  2 +-
 .../gdb.dwarf2/dw2-plus-uconst-type.exp       | 75 +++++++++++++++++++
 2 files changed, 76 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.dwarf2/dw2-plus-uconst-type.exp

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 3a6b8f58199..2d9408a3a27 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -2063,7 +2063,7 @@ dwarf_expr_context::execute_stack_op (gdb::array_view<const gdb_byte> expr)
 		result = value_as_long (result_val);
 		op_ptr = safe_read_uleb128 (op_ptr, op_end, &reg);
 		result += reg;
-		result_val = value_from_ulongest (address_type, result);
+		result_val = value_from_ulongest (result_val->type (), result);
 		break;
 	      }
 	  }
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-plus-uconst-type.exp b/gdb/testsuite/gdb.dwarf2/dw2-plus-uconst-type.exp
new file mode 100644
index 00000000000..224324798c6
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-plus-uconst-type.exp
@@ -0,0 +1,75 @@
+# Copyright 2026 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/>.
+
+# Test that DW_OP_plus_uconst preserves the type of the popped stack value.
+# A following DW_OP_plus checks this: it reports an error if the intermediate
+# result and the second explicitly typed value have incompatible types.
+
+load_lib dwarf.exp
+
+require dwarf2_support
+
+standard_testfile main.c -dw.S
+
+set asm_file [standard_output_file $srcfile2]
+
+Dwarf::assemble $asm_file {
+    cu {version 5} {
+	compile_unit {} {
+	    declare_labels uint32_label
+
+	    uint32_label: base_type {
+		DW_AT_name "uint32_t"
+		DW_AT_encoding @DW_ATE_unsigned
+		DW_AT_byte_size 4 DW_FORM_sdata
+	    }
+
+	    DW_TAG_variable {
+		DW_AT_name "plus_uconst_preserves_type"
+		DW_AT_type :$uint32_label
+		DW_AT_external 1 DW_FORM_flag
+		DW_AT_location {
+		    variable _constants
+		    variable _cu_label
+
+		    _op .byte $_constants(DW_OP_const_type)
+		    _op .uleb128 "$uint32_label - $_cu_label" \
+			"base type DIE offset"
+		    _op .byte 4 "constant size"
+		    _op .4byte 40 "constant data"
+		    DW_OP_plus_uconst 1
+		    _op .byte $_constants(DW_OP_const_type)
+		    _op .uleb128 "$uint32_label - $_cu_label" \
+			"base type DIE offset"
+		    _op .byte 4 "constant size"
+		    _op .4byte 1 "constant data"
+		    DW_OP_plus
+		    DW_OP_stack_value
+		} SPECIAL_expr
+	    }
+	}
+    }
+}
+
+if {[prepare_for_testing "failed to prepare" ${testfile} \
+	 [list $srcfile $asm_file] nodebug]} {
+    return
+}
+
+if {![runto_main]} {
+    return
+}
+
+gdb_test "print plus_uconst_preserves_type" " = 42"
-- 
2.34.1