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Handle DW_AT_encoding on DW_TAG_enumeration_type

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A user pointed out a problem when printing certain values from an Ada
enumeration type.  Investigation showed that the problem was that some
enumeration constants were emitted using DW_FORM_data1, and were
incorrectly sign-extended by gdb.

First, this is yet another instance of a general problem with DWARF.
See https://sourceware.org/bugzilla/show_bug.cgi?id=32680 for the
analysis.

Meanwhile, it turns out that GCC implements an extension to handle
this scenario.  In particular, in non-strict mode, it will emit
DW_AT_encoding using either DW_ATE_signed or DW_ATE_unsigned.  This
was done back in 2017 by Pierre-Marie, in support of Ada -- but then
somehow nothing was ever implemented on the gdb side.  For this see
GCC commit f76f096e ("DWARF: add DW_AT_encoding attributes for
DW_TAG_enumeration_type DIEs").

This patch adds the missing code to gdb.  The included test case shows
the bug that was originally reported.  I've also included the snippet
from Pierre-Marie's commit message for good measure.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32680
Approved-By: Andrew Burgess <aburgess@redhat.com>
This commit is contained in:
Tom Tromey 2026-05-07 12:08:40 -06:00
parent 5cb6772600
commit ebc3d2cc69
3 changed files with 387 additions and 0 deletions
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16
gdb/dwarf2/read.c
View file

@ -11024,6 +11024,22 @@ read_enumeration_type (struct die_info *die, struct dwarf2_cu *cu)
set_type_align (type, TYPE_RAW_ALIGN (underlying_type));
}
/* DW_AT_encoding on an enumeration type is a GCC extension. GCC
will only emit DW_ATE_signed or DW_ATE_unsigned here. If this is
seen, it provides a way to find the signed-ness without having to
guess based on the constants, which is somewhat fraught anyway
(see PR symtab/32680). */
if (!is_unsigned.has_value ())
{
attribute *encoding_attr = dwarf2_attr (die, DW_AT_encoding, cu);
if (encoding_attr != nullptr)
{
std::optional<ULONGEST> val = encoding_attr->unsigned_constant ();
if (val.has_value ())
is_unsigned = *val == DW_ATE_unsigned;
}
}
type->set_is_declared_class (dwarf2_flag_true_p (die, DW_AT_enum_class, cu));
type->set_endianity_is_not_default (die_byte_order (die, cu, nullptr));

40
gdb/testsuite/gdb.ada/enum-sign.exp Normal file
View file

@ -0,0 +1,40 @@
# 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/>.
load_lib "ada.exp"
require allow_ada_tests
standard_ada_testfile prog
if {[gdb_compile_ada "${srcfile}" "${binfile}" executable debug] != ""} {
return
}
clean_restart ${testfile}
set bp_location [gdb_get_line_number "STOP" ${testdir}/prog.adb]
runto "prog.adb:$bp_location"
for {set num 0} {$num <= 300} {incr num} {
gdb_test "print Value_$num" " = value_$num"
gdb_test "print Unsigned_Enumeration'Val($num)" " = value_$num"
gdb_test "print/d Unsigned_Enumeration'Val($num)" " = $num"
}
foreach {name dec} {se_a -1 se_b 0 se_c 1 se_d 2} {
gdb_test "print $name" " = $name"
gdb_test "print/d $name" " = $dec"
}

331
gdb/testsuite/gdb.ada/enum-sign/prog.adb Normal file
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@ -0,0 +1,331 @@
-- 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/>.
procedure Prog is
type Unsigned_Enumeration is
(
Value_0,
Value_1,
Value_2,
Value_3,
Value_4,
Value_5,
Value_6,
Value_7,
Value_8,
Value_9,
Value_10,
Value_11,
Value_12,
Value_13,
Value_14,
Value_15,
Value_16,
Value_17,
Value_18,
Value_19,
Value_20,
Value_21,
Value_22,
Value_23,
Value_24,
Value_25,
Value_26,
Value_27,
Value_28,
Value_29,
Value_30,
Value_31,
Value_32,
Value_33,
Value_34,
Value_35,
Value_36,
Value_37,
Value_38,
Value_39,
Value_40,
Value_41,
Value_42,
Value_43,
Value_44,
Value_45,
Value_46,
Value_47,
Value_48,
Value_49,
Value_50,
Value_51,
Value_52,
Value_53,
Value_54,
Value_55,
Value_56,
Value_57,
Value_58,
Value_59,
Value_60,
Value_61,
Value_62,
Value_63,
Value_64,
Value_65,
Value_66,
Value_67,
Value_68,
Value_69,
Value_70,
Value_71,
Value_72,
Value_73,
Value_74,
Value_75,
Value_76,
Value_77,
Value_78,
Value_79,
Value_80,
Value_81,
Value_82,
Value_83,
Value_84,
Value_85,
Value_86,
Value_87,
Value_88,
Value_89,
Value_90,
Value_91,
Value_92,
Value_93,
Value_94,
Value_95,
Value_96,
Value_97,
Value_98,
Value_99,
Value_100,
Value_101,
Value_102,
Value_103,
Value_104,
Value_105,
Value_106,
Value_107,
Value_108,
Value_109,
Value_110,
Value_111,
Value_112,
Value_113,
Value_114,
Value_115,
Value_116,
Value_117,
Value_118,
Value_119,
Value_120,
Value_121,
Value_122,
Value_123,
Value_124,
Value_125,
Value_126,
Value_127,
Value_128,
Value_129,
Value_130,
Value_131,
Value_132,
Value_133,
Value_134,
Value_135,
Value_136,
Value_137,
Value_138,
Value_139,
Value_140,
Value_141,
Value_142,
Value_143,
Value_144,
Value_145,
Value_146,
Value_147,
Value_148,
Value_149,
Value_150,
Value_151,
Value_152,
Value_153,
Value_154,
Value_155,
Value_156,
Value_157,
Value_158,
Value_159,
Value_160,
Value_161,
Value_162,
Value_163,
Value_164,
Value_165,
Value_166,
Value_167,
Value_168,
Value_169,
Value_170,
Value_171,
Value_172,
Value_173,
Value_174,
Value_175,
Value_176,
Value_177,
Value_178,
Value_179,
Value_180,
Value_181,
Value_182,
Value_183,
Value_184,
Value_185,
Value_186,
Value_187,
Value_188,
Value_189,
Value_190,
Value_191,
Value_192,
Value_193,
Value_194,
Value_195,
Value_196,
Value_197,
Value_198,
Value_199,
Value_200,
Value_201,
Value_202,
Value_203,
Value_204,
Value_205,
Value_206,
Value_207,
Value_208,
Value_209,
Value_210,
Value_211,
Value_212,
Value_213,
Value_214,
Value_215,
Value_216,
Value_217,
Value_218,
Value_219,
Value_220,
Value_221,
Value_222,
Value_223,
Value_224,
Value_225,
Value_226,
Value_227,
Value_228,
Value_229,
Value_230,
Value_231,
Value_232,
Value_233,
Value_234,
Value_235,
Value_236,
Value_237,
Value_238,
Value_239,
Value_240,
Value_241,
Value_242,
Value_243,
Value_244,
Value_245,
Value_246,
Value_247,
Value_248,
Value_249,
Value_250,
Value_251,
Value_252,
Value_253,
Value_254,
Value_255,
Value_256,
Value_257,
Value_258,
Value_259,
Value_260,
Value_261,
Value_262,
Value_263,
Value_264,
Value_265,
Value_266,
Value_267,
Value_268,
Value_269,
Value_270,
Value_271,
Value_272,
Value_273,
Value_274,
Value_275,
Value_276,
Value_277,
Value_278,
Value_279,
Value_280,
Value_281,
Value_282,
Value_283,
Value_284,
Value_285,
Value_286,
Value_287,
Value_288,
Value_289,
Value_290,
Value_291,
Value_292,
Value_293,
Value_294,
Value_295,
Value_296,
Value_297,
Value_298,
Value_299,
Value_300
);
X : Unsigned_Enumeration := Value_23;
type Signed_Enumeration is ( SE_A, SE_B, SE_C, SE_D);
for Signed_Enumeration use (-1, 0, 1, 2);
Y : Signed_Enumeration := SE_D;
begin
null; -- STOP
end;