Handle bit offset and bit size in base types

PR symtab/25470 points out that the Zig programming language allows
integers of various bit sizes (including zero), not just sizes that
are a multiple of 8.

This is supported in DWARF by applying both a byte size and a
DW_AT_bit_size.

This patch adds support for this feature to integer and boolean types.
Other base types are not handled -- for floating-point types, this
didn't seem to make sense, and for character types I didn't see much
need.  (These can be added later if desired.)

I've also added support for DW_AT_data_bit_offset at the same time.  I
don't know whether the Zig compiler requires this, but it was
described in the same section in the DWARF standard and was easy to
add.

A new test case is supplied, using the DWARF assembler.

gdb/ChangeLog
2020-09-23  Tom Tromey  <tom@tromey.com>

	PR symtab/25470:
	* value.c (unpack_long, pack_long, pack_unsigned_long): Handle bit
	offset and bit size.
	* printcmd.c (print_scalar_formatted): Handle zero-length
	integer.
	(print_scalar_formatted): Use bit_size_differs_p.
	* gdbtypes.h (enum type_specific_kind) <TYPE_SPECIFIC_INT>: New
	constant.
	(union type_specific): <int_stuff>: New member.
	(struct type) <bit_size_differs_p, bit_size, bit_offset>: New
	methods.
	* gdbtypes.c (init_integer_type, init_boolean_type): Initialize
	TYPE_SPECIFIC_FIELD.
	(recursive_dump_type, copy_type_recursive): Update.
	* dwarf2/read.c (read_base_type): Handle DW_AT_bit_size and
	DW_AT_data_bit_offset.

gdb/testsuite/ChangeLog
2020-09-23  Tom Tromey  <tom@tromey.com>

	* gdb.dwarf2/intbits.exp: New file.
	* gdb.dwarf2/intbits.c: New file.

1 files changed, 201 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/intbits.exp b/gdb/testsuite/gdb.dwarf2/intbits.exp
new file mode 100644
index 0000000..3118018
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/intbits.exp
@@ -0,0 +1,201 @@
+# Copyright 2020 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 support for non-byte-sized integer base types.
+
+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 .S
+
+set executable ${testfile}
+set asm_file [standard_output_file ${srcfile2}]
+
+if [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] {
+    return -1
+}
+
+# Create the DWARF.
+Dwarf::assemble ${asm_file} {
+    cu {} {
+	DW_TAG_compile_unit {
+	    {DW_AT_language @DW_LANG_C_plus_plus}
+	} {
+	    declare_labels i7_type u1_type u17_type u31_type \
+		u31_1_type u32_0_type u0_0_type be30_1_type
+
+	    i7_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_signed}
+		{DW_AT_endianity @DW_END_little}
+		{DW_AT_name "i7"}
+		{DW_AT_byte_size 2 DW_FORM_udata}
+		{DW_AT_bit_size 7 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_i16_m1"}
+		{DW_AT_type :${i7_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "i16_m1"]}
+		    SPECIAL_expr}
+	    }
+
+	    u1_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_boolean}
+		{DW_AT_endianity @DW_END_little}
+		{DW_AT_name "u1"}
+		{DW_AT_byte_size 2 DW_FORM_udata}
+		{DW_AT_bit_size 1 DW_FORM_udata}
+		{DW_AT_data_bit_offset 2 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_u16_1"}
+		{DW_AT_type :${u1_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "u16_1"]}
+		    SPECIAL_expr}
+	    }
+
+	    u17_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_signed}
+		{DW_AT_endianity @DW_END_little}
+		{DW_AT_name "u17"}
+		{DW_AT_byte_size 4 DW_FORM_udata}
+		{DW_AT_bit_size 17 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_u32_m2"}
+		{DW_AT_type :${u17_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "u32_m2"]}
+		    SPECIAL_expr}
+	    }
+
+	    u31_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_unsigned}
+		{DW_AT_endianity @DW_END_little}
+		{DW_AT_name "u31"}
+		{DW_AT_byte_size 4 DW_FORM_udata}
+		{DW_AT_bit_size 31 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_u32_1"}
+		{DW_AT_type :${u31_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "u32_1"]}
+		    SPECIAL_expr}
+	    }
+
+	    u31_1_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_unsigned}
+		{DW_AT_endianity @DW_END_little}
+		{DW_AT_name "u31_1"}
+		{DW_AT_byte_size 4 DW_FORM_udata}
+		{DW_AT_bit_size 31 DW_FORM_udata}
+		{DW_AT_data_bit_offset 1 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_u32_1_off"}
+		{DW_AT_type :${u31_1_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "u32_1_off"]}
+		    SPECIAL_expr}
+	    }
+
+	    be30_1_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_unsigned}
+		{DW_AT_endianity @DW_END_big}
+		{DW_AT_name "be30_1"}
+		{DW_AT_byte_size 4 DW_FORM_udata}
+		{DW_AT_bit_size 30 DW_FORM_udata}
+		{DW_AT_data_bit_offset 1 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_be30_1_off"}
+		{DW_AT_type :${be30_1_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "be30_1_off"]}
+		    SPECIAL_expr}
+	    }
+
+	    u32_0_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_unsigned}
+		{DW_AT_endianity @DW_END_little}
+		{DW_AT_name "u32_0"}
+		{DW_AT_byte_size 4 DW_FORM_udata}
+		{DW_AT_bit_size 0 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_u32_0"}
+		{DW_AT_type :${u32_0_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "u32_0"]}
+		    SPECIAL_expr}
+	    }
+
+	    u0_0_type: DW_TAG_base_type {
+		{DW_AT_encoding @DW_ATE_unsigned}
+		{DW_AT_endianity @DW_END_little}
+		{DW_AT_name "u0_0"}
+		{DW_AT_byte_size 0 DW_FORM_udata}
+	    }
+
+	    DW_TAG_variable {
+		{DW_AT_name "v_u0_0"}
+		{DW_AT_type :${u0_0_type}}
+		{DW_AT_external 1 DW_FORM_flag}
+		{DW_AT_location {DW_OP_addr [gdb_target_symbol "u32_0"]}
+		    SPECIAL_expr}
+	    }
+	}
+    }
+}
+
+if {[prepare_for_testing "failed to prepare" ${executable} \
+	 [list ${asm_file} ${srcfile}] {}]} {
+    return -1
+}
+
+if {![runto_main]} {
+    return -1
+}
+
+gdb_test "print v_i16_m1" "= -1"
+gdb_test "print v_u16_1" "= true"
+gdb_test "print v_u32_m2" "= -2"
+gdb_test "print v_u32_1" "= 1"
+gdb_test "print v_u32_0" "= 0"
+gdb_test "print v_u0_0" "= 0"
+
+gdb_test "print v_i16_m1 = 7" "= 7"
+gdb_test "print v_i16_m1" "= 7" "print v_i16_m1 after assignment"
+
+gdb_test "print v_u32_1_off" "= 1"
+gdb_test "print v_u32_1_off = 7" " = 7"
+gdb_test "x/4xb &v_u32_1_off" ":\t0x0e\t0x00\t0x00\t0x00"
+
+gdb_test "print v_be30_1_off" "= 1"
+gdb_test "print v_be30_1_off = 7" " = 7"
+gdb_test "x/4xb &v_be30_1_off" ":\t0x00\t0x00\t0x00\t0x0e"