[PATCH] Handle bit offset and bit size in base types
Tom Tromey
tom@tromey.com
Mon Aug 17 02:04:36 GMT 2020
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
2020-08-16 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
2020-08-16 Tom Tromey <tom@tromey.com>
* gdb.dwarf2/intbits.exp: New file.
* gdb.dwarf2/intbits.c: New file.
---
gdb/ChangeLog | 19 +++
gdb/dwarf2/read.c | 20 +++
gdb/gdbtypes.c | 24 ++++
gdb/gdbtypes.h | 43 +++++-
gdb/printcmd.c | 16 ++-
gdb/testsuite/ChangeLog | 5 +
gdb/testsuite/gdb.dwarf2/intbits.c | 48 +++++++
gdb/testsuite/gdb.dwarf2/intbits.exp | 201 +++++++++++++++++++++++++++
gdb/value.c | 37 ++++-
9 files changed, 406 insertions(+), 7 deletions(-)
create mode 100644 gdb/testsuite/gdb.dwarf2/intbits.c
create mode 100644 gdb/testsuite/gdb.dwarf2/intbits.exp
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 0ac8533263a..873bc240a99 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -18060,6 +18060,26 @@ read_base_type (struct die_info *die, struct dwarf2_cu *cu)
TYPE_ENDIANITY_NOT_DEFAULT (type) = gdbarch_byte_order (arch) != byte_order;
+ if (TYPE_SPECIFIC_FIELD (type) == TYPE_SPECIFIC_INT)
+ {
+ attr = dwarf2_attr (die, DW_AT_bit_size, cu);
+ if (attr != nullptr && DW_UNSND (attr) <= 8 * TYPE_LENGTH (type))
+ {
+ unsigned real_bit_size = DW_UNSND (attr);
+ attr = dwarf2_attr (die, DW_AT_data_bit_offset, cu);
+ /* Only use the attributes if they make sense together. */
+ if (attr == nullptr
+ || DW_UNSND (attr) + real_bit_size <= 8 * TYPE_LENGTH (type))
+ {
+ TYPE_MAIN_TYPE (type)->type_specific.int_stuff.bit_size
+ = real_bit_size;
+ if (attr != nullptr)
+ TYPE_MAIN_TYPE (type)->type_specific.int_stuff.bit_offset
+ = DW_UNSND (attr);
+ }
+ }
+ }
+
return set_die_type (die, type, cu);
}
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index da1c58c65c1..1764e1c60b4 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -3189,6 +3189,10 @@ init_integer_type (struct objfile *objfile,
if (unsigned_p)
TYPE_UNSIGNED (t) = 1;
+ TYPE_SPECIFIC_FIELD (t) = TYPE_SPECIFIC_INT;
+ TYPE_MAIN_TYPE (t)->type_specific.int_stuff.bit_size = bit;
+ TYPE_MAIN_TYPE (t)->type_specific.int_stuff.bit_offset = 0;
+
return t;
}
@@ -3223,6 +3227,10 @@ init_boolean_type (struct objfile *objfile,
if (unsigned_p)
TYPE_UNSIGNED (t) = 1;
+ TYPE_SPECIFIC_FIELD (t) = TYPE_SPECIFIC_INT;
+ TYPE_MAIN_TYPE (t)->type_specific.int_stuff.bit_size = bit;
+ TYPE_MAIN_TYPE (t)->type_specific.int_stuff.bit_offset = 0;
+
return t;
}
@@ -5162,6 +5170,16 @@ recursive_dump_type (struct type *type, int spaces)
gdb_print_host_address (TYPE_SELF_TYPE (type), gdb_stdout);
puts_filtered ("\n");
break;
+
+ case TYPE_SPECIFIC_INT:
+ if (type->bit_size_differs_p ())
+ {
+ unsigned bit_size = type->bit_size ();
+ unsigned bit_off = type->bit_offset ();
+ printfi_filtered (spaces, " bit size = %u, bit offset = %u\n",
+ bit_size, bit_off);
+ }
+ break;
}
if (spaces == 0)
@@ -5385,6 +5403,12 @@ copy_type_recursive (struct objfile *objfile,
copy_type_recursive (objfile, TYPE_SELF_TYPE (type),
copied_types));
break;
+ case TYPE_SPECIFIC_INT:
+ TYPE_SPECIFIC_FIELD (new_type) = TYPE_SPECIFIC_INT;
+ TYPE_MAIN_TYPE (new_type)->type_specific.int_stuff
+ = TYPE_MAIN_TYPE (type)->type_specific.int_stuff;
+ break;
+
default:
gdb_assert_not_reached ("bad type_specific_kind");
}
diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index 55a6dafb7e2..d779c803cc9 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -673,7 +673,8 @@ enum type_specific_kind
TYPE_SPECIFIC_FLOATFORMAT,
/* Note: This is used by TYPE_CODE_FUNC and TYPE_CODE_METHOD. */
TYPE_SPECIFIC_FUNC,
- TYPE_SPECIFIC_SELF_TYPE
+ TYPE_SPECIFIC_SELF_TYPE,
+ TYPE_SPECIFIC_INT
};
union type_owner
@@ -838,6 +839,21 @@ union type_specific
is a member of. */
struct type *self_type;
+
+ /* * An integer-like scalar type may be stored in just part of its
+ enclosing storage bytes. This structure describes this
+ situation. */
+ struct
+ {
+ /* * The bit size of the integer. This can be 0. For integers
+ that fill their storage (the ordinary case), this field holds
+ the byte size times 8. */
+ unsigned short bit_size;
+ /* * The bit offset of the integer. This is ordinarily 0, and can
+ only be non-zero if the bit size is less than the storage
+ size. */
+ unsigned short bit_offset;
+ } int_stuff;
};
/* * Main structure representing a type in GDB.
@@ -1081,6 +1097,31 @@ struct type
/* * Remove dynamic property of kind KIND from this type, if it exists. */
void remove_dyn_prop (dynamic_prop_node_kind kind);
+ /* * Return true if this is an integer type whose logical (bit) size
+ differs from its storage size; false otherwise. Always return
+ false for non-integer (i.e., non-TYPE_SPECIFIC_INT) types. */
+ bool bit_size_differs_p () const
+ {
+ return (main_type->type_specific_field == TYPE_SPECIFIC_INT
+ && main_type->type_specific.int_stuff.bit_size != 8 * length);
+ }
+
+ /* * Return the logical (bit) size for this integer type. Only
+ valid for integer (TYPE_SPECIFIC_INT) types. */
+ unsigned short bit_size () const
+ {
+ gdb_assert (main_type->type_specific_field == TYPE_SPECIFIC_INT);
+ return main_type->type_specific.int_stuff.bit_size;
+ }
+
+ /* * Return the bit offset for this integer type. Only valid for
+ integer (TYPE_SPECIFIC_INT) types. */
+ unsigned short bit_offset () const
+ {
+ gdb_assert (main_type->type_specific_field == TYPE_SPECIFIC_INT);
+ return main_type->type_specific.int_stuff.bit_offset;
+ }
+
/* * Type that is a pointer to this type.
NULL if no such pointer-to type is known yet.
The debugger may add the address of such a type
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 309d2cabfff..fede8a08151 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -374,6 +374,15 @@ print_scalar_formatted (const gdb_byte *valaddr, struct type *type,
valaddr += TYPE_LENGTH (type) - len;
}
+ /* Allow LEN == 0, and in this case, don't assume that VALADDR is
+ valid. */
+ const gdb_byte zero = 0;
+ if (len == 0)
+ {
+ len = 1;
+ valaddr = &zero;
+ }
+
if (size != 0 && (options->format == 'x' || options->format == 't'))
{
/* Truncate to fit. */
@@ -404,8 +413,8 @@ print_scalar_formatted (const gdb_byte *valaddr, struct type *type,
long, and then printing the long. PR cli/16242 suggests changing
this to using C-style hex float format.
- Biased range types must also be unbiased here; the unbiasing is
- done by unpack_long. */
+ Biased range types and sub-word scalar types must also be handled
+ here; the value is correctly computed by unpack_long. */
gdb::byte_vector converted_bytes;
/* Some cases below will unpack the value again. In the biased
range case, we want to avoid this, so we store the unpacked value
@@ -418,7 +427,8 @@ print_scalar_formatted (const gdb_byte *valaddr, struct type *type,
|| options->format == 'z'
|| options->format == 'd'
|| options->format == 'u'))
- || (type->code () == TYPE_CODE_RANGE && type->bounds ()->bias != 0))
+ || (type->code () == TYPE_CODE_RANGE && type->bounds ()->bias != 0)
+ || type->bit_size_differs_p ())
{
val_long.emplace (unpack_long (type, valaddr));
converted_bytes.resize (TYPE_LENGTH (type));
diff --git a/gdb/testsuite/gdb.dwarf2/intbits.c b/gdb/testsuite/gdb.dwarf2/intbits.c
new file mode 100644
index 00000000000..72b70d40903
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/intbits.c
@@ -0,0 +1,48 @@
+/* Copyright (C) 2020 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/>. */
+
+/* A 16 bit slot holding a 7-bit value of -1. Note that, for all
+ these values, we explicitly set the endian-ness in the DWARF to
+ avoid issues. */
+unsigned char i16_m1[2] = { 0x7f, 0 };
+
+/* A 16 bit slot holding a 1-bit value of 1 at offset 2. */
+unsigned char u16_1[2] = { 0x4, 0 };
+
+/* A 32 bit slot holding a 17-bit value of -2. */
+unsigned char u32_m2[4] = { 0xfe, 0xff, 0x01, 0 };
+
+/* A 32 bit slot holding a 31 bit value of 1. The high bit should be
+ ignored when reading. */
+unsigned char u32_1[4] = { 1, 0, 0, 0x80 };
+
+/* A 32 bit slot holding a 31 bit value of 1, offset by 1 bit. */
+unsigned char u32_1_off[4] = { 2, 0, 0, 0 };
+
+/* A 32 bit slot holding a 30 bit value of 1, offset by 1 bit.
+ Big-endian. */
+unsigned char be30_1_off[4] = { 0x80, 0, 0, 2 };
+
+/* A 32 bit slot holding a 0 bit value. We don't use 0 in the array
+ here, to catch any situation where gdb tries to use the memory. */
+unsigned char u32_0[4] = { 0xff, 0xff, 0xff, 0xff };
+
+int
+main (void)
+{
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.dwarf2/intbits.exp b/gdb/testsuite/gdb.dwarf2/intbits.exp
new file mode 100644
index 00000000000..311801869e9
--- /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"
diff --git a/gdb/value.c b/gdb/value.c
index a6e21309f85..1819e50d639 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -2776,10 +2776,27 @@ unpack_long (struct type *type, const gdb_byte *valaddr)
case TYPE_CODE_MEMBERPTR:
{
LONGEST result;
- if (nosign)
- result = extract_unsigned_integer (valaddr, len, byte_order);
+
+ if (type->bit_size_differs_p ())
+ {
+ unsigned bit_off = type->bit_offset ();
+ unsigned bit_size = type->bit_size ();
+ if (bit_size == 0)
+ {
+ /* unpack_bits_as_long doesn't handle this case the
+ way we'd like, so handle it here. */
+ result = 0;
+ }
+ else
+ result = unpack_bits_as_long (type, valaddr, bit_off, bit_size);
+ }
else
- result = extract_signed_integer (valaddr, len, byte_order);
+ {
+ if (nosign)
+ result = extract_unsigned_integer (valaddr, len, byte_order);
+ else
+ result = extract_signed_integer (valaddr, len, byte_order);
+ }
if (code == TYPE_CODE_RANGE)
result += type->bounds ()->bias;
return result;
@@ -3339,6 +3356,13 @@ pack_long (gdb_byte *buf, struct type *type, LONGEST num)
case TYPE_CODE_FLAGS:
case TYPE_CODE_BOOL:
case TYPE_CODE_MEMBERPTR:
+ if (type->bit_size_differs_p ())
+ {
+ unsigned bit_off = type->bit_offset ();
+ unsigned bit_size = type->bit_size ();
+ num &= ((ULONGEST) 1 << bit_size) - 1;
+ num <<= bit_off;
+ }
store_signed_integer (buf, len, byte_order, num);
break;
@@ -3381,6 +3405,13 @@ pack_unsigned_long (gdb_byte *buf, struct type *type, ULONGEST num)
case TYPE_CODE_BOOL:
case TYPE_CODE_RANGE:
case TYPE_CODE_MEMBERPTR:
+ if (type->bit_size_differs_p ())
+ {
+ unsigned bit_off = type->bit_offset ();
+ unsigned bit_size = type->bit_size ();
+ num &= ((ULONGEST) 1 << bit_size) - 1;
+ num <<= bit_off;
+ }
store_unsigned_integer (buf, len, byte_order, num);
break;
--
2.17.2
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