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Handle bit offset and bit size in base types

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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.
This commit is contained in:
Tom Tromey
2020-09-23 09:39:24 -06:00
parent bac51ab78d
commit 20a5fcbd5b
9 changed files with 406 additions and 7 deletions
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43
gdb/gdbtypes.h
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@ -599,7 +599,8 @@ 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
@ -764,6 +765,21 @@ 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.
@ -1182,6 +1198,31 @@ 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