binutils-gdb/gdb/testsuite/gdb.dwarf2/variant.exp
Tom Tromey 2ddeaf8a7d Handle DW_TAG_variant_part and DW_TAG_variant
This changes dwarf2read to understand DW_TAG_variant_part and
DW_TAG_variant.

Note that DW_AT_discr_list is not handled.  I did not need this for
Rust.  I imagine this should not be too hard to add later, should
someone need it.  Meanwhile I have gdb emit a complaint if it is seen.

There is a lurking issue concerning the placement of the discriminant
in the DWARF.  For Rust, I ended up following the letter of the
standard and having the discriminant be a child of the
DW_TAG_variant_part.  However, GCC's Ada support does not do this.
Pierre-Marie filed this with the DWARF committee:

    http://dwarfstd.org/ShowIssue.php?issue=180123.1

However as that is read-only, if you have comments you might consider
adding them to the GCC bug:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83935

Finally, there is a DWARF extension lurking in here.  In Rust, a
univariant enum will not have a discriminant.  However, in order to
unify the representation of all data-carrying enums, I've made LLVM
(and my forthcoming rustc patch) emit a univariant enum using a
DW_TAG_variant with a single variant part and without DW_AT_discr.
The lack of this DW_AT_discr is the extension.  I will submit an issue
on dwarfstd.org about this.

2018-02-26  Tom Tromey  <tom@tromey.com>

	* dwarf2read.c (struct variant_field): New.
	(struct nextfield) <variant>: New field.
	(dwarf2_add_field): Handle DW_TAG_variant_part.
	(dwarf2_attach_fields_to_type): Attach a discriminant_info to a
	discriminated union.
	(read_structure_type): Handle DW_TAG_variant_part.
	(handle_struct_member_die): New function, extracted from
	process_structure_scope.  Handle DW_TAG_variant.
	(process_structure_scope): Handle discriminated unions.  Call
	handle_struct_member_die.

2018-02-26  Tom Tromey  <tom@tromey.com>

	* gdb.dwarf2/variant.c: New file.
	* gdb.dwarf2/variant.exp: New file.
2018-02-26 09:21:08 -07:00

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# Copyright 2018 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 DW_TAG_variant_part and DW_TAG_variant.
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 variant.S
# Make some DWARF for the test.
set asm_file [standard_output_file $srcfile2]
Dwarf::assemble $asm_file {
upvar cu_lang cu_lang
declare_labels uinteger_label float_label int8_label
declare_labels discr_1_label discr_2_label discr_3_label
declare_labels one_label two_label
# Creating a CU with 4-byte addresses lets this test link on
# both 32- and 64-bit machines.
cu { addr_size 4 } {
compile_unit {
{name file1.txt}
{language @DW_LANG_Rust}
} {
uinteger_label: DW_TAG_base_type {
{DW_AT_byte_size 4 DW_FORM_sdata}
{DW_AT_encoding @DW_ATE_unsigned}
{DW_AT_name {unsigned integer}}
}
int8_label: DW_TAG_base_type {
{DW_AT_byte_size 1 DW_FORM_sdata}
{DW_AT_encoding @DW_ATE_signed}
{DW_AT_name i8}
}
float_label: base_type {
{name float}
{encoding @DW_ATE_float}
{byte_size 4 DW_FORM_sdata}
}
one_label: structure_type {
{name One}
{byte_size 4 DW_FORM_sdata}
} {
member {
{name __0}
{type :$uinteger_label}
{data_member_location 0 data1}
}
}
two_label: structure_type {
{name Two}
{byte_size 4 DW_FORM_sdata}
} {
member {
{name __0}
{type :$float_label}
{data_member_location 0 data1}
}
}
structure_type {
{name Simple}
{byte_size 8 DW_FORM_sdata}
} {
variant_part {
{discr :$discr_1_label DW_FORM_ref4}
} {
discr_1_label: member {
{type :$uinteger_label}
{data_member_location 0 data1}
}
variant {
{discr_value 23 udata}
} {
member {
{type :$one_label}
{data_member_location 4 data1}
}
}
variant {
{discr_value 1 udata}
} {
member {
{type :$two_label}
{data_member_location 4 data1}
}
}
}
}
structure_type {
{name Defaulted}
{byte_size 8 DW_FORM_sdata}
} {
variant_part {
{discr :$discr_2_label DW_FORM_ref4}
} {
discr_2_label: member {
{type :$uinteger_label}
{data_member_location 0 data1}
}
variant {
} {
member {
{type :$one_label}
{data_member_location 4 data1}
}
}
variant {
{discr_value 1 udata}
} {
member {
{type :$two_label}
{data_member_location 4 data1}
}
}
}
}
structure_type {
{name Univariant}
{byte_size 8 DW_FORM_sdata}
} {
variant_part {
} {
variant {
} {
member {
{type :$one_label}
{data_member_location 4 data1}
}
}
}
}
# Rust won't emit a negative discriminant like this, but
# we want to test the code path anyway.
structure_type {
{name Negative}
{byte_size 8 DW_FORM_sdata}
} {
variant_part {
{discr :$discr_3_label DW_FORM_ref4}
} {
discr_3_label: member {
{type :$int8_label}
{data_member_location 0 data1}
}
variant {
{discr_value -1 sdata}
} {
member {
{type :$one_label}
{data_member_location 4 data1}
}
}
# Make this the default value so we'll see an
# incorrect result if we mishandle signed
# discriminants.
variant {
} {
member {
{type :$two_label}
{data_member_location 4 data1}
}
}
}
}
}
}
}
if { [prepare_for_testing "failed to prepare" ${testfile} \
[list $srcfile $asm_file] debug] } {
return -1
}
if ![runto func] {
return -1
}
# Get the values into history so we can use it from Rust.
gdb_test "print (void *) buffer" "\\\$1 = .void .. $hex .buffer."
gdb_test "print (void *) buffer2" "\\\$2 = .void .. $hex .buffer2."
gdb_test "set language rust"
gdb_test "print *(\$1 as *mut Simple)" " = One\\(23\\)" \
"print as Simple"
gdb_test "print *(\$1 as *mut Defaulted)" " = One\\(23\\)" \
"print as Defaulted"
gdb_test "print *(\$1 as *mut Univariant)" " = One\\(23\\)" \
"print as Univariant"
gdb_test "print *(\$2 as *mut Negative)" " = One\\(23\\)" \
"print as Negative"