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2ddeaf8a7d
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.
48 lines
1.1 KiB
C
48 lines
1.1 KiB
C
/* Copyright 2018 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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unsigned char buffer[8];
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unsigned char buffer2[8];
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static void
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func (void)
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{
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}
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int
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main (void)
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{
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/* Write the expected values into the buffer. */
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unsigned int x = 23;
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if (*(char *) &x)
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{
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/* Little endian. */
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buffer[0] = 23;
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buffer[4] = 23;
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buffer2[0] = 255;
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buffer2[4] = 23;
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}
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else
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{
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buffer[3] = 23;
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buffer[7] = 23;
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buffer2[0] = 255;
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buffer2[7] = 23;
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}
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func ();
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return 0;
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}
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