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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug exp/26875] Incorrect value printed for address of first element
 of zero-length array
Date: Fri, 20 Nov 2020 22:16:22 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D26875

--- Comment #11 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Simon Marchi from comment #7)
> I am not able to reproduce.  In my version of the compiled test case, both
> bounds are const:
>=20
> (top-gdb) p type->bounds ()->low.kind ()
> $4 =3D PROP_CONST
> (top-gdb) p type->bounds ()->high.kind ()
> $5 =3D PROP_CONST
>=20
> What compiler do you use to build the test case?

Gcc 7.5.0

> In my version, this is the
> DIE that corresponds to the type of the zero-length field:
>=20
> 0x00000076:   DW_TAG_array_type
>                 DW_AT_type [DW_FORM_ref4]       (0x00000044 "int")
>                 DW_AT_sibling [DW_FORM_ref4]    (0x00000086)
>=20
> 0x0000007f:     DW_TAG_subrange_type
>                   DW_AT_type [DW_FORM_ref4]     (0x0000003d "long unsigned
> int")
>                   DW_AT_count [DW_FORM_data1]   (0x00)
>=20

I get:
...
 <1><13a>: Abbrev Number: 2 (DW_TAG_array_type)
    <13b>   DW_AT_type        : <0x10b>
    <13f>   DW_AT_sibling     : <0x149>
 <2><143>: Abbrev Number: 9 (DW_TAG_subrange_type)
    <144>   DW_AT_type        : <0x104>
...
without DW_AT_count.

The DW_AT_count is added at gcc-9, and using that the test-cases passes for=
 me.

> So I presume GDB translates that to two constant bounds with value 0.  Wh=
at
> does it look like in yours?
>=20
> I stumbled on a similar problem and filed this bug here, they are likely
> related:
>=20
> https://sourceware.org/bugzilla/show_bug.cgi?id=3D26901
>=20
> I have this patch series in the pipeline that I made to address 26901:
>=20
> https://review.lttng.org/c/binutils-gdb/+/4399/4
>=20

Ah, thanks for the pointer, I'll take a look.

> If/when I am able to reproduce this (26875) bug, I can check if that helps
> with it too.

That would be great.

--=20
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