Re: debugging custom array types

[Jan Kratochvil <jan.kratochvil@redhat.com>]

On Mon, 11 Feb 2013 17:51:36 +0100, Michael Haupt wrote:
> The internal layout of an array instance is as follows:
> +0    hub reference (reference to meta-information, e.g., class, vtable, ...)
> +8    length
> +12   beginning of array contents (offset depends on type, 12 is for char, for instance)

THis means the type length is stored in inferior memory.  I call it 'dynamic
type', FSF GDB does not support it, it is supported in
archer-jankratochvil-vla from
	http://sourceware.org/gdb/wiki/ArcherBranchManagement
or in any Fedora GDB.

But FSF GDB generally displays such arrays as pointers instead:

34	foo (int size) {
36	  char temp1[size];
FSF GDB:
(gdb) p temp1
$1 = 0x7fffffffd9e0 "XXX"
(gdb) ptype temp1
type = char []
archer-jankratochvil-vla:
(gdb) p temp1
$1 = "XXX"
(gdb) ptype temp1
type = char [26]


> The DWARF I'm generating right now looks as pasted at the end of this message.

Could you display it with GNU binutils "readelf -wi"?  There aren't the DWARF
expressions decoded so it is not easy to read what you have there.

BTW such dynamic types are in the archer-jankratochvil-vla branch above, for a
simple one see gdb.base/vla.exp.

 <1><12c>: Abbrev Number: 11 (DW_TAG_array_type)
    <12d>   DW_AT_type        : <0x49>  
 <2><135>: Abbrev Number: 12 (DW_TAG_subrange_type)
    <136>   DW_AT_type        : <0x34>  
    <13a>   DW_AT_upper_bound : 3 byte block: 91 48 6   (DW_OP_fbreg: -56; DW_OP_deref)
 <2><13e>: Abbrev Number: 0



Regards,
Jan