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DWARF: Add array DW_AT_bit_stride and DW_AT_byte_stride support

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Consider the following declarations in Ada...

   type Item is range -32 .. 31;
   for Item'Size use 6;

   type Table is array (Natural range 0 .. 4) of Item;
   pragma Pack (Table);

... which declare a packed array whose elements are 6 bits long.
The debugger currently does not notice that the array is packed,
and thus prints values of this type incorrectly. This can be seen
in the "ptype" output:

    (gdb) ptype table
    type = array (0 .. 4) of foo.item

Normally, the debugger should print:

    (gdb) ptype table
    type = array (0 .. 4) of foo.item <packed: 6-bit elements>

The debugging information for this array looks like this:

        .uleb128 0xf    # (DIE (0x15c) DW_TAG_array_type)
        .long   .LASF9  # DW_AT_name: "pck__table"
        .byte   0x6     # DW_AT_bit_stride
        .long   0x1a9   # DW_AT_type
        .uleb128 0x10   # (DIE (0x16a) DW_TAG_subrange_type)
        .long   0x3b    # DW_AT_type
        .byte   0       # DW_AT_lower_bound
        .byte   0x4     # DW_AT_upper_bound
        .byte   0       # end of children of DIE 0x15c

The interesting part is the DW_AT_bit_stride attribute, which tells
the size of the array elements is 6 bits, rather than the normal
element type's size.

This patch adds support for this attribute by first creating
gdbtypes.c::create_array_type_with_stride, which is an enhanced
version of create_array_type taking an extra parameter as the stride.
The old create_array_type can then be re-implemented very simply
by calling the new create_array_type_with_stride.

We can then use this new function from dwarf2read, to create
arrays with or without stride.

gdb/ChangeLog:

        * gdbtypes.h (create_array_type_with_stride): Add declaration.
        * gdbtypes.c (create_array_type_with_stride): New function,
        renaming create_array_type, but with an added parameter
        called "bit_stride".
        (create_array_type): Re-implement using
        create_array_type_with_stride.
        * dwarf2read.c (read_array_type): Add support for DW_AT_byte_stride
        and DW_AT_bit_stride attributes.

gdb/testsuite/ChangeLog:

        * gdb.dwarf2/arr-stride.c: New file.
        * gdb.dwarf2/arr-stride.exp: New file.

The test, relying purely on generating an assembly file, only
verifies the type description of our array. But I was also
able to verify manually that the debugger print values of these
types correctly as well (which was not the case prior to this
patch).
This commit is contained in:
Joel Brobecker 2014-01-29 17:39:56 +04:00
parent 12ab52e977
commit dc53a7adb5
7 changed files with 187 additions and 6 deletions
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18
gdb/dwarf2read.c
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@ -13281,6 +13281,7 @@ read_array_type (struct die_info *die, struct dwarf2_cu *cu)
int ndim = 0;
struct cleanup *back_to;
const char *name;
unsigned int bit_stride = 0;
element_type = die_type (die, cu);
@ -13289,13 +13290,22 @@ read_array_type (struct die_info *die, struct dwarf2_cu *cu)
if (type)
return type;
attr = dwarf2_attr (die, DW_AT_byte_stride, cu);
if (attr != NULL)
bit_stride = DW_UNSND (attr) * 8;
attr = dwarf2_attr (die, DW_AT_bit_stride, cu);
if (attr != NULL)
bit_stride = DW_UNSND (attr);
/* Irix 6.2 native cc creates array types without children for
arrays with unspecified length. */
if (die->child == NULL)
{
index_type = objfile_type (objfile)->builtin_int;
range_type = create_range_type (NULL, index_type, 0, -1);
type = create_array_type (NULL, element_type, range_type);
type = create_array_type_with_stride (NULL, element_type, range_type,
bit_stride);
return set_die_type (die, type, cu);
}
@ -13335,12 +13345,14 @@ read_array_type (struct die_info *die, struct dwarf2_cu *cu)
int i = 0;
while (i < ndim)
type = create_array_type (NULL, type, range_types[i++]);
type = create_array_type_with_stride (NULL, type, range_types[i++],
bit_stride);
}
else
{
while (ndim-- > 0)
type = create_array_type (NULL, type, range_types[ndim]);
type = create_array_type_with_stride (NULL, type, range_types[ndim],
bit_stride);
}
/* Understand Dwarf2 support for vector types (like they occur on