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Consider the following Ada code:
procedure Nested (L, U : Integer) is
subtype Small_Type is Integer range L .. U;
type Record_Type (I : Small_Type := L) is record
S : String (1 .. I);
end record;
type Array_Type is array (Integer range <>) of Record_Type;
A1 : Array_Type :=
(1 => (I => 0, S => <>),
2 => (I => 1, S => "A"),
3 => (I => 2, S => "AB"));
procedure Discard (R : Record_Type) is
begin
null;
end Discard;
begin
Discard (A1 (1)); -- STOP
end;
Trying to print a slice of that array currently yields:
(gdb) p a1(1..3)
$1 = ((i => 0, s => ""), (i => 0, s => ""), (i => 0, s => ""))
We expected instead:
(gdb) p a1(1..3)
$1 = ((i => 0, s => ""), (i => 1, s => "A"), (i => 2, s => "AB"))
This is because the functions we use in ada-lang.c to create the type
of the array slice (ada_value_slice and ada_value_slice_from_ptr) was
not taking into account the stride of the array. This patch fixes this.
gdb/ChangeLog:
* ada-lang.c (ada_value_slice_from_ptr): Take array stride into
account when creating the array type of the slice.
(ada_value_slice): Likewise.
gdb/testsuite/ChangeLog:
* gdb.ada/dyn_stride.exp: Add slice test.
Note that, with the current use of ada_value_slice, the enhancement
to handle dynamic array strides seems unnecessary, because I do not
see how an array with a dynamic stride can be referenced by either
by reference or pointer. Since references are coerced to array pointers,
in both cases, the slice is performed by ada_value_slice_from_ptr.
But ada_value_slice is enhanced nonetheless, in the spirit of making
the code more robust, in case we missed something, and also as similar
as possible with its from_ptr counterpart.
tested on x86_64-linux.
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This patch adds support for DW_AT_byte_stride, using Ada as one
example of where this would be useful. However, the implementation
is language-agnostic.
Consider the following Ada code:
procedure Nested (L, U : Integer) is
subtype Small_Type is Integer range L .. U;
type Record_Type (I : Small_Type := L) is record
S : String (1 .. I);
end record;
type Array_Type is array (Integer range <>) of Record_Type;
A1 : Array_Type :=
(1 => (I => 0, S => <>),
2 => (I => 1, S => "A"),
3 => (I => 2, S => "AB"));
procedure Discard (R : Record_Type) is
begin
null;
end Discard;
begin
Discard (A1 (1)); -- STOP
end;
It defines an array A1 of Record_Type, which is a variant record
type whose maximum size actually depends on the value of the
parameters passed when calling Nested. As a result, the stride
of the array A1 cannot be known statically, which leads the compiler
to generate a dynamic DW_AT_byte_stride attribute for our type.
Here is what the debugging info looks like with GNAT:
.uleb128 0x10 # (DIE (0x14e) DW_TAG_array_type)
.long .LASF17 # DW_AT_name: "foo__nested__T18b"
.long 0x141 # DW_AT_byte_stride
.long 0xdc # DW_AT_type
.uleb128 0x11 # (DIE (0x15f) DW_TAG_subrange_type)
.long 0x166 # DW_AT_type
.byte 0x3 # DW_AT_upper_bound
.byte 0 # end of children of DIE 0x14e
There DW_AT_byte_stride is a reference to a local (internal)
variable:
.uleb128 0x9 # (DIE (0x141) DW_TAG_variable)
.long .LASF6 # DW_AT_name: "foo__nested__T18b___PAD___XVZ"
This patch enhances GDB to handle this dynamic byte stride attribute
by first adding a new dynamic_prop_node_kind (DYN_PROP_BYTE_STRIDE)
to store the array dynamic stride info (when dynamic). It then enhances
the dynamic type resolver to handle this dynamic property.
Before applying this patch, trying to print the value of some of
A1's elements after having stopped at the "STOP" comment does not
work. For instance:
(gdb) p a1(2)
Cannot access memory at address 0x80000268dec0
With this patch applied, GDB now prints the value of all 3 elements
correctly:
(gdb) print A1(1)
$1 = (i => 0, s => "")
(gdb) print A1(2)
$2 = (i => 1, s => "A")
(gdb) print A1(3)
$3 = (i => 2, s => "AB")
gdb/ChangeLog:
* gdbtypes.h (enum dynamic_prop_node_kind) <DYN_PROP_BYTE_STRIDE>:
New enum value.
(create_array_type_with_stride): Add byte_stride_prop parameter.
* gdbtypes.c (create_array_type_with_stride) <byte_stride_prop>:
New parameter. Update all callers in this file.
(array_type_has_dynamic_stride): New function.
(is_dynamic_type_internal, resolve_dynamic_array): Add handling
of arrays with dynamic byte strides.
* dwarf2read.c (read_array_type): Add support for dynamic
DW_AT_byte_stride attributes.
gdb/testsuite/ChangeLog:
* gdb.ada/dyn_stride: New testcase.
Tested on x86_64-linux.
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