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[Ada] array pointers encoded as typedef to fat pointer 

A recent change in check_typedef caused the following regression,
considering:

        type String_Access is access String;
        S1 : String_Access := null;

Trying to print S1, we get:

        (gdb) print s1
        $1 = (string) (null)

The type name is wrong.  We were expecting:

        (gdb) print s1
        $1 = (string_bug.string_access) (null)

The extensive comment in this patch explains how pointers to arrays
are encoded when the array is a "fat pointer".  What happened is
that the change in check_typedef broke a type-equality test that
we were performing.   The test really was on the fringe, but it
turns out that, for what we're doing, we're really only interested
in the main-type portion of the type.

The patch adjust the check accordingly.

gdb/ChangeLog:

        * ada-lang.c (ada_to_fixed_type): Expand function documentation.
        Return the original type if the main type portions match rather
         than when the type themselves match.
This commit is contained in:
Joel Brobecker 2010-11-23 01:10:54 +00:00
parent 27f2a97baf
commit 96dbd2c132
2 changed files with 42 additions and 2 deletions
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6
gdb/ChangeLog
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@ -1,3 +1,9 @@
2010-11-22 Joel Brobecker <brobecker@adacore.com>
* ada-lang.c (ada_to_fixed_type): Expand function documentation.
Return the original type if the main type portions match rather
than when the type themselves match.
2010-11-22 Joel Brobecker <brobecker@adacore.com>
* ada-lang.c (ada_template_to_fixed_record_type_1):

38
gdb/ada-lang.c
View File

@ -7659,7 +7659,23 @@ ada_to_fixed_type_1 (struct type *type, const gdb_byte *valaddr,
/* The same as ada_to_fixed_type_1, except that it preserves the type
if it is a TYPE_CODE_TYPEDEF of a type that is already fixed.
ada_to_fixed_type_1 would return the type referenced by TYPE. */
The typedef layer needs be preserved in order to differentiate between
arrays and array pointers when both types are implemented using the same
fat pointer. In the array pointer case, the pointer is encoded as
a typedef of the pointer type. For instance, considering:
type String_Access is access String;
S1 : String_Access := null;
To the debugger, S1 is defined as a typedef of type String. But
to the user, it is a pointer. So if the user tries to print S1,
we should not dereference the array, but print the array address
instead.
If we didn't preserve the typedef layer, we would lose the fact that
the type is to be presented as a pointer (needs de-reference before
being printed). And we would also use the source-level type name. */
struct type *
ada_to_fixed_type (struct type *type, const gdb_byte *valaddr,
@ -7669,8 +7685,26 @@ ada_to_fixed_type (struct type *type, const gdb_byte *valaddr,
struct type *fixed_type =
ada_to_fixed_type_1 (type, valaddr, address, dval, check_tag);
/* If TYPE is a typedef and its target type is the same as the FIXED_TYPE,
then preserve the typedef layer.
Implementation note: We can only check the main-type portion of
the TYPE and FIXED_TYPE, because eliminating the typedef layer
from TYPE now returns a type that has the same instance flags
as TYPE. For instance, if TYPE is a "typedef const", and its
target type is a "struct", then the typedef elimination will return
a "const" version of the target type. See check_typedef for more
details about how the typedef layer elimination is done.
brobecker/2010-11-19: It seems to me that the only case where it is
useful to preserve the typedef layer is when dealing with fat pointers.
Perhaps, we could add a check for that and preserve the typedef layer
only in that situation. But this seems unecessary so far, probably
because we call check_typedef/ada_check_typedef pretty much everywhere.
*/
if (TYPE_CODE (type) == TYPE_CODE_TYPEDEF
&& TYPE_TARGET_TYPE (type) == fixed_type)
&& (TYPE_MAIN_TYPE (TYPE_TARGET_TYPE (type))
== TYPE_MAIN_TYPE (fixed_type)))
return type;
return fixed_type;