OpenE2K
/
binutils-gdb
12
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

gdb/dwarf2read: Minimal handling of non-constant struct sizes. 

Using the gdb.ada/var_rec_arr.exp test, where the program declares
an array of variant records...

   type Record_Type (I : Small_Type := 0) is record
      S : String (1 .. I);
   end record;
   type Array_Type is array (Integer range <>) of Record_Type;

... and then a variable A1 of type Array_Type, the following command
ocassionally trigger an internal error trying to allocate more memory
than we have left:

    (gdb) ptype a1(1)
    [...]/utils.c:1089: internal-error: virtual memory exhausted.
    A problem internal to GDB has been detected,
    [...]

What happens is that recent versions of GNAT are able to generate
DWARF expressions for type Record_Type, and therefore the record's
DW_AT_byte_size is not a constant, which unfortunately breaks
an assumption made by dwarf2read.c:read_structure_type when it does:

   attr = dwarf2_attr (die, DW_AT_byte_size, cu);
   if (attr)
     {
       TYPE_LENGTH (type) = DW_UNSND (attr);
     }

As a result of this, when ada_evaluate_subexp tries to create
a value_zero for a1(1) while processing the OP_FUNCALL operator
as part of evaluating the subscripting operation in no-side-effect
mode, we try to allocate a value with a bogus size, potentially
triggering the out-of-memory internal error.

This patch avoids this issue by setting the length to zero in
this case.  Until we decide to start supporting dynamic type
lengths in GDB's type struct, and it's not clear yet that
this is worth the effort (see added comment), that's probably
the best we can do.

gdb/ChangeLog:

        * dwarf2read.c (read_structure_type): Set the type's length
        to zero if it has a DW_AT_byte_size attribute which is not
        a constant.

gdb/testsuite/ChangeLog:

        * testsuite/gdb.ada/var_rec_arr.exp: Add "ptype a1(1)" test.
This commit is contained in:
Joel Brobecker 2015-11-23 09:44:16 -08:00
parent e49d43ff73
commit 155bfbd30a
4 changed files with 30 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
gdb/ChangeLog
View File

@ -1,3 +1,9 @@
2015-11-23 Joel Brobecker <brobecker@adacore.com>
* dwarf2read.c (read_structure_type): Set the type's length
to zero if it has a DW_AT_byte_size attribute which is not
a constant.
2015-11-23 Tristan Gingold <gingold@adacore.com>
* darwin-nat.c (darwin_ptrace): Avoid a cast.

15
gdb/dwarf2read.c
View File

@ -13218,7 +13218,20 @@ read_structure_type (struct die_info *die, struct dwarf2_cu *cu)
attr = dwarf2_attr (die, DW_AT_byte_size, cu);
if (attr)
{
TYPE_LENGTH (type) = DW_UNSND (attr);
if (attr_form_is_constant (attr))
TYPE_LENGTH (type) = DW_UNSND (attr);
else
{
/* For the moment, dynamic type sizes are not supported
by GDB's struct type. The actual size is determined
on-demand when resolving the type of a given object,
so set the type's length to zero for now. Otherwise,
we record an expression as the length, and that expression
could lead to a very large value, which could eventually
lead to us trying to allocate that much memory when creating
a value of that type. */
TYPE_LENGTH (type) = 0;
}
}
else
{

4
gdb/testsuite/ChangeLog
View File

@ -1,3 +1,7 @@
2015-11-23 Joel Brobecker <brobecker@adacore.com>
* testsuite/gdb.ada/var_rec_arr.exp: Add "ptype a1(1)" test.
2015-11-20 Jose E. Marchesi <jose.marchesi@oracle.com>
* gdb.base/callfuncs.exp (fetch_all_registers): Filter out the

6
gdb/testsuite/gdb.ada/var_rec_arr.exp
View File

@ -49,3 +49,9 @@ gdb_test "print a2(2)" \
gdb_test "print a2(3)" \
" = \\(i => 0, s => \"\"\\)"
gdb_test "ptype a1(1)" \
[multi_line "type = record" \
" i: pck\\.small_type;" \
" s: access array \\((<>|1 \\.\\. i)\\) of character;" \
"end record"]