From 155bfbd30aacd4e01a9ac8ca8032d804ed7ece47 Mon Sep 17 00:00:00 2001 From: Joel Brobecker Date: Mon, 23 Nov 2015 09:44:16 -0800 Subject: 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. --- gdb/dwarf2read.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) (limited to 'gdb/dwarf2read.c') diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c index 48921e7..298757c 100644 --- a/gdb/dwarf2read.c +++ b/gdb/dwarf2read.c @@ -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 { -- cgit v1.1