New class allocate_on_obstack
Commit Message
This patch adds a new class allocate_on_obstack, and let dwarf2_per_objfile
inherit it, so that dwarf2_per_objfile is automatically allocated on
obstack, and "delete dwarf2_per_objfile" doesn't de-allocate any space.
Regression tested on x86_64-linux.
gdb:
2018-02-06 Yao Qi <yao.qi@linaro.org>
* block.c (block_namespace_info): Inherit allocate_on_obstack.
(block_initialize_namespace): Use new.
* dwarf2read.c (dwarf2_per_objfile): Inherit allocate_on_obstack.
(dwarf2_free_objfile): Use delete.
* gdbtypes.c (type_pair): Inherit allocate_on_obstack.
(copy_type_recursive): Use new.
* gdb_obstack.h (allocate_on_obstack): New.
---
gdb/block.c | 12 ++++--------
gdb/dwarf2read.c | 14 +++++---------
gdb/gdb_obstack.h | 20 ++++++++++++++++++++
gdb/gdbtypes.c | 18 +++++++++++-------
4 files changed, 40 insertions(+), 24 deletions(-)
Comments
On 02/07/2018 09:40 AM, Yao Qi wrote:
> This patch adds a new class allocate_on_obstack, and let dwarf2_per_objfile
> inherit it, so that dwarf2_per_objfile is automatically allocated on
> obstack, and "delete dwarf2_per_objfile" doesn't de-allocate any space.
>
> Regression tested on x86_64-linux.
LGTM.
Thanks,
Pedro Alves
>>>>> "Yao" == Yao Qi <qiyaoltc@gmail.com> writes:
Yao> This patch adds a new class allocate_on_obstack, and let dwarf2_per_objfile
Yao> inherit it, so that dwarf2_per_objfile is automatically allocated on
Yao> obstack, and "delete dwarf2_per_objfile" doesn't de-allocate any space.
I still think it should be restricted to types with a trivial
destructor. Otherwise, someday, the lack of actual destruction is going
to cause a bug.
Tom
On Wed, Feb 7, 2018 at 3:29 PM, Tom Tromey <tom@tromey.com> wrote:
>>>>>> "Yao" == Yao Qi <qiyaoltc@gmail.com> writes:
>
> Yao> This patch adds a new class allocate_on_obstack, and let dwarf2_per_objfile
> Yao> inherit it, so that dwarf2_per_objfile is automatically allocated on
> Yao> obstack, and "delete dwarf2_per_objfile" doesn't de-allocate any space.
>
> I still think it should be restricted to types with a trivial
> destructor. Otherwise, someday, the lack of actual destruction is going
> to cause a bug.
>
Can you give me some clues on how to do the restriction? I think I need to
use std::enable_if and std::is_trivially_destructible, but don't know how to put
them into the code.
Lack of destruction causes a bug in any case. If object is allocated on heap,
and don't do "delete p", the dtor isn't called and memory is leaked. I
expect use "delete p" no matter where the object is allocated (on heap or
on obstack).
On Wed, Feb 7, 2018 at 5:34 PM, Yao Qi <qiyaoltc@gmail.com> wrote:
> On Wed, Feb 7, 2018 at 3:29 PM, Tom Tromey <tom@tromey.com> wrote:
>>>>>>> "Yao" == Yao Qi <qiyaoltc@gmail.com> writes:
>>
>> Yao> This patch adds a new class allocate_on_obstack, and let dwarf2_per_objfile
>> Yao> inherit it, so that dwarf2_per_objfile is automatically allocated on
>> Yao> obstack, and "delete dwarf2_per_objfile" doesn't de-allocate any space.
>>
>> I still think it should be restricted to types with a trivial
>> destructor. Otherwise, someday, the lack of actual destruction is going
>> to cause a bug.
>>
>
> Can you give me some clues on how to do the restriction? I think I need to
> use std::enable_if and std::is_trivially_destructible, but don't know how to put
> them into the code.
>
I somehow managed to write static_assert std::is_trivially_destructible<T>
for these classes, and dwarf2_per_objfile is not trivially destructible.
Classes inherit allocate_on_obstack don't have to be is_trivially_destructible,
IMO.
> Lack of destruction causes a bug in any case. If object is allocated on heap,
> and don't do "delete p", the dtor isn't called and memory is leaked. I
> expect use "delete p" no matter where the object is allocated (on heap or
> on obstack).
We can still let dwarf2_per_objfile inherit allocate_on_obstack or allocate
dwarf2_per_objfile on obstack, but is still better to use "delete" to call dtor.
Yao Qi <qiyaoltc@gmail.com> writes:
> 2018-02-06 Yao Qi <yao.qi@linaro.org>
>
> * block.c (block_namespace_info): Inherit allocate_on_obstack.
> (block_initialize_namespace): Use new.
> * dwarf2read.c (dwarf2_per_objfile): Inherit allocate_on_obstack.
> (dwarf2_free_objfile): Use delete.
> * gdbtypes.c (type_pair): Inherit allocate_on_obstack.
> (copy_type_recursive): Use new.
> * gdb_obstack.h (allocate_on_obstack): New.
I pushed it in.
@@ -31,10 +31,10 @@
C++ files, namely using declarations and the current namespace in
scope. */
-struct block_namespace_info
+struct block_namespace_info : public allocate_on_obstack
{
- const char *scope;
- struct using_direct *using_decl;
+ const char *scope = nullptr;
+ struct using_direct *using_decl = nullptr;
};
static void block_initialize_namespace (struct block *block,
@@ -350,11 +350,7 @@ static void
block_initialize_namespace (struct block *block, struct obstack *obstack)
{
if (BLOCK_NAMESPACE (block) == NULL)
- {
- BLOCK_NAMESPACE (block) = XOBNEW (obstack, struct block_namespace_info);
- BLOCK_NAMESPACE (block)->scope = NULL;
- BLOCK_NAMESPACE (block)->using_decl = NULL;
- }
+ BLOCK_NAMESPACE (block) = new (obstack) struct block_namespace_info ();
}
/* Return the static block associated to BLOCK. Return NULL if block
@@ -380,7 +380,7 @@ struct tu_stats
/* Collection of data recorded per objfile.
This hangs off of dwarf2_objfile_data_key. */
-struct dwarf2_per_objfile
+struct dwarf2_per_objfile : public allocate_on_obstack
{
/* Construct a dwarf2_per_objfile for OBJFILE. NAMES points to the
dwarf2 section names, or is NULL if the standard ELF names are
@@ -2490,10 +2490,9 @@ dwarf2_has_info (struct objfile *objfile,
if (dwarf2_per_objfile == NULL)
{
/* Initialize per-objfile state. */
- struct dwarf2_per_objfile *data
- = XOBNEW (&objfile->objfile_obstack, struct dwarf2_per_objfile);
-
- dwarf2_per_objfile = new (data) struct dwarf2_per_objfile (objfile, names);
+ dwarf2_per_objfile
+ = new (&objfile->objfile_obstack) struct dwarf2_per_objfile (objfile,
+ names);
set_dwarf2_per_objfile (objfile, dwarf2_per_objfile);
}
return (!dwarf2_per_objfile->info.is_virtual
@@ -25191,10 +25190,7 @@ dwarf2_free_objfile (struct objfile *objfile)
struct dwarf2_per_objfile *dwarf2_per_objfile
= get_dwarf2_per_objfile (objfile);
- if (dwarf2_per_objfile == NULL)
- return;
-
- dwarf2_per_objfile->~dwarf2_per_objfile ();
+ delete dwarf2_per_objfile;
}
/* A set of CU "per_cu" pointer, DIE offset, and GDB type pointer.
@@ -78,4 +78,24 @@ struct auto_obstack : obstack
{ obstack_free (this, obstack_base (this)); }
};
+/* Objects are allocated on obstack instead of heap. */
+
+struct allocate_on_obstack
+{
+ allocate_on_obstack () = default;
+
+ void* operator new (size_t size, struct obstack *obstack)
+ {
+ return obstack_alloc (obstack, size);
+ }
+
+ void* operator new[] (size_t size, struct obstack *obstack)
+ {
+ return obstack_alloc (obstack, size);
+ }
+
+ void operator delete (void* memory) {}
+ void operator delete[] (void* memory) {}
+};
+
#endif
@@ -4699,9 +4699,13 @@ recursive_dump_type (struct type *type, int spaces)
/* Trivial helpers for the libiberty hash table, for mapping one
type to another. */
-struct type_pair
+struct type_pair : public allocate_on_obstack
{
- struct type *old, *newobj;
+ type_pair (struct type *old_, struct type *newobj_)
+ : old (old_), newobj (newobj_)
+ {}
+
+ struct type * const old, * const newobj;
};
static hashval_t
@@ -4769,7 +4773,6 @@ copy_type_recursive (struct objfile *objfile,
struct type *type,
htab_t copied_types)
{
- struct type_pair *stored, pair;
void **slot;
struct type *new_type;
@@ -4780,7 +4783,8 @@ copy_type_recursive (struct objfile *objfile,
if it did, the type might disappear unexpectedly. */
gdb_assert (TYPE_OBJFILE (type) == objfile);
- pair.old = type;
+ struct type_pair pair (type, nullptr);
+
slot = htab_find_slot (copied_types, &pair, INSERT);
if (*slot != NULL)
return ((struct type_pair *) *slot)->newobj;
@@ -4789,9 +4793,9 @@ copy_type_recursive (struct objfile *objfile,
/* We must add the new type to the hash table immediately, in case
we encounter this type again during a recursive call below. */
- stored = XOBNEW (&objfile->objfile_obstack, struct type_pair);
- stored->old = type;
- stored->newobj = new_type;
+ struct type_pair *stored
+ = new (&objfile->objfile_obstack) struct type_pair (type, new_type);
+
*slot = stored;
/* Copy the common fields of types. For the main type, we simply