Re: [PATCH] Initialize the entire obstack struct [BZ #17919]

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Tue, Feb 3, 2015 at 7:38 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Feb 3, 2015 at 7:00 AM, Siddhesh Poyarekar <siddhesh@redhat.com> wrote:
>> ... and I forgot to add bug-gnulib to cc before I hit send.
>>
>> Siddhesh
>>
>> On Tue, Feb 03, 2015 at 08:26:49PM +0530, Siddhesh Poyarekar wrote:
>>> Hi,
>>>
>>> obstack_init does not completely initialize the obstack structure; it
>>> leaves out the padding bits and valgrind complains about it on s390x:
>>>
>>> ==15793== Memcheck, a memory error detector
>>> ==15793== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
>>> ==15793== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
>>> ==15793== Command: /root/obstack
>>> ==15793==
>>> ==15793== Conditional jump or move depends on uninitialised value(s)
>>> ==15793==    at 0x403E48CA4E: obstack_free (in /lib64/libc-2.12.so)
>>> ==15793==    by 0x8000072D: main (obstack.c:12)
>>> ==15793==
>>> ==15793==
>>> ==15793== HEAP SUMMARY:
>>> ==15793==     in use at exit: 0 bytes in 0 blocks
>>> ==15793==   total heap usage: 1 allocs, 1 frees, 4,064 bytes allocated
>>> ==15793==
>>> ==15793== All heap blocks were freed -- no leaks are possible
>>> ==15793==
>>> ==15793== For counts of detected and suppressed errors, rerun with: -v
>>> ==15793== Use --track-origins=yes to see where uninitialised values come from
>>> ==15793== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)
>>>
>>>
>>> The fix below (against gnulib, but is identical for glibc) initializes
>>> all of the obstack struct at once.  Verified that the valgrind warning
>>> is fixed.  OK for 2.22 and gnulib?
>>>
>>> Siddhesh
>>>
>>> ChangeLog for gnulib:
>>>
>>>       obstack: Initialize whole obstack structure.
>>>       * lib/obstack.c (_obstack_begin): Initialize all of H.
>>>
>>> ChangeLog for glibc:
>>>
>>>       [BZ #17919]
>>>       * malloc/obstack.c (_obstack_begin): Initialize all of H.
>>>
>>> diff --git a/malloc/obstack.c b/malloc/obstack.c
>>> index 5bb3f0d..c1d6ded 100644
>>> --- a/lib/obstack.c
>>> +++ b/lib/obstack.c
>>> @@ -148,6 +148,8 @@ _obstack_begin (struct obstack *h,
>>>  {
>>>    struct _obstack_chunk *chunk; /* points to new chunk */
>>>
>>> +  memset (h, 0, sizeof (struct obstack));
>>> +
>>>    if (alignment == 0)
>>>      alignment = DEFAULT_ALIGNMENT;
>>>    if (size == 0)
>>
>>
>
> I think you should also remove
>
> h->use_extra_arg = 0;
>

And

  /* The initial chunk now contains no empty object.  */
  h->maybe_empty_object = 0;
  h->alloc_failed = 0;



-- 
H.J.