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 7:00 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;


-- 
H.J.