From: Martin Sebor <msebor@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Martin Sebor via Libc-alpha <libc-alpha@sourceware.org>,
Joseph Myers <joseph@codesourcery.com>
Subject: Ping: [PATCH] add support for -Wmismatched-dealloc
Date: Sun, 10 Jan 2021 13:42:28 -0700 [thread overview]
Message-ID: <a0377d83-5adf-28fe-6dc7-79983425df0a@gmail.com> (raw)
In-Reply-To: <ee04d104-e46e-1501-ce96-ee7f9b3fd322@gmail.com>
Florian, do you have any outstanding concerns or is the most recent
patch good to go?
Thanks
Martin
On 1/4/21 4:18 PM, Martin Sebor wrote:
> On 1/4/21 9:57 AM, Florian Weimer wrote:
>> * Martin Sebor:
>>
>>> On 1/4/21 9:07 AM, Florian Weimer wrote:
>>>> * Martin Sebor via Libc-alpha:
>>>>
>>>>> diff --git a/wcsmbs/wchar.h b/wcsmbs/wchar.h
>>>>> index 9cf8b05a87..4c1c7f1119 100644
>>>>> --- a/wcsmbs/wchar.h
>>>>> +++ b/wcsmbs/wchar.h
>>>>> @@ -151,7 +151,8 @@ extern size_t wcsxfrm_l (wchar_t *__s1, const
>>>>> wchar_t *__s2,
>>>>> size_t __n, locale_t __loc) __THROW;
>>>>> /* Duplicate S, returning an identical malloc'd string. */
>>>>> -extern wchar_t *wcsdup (const wchar_t *__s) __THROW
>>>>> __attribute_malloc__;
>>>>> +extern wchar_t *wcsdup (const wchar_t *__s) __THROW
>>>>> + __attribute_malloc__ __attr_dealloc_free;
>>>>> #endif
>>>>> /* Find the first occurrence of WC in WCS. */
>>>>> @@ -562,9 +563,18 @@ extern wchar_t *wcpncpy (wchar_t *__restrict
>>>>> __dest,
>>>>> /* Wide character I/O functions. */
>>>>> #if defined __USE_XOPEN2K8 || __GLIBC_USE (LIB_EXT2)
>>>>> +# ifdef __REDIRECT
>>>>> +/* Declare the __fclose alias and associate it as a deallocator
>>>>> + with open_wmemstream below. */
>>>>> +extern int __REDIRECT (__fclose, (FILE *), fclose);
>>>>> +# define __attr_dealloc_fclose __attr_dealloc (__fclose, 1)
>>>>> +# else
>>>>> +# define __attr_dealloc_fclose /* empty */
>>>>> +# endif
>>>>> /* Like OPEN_MEMSTREAM, but the stream is wide oriented and
>>>>> produces
>>>>> a wide character string. */
>>>>> -extern __FILE *open_wmemstream (wchar_t **__bufloc, size_t
>>>>> *__sizeloc) __THROW;
>>>>> +extern __FILE *open_wmemstream (wchar_t **__bufloc, size_t
>>>>> *__sizeloc) __THROW
>>>>> + __attribute_malloc__ __attr_dealloc_fclose;
>>>>> #endif
>>>>> #if defined __USE_ISOC95 || defined __USE_UNIX98
>>>> Why is an alias for fclose needed here, but not for free?
>>>
>>> Because fclose is not a built-in so there's no __builtin_fclose
>>> to associate open_wmemstream with. free is a built-in and so
>>> __attr_dealloc_free just references __builtin_free and doesn't
>>> need an explicit declaration.
>>
>> Ahh, that explains the discrepancy.
>>
>> I'm a bit worried that the __fclose alias causes problems. Would it be
>> possible to add __builtin_fclose to GCC instead?
>
> I don't like the alias hack either. Adding a built-in is possible
> but it's late in GCC stage 3 and I'm doubtful the change would be
> accepted before the Glibc deadline (that's this week, right?)
>
> The alias isn't necessary in <stdio.h> where fclose is declared
> so I've removed it from there. It would have been only marginally
> useful in <wchar.h>, and only when fclose isn't declared, but it's
> probably best avoided. So one possibility is to prepare the header
> for __builtin_fclose if/when it's added, fall back on fclose when
> it's declared (i.e., when <stdio.h> is included), and do nothing
> otherwise (and accept that calling, say free, on a pointer returned
> from open_wmemstteam, will not be diagnosed in those translation
> units).
>
> Attached is a patch that does that. If you want to change it
> to something else (e.g, forget about open_wmemstream altogether
> for now or conditionally declare it in <stdio.h> when <wchar.h>
> is included, or any other viable alternative) please let me know.
>
>> Based on how this patch appears to make both __fclose and fclose
>> acceptable as a deallocator, GCC resolves redirects as part of the
>> matching check. I wonder if this constrains the usefulness of the
>> attribute in some way. I can imagine situations where at the source
>> level, different deallocators should be used (say to support debugging
>> builds), but release builds redirect different deallocators to the same
>> implementation.
>
> The attribute doesn't do anything special with aliases (it was
> just a way to get around the problem with functions not being
> declared in some headers).
>
> As for different configurations, the attribute is designed for
> standard C/POSIX APIs and others like those. A user-defined API
> with different deallocators in one configuration than in another
> has to create the associations conditionally, based on those
> configurations. But there's no way to change these associations
> for GCC built-ins, just like there's no way to change their
> semantics. They're hardwired into GCC and the only way to
> affect them is to disable the built-ins.
>
> Martin
>
>>
>> Thanks,
>> Florian
>>
>
next prev parent reply other threads:[~2021-01-10 20:42 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-08 22:52 Martin Sebor
2020-12-09 0:07 ` Joseph Myers
2020-12-12 2:25 ` Martin Sebor
2020-12-14 21:39 ` Martin Sebor
2020-12-14 22:16 ` Florian Weimer
2020-12-15 1:01 ` Joseph Myers
2020-12-15 16:52 ` Martin Sebor
2020-12-27 23:13 ` Martin Sebor
2021-01-04 15:56 ` Ping: " Martin Sebor
2021-01-04 16:07 ` Florian Weimer
2021-01-04 16:18 ` Martin Sebor
2021-01-04 16:57 ` Florian Weimer
2021-01-04 23:18 ` Martin Sebor
2021-01-10 20:42 ` Martin Sebor [this message]
2021-01-11 9:13 ` Florian Weimer
2021-01-12 0:00 ` Martin Sebor
2021-01-12 0:01 ` Martin Sebor
2021-01-12 8:59 ` Florian Weimer
2021-01-19 1:08 ` Martin Sebor
2021-01-19 16:54 ` David Malcolm
2021-01-22 21:26 ` DJ Delorie
2021-01-25 10:56 ` Florian Weimer
2021-01-25 11:31 ` Florian Weimer
2021-04-23 0:00 ` Martin Sebor
2021-05-06 23:54 ` Martin Sebor
2021-05-13 21:49 ` Martin Sebor
2021-05-16 21:25 ` Martin Sebor
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