* [Qemu-devel] [PATCH] oslib-posix: change free to g_free
@ 2014-10-11 2:54 arei.gonglei
2014-10-11 3:10 ` zhanghailiang
2014-10-11 3:23 ` Eric Blake
0 siblings, 2 replies; 9+ messages in thread
From: arei.gonglei @ 2014-10-11 2:54 UTC (permalink / raw)
To: qemu-devel
Cc: kwolf, weidong.huang, qemu-trivial, Gonglei, stefanha, pbonzini
From: Gonglei <arei.gonglei@huawei.com>
The caller of qemu_vfree() maybe not check whether parameter
ptr pointer is NULL or not, such as vpc_open().
Using g_free() is more safe.
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
---
util/oslib-posix.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 016a047..ca435d0 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -153,7 +153,7 @@ void *qemu_anon_ram_alloc(size_t size)
void qemu_vfree(void *ptr)
{
trace_qemu_vfree(ptr);
- free(ptr);
+ g_free(ptr);
}
void qemu_anon_ram_free(void *ptr, size_t size)
--
1.7.12.4
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 2:54 [Qemu-devel] [PATCH] oslib-posix: change free to g_free arei.gonglei
@ 2014-10-11 3:10 ` zhanghailiang
2014-10-11 3:21 ` Gonglei
2014-10-11 3:23 ` Eric Blake
1 sibling, 1 reply; 9+ messages in thread
From: zhanghailiang @ 2014-10-11 3:10 UTC (permalink / raw)
To: arei.gonglei, qemu-devel
Cc: kwolf, qemu-trivial, weidong.huang, stefanha, pbonzini
On 2014/10/11 10:54, arei.gonglei@huawei.com wrote:
> From: Gonglei <arei.gonglei@huawei.com>
>
> The caller of qemu_vfree() maybe not check whether parameter
> ptr pointer is NULL or not, such as vpc_open().
> Using g_free() is more safe.
>
It seems that free(NULL) is harmless.
From section 7.20.3.2/2 of the C99 standard:
The free function causes the space pointed to by ptr to be deallocated, that is,
made available for further allocation. If ptr is a null pointer, no action occurs.
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
> util/oslib-posix.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 016a047..ca435d0 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -153,7 +153,7 @@ void *qemu_anon_ram_alloc(size_t size)
> void qemu_vfree(void *ptr)
> {
> trace_qemu_vfree(ptr);
> - free(ptr);
> + g_free(ptr);
> }
>
> void qemu_anon_ram_free(void *ptr, size_t size)
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 3:10 ` zhanghailiang
@ 2014-10-11 3:21 ` Gonglei
2014-10-11 3:26 ` Eric Blake
0 siblings, 1 reply; 9+ messages in thread
From: Gonglei @ 2014-10-11 3:21 UTC (permalink / raw)
To: Zhanghailiang
Cc: kwolf, Huangweidong (C), qemu-trivial, qemu-devel, stefanha, pbonzini
On 2014/10/11 11:10, Zhanghailiang wrote:
> On 2014/10/11 10:54, arei.gonglei@huawei.com wrote:
>> From: Gonglei <arei.gonglei@huawei.com>
>>
>> The caller of qemu_vfree() maybe not check whether parameter
>> ptr pointer is NULL or not, such as vpc_open().
>> Using g_free() is more safe.
>>
>
> It seems that free(NULL) is harmless.
>
Actually, I had noted that C standard says it is a no-operation.
But that doesn't mean that every C-library handles it like that.
Some people saw crashes for free(NULL), so it's best to avoid
calling the free in the first place (caller) or using g_free() in qemu_vfree().
Best regards,
-Gonglei
> From section 7.20.3.2/2 of the C99 standard:
> The free function causes the space pointed to by ptr to be deallocated, that is,
> made available for further allocation. If ptr is a null pointer, no action occurs.
>
>> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
>> ---
>> util/oslib-posix.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
>> index 016a047..ca435d0 100644
>> --- a/util/oslib-posix.c
>> +++ b/util/oslib-posix.c
>> @@ -153,7 +153,7 @@ void *qemu_anon_ram_alloc(size_t size)
>> void qemu_vfree(void *ptr)
>> {
>> trace_qemu_vfree(ptr);
>> - free(ptr);
>> + g_free(ptr);
>> }
>>
>> void qemu_anon_ram_free(void *ptr, size_t size)
>>
>
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 2:54 [Qemu-devel] [PATCH] oslib-posix: change free to g_free arei.gonglei
2014-10-11 3:10 ` zhanghailiang
@ 2014-10-11 3:23 ` Eric Blake
2014-10-12 7:44 ` Kevin Wolf
1 sibling, 1 reply; 9+ messages in thread
From: Eric Blake @ 2014-10-11 3:23 UTC (permalink / raw)
To: arei.gonglei, qemu-devel
Cc: kwolf, qemu-trivial, weidong.huang, stefanha, pbonzini
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On 10/10/2014 08:54 PM, arei.gonglei@huawei.com wrote:
> From: Gonglei <arei.gonglei@huawei.com>
>
> The caller of qemu_vfree() maybe not check whether parameter
> ptr pointer is NULL or not, such as vpc_open().
> Using g_free() is more safe.
NACK. g_free is only safe for pointers allocated by g_malloc.
qemu_vfree is for use on pointers allocated by qemu_try_memalign and
friends (matching the name valloc which is an older spelling of
posix_memalign), which are NOT allocated by g_malloc. Furthermore,
free(NULL) is safe.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 3:21 ` Gonglei
@ 2014-10-11 3:26 ` Eric Blake
2014-10-11 3:32 ` Gonglei
0 siblings, 1 reply; 9+ messages in thread
From: Eric Blake @ 2014-10-11 3:26 UTC (permalink / raw)
To: Gonglei, Zhanghailiang
Cc: kwolf, Huangweidong (C), qemu-trivial, qemu-devel, stefanha, pbonzini
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On 10/10/2014 09:21 PM, Gonglei wrote:
>
> Actually, I had noted that C standard says it is a no-operation.
> But that doesn't mean that every C-library handles it like that.
EVERY libc that is C89 compliant handles it like that. The last
platform that failed on free(NULL) was SunOS 4, which is such
museum-ware it's not funny. There is no need to cater to platforms from
25 years ago.
> Some people saw crashes for free(NULL), so it's best to avoid
> calling the free in the first place (caller) or using g_free() in qemu_vfree().
Absolutely not. g_free is unsafe to use except for pointers from
g_malloc, which is NOT the case that qemu_vfree is used on.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 3:26 ` Eric Blake
@ 2014-10-11 3:32 ` Gonglei
2014-10-11 3:44 ` Eric Blake
0 siblings, 1 reply; 9+ messages in thread
From: Gonglei @ 2014-10-11 3:32 UTC (permalink / raw)
To: Eric Blake
Cc: kwolf, Huangweidong (C),
Zhanghailiang, qemu-trivial, qemu-devel, stefanha, pbonzini
On 2014/10/11 11:26, Eric Blake wrote:
> On 10/10/2014 09:21 PM, Gonglei wrote:
>
>>
>> Actually, I had noted that C standard says it is a no-operation.
>> But that doesn't mean that every C-library handles it like that.
>
> EVERY libc that is C89 compliant handles it like that. The last
> platform that failed on free(NULL) was SunOS 4, which is such
> museum-ware it's not funny. There is no need to cater to platforms from
> 25 years ago.
>
OK.Thanks for explanation!
>> Some people saw crashes for free(NULL), so it's best to avoid
>> calling the free in the first place (caller) or using g_free() in qemu_vfree().
>
> Absolutely not. g_free is unsafe to use except for pointers from
> g_malloc, which is NOT the case that qemu_vfree is used on.
>
Got it, thanks :)
But why some callers make a check,
but some other callers don't do this check?
Can I consider those check is superfluous?
-Best regards,
-Gonglei
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 3:32 ` Gonglei
@ 2014-10-11 3:44 ` Eric Blake
2014-10-11 3:47 ` Gonglei
0 siblings, 1 reply; 9+ messages in thread
From: Eric Blake @ 2014-10-11 3:44 UTC (permalink / raw)
To: Gonglei
Cc: kwolf, Huangweidong (C),
Zhanghailiang, qemu-trivial, qemu-devel, stefanha, pbonzini
[-- Attachment #1: Type: text/plain, Size: 864 bytes --]
On 10/10/2014 09:32 PM, Gonglei wrote:
>>> Actually, I had noted that C standard says it is a no-operation.
>>> But that doesn't mean that every C-library handles it like that.
>>
>> EVERY libc that is C89 compliant handles it like that. The last
>> platform that failed on free(NULL) was SunOS 4, which is such
>> museum-ware it's not funny. There is no need to cater to platforms from
>> 25 years ago.
>
> But why some callers make a check,
> but some other callers don't do this check?
Because some people haven't learned that free(NULL) is safe yet. You're
welcome to simplify code as you touch it.
> Can I consider those check is superfluous?
Yes. Checking for NULL before calling free() or g_free() is wasted effort.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 3:44 ` Eric Blake
@ 2014-10-11 3:47 ` Gonglei
0 siblings, 0 replies; 9+ messages in thread
From: Gonglei @ 2014-10-11 3:47 UTC (permalink / raw)
To: Eric Blake
Cc: kwolf, Huangweidong (C),
Zhanghailiang, qemu-trivial, qemu-devel, stefanha, pbonzini
On 2014/10/11 11:44, Eric Blake wrote:
> On 10/10/2014 09:32 PM, Gonglei wrote:
>
>>>> Actually, I had noted that C standard says it is a no-operation.
>>>> But that doesn't mean that every C-library handles it like that.
>>>
>>> EVERY libc that is C89 compliant handles it like that. The last
>>> platform that failed on free(NULL) was SunOS 4, which is such
>>> museum-ware it's not funny. There is no need to cater to platforms from
>>> 25 years ago.
>
>>
>> But why some callers make a check,
>> but some other callers don't do this check?
>
> Because some people haven't learned that free(NULL) is safe yet. You're
> welcome to simplify code as you touch it.
>
OK, I will. Thanks again :)
>> Can I consider those check is superfluous?
>
> Yes. Checking for NULL before calling free() or g_free() is wasted effort.
>
Best regards,
-Gonglei
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] oslib-posix: change free to g_free
2014-10-11 3:23 ` Eric Blake
@ 2014-10-12 7:44 ` Kevin Wolf
0 siblings, 0 replies; 9+ messages in thread
From: Kevin Wolf @ 2014-10-12 7:44 UTC (permalink / raw)
To: Eric Blake
Cc: weidong.huang, qemu-trivial, qemu-devel, arei.gonglei, stefanha,
pbonzini
Am 11.10.2014 um 05:23 hat Eric Blake geschrieben:
> On 10/10/2014 08:54 PM, arei.gonglei@huawei.com wrote:
> > From: Gonglei <arei.gonglei@huawei.com>
> >
> > The caller of qemu_vfree() maybe not check whether parameter
> > ptr pointer is NULL or not, such as vpc_open().
> > Using g_free() is more safe.
>
> NACK. g_free is only safe for pointers allocated by g_malloc.
> qemu_vfree is for use on pointers allocated by qemu_try_memalign and
> friends (matching the name valloc which is an older spelling of
> posix_memalign), which are NOT allocated by g_malloc. Furthermore,
> free(NULL) is safe.
I second that. Strong NACK.
Kevin
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2014-10-12 7:44 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-10-11 2:54 [Qemu-devel] [PATCH] oslib-posix: change free to g_free arei.gonglei
2014-10-11 3:10 ` zhanghailiang
2014-10-11 3:21 ` Gonglei
2014-10-11 3:26 ` Eric Blake
2014-10-11 3:32 ` Gonglei
2014-10-11 3:44 ` Eric Blake
2014-10-11 3:47 ` Gonglei
2014-10-11 3:23 ` Eric Blake
2014-10-12 7:44 ` Kevin Wolf
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