Re: [Qemu-devel] [PATCH] Do not abort on qemu_malloc(0) in production builds

[Anthony Liguori <aliguori@linux.vnet.ibm.com>]

Markus Armbruster wrote:
> Anthony Liguori <aliguori@us.ibm.com> writes:
>
>   
>> qemu_malloc() does not allow size=0 to be passed in and aborts on this behavior.
>>
>> Unfortunately, there is good reason to believe that within qemu, there are a
>> number of, so far, undetected places that assume size=0 can be safely passed.
>> Since we do not want to abort unnecessarily in production builds, return
>> qemu_malloc(1) whenever the version file indicates that this is a production
>> build.
>>
>> Also introduce --enable-zero-malloc/--disable-zero-malloc to make this behavior
>> overridable.
>>
>> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
>> ---
>>  configure     |   24 +++++++++++++++++++++++-
>>  qemu-malloc.c |   17 +++++++++++++----
>>  2 files changed, 36 insertions(+), 5 deletions(-)
>>
>>     
> [...]
>   
>> diff --git a/qemu-malloc.c b/qemu-malloc.c
>> index 295d185..e82af26 100644
>> --- a/qemu-malloc.c
>> +++ b/qemu-malloc.c
>> @@ -42,21 +42,30 @@ void qemu_free(void *ptr)
>>      free(ptr);
>>  }
>>  
>> +static int allow_zero_malloc(void)
>> +{
>> +#if defined(CONFIG_ZERO_MALLOC)
>> +    return 1;
>> +#else
>> +    return 0;
>> +#endif
>> +}
>> +
>>  void *qemu_malloc(size_t size)
>>  {
>> -    if (!size) {
>> +    if (!size && !allow_zero_malloc()) {
>>          abort();
>>      }
>> -    return oom_check(malloc(size));
>> +    return oom_check(malloc(size ? size : 1));
>>  }
>>  
>>  void *qemu_realloc(void *ptr, size_t size)
>>  {
>>      if (size) {
>>          return oom_check(realloc(ptr, size));
>> -    } else {
>> +    } else if (allow_zero_malloc()) {
>>          if (ptr) {
>> -            return realloc(ptr, size);
>> +            return realloc(ptr, size ? size : 1);
>>          }
>>      }
>>      abort();
>>     
>
> This still aborts on qemu_realloc(NULL, 0), even with
> CONFIG_ZERO_MALLOC.  Intentional?
>   
I guess not.  Should it?  Seems like a very strange case..

Regards,

Anthony Liguori


-- 
Regards,

Anthony Liguori