Re: memory address represented as a string

[Rahul K Patel <rahulk.patel@einfochips.com>]

Hi,

Saurabh Sehgal wrote:
> Hi all,
>
> Thanks for the reply !
>
> I was able to write this function successfully.
>
> This would lead me to my next question.
>
> Is there anyway to test if a memory address is valid or not without causing a
> segmentation fault and catching this maybe in a signal handler ?
>
> Is there a safe way in the same function " void * foo (char * addr)"
> to check that
> if the address contained in the string represented by "char * addr"  is valid
> before returning it.
>   

static inline int is_invalid_addr( const void *p )
{
       int dev_null_fd = open("/dev/null", O_RDWR);
       if(dev_null_fd < 0)
          return -1;
   
        /* HACK: on some systems we can not write to check for pointer 
validity */
        size_t ret = fcntl( dev_null_fd, F_GETLK, p );

        ret = ( errno == EFAULT );
        errno = 0;
        return ret;
}

You can use this function to check whether given address is accessible.

-- Rahul Patel.
> Thank you !
>
> Saurabh
>
> On Sun, Jul 26, 2009 at 4:14 AM, Eric Polino<aluink@gmail.com> wrote:
>   
>> sure, you can just write a function that declares a void * and uses it as a
>> regular numeric type such as int or whatnot and parses the string
>> representation as a numeric value into that variable.  You can do stuff the
>> same as you would with any other integer type, "x += 10; x -= 18;".  So the
>> function would look something like
>>
>> void *foo(const char *addr){
>>   void *parsed_value = 0;
>>   ....
>>   /* Parse addr into parsed_value */
>>   ....
>>   /* parsed_value == value_described_by(addr) */
>>
>>   return parsed_value;
>> }
>>
>> Parsing addr into parsed_value is left as an exercise to the reader ;)
>>
>> "None are more hopelessly enslaved than those who falsely believe they are
>> free."
>>                                      --Goethe
>>
>> "Freedom is living without government coercion."
>>                   --Ron Paul (www.ronpaul2008.com)
>>
>>
>> On Sun, Jul 26, 2009 at 03:39, Saurabh Sehgal <saurabh.r.s@gmail.com> wrote:
>>     
>>> Hi all,
>>>
>>> I had a quick question:
>>>
>>> Let's say I design a function with the signature:
>>>
>>> void * foo( char * addr ) ; ,
>>>
>>> where addr is a string that represents a valid memory address  ...
>>> so the way someone can call this function is ...
>>>
>>> char * addr = "0xae456778" // assume this is a valid memory address on
>>> the machine
>>> foo( addr ) ;
>>>
>>> Is it possible to take this address in string form, and assign it to
>>> an actual pointer of void * type ?
>>> I want the function "foo" to return a pointer pointing to the memory
>>> location as indicated
>>> by the string passed in.
>>>
>>> Thank you !
>>>
>>> Saurabh
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>>>       
>>     
>
>
>
>   
-- 
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