[Libguestfs] Note regarding bin2s.pl

[Helge Deller]

On 12.01.2016 12:10, Richard W.M. Jones wrote:
> On Tue, Jan 12, 2016 at 10:05:00AM +0000, Richard W.M. Jones wrote:
>> On Tue, Jan 12, 2016 at 07:57:03AM +0100, Hilko Bengen wrote:
>>> Helge,
>>>
>>> I have applied all the architecture-specific bits but not the bin2s
>>> script yet. TBH, so far I don't see what is wrong about export and use
>>> of the "_binary_init_size" constant.
>>
>> [https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=809185]
>>
>> I see it as a reasonable simplification - it allows us to get rid of
>> that conditional code for HP-UX in bin2s.pl.
>>
>> However looking at the patch, I don't like the casts in:
>>
>> -  size_t n = (size_t) &_binary_init_size;
>> +  size_t n = ((size_t) &_binary_init_end) - ((size_t) &_binary_init_start);
>>
>> Since those are pointers, it seems better to simply subtract them.
>> (Though it would be better if we'd declared the type of
>> _binary_init_start/_end as uint8_t instead of char.)
>>
>> If we must cast them then the correct integer to use is 'intptr_t', an
>> int type that's guaranteed by C99 to be long enough to store a
>> pointer.
> 
> How about the attached patch?

In general I'd say it looks OK.
Just a few comments:

-extern char _binary_init_start, _binary_init_end, _binary_init_size;
+extern uint8_t _binary_init_start, _binary_init_end;

Does the char to uint8_t change really makes such a big difference?
We will just use the address of the variable anyway.  
 
-  size_t n = (size_t) &_binary_init_size;
+  size_t n = &_binary_init_end - &_binary_init_start;

It's OK, but maybe some compilers/platforms might complain with a warning.
It might be better to keep a cast to (size_t), e.g.:
+ size_t n = (size_t) (&_binary_init_end - &_binary_init_start);

But either way, I'm fine with both approaches.

Thanks!
Helge