[Pkg-libvirt-maintainers] Bug#809185: [Libguestfs] Note regarding bin2s.pl
Richard W.M. Jones
rjones at redhat.com
Tue Jan 12 17:27:54 UTC 2016
On Tue, Jan 12, 2016 at 06:21:14PM +0100, Helge Deller wrote:
> 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.
It seems from this answer:
that sizeof (char) is always 1 so it would never make a difference.
However I suppose it's better to be clearer about what we intend.
> - 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);
I tested the patch today on 32- and 64-bit Linux x86 systems, but
nothing beyond that.
Actually I think if it warns, I want to know about that -- eg. in some
bizarre case where size_t isn't sufficient to store the result.
Patch applied anyway, thanks.
> But either way, I'm fine with both approaches.
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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