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Re: [Libguestfs] [nbdkit] [filter/nozero] large binary size with GCC 9



On Fri, 2019-07-05T08:48-0500, Eric Blake wrote:
> On 7/5/19 8:21 AM, Thomas Weißschuh wrote:
> > On Fri, 2019-07-05T08:04-0500, Eric Blake wrote:
> >> On 7/4/19 1:38 PM, Thomas Weißschuh wrote:
> >>> In filter/nozero a 64M large, static, zeroed, read-only array is declared.
> >>> The new behavior of GCC puts this array as-is into the binary inflating the
> >>> size by a factor of around 10000.
> >>
> >> Odd that you are only seeing this for the nozero filter, since we also
> >> have the same sort of buffer in server/plugins.c.  Oh, I see a
> >> difference between the two - one is function-local, the other is
> >> file-local.  Does this patch make a difference? (I need to fire up a
> >> rawhide VM to test it myself...)
> 
> Thanks for your fast reply - you did beat me in getting my rawhide VM
> running.
> 
> > It actually also happens for server/plugins.c.
> 
> Good to know. So the fix is indeed removing 'const', rather than
> reducing scope (although I might as well reduce scope while at it, for
> consistency).

Does this not mean, the 64M are zeroed on every loop iteration in every call to
these functions?
(Probably also depends on compiler optimizations)

Maybe this will have some performance impact, or does it not matter with these
functions?

Maybe the

> The fix is in git now.

Thanks!


Thomas


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