[Bug pch/14400] Cannot compile qt-x11-free-3.3.0

[Geoffrey Keating]

On 02/04/2004, at 7:17 AM, Ian Lance Taylor wrote:

> "geoffk at apple dot com" <gcc-bugzilla@gcc.gnu.org> writes:
>
>> On Mar 29, 2004, at 11:06 PM, Ian Lance Taylor wrote:
>
>>> PR 14206 is fixed on mainline by RTH's patch.  For 3.4 I put in a doc
>>> fix.
>
>> I've now caught up enough that I read RTH's patch (I've been on
>> vacation).  Yes, that patch should fix this problem too.  I'd suggest
>> backporting it to 3.4.
>
> We can do that.  However, I am still troubled by the fact that the
> default fallback for gt_pch_get_address/gt_pch_use_address is
> unreliable.  RTH's patch may well fix the problem on GNU/Linux for all
> but strange cases.  But it seems to me that with that patch PCH will
> work reasonably on GNU/Linux and on Darwin, but will not work reliably
> on any other system.
>
> That is, I don't think that any system can reliably use
> mmap_gt_pch_get_address/mmap_gt_pch_use_address, although they are the
> default functions on a system which supports mmap.
>
> Is it better to have PCH which unpredictably fails or PCH which
> reliably fails?  Right now, in mainline, I think we have the former,
> except on GNU/Linux and Darwin.

I think that PCH that fails on one case out of a thousand is better 
than PCH that fails in one thousand cases out of one thousand.  
However, it would be better if we could make failure even less frequent 
by tweaking the heuristic.  Ian, you've studied the problem, do you 
have any suggestions for a better heuristic?  Maybe gt_pch_get_address 
should map, say, 32M of unused memory before trying to allocate space 
for the PCH.