From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Florian Pflug <fgp(at)phlo(dot)org> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: same-address mappings vs. relative pointers |
Date: | 2013-12-11 10:47:37 |
Message-ID: | 20131211104737.GA1721@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2013-12-11 11:42:25 +0100, Florian Pflug wrote:
> On Dec5, 2013, at 15:44 , Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> > There might be some ugly compiler dependent magic we could do. Depending
> > on how we decide to declare offsets. Like (very, very roughly)
> >
> > #define relptr(type, struct_name, varname) union struct_name##_##varname{ \
> > type relptr_type; \
> > Offset relptr_off;
> > }
> >
> > And then, for accessing have:
> > #define relptr_access(seg, off) \
> > typeof(off.relptr_type)* (((char *)seg->base_address) + off.relptr_off)
> >
> > But boy, that's ugly.
>
> Well, uglyness we can live with, especially if it's less ugly than the
> alternatives. But I'm afraid is also unportable - typeof() is a GCC
> extension, not a part of ANSI C, no?
Yes (although there's C11 stuff to do equivalent stuff afair) - I was
thinking of only doing it for compilers we support that dark magic for
and fall back to returning a void* for the others. We'll probably miss a
cast or two required on !gcc that way, but it's still likely to be less
error prone.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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