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List:       gcc
Subject:    Re: PCH versus --enable-mapped-location
From:       Geoffrey Keating <geoffk () geoffk ! org>
Date:       2005-03-31 23:52:01
Message-ID: m2is37gyqm.fsf () greed ! local
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Per Bothner <per@bothner.com> writes:

> Daniel Jacobowitz wrote:
>   > That's exactly what Geoff said.  There are two relevant properties of
> > GCed memory here:
> >   - Anything in GCed memory will be saved to the PCH
> >   - Anything in GCed memory will be overwritten by loading the PCH.
> 
> So the corrollary: After a restore any pointers from non-gc'd memory to
> gc'd memory will be a dangling pointer, if we count static variables
> marked with GTY as "gc'd memory" in this context.

Yes.  Don't keep pointers to GCed memory in non-GCed memory.  The GC/PCH
machinery assumes that it can see all pointers to the objects it
allocates.

> Right now, as far as I can tell, the filenames in the line_table are
> allocated from non-gc'd memory.  This complicates using gc.

This is the reverse case: pointers to non-GCed memory in GCed memory.
There is one case where this is allowed, which just happens to be the
case that you want: a pointer to a C string.
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