precompiled header support

[Gunther Nikl]

On Fri, May 07, 2004 at 11:22:40AM -0400, Ian Lance Taylor wrote:
> Gunther Nikl <gni@gecko.de> writes:
> 
> > What host capabilites are required to use precompiled headers? The sources
> > seem to imply that mmap() is required to load a PCH to fixed address. What
> > happens if a host doesn't support mmap? To which address the PCH will be
> > loaded?
> 
> Really what is required is that the host provide a fixed address at which
> a PCH can be loaded.  This address must be fixed for a particular instance
> of cc1, not necessarily fixed in general.

  What is "fixed for a particular instance of cc1"? That the address is
  always the same for a specific cc1 but might be different with another
  cc1? However, that doesn't really matter in this case.

> On some hosts the natural way to implement this is to use mmap with a
> fixed address.  See config/host-linux.c in mainline.  On at least one
> host, the natural way to implement this is to define a large array
> within gcc1 itself.  See config/rs6000/host-darwin.c.

  Both approaches don't work with "my" host since the OS always loads
  executables to random addresses. This is by design to not require a MMU.
  An executable might have an relocation table if necessary to allow the
  loader to adapt the program for the real address in memory.

> > Is it possible to disable generating/using precompiled headers for hosts
> > that don't support it?
> 
> Well, nobody requires you to generate a precompiled header.

  Generating a precompiled header works :) Using it doesn't work. If I am
  lucky I get "text segment moved". If I am not lucky the compiler crashes.
  What I am after is: I want prevent other users on that host (if any) to
  use a feature that doesn't work. I suppose they would try it regardless
  of what documentation states.

  Gunther