Re: Revised^2 precompiled header support for cygwin

[Earl Chew <earl_chew at agilent dot com>]

Billinghurst, David (CALCRTS) wrote:
> This patch is based on  Earl Chew's 3.4 patch for precompiled header support for cygwin
> 	http://gcc.gnu.org/ml/gcc-patches/2004-10/msg01211.html
> Earl:  Let we know if you no longer want your name associated with this?

David, thanks for following up and integrating my patch into something
more recent.

> Mainline has the additional hooks required, so this is much less intrusive.

Yes, the new scheme has improvements over the older one.

> One thing I was unsure about.  In host-cygwin.c(cygwin_gt_pch_get_address)
> I use fdopen to associate a stream with a file descriptor.  Should I
> close the stream or not?  I don't see any "bad things" if I leave the 
> stream open.

This is not nice in the sense that the FILE* is leaked. In hindsight,
I think it's better if the code simply use the raw fd as is, rather
than trying to paste a FILE* over the top of it. At this point, this
code is Cygwin specific, so there is no need to attempt to try to
use stdio for portability.

I think the following would be better:

static void *
cygwin_gt_pch_get_address (size_t sz, int fd)
{
  void *base;
  off_t p = lseek(fd, 0, SEEK_CUR);

  if (p == (off_t) -1)
    fatal_error ("can't get position in PCH file: %m");

   /* Cygwin requires that the underlying file be at least
      as large as the requested mapping.  */
  if ((size_t) p < sz)
  {
    if ( lseek (fd, sz-1, SEEK_SET) != 0
      || write (fd, '\0', 1) == 1 )
      fatal_error ("can't extend PCH file: %m");
  }

  base = mmap (NULL, sz, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);

  if (base == MAP_FAILED)
    base = NULL;
  else
    munmap (base, sz);

  if (lseek (fd, p, SEEK_SET) != 0)
    fatal_error ("can't set position in PCH file: %m");

  return base;
}

Earl
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