Re: alpha 2.4.13: fix taso osf emulation

[Maciej W. Rozycki]

On Fri, 26 Oct 2001, Richard Henderson wrote:

> >  The following trivial patch reportedly fixes OSF/1 programs using 31-bit
> > addressing.  It's already present in the -ac tree; I guess it just got
> > lost during a merge.  It applies fine to 2.4.13. 
> 
> This is the patch that Jay Estabrook forwarded me that I rejected
> in favour of writing a special arch_get_unmapped_area.

 Ah, that is a fine approach as well; I just considered the change small
enough it's not worth making it arch-specific.  Besides, my patch alsoo 
has a small advantage of keeping the search algorithm the same across all
the archs.

> > It used to do so.  It breaks things such as dynamic linking of shared
> > objects linked at high load address.
> 
> Err, how?

 I mean, the original algorithm as implemented in 2.4.9.  If you had asked
e.g. for memory above TASK_SIZE you would have got an error no matter how
much address space was still available below.

> > It breaks mmap() in principle, as it shouldn't fail when invoked with
> > a non-zero, non-MAP_FIXED, invalid address if there is still address
> > space available elsewhere. 
> 
> No, it doesn't.  Or rather, it only does if you only bothered
> to search once.  IMO one should search thrice: once at addr,
> once at TASK_UNMAPPED_BASE, and once at PAGE_SIZE.

 OK, but I'd prefer to avoid searching overlapping areas over and over
again for performance's sake.  My solution does a single lookup and a
single search, effectively covering at least the whole space that would be
used if no address preference was specified; more if a program asked for
space below TASK_UNMAPPED_BASE (= "yes, I know what I'm doing, I want to
limit my brk() space"). 

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: [e-mail], PGP key available        +