Re: kde4libs vs qt4

[Helge Deller <deller@gmx.de>]

Carlos O'Donell wrote:
> On Mon, Jun 9, 2008 at 6:26 PM, Helge Deller <deller@gmx.de> wrote:
> > attached is a _completely_ untested patch which should
> > show what's needed. In principle we could
> > a) copy over the HPUX-parisc architecture files to arch/hppa and apply the
> > patch on top of the copy (as you suggest above), or
> > b) alternatively, we could try to merge HPUX's parisc and Linux's HPPA
> > architecture into the existing Trolltech codebase of parisc.
> >
> > I'll continue to look into it and will try to clean it up, depending on what
> > you think which solution (a or b) is best.
>
> Unfortunately I think you're approach won't work due to the alignment
> requirements placed on ldcw? It has to be 16-byte aligned according to
> the architecture docs.
>
> I was looking into the kde4libs issue, and I think the solution is to
> copy atomic.h from glibc and use that interface.
> http://sourceware.org/cgi-bin/cvsweb.cgi/ports/sysdeps/unix/sysv/linux/hppa/bits/atomic.h?rev=1.4&content-type=text/x-cvsweb-markup&cvsroot=glibc
>
> This obviously only works when we have the linux kernel helper routines.
>
> (better yet would be to put atomic.h into gcc, implement the atomic
> builtins with that, and then propgate the use of the atomic builtins
> to glibc and other software that needs it).

For Qt it might work as I mentioned without copying atomic.h from glibc.
Qt uses ldcw() not directly. Instead it uses q_atomic_lock(), which then 
utilizes q_ldcw().

Here is the code (from src/corelib/arch/parisc/qatomic_parisc.cpp):
    void q_atomic_lock(int *lock)
    {
        // ldcw requires a 16-byte aligned address
        volatile int *x = align16(lock);
        while (q_ldcw(x) == 0)
            ;
    }
So, the 16byte alignment is taken care of by align16().
My attempt was based on having a minimal patch against Qt.

Helge