Re: RFC: Cygwin 64 bit?

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Jan 19 11:13, Pedro Alves wrote:
> On 01/19/2012 10:25 AM, Corinna Vinschen wrote:
> > On Jan 18 15:54, Corinna Vinschen wrote:
> >>  From the LLP64 code:
> >>
> >>    <1><d0>: Abbrev Number: 2 (DW_TAG_base_type)
> >>       <d1>   DW_AT_byte_size   : 4        
> >>       <d2>   DW_AT_encoding    : 5        (signed)
> >>       <d3>   DW_AT_name        : long int 
> >>
> >>  From the LP64 code in the same CU:
> >>
> >>    <1><dc>: Abbrev Number: 2 (DW_TAG_base_type)
> >>       <dd>   DW_AT_byte_size   : 8        
> >>       <de>   DW_AT_encoding    : 5        (signed)
> >>       <df>   DW_AT_name        : long int     
> > 
> > That won't be the case, fortunately.  A collegue has created a POC patch
> > which would result in only one entry for long, the "right" one with
> > DW_AT_byte_size 8, while the LLP64 usage of long would be converted to
> > the type int internally.
> 
> Sounds like there's potential for gdb getting confused.
> 
> There's also C++ mangling to consider:
> 
> #pragma model64 (push, LLP64)
> void foo (long i);
> #pragma model64 (pop)
> void foo (long i);
> void foo (int i);
> 
> What does the llp64 version mangle to?  If it's auto converted to
> int internally, then it conflicts with the int version.  If it's
> kept as long, then it conflicts with the lp64 long version.

Yes, there is a downside to the concept.  Of course the LLP64 version
would collide with one of the LP64 versions.  But is that a realistic
problem?  The usage of such a, let's say, dangerous #pragma would be to
fix a specific problem.  The idea is to find an easy solution to use the
strict LLP64 Win32 headers with an LP64 compiler.  Everything beyond that
falls under "you're doing that at your own risk".

So far we had four potential ways to tackle this problem in this thread:

1. Use `#ifdef __LP64__' and define as `int' and `unsigned int'
   only on LP64 compilers.

2. Change all `long' and `unsigned long' to `int' and `unsigned int'
   unconditionally.

3. Add `__attribute__ ((mode(SI)))' to affected typedefs.

4. Introduce a #pragme to redefine long.

What solution would you prefer?  Or is there another, perhaps more
inelligent way to do it which we didn't discuss yet?

And then again, which of these methods, if any, would be acceptable
upstream?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat