Re: [PATCH] Abort if gcc4 was used to compile qemu and kvm is not enabled

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Carlo Marcelo Arenas Belon wrote:
> On Mon, Oct 08, 2007 at 02:29:32PM -0500, Anthony Liguori wrote:
>   
> 3) We do nothing, add a warning to the compilation for the users to read at
> compile time (most of them not aware that they should be using gcc-3.x instead
> as they are used to see all the other compilation warnings anyway) and then
> let kvm segfault when they start it without loading the module first.
>   

Here are some alternatives that I think are more reasonable:

1) implement a KVM target for QEMU that doesn't use dyngen at all.  Some 
of the architecture ports (like ia64 and s390) are going to require this 
anyway since dyngen doesn't support ia64 or s390.  There's no reason 
this can be used for x86 too.

2) work on getting the assembly post-processor merged into upstream 
QEMU.  IMHO, this is the best long term strategy for QEMU GCC4 support.

3) you have to pass an option to ./configure to disable the gcc4 check.  
Issue a big fat warning when the user does this saying that the 
resulting QEMU will not probably work with -no-kvm or if the KVM modules 
are loaded.  The user is smart enough to disable the gcc4 check so I 
have to imagine that they are smart enough to not completely ignore this 
warning.

Regards,

Anthony Liguori

> If nothing, a message saying this won't work because you used the wrong
> compiler, is IMHO better than a plain segfault.
>
> Carlo
>
> PS. if qemu gets upstream officially a solution to compile with gcc4, I'll be
> the first one getting that merged and removing this patch.
>
> PS2. getting gcc4 to generate valid chunks of "copyable" code as required by
> qemu's dyngen is not something that would happen accidentally, for a promising
> alternative look at the GCC 2007 proceedings abstract "Towards GCC as a
> compiler for multiple VMs", pages 117-130,
> http://ols2006.108.redhat.com/2007/GCC-Reprints/GCC2007-Proceedings.pdf
>
>   


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