[Qemu-devel] [RFC] env stored in segment register for i386

[Richard Henderson <rth@twiddle.net>]

On 07/02/2010 08:37 AM, Paolo Bonzini wrote:
> The second (more real) reason is inline assembly failures, for example
> (32-bit x86):
> 
>     register int e asm("edi");
> 
>     static inline int h()
>     {
>         int x;
>         asm volatile ("mov $0, %0" : "=D" (x));
>     }
> 
>     int g()
>     {
>         int f = e;
>         h();
>         return e - f;
>     }
> 
> fails to compile because gcc cannot assign edi to %0 in h().  Some host
> headers may use assembly in a way that breaks qemu.  With only one
> global register in use, however, it makes sense IMO to drop the custom
> inclusion hacks and see if anyone screams.

A few months ago I developed a patch that would allow the global env
variable to be accessed via %fs (plus a backing TLS variable), which
means that no hardware register needs to be reserved for i386.

I never quite got around to finishing it because I don't know how to
set up a segment register in Windows, and it seemed like the kind of
patch that could easily get quagmired.

Is there any interest in a patch like this?  Should I try to revive it?


r~