From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tim Deegan <tim@xen.org>
Subject: Re: [RFC PATCH 1/15]: PVH xen: turn gdb_frames/gdt_ents
	into union
Date: Thu, 24 Jan 2013 14:29:32 +0000
Message-ID: <20130124142932.GC20551@ocelot.phlegethon.org>
References: <20130111172522.6e73d884@mantra.us.oracle.com>
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To: Mukesh Rathor <mukesh.rathor@oracle.com>
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At 17:25 -0800 on 11 Jan (1357925122), Mukesh Rathor wrote:
> diff -r bf249cd5f2c1 -r 278d7a933d88 xen/include/public/arch-x86/xen.h
> --- a/xen/include/public/arch-x86/xen.h	Tue Oct 30 18:12:11 2012 +0000
> +++ b/xen/include/public/arch-x86/xen.h	Fri Jan 11 16:19:40 2013 -0800
> @@ -157,7 +157,16 @@ struct vcpu_guest_context {
>      struct cpu_user_regs user_regs;         /* User-level CPU registers     */
>      struct trap_info trap_ctxt[256];        /* Virtual IDT                  */
>      unsigned long ldt_base, ldt_ents;       /* LDT (linear address, # ents) */
> -    unsigned long gdt_frames[16], gdt_ents; /* GDT (machine frames, # ents) */
> +    union {
> +        struct {
> +            /* GDT (machine frames, # ents) */
> +            unsigned long gdt_frames[16], gdt_ents;
> +        } pv;
> +        struct {
> +            /* PVH: GDTR addr and size */   
> +            unsigned long gdtaddr, gdtsz;

The GDT size is always 16 bits; I'd be inclined to make the addr
explicitly 64 bits too, to help out 32-bit toolstacks. 

> +        } pvh;
> +    } u;

Also, would you consider renaming this as:

    union {
        struct {
            /* GDT (machine frames, # ents) */
            unsigned long frames[16], ents;
        } pv;
        struct {
            /* PVH: GDTR addr and size */   
            unsigned long addr, sz;
        } pvh;
    } gdt;

?  Then the calling code looks a little nicer. 

Cheers,

Tim.