Re: [PATCH 5/5] x86: don't build unused entry code when !PV32

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 25/11/2020 08:51, Jan Beulich wrote:
> Except for the initial part of cstar_enter compat/entry.S is all dead
> code in this case. Further, along the lines of the PV conditionals we
> already have in entry.S, make code PV32-conditional there too (to a
> fair part because this code actually references compat/entry.S).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> TBD: I'm on the fence of whether (in a separate patch) to also make
>      conditional struct pv_domain's is_32bit field.
>
> --- a/xen/arch/x86/x86_64/asm-offsets.c
> +++ b/xen/arch/x86/x86_64/asm-offsets.c
> @@ -9,7 +9,7 @@
>  #include <xen/perfc.h>
>  #endif
>  #include <xen/sched.h>
> -#ifdef CONFIG_PV
> +#ifdef CONFIG_PV32
>  #include <compat/xen.h>
>  #endif
>  #include <asm/hardirq.h>
> @@ -102,19 +102,21 @@ void __dummy__(void)
>      BLANK();
>  #endif
>  
> -#ifdef CONFIG_PV
> +#ifdef CONFIG_PV32
>      OFFSET(DOMAIN_is_32bit_pv, struct domain, arch.pv.is_32bit);

Even if PV32 is compiled out, the is_32bit field still exists, and is
still necessary for crash analysis.  XCA parses this offset information
as part of dissecting /proc/vmcore.

It's one single bool in a fixed size allocation which we've got plenty
of room in.  It can and should stay to avoid impacting the existing
diagnostic tools.

~Andrew