Re: [PATCH 1/4] xen/PVH: Replace GDT_ENTRY with explicit constant

[Boris Ostrovsky]

On 05/01/2018 07:31 AM, David Laight wrote:
> From: Boris Ostrovsky
> > Sent: 30 April 2018 17:24
> > To: linux-kernel@xxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: jgross@xxxxxxxx; Boris Ostrovsky; stable@xxxxxxxxxxxxxxx
> > Subject: [PATCH 1/4] xen/PVH: Replace GDT_ENTRY with explicit constant
> >
> > Latest binutils release (2.29.1) will no longer allow proper computation
> > of GDT entries on 32-bits, with warning:
> >
> > arch/x86/xen/xen-pvh.S: Assembler messages:
> > arch/x86/xen/xen-pvh.S:150: Warning: shift count out of range (32 is not between 0 and 31)
> > arch/x86/xen/xen-pvh.S:150: Warning: shift count out of range (40 is not between 0 and 31)
> > arch/x86/xen/xen-pvh.S:150: Warning: shift count out of range (32 is not between 0 and 31)
> > arch/x86/xen/xen-pvh.S:152: Warning: shift count out of range (32 is not between 0 and 31)
> > arch/x86/xen/xen-pvh.S:152: Warning: shift count out of range (40 is not between 0 and 31)
> > arch/x86/xen/xen-pvh.S:152: Warning: shift count out of range (32 is not between 0 and 31)
> >
> > Use explicit value of the entry instead of using GDT_ENTRY() macro.
> ...
> >   #ifdef CONFIG_X86_64
> > -	.quad GDT_ENTRY(0xa09a, 0, 0xfffff) /* __KERNEL_CS */
> > +	.quad 0x00af9a000000ffff            /* __BOOT_CS */
> >   #else
> > -	.quad GDT_ENTRY(0xc09a, 0, 0xfffff) /* __KERNEL_CS */
> > +	.quad 0x00cf9a000000ffff            /* __BOOT_CS */
> >   #endif
> > -	.quad GDT_ENTRY(0xc092, 0, 0xfffff) /* __KERNEL_DS */
> > +	.quad 0x00cf92000000ffff            /* __BOOT_DS */
> >   gdt_end:
>
> It has to be possible to fix the GDT_ENTRY() macro.
> Even if you end up with one that generates two 32bit values.


Is it worth it though? We seem to be using GDT_ENTRY_INIT() everywhere 
and the only other reference that I see is in pm.c and it also probably 
ought to use GDT_ENTRY_INIT().


> You've also changed the name in the comments.

Yes, I should mention this in the commit message.


-boris