Re: [tip:x86/asm] x86: Introduce GDT_ENTRY_INIT()

Ingo Molnar
2009-08-04T12:18:54Z

* H. Peter Anvin <hpa@zytor.com> wrote:

> On 08/03/2009 08:11 AM, Akinobu Mita wrote:
> >>>>
> >> OK, I spotted the following error, which certainly would explain a crash on
> >> an APM machine:
> >>
> >> /* data */
> >> - [GDT_ENTRY_APMBIOS_BASE+2] = { { { 0x0000ffff, 0x00409200 } }
> >> },
> >> + [GDT_ENTRY_APMBIOS_BASE+2] = GDT_ENTRY_INIT(0x409a, 0, 0xffff),
> >
> > Oops, I really should have checked the binary because the compiler should
> > generate same code with this patch.
> >
>
> Well, it doesn't even on the best of days, because the last hunk changes
> a dynamic initializer to a strange mix between static and dynamic:
>
> -static struct desc_struct bad_bios_desc;
> +static struct desc_struct bad_bios_desc = GDT_ENTRY_INIT(0x4092, 0, 0);
>
> /*
> * At some point we want to use this stack frame pointer to unwind
> @@ -476,9 +476,6 @@ void pnpbios_calls_init(union
> pnp_bios_install_struct *header)
> pnp_bios_callpoint.offset = header->fields.pm16offset;
> pnp_bios_callpoint.segment = PNP_CS16;
>
> - bad_bios_desc.a = 0;
> - bad_bios_desc.b = 0x00409200;
> -
> set_desc_base(&bad_bios_desc, (unsigned long)__va(0x40UL << 4));
> set_desc_limit(&bad_bios_desc, 4095 - (0x40 << 4));
>
> This is about at strange as it comes; I think we could simply do:
>
> GDT_ENTRY_INIT(0x4092, (unsigned long)__va(0x400UL), 4095-0x400);
>
> Although perhaps the 4095 should really be PAGE_SIZE-1...

I've removed the patch for now - please resubmit when fixed.

Ingo