[LinuxBIOS] PATCH: relocate GDT before invoking payload

[yhlu]

why?

The payload will have its own GDT.

YH

On 9/9/05, Steven J. Magnani <steve at digidescorp.com> wrote:
> 
> I posted this patch previously; see
> http://openbios.org/pipermail/linuxbios/2005-August/012063.html for the
> original issue.
> 
> Here's another chance to comment before I commit it.
> 
> PATCH:
> 
> --- src/arch/i386/boot/tables.c.orig 2005-09-08 13:35:39.125000000
> -0500
> +++ src/arch/i386/boot/tables.c 2005-08-16 16:17:41.766000000 -0500
> @@ -7,6 +7,32 @@
> #include <arch/acpi.h>
> #include "linuxbios_table.h"
> 
> +// Global Descriptor Table, defined in c_start.S
> +extern uint8_t gdt;
> +extern uint8_t gdt_end;
> +
> +/* i386 lgdt argument */
> +struct gdtarg {
> + unsigned short limit;
> + unsigned int base;
> +} __attribute__((packed));
> +
> +// Copy GDT to new location and reload it
> +// 2003-07 by SONE Takeshi
> +// Ported from Etherboot to LinuxBIOS 2005-08 by Steve Magnani
> +void move_gdt(unsigned long newgdt)
> +{
> + uint16_t num_gdt_bytes = &gdt_end - &gdt;
> + struct gdtarg gdtarg;
> +
> + printk_debug("Moving GDT to %#lx...", newgdt);
> + memcpy((void*)newgdt, &gdt, num_gdt_bytes);
> + gdtarg.base = newgdt;
> + gdtarg.limit = num_gdt_bytes - 1;
> + __asm__ __volatile__ ("lgdt %0\n\t" : : "m" (gdtarg));
> + printk_debug("ok\n");
> +}
> +
> struct lb_memory *write_tables(void)
> {
> unsigned long low_table_start, low_table_end;
> @@ -45,6 +71,10 @@
> low_table_end = 0x500;
> }
> 
> + // Relocate the GDT to reserved memory, so it won't get
> clobbered
> + move_gdt(low_table_end);
> + low_table_end += &gdt_end - &gdt;
> +
> /* The linuxbios table must be in 0-4K or 960K-1M */
> write_linuxbios_table(
> low_table_start, low_table_end,
> 
> ------------------------------------------------------------------------
> Steven J. Magnani "I claim this network for MARS!
> www.digidescorp.com <http://www.digidescorp.com> Earthling, return my 
> space modulator!"
> 
> #include <standard.disclaimer>
> 
> 
> 
> 
> --
> LinuxBIOS mailing list
> LinuxBIOS at openbios.org
> http://www.openbios.org/mailman/listinfo/linuxbios
>
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