RE: [LinuxBIOS] PATCH: relocate GDT before invoking payload

[Lu, Yinghai]

I'm ok with this patch.

YH

________________________________

From: [e-mail]
[mailto:[e-mail]] On Behalf Of Steven J. Magnani
Sent: Friday, September 09, 2005 9:35 AM
To: [e-mail]
Cc: [e-mail]
Subject: RE: [LinuxBIOS] PATCH: relocate GDT before invoking payload

QNX Neutrino doesn't set up its own GDT right away. Its startup code has
some defensive logic that attempts to put the system into a known state.
This causes an exception when booted from LinuxBIOS, if its GDT got
trashed when elfboot() loaded the Neutrino image. See the hyperlink
below for more discussion.

The fix seems straightforward, and the increased amount of "table"
memory very modest. Do you object to this patch?

Steve

-----Original Message-----
    From: yhlu [mailto:[e-mail]] 
    Sent: Friday, September 09, 2005 10:03 AM
    To: Steven J. Magnani
    Cc: [e-mail]
    Subject: Re: [LinuxBIOS] PATCH: relocate GDT before invoking
payload

why?
    
    The payload will have its own GDT.
    
    YH

On 9/9/05, Steven J. Magnani  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              Earthling, return my space
modulator!"
    
    #include <standard.disclaimer>
    
    
    
    
    --
    LinuxBIOS mailing list
    [e-mail]
    http://www.openbios.org/mailman/listinfo/linuxbios