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>
why?
The payload will have its own GDT.
YH
On 9/9/05, Steven J. Magnani steve@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@openbios.org http://www.openbios.org/mailman/listinfo/linuxbios
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:yinghailu@gmail.com] Sent: Friday, September 09, 2005 10:03 AM To: Steven J. Magnani Cc: linuxbios@openbios.org 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 steve@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 Earthling, return my space modulator!"
#include <standard.disclaimer>
-- LinuxBIOS mailing list LinuxBIOS@openbios.org http://www.openbios.org/mailman/listinfo/linuxbios
-
Steven J. Magnani -
yhlu