Stefan Reinauer (stefan.reinauer@coreboot.org) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/259
-gerrit
commit 7f8e685996f65f2c67d1113fcfaab33ccc385da7 Author: Stefan Reinauer reinauer@chromium.org Date: Wed Jun 1 14:01:46 2011 -0700
Load an IDT with NULL limit
Load an IDT with NULL limit to prevent the 16bit IDT being used in protected mode before c_start.S sets up a 32bit IDT when entering ram stage.
Signed-off-by: Stefan Reinauer reinauer@google.com Change-Id: I8d048c894c863ac4971fcef8f065be6b899e1d3e --- src/cpu/x86/16bit/entry16.inc | 15 ++++++++++++++- src/cpu/x86/16bit/entry16.lds | 1 + 2 files changed, 15 insertions(+), 1 deletions(-)
diff --git a/src/cpu/x86/16bit/entry16.inc b/src/cpu/x86/16bit/entry16.inc index 1eb92c8..9f4c0e3 100644 --- a/src/cpu/x86/16bit/entry16.inc +++ b/src/cpu/x86/16bit/entry16.inc @@ -45,7 +45,6 @@ _start: xorl %eax, %eax movl %eax, %cr3 /* Invalidate TLB*/
- /* Invalidating the cache here seems to be a bad idea on * modern processors. Don't. * If we are hyperthreaded or we have multiple cores it is bad, @@ -55,6 +54,13 @@ _start: * entry16.inc. */
+ /* Load an IDT with NULL limit to prevent the 16bit IDT being used + * in protected mode before c_start.S sets up a 32bit IDT when entering + * ram stage. + */ + movw $nullidt_offset, %bx + lidt %cs:(%bx) + /* Note: gas handles memory addresses in 16 bit code very poorly. * In particular it doesn't appear to have a directive allowing you * associate a section or even an absolute offset with a segment register. @@ -118,6 +124,13 @@ gdtptr16: .word gdt_end - gdt -1 /* compute the table limit */ .long gdt /* we know the offset */
+.align 4 +.globl nullidt +nullidt: + .word 0 /* limit */ + .long 0 + .word 0 + .globl _estart _estart: .code32 diff --git a/src/cpu/x86/16bit/entry16.lds b/src/cpu/x86/16bit/entry16.lds index 0580f0e..112d429 100644 --- a/src/cpu/x86/16bit/entry16.lds +++ b/src/cpu/x86/16bit/entry16.lds @@ -1 +1,2 @@ gdtptr16_offset = gdtptr16 & 0xffff; + nullidt_offset = nullidt & 0xffff;