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authorKyösti Mälkki <kyosti.malkki@gmail.com>2012-03-05 09:25:12 +0200
committerPatrick Georgi <patrick@georgi-clan.de>2012-03-16 19:34:14 +0100
commit7863015c3eabe94c360ff893723f48af23a47a33 (patch)
tree90a86cfbee75d7cd3cb51c11936c79d30786d161 /src/cpu
parent5750ed253a6ed45e574a8855a7b7b1abe16eae88 (diff)
downloadcoreboot-7863015c3eabe94c360ff893723f48af23a47a33.tar.xz
Fix address of IDT in real-mode entry
In a case of CS & 0x0fff != 0x0, lidt memory operand does not point to nullidt, this can raise an exception and shutdown the CPU. When an AP CPU receives 8-bit Start-Up IPI vector yzH, it starts execute at physical address 000yz000H. Seems this translates to either yz00:0000 or y000:z000 (CS:IP), depending of the CPU model. With the change entry16.inc is relocatable as the commentary suggests and can be used as ap_sipi_vector on SMP systems. Change-Id: I885a2888179700ba6e2b11d4f2d6a64ddea4c2dc Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com> Reviewed-on: http://review.coreboot.org/707 Tested-by: build bot (Jenkins) Reviewed-by: Idwer Vollering <vidwer@gmail.com> Reviewed-by: Ronald G. Minnich <rminnich@gmail.com> Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
Diffstat (limited to 'src/cpu')
-rw-r--r--src/cpu/x86/16bit/entry16.inc15
1 files changed, 8 insertions, 7 deletions
diff --git a/src/cpu/x86/16bit/entry16.inc b/src/cpu/x86/16bit/entry16.inc
index 0fa8c11524..e4613bf986 100644
--- a/src/cpu/x86/16bit/entry16.inc
+++ b/src/cpu/x86/16bit/entry16.inc
@@ -57,13 +57,6 @@ _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.
@@ -98,10 +91,18 @@ _start:
* the low 16 bits. This means that the intial segment used
* when start is called must be 64K aligned. This should not
* restrict the address as the ip address can be anything.
+ *
+ * Also 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. In practise: CPU will shutdown on any exception.
+ * See IA32 manual Vol 3A 19.26 Interrupts.
*/
movw %cs, %ax
shlw $4, %ax
+ movw $nullidt_offset, %bx
+ subw %ax, %bx
+ lidt %cs:(%bx)
movw $gdtptr16_offset, %bx
subw %ax, %bx
data32 lgdt %cs:(%bx)