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authorMathias Krause <minipli@googlemail.com>2012-04-01 11:32:09 +0200
committerStefan Reinauer <stefan.reinauer@coreboot.org>2012-04-02 19:50:22 +0200
commit971804ed68347f4fe7ca985a3c924b28041a4079 (patch)
tree2aca2a92d30e62c44b9f03c589f48bd2078b015a
parent74a0efe09a203959d5ab4879e4c1cf139c93b410 (diff)
x86, oprom: ensure DF is always cleared
The Option ROM might mess with the EFLAGS register and break assumptions the C part of coreboot implicitly has, e.g. the state of the direction flag. Prevent Option ROMs from confusing coreboot by restoring the old EFLAGS value after the Option ROMs has finished and always clear the direction flag before calling the C part of the interrupt handler. Change-Id: I84663be6681b17f95f48d93f0b730e443336b4a8 Signed-off-by: Mathias Krause <minipli@googlemail.com> Reviewed-on: http://review.coreboot.org/837 Tested-by: build bot (Jenkins) Reviewed-by: Ronald G. Minnich <rminnich@gmail.com> Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
-rw-r--r--src/devices/oprom/x86_asm.S65
1 files changed, 37 insertions, 28 deletions
diff --git a/src/devices/oprom/x86_asm.S b/src/devices/oprom/x86_asm.S
index 488bfa6b91..56ebb3a885 100644
--- a/src/devices/oprom/x86_asm.S
+++ b/src/devices/oprom/x86_asm.S
@@ -75,35 +75,36 @@ __buffer = RELOCATED(.)
.globl __realmode_call
__realmode_call = RELOCATED(.)
/* save all registers to the stack */
- pushal
+ pusha
+ pushf
- /* Move the protected mode stack to a safe place */
+ /* Move the protected mode stack pointer to a safe place */
movl %esp, __stack
- movl %esp, %ebp
+ movl %esp, %ebp
- /* This function is called with regparm=0 and we have
- * to skip the 32 byte from pushal. Hence start at 36.
+ /* This function is called with regparm=0 and we have to
+ * skip the 36 byte from pushf+pusha. Hence start at 40.
*/
/* entry point */
- movl 36(%ebp), %eax
+ movl 40(%ebp), %eax
mov %ax, __lcall_instr + 1
andl $0xffff0000, %eax
shrl $4, %eax
mov %ax, __lcall_instr + 3
/* initial register values */
- movl 40(%ebp), %eax
- movl %eax, __registers + 0 /* eax */
movl 44(%ebp), %eax
- movl %eax, __registers + 4 /* ebx */
+ movl %eax, __registers + 0 /* eax */
movl 48(%ebp), %eax
- movl %eax, __registers + 8 /* ecx */
+ movl %eax, __registers + 4 /* ebx */
movl 52(%ebp), %eax
- movl %eax, __registers + 12 /* edx */
+ movl %eax, __registers + 8 /* ecx */
movl 56(%ebp), %eax
- movl %eax, __registers + 16 /* esi */
+ movl %eax, __registers + 12 /* edx */
movl 60(%ebp), %eax
+ movl %eax, __registers + 16 /* esi */
+ movl 64(%ebp), %eax
movl %eax, __registers + 20 /* edi */
/* Activate the right segment descriptor real mode. */
@@ -193,41 +194,45 @@ __lcall_instr = RELOCATED(.)
/* restore proper idt */
lidt idtarg
- /* and exit */
+ /* restore stack pointer, eflags and register values */
movl __stack, %esp
- popal
+ popf
+ popa
+ /* and exit */
// TODO return AX from OPROM call
ret
.globl __realmode_interrupt
__realmode_interrupt = RELOCATED(.)
/* save all registers to the stack */
- pushal
- /* save the stack */
+ pusha
+ pushf
+
+ /* save the stack pointer */
movl %esp, __stack
- movl %esp, %ebp
+ movl %esp, %ebp
- /* This function is called with regparm=0 and we have
- * to skip the 32 byte from pushal. Hence start at 36.
+ /* This function is called with regparm=0 and we have to
+ * skip the 36 byte from pushf+pusha. Hence start at 40.
*/
/* prepare interrupt calling code */
- movl 36(%ebp), %eax
+ movl 40(%ebp), %eax
movb %al, __intXX_instr + 1 /* intno */
/* initial register values */
- movl 40(%ebp), %eax
- movl %eax, __registers + 0 /* eax */
movl 44(%ebp), %eax
- movl %eax, __registers + 4 /* ebx */
+ movl %eax, __registers + 0 /* eax */
movl 48(%ebp), %eax
- movl %eax, __registers + 8 /* ecx */
+ movl %eax, __registers + 4 /* ebx */
movl 52(%ebp), %eax
- movl %eax, __registers + 12 /* edx */
+ movl %eax, __registers + 8 /* ecx */
movl 56(%ebp), %eax
- movl %eax, __registers + 16 /* esi */
+ movl %eax, __registers + 12 /* edx */
movl 60(%ebp), %eax
+ movl %eax, __registers + 16 /* esi */
+ movl 64(%ebp), %eax
movl %eax, __registers + 20 /* edi */
/* This configures CS properly for real mode. */
@@ -309,9 +314,10 @@ __intXX_instr = RELOCATED(.)
/* restore coreboot's 32-bit IDT */
lidt idtarg
- /* Exit */
+ /* restore stack pointer, eflags and register values and exit */
movl __stack, %esp
- popal
+ popf
+ popa
ret
/* This is the 16-bit interrupt entry point called by the IDT stub code.
@@ -327,6 +333,9 @@ __interrupt_handler_16bit = RELOCATED(.)
push %fs
push %gs
+ /* Clear DF to not break ABI assumptions */
+ cld
+
/* Clean up the interrupt number. We could have done this in the stub,
* but it would have cost 2 more bytes per stub entry.
*/