From: Jian Luo jian.luo4@boschrexroth.de

PCI option rom may use different SS during its execution, so it is not safe to assume esp pointed to the same location in the protected mode.

Signed-off-by: Jian Luo jian.luo4@boschrexroth.de Signed-off-by: Bin Meng bmeng.cn@gmail.com

--- Changes in v2 respin: - Use *protected* mode instead of 'protect mode' - Correct typo of 'read mode'

Changes in v2: - Add comments for the changes in the assembly codes

arch/x86/lib/bios_asm.S | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)

diff --git a/arch/x86/lib/bios_asm.S b/arch/x86/lib/bios_asm.S index 4faa70e..9dbf969 100644 --- a/arch/x86/lib/bios_asm.S +++ b/arch/x86/lib/bios_asm.S @@ -246,6 +246,9 @@ __interrupt_handler_16bit = PTR_TO_REAL_MODE(.) push %fs push %gs

+ /* Save real mode SS */ + movw %ss, %cs:__realmode_ss + /* Clear DF to not break ABI assumptions */ cld

@@ -258,12 +261,29 @@ __interrupt_handler_16bit = PTR_TO_REAL_MODE(.)

enter_protected_mode

+ /* + * Now we are in protected mode. We need compute the right ESP based + * on saved real mode SS otherwise interrupt_handler() won't get + * correct parameters from the stack. + */ + movzwl %cs:__realmode_ss, %ecx + shll $4, %ecx + addl %ecx, %esp + /* Call the C interrupt handler */ movl $interrupt_handler, %eax call *%eax

+ /* Restore real mode ESP based on saved SS */ + movzwl %cs:__realmode_ss, %ecx + shll $4, %ecx + subl %ecx, %esp + enter_real_mode

+ /* Restore real mode SS */ + movw %cs:__realmode_ss, %ss + /* * Restore all registers, including those manipulated by the C * handler @@ -276,6 +296,9 @@ __interrupt_handler_16bit = PTR_TO_REAL_MODE(.) popal iret

+__realmode_ss = PTR_TO_REAL_MODE(.) + .word 0 + .globl asm_realmode_code_size asm_realmode_code_size: .long . - asm_realmode_code