88 lines
2.3 KiB
ArmAsm
88 lines
2.3 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
|
|
/*
|
|
* EFI call stub for IA32.
|
|
*
|
|
* This stub allows us to make EFI calls in physical mode with interrupts
|
|
* turned off. Note that this implementation is different from the one in
|
|
* arch/x86/platform/efi/efi_stub_32.S because we're _already_ in physical
|
|
* mode at this point.
|
|
*/
|
|
|
|
#include <linux/linkage.h>
|
|
#include <asm/page_types.h>
|
|
|
|
/*
|
|
* efi_call_phys(void *, ...) is a function with variable parameters.
|
|
* All the callers of this function assure that all the parameters are 4-bytes.
|
|
*/
|
|
|
|
/*
|
|
* In gcc calling convention, EBX, ESP, EBP, ESI and EDI are all callee save.
|
|
* So we'd better save all of them at the beginning of this function and restore
|
|
* at the end no matter how many we use, because we can not assure EFI runtime
|
|
* service functions will comply with gcc calling convention, too.
|
|
*/
|
|
|
|
.text
|
|
ENTRY(efi_call_phys)
|
|
/*
|
|
* 0. The function can only be called in Linux kernel. So CS has been
|
|
* set to 0x0010, DS and SS have been set to 0x0018. In EFI, I found
|
|
* the values of these registers are the same. And, the corresponding
|
|
* GDT entries are identical. So I will do nothing about segment reg
|
|
* and GDT, but change GDT base register in prelog and epilog.
|
|
*/
|
|
|
|
/*
|
|
* 1. Because we haven't been relocated by this point we need to
|
|
* use relative addressing.
|
|
*/
|
|
call 1f
|
|
1: popl %edx
|
|
subl $1b, %edx
|
|
|
|
/*
|
|
* 2. Now on the top of stack is the return
|
|
* address in the caller of efi_call_phys(), then parameter 1,
|
|
* parameter 2, ..., param n. To make things easy, we save the return
|
|
* address of efi_call_phys in a global variable.
|
|
*/
|
|
popl %ecx
|
|
movl %ecx, saved_return_addr(%edx)
|
|
/* get the function pointer into ECX*/
|
|
popl %ecx
|
|
movl %ecx, efi_rt_function_ptr(%edx)
|
|
|
|
/*
|
|
* 3. Call the physical function.
|
|
*/
|
|
call *%ecx
|
|
|
|
/*
|
|
* 4. Balance the stack. And because EAX contain the return value,
|
|
* we'd better not clobber it. We need to calculate our address
|
|
* again because %ecx and %edx are not preserved across EFI function
|
|
* calls.
|
|
*/
|
|
call 1f
|
|
1: popl %edx
|
|
subl $1b, %edx
|
|
|
|
movl efi_rt_function_ptr(%edx), %ecx
|
|
pushl %ecx
|
|
|
|
/*
|
|
* 10. Push the saved return address onto the stack and return.
|
|
*/
|
|
movl saved_return_addr(%edx), %ecx
|
|
pushl %ecx
|
|
ret
|
|
ENDPROC(efi_call_phys)
|
|
.previous
|
|
|
|
.data
|
|
saved_return_addr:
|
|
.long 0
|
|
efi_rt_function_ptr:
|
|
.long 0
|