[linux-2.6-block.git] / arch / x86 / boot / compressed / efi_stub_32.S

/* 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
Commit	Line	Data
b2441318	1	/* SPDX-License-Identifier: GPL-2.0 */
291f3632 MF	2	/*
	3	* EFI call stub for IA32.
	4	*
	5	* This stub allows us to make EFI calls in physical mode with interrupts
	6	* turned off. Note that this implementation is different from the one in
	7	* arch/x86/platform/efi/efi_stub_32.S because we're _already_ in physical
	8	* mode at this point.
	9	*/
	10
	11	#include <linux/linkage.h>
	12	#include <asm/page_types.h>
	13
	14	/*
	15	* efi_call_phys(void *, ...) is a function with variable parameters.
	16	* All the callers of this function assure that all the parameters are 4-bytes.
	17	*/
	18
	19	/*
	20	* In gcc calling convention, EBX, ESP, EBP, ESI and EDI are all callee save.
	21	* So we'd better save all of them at the beginning of this function and restore
	22	* at the end no matter how many we use, because we can not assure EFI runtime
	23	* service functions will comply with gcc calling convention, too.
	24	*/
	25
	26	.text
	27	ENTRY(efi_call_phys)
	28	/*
	29	* 0. The function can only be called in Linux kernel. So CS has been
	30	* set to 0x0010, DS and SS have been set to 0x0018. In EFI, I found
	31	* the values of these registers are the same. And, the corresponding
	32	* GDT entries are identical. So I will do nothing about segment reg
	33	* and GDT, but change GDT base register in prelog and epilog.
	34	*/
	35
	36	/*
	37	* 1. Because we haven't been relocated by this point we need to
	38	* use relative addressing.
	39	*/
	40	call 1f
	41	1: popl %edx
	42	subl $1b, %edx
	43
	44	/*
	45	* 2. Now on the top of stack is the return
	46	* address in the caller of efi_call_phys(), then parameter 1,
	47	* parameter 2, ..., param n. To make things easy, we save the return
	48	* address of efi_call_phys in a global variable.
	49	*/
	50	popl %ecx
	51	movl %ecx, saved_return_addr(%edx)
	52	/* get the function pointer into ECX*/
	53	popl %ecx
	54	movl %ecx, efi_rt_function_ptr(%edx)
	55
	56	/*
	57	* 3. Call the physical function.
	58	*/
	59	call *%ecx
	60
	61	/*
	62	* 4. Balance the stack. And because EAX contain the return value,
	63	* we'd better not clobber it. We need to calculate our address
	64	* again because %ecx and %edx are not preserved across EFI function
	65	* calls.
66	*/
67	call 1f
68	1: popl %edx
69	subl $1b, %edx
70
71	movl efi_rt_function_ptr(%edx), %ecx
72	pushl %ecx
73
74	/*
75	* 10. Push the saved return address onto the stack and return.
76	*/
77	movl saved_return_addr(%edx), %ecx
78	pushl %ecx
79	ret
80	ENDPROC(efi_call_phys)
81	.previous
82
83	.data
84	saved_return_addr:
85	.long 0
86	efi_rt_function_ptr:
87	.long 0