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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 |