Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | /* |
2 | * EFI call stub for IA32. | |
3 | * | |
4 | * This stub allows us to make EFI calls in physical mode with interrupts | |
5 | * turned off. | |
6 | */ | |
7 | ||
1da177e4 LT |
8 | #include <linux/linkage.h> |
9 | #include <asm/page.h> | |
1da177e4 LT |
10 | |
11 | /* | |
12 | * efi_call_phys(void *, ...) is a function with variable parameters. | |
13 | * All the callers of this function assure that all the parameters are 4-bytes. | |
14 | */ | |
15 | ||
16 | /* | |
17 | * In gcc calling convention, EBX, ESP, EBP, ESI and EDI are all callee save. | |
18 | * So we'd better save all of them at the beginning of this function and restore | |
19 | * at the end no matter how many we use, because we can not assure EFI runtime | |
20 | * service functions will comply with gcc calling convention, too. | |
21 | */ | |
22 | ||
23 | .text | |
24 | ENTRY(efi_call_phys) | |
25 | /* | |
26 | * 0. The function can only be called in Linux kernel. So CS has been | |
27 | * set to 0x0010, DS and SS have been set to 0x0018. In EFI, I found | |
28 | * the values of these registers are the same. And, the corresponding | |
29 | * GDT entries are identical. So I will do nothing about segment reg | |
30 | * and GDT, but change GDT base register in prelog and epilog. | |
31 | */ | |
32 | ||
33 | /* | |
34 | * 1. Now I am running with EIP = <physical address> + PAGE_OFFSET. | |
35 | * But to make it smoothly switch from virtual mode to flat mode. | |
36 | * The mapping of lower virtual memory has been created in prelog and | |
37 | * epilog. | |
38 | */ | |
39 | movl $1f, %edx | |
40 | subl $__PAGE_OFFSET, %edx | |
41 | jmp *%edx | |
42 | 1: | |
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 %edx | |
51 | movl %edx, saved_return_addr | |
52 | /* get the function pointer into ECX*/ | |
53 | popl %ecx | |
54 | movl %ecx, efi_rt_function_ptr | |
55 | movl $2f, %edx | |
56 | subl $__PAGE_OFFSET, %edx | |
57 | pushl %edx | |
58 | ||
59 | /* | |
60 | * 3. Clear PG bit in %CR0. | |
61 | */ | |
62 | movl %cr0, %edx | |
63 | andl $0x7fffffff, %edx | |
64 | movl %edx, %cr0 | |
65 | jmp 1f | |
66 | 1: | |
67 | ||
68 | /* | |
69 | * 4. Adjust stack pointer. | |
70 | */ | |
71 | subl $__PAGE_OFFSET, %esp | |
72 | ||
73 | /* | |
74 | * 5. Call the physical function. | |
75 | */ | |
76 | jmp *%ecx | |
77 | ||
78 | 2: | |
79 | /* | |
80 | * 6. After EFI runtime service returns, control will return to | |
81 | * following instruction. We'd better readjust stack pointer first. | |
82 | */ | |
83 | addl $__PAGE_OFFSET, %esp | |
84 | ||
85 | /* | |
86 | * 7. Restore PG bit | |
87 | */ | |
88 | movl %cr0, %edx | |
89 | orl $0x80000000, %edx | |
90 | movl %edx, %cr0 | |
91 | jmp 1f | |
92 | 1: | |
93 | /* | |
94 | * 8. Now restore the virtual mode from flat mode by | |
95 | * adding EIP with PAGE_OFFSET. | |
96 | */ | |
97 | movl $1f, %edx | |
98 | jmp *%edx | |
99 | 1: | |
100 | ||
101 | /* | |
102 | * 9. Balance the stack. And because EAX contain the return value, | |
103 | * we'd better not clobber it. | |
104 | */ | |
105 | leal efi_rt_function_ptr, %edx | |
106 | movl (%edx), %ecx | |
107 | pushl %ecx | |
108 | ||
109 | /* | |
110 | * 10. Push the saved return address onto the stack and return. | |
111 | */ | |
112 | leal saved_return_addr, %edx | |
113 | movl (%edx), %ecx | |
114 | pushl %ecx | |
115 | ret | |
116 | .previous | |
117 | ||
118 | .data | |
119 | saved_return_addr: | |
120 | .long 0 | |
121 | efi_rt_function_ptr: | |
122 | .long 0 |