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 8#include <linux/linkage.h> 9#include <asm/page_types.h> 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 24ENTRY(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 prolog 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 prolog and 37 * epilog. 38 */ 39 movl $1f, %edx 40 subl $__PAGE_OFFSET, %edx 41 jmp *%edx 421: 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 661: 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 77 782: 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 921: 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 991: 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 116ENDPROC(efi_call_phys) 117.previous 118 119.data 120saved_return_addr: 121 .long 0 122efi_rt_function_ptr: 123 .long 0 124