1/* 2 * Code for the vsyscall page. This version uses the sysenter instruction. 3 * 4 * NOTE: 5 * 1) __kernel_vsyscall _must_ be first in this page. 6 * 2) there are alignment constraints on this stub, see vsyscall-sigreturn.S 7 * for details. 8 */ 9 10/* 11 * The caller puts arg2 in %ecx, which gets pushed. The kernel will use 12 * %ecx itself for arg2. The pushing is because the sysexit instruction 13 * (found in entry.S) requires that we clobber %ecx with the desired %esp. 14 * User code might expect that %ecx is unclobbered though, as it would be 15 * for returning via the iret instruction, so we must push and pop. 16 * 17 * The caller puts arg3 in %edx, which the sysexit instruction requires 18 * for %eip. Thus, exactly as for arg2, we must push and pop. 19 * 20 * Arg6 is different. The caller puts arg6 in %ebp. Since the sysenter 21 * instruction clobbers %esp, the user's %esp won't even survive entry 22 * into the kernel. We store %esp in %ebp. Code in entry.S must fetch 23 * arg6 from the stack. 24 * 25 * You can not use this vsyscall for the clone() syscall because the 26 * three dwords on the parent stack do not get copied to the child. 27 */ 28 .text 29 .globl __kernel_vsyscall 30 .type __kernel_vsyscall,@function 31__kernel_vsyscall: 32.LSTART_vsyscall: 33 push %ecx 34.Lpush_ecx: 35 push %edx 36.Lpush_edx: 37 push %ebp 38.Lenter_kernel: 39 movl %esp,%ebp 40 sysenter 41 42 /* 7: align return point with nop's to make disassembly easier */ 43 .space 7,0x90 44 45 /* 14: System call restart point is here! (SYSENTER_RETURN-2) */ 46 jmp .Lenter_kernel 47 /* 16: System call normal return point is here! */ 48 .globl SYSENTER_RETURN /* Symbol used by sysenter.c */ 49SYSENTER_RETURN: 50 pop %ebp 51.Lpop_ebp: 52 pop %edx 53.Lpop_edx: 54 pop %ecx 55.Lpop_ecx: 56 ret 57.LEND_vsyscall: 58 .size __kernel_vsyscall,.-.LSTART_vsyscall 59 .previous 60 61 .section .eh_frame,"a",@progbits 62.LSTARTFRAMEDLSI: 63 .long .LENDCIEDLSI-.LSTARTCIEDLSI 64.LSTARTCIEDLSI: 65 .long 0 /* CIE ID */ 66 .byte 1 /* Version number */ 67 .string "zR" /* NUL-terminated augmentation string */ 68 .uleb128 1 /* Code alignment factor */ 69 .sleb128 -4 /* Data alignment factor */ 70 .byte 8 /* Return address register column */ 71 .uleb128 1 /* Augmentation value length */ 72 .byte 0x1b /* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */ 73 .byte 0x0c /* DW_CFA_def_cfa */ 74 .uleb128 4 75 .uleb128 4 76 .byte 0x88 /* DW_CFA_offset, column 0x8 */ 77 .uleb128 1 78 .align 4 79.LENDCIEDLSI: 80 .long .LENDFDEDLSI-.LSTARTFDEDLSI /* Length FDE */ 81.LSTARTFDEDLSI: 82 .long .LSTARTFDEDLSI-.LSTARTFRAMEDLSI /* CIE pointer */ 83 .long .LSTART_vsyscall-. /* PC-relative start address */ 84 .long .LEND_vsyscall-.LSTART_vsyscall 85 .uleb128 0 86 /* What follows are the instructions for the table generation. 87 We have to record all changes of the stack pointer. */ 88 .byte 0x04 /* DW_CFA_advance_loc4 */ 89 .long .Lpush_ecx-.LSTART_vsyscall 90 .byte 0x0e /* DW_CFA_def_cfa_offset */ 91 .byte 0x08 /* RA at offset 8 now */ 92 .byte 0x04 /* DW_CFA_advance_loc4 */ 93 .long .Lpush_edx-.Lpush_ecx 94 .byte 0x0e /* DW_CFA_def_cfa_offset */ 95 .byte 0x0c /* RA at offset 12 now */ 96 .byte 0x04 /* DW_CFA_advance_loc4 */ 97 .long .Lenter_kernel-.Lpush_edx 98 .byte 0x0e /* DW_CFA_def_cfa_offset */ 99 .byte 0x10 /* RA at offset 16 now */ 100 .byte 0x85, 0x04 /* DW_CFA_offset %ebp -16 */ 101 /* Finally the epilogue. */ 102 .byte 0x04 /* DW_CFA_advance_loc4 */ 103 .long .Lpop_ebp-.Lenter_kernel 104 .byte 0x0e /* DW_CFA_def_cfa_offset */ 105 .byte 0x0c /* RA at offset 12 now */ 106 .byte 0xc5 /* DW_CFA_restore %ebp */ 107 .byte 0x04 /* DW_CFA_advance_loc4 */ 108 .long .Lpop_edx-.Lpop_ebp 109 .byte 0x0e /* DW_CFA_def_cfa_offset */ 110 .byte 0x08 /* RA at offset 8 now */ 111 .byte 0x04 /* DW_CFA_advance_loc4 */ 112 .long .Lpop_ecx-.Lpop_edx 113 .byte 0x0e /* DW_CFA_def_cfa_offset */ 114 .byte 0x04 /* RA at offset 4 now */ 115 .align 4 116.LENDFDEDLSI: 117 .previous 118 119/* 120 * Get the common code for the sigreturn entry points. 121 */ 122#include "vsyscall-sigreturn.S" 123