arch/x86/kernel/vsyscall-sysenter_32.S

   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  */
  49 SYSENTER_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_32.S"