linux/arch/x86/vdso/vdso32/sysenter.S
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   1/*
   2 * Code for the vDSO.  This version uses the sysenter instruction.
   3 *
   4 * First get the common code for the sigreturn entry points.
   5 * This must come first.
   6 */
   7#include "sigreturn.S"
   8
   9/*
  10 * The caller puts arg2 in %ecx, which gets pushed. The kernel will use
  11 * %ecx itself for arg2. The pushing is because the sysexit instruction
  12 * (found in entry.S) requires that we clobber %ecx with the desired %esp.
  13 * User code might expect that %ecx is unclobbered though, as it would be
  14 * for returning via the iret instruction, so we must push and pop.
  15 *
  16 * The caller puts arg3 in %edx, which the sysexit instruction requires
  17 * for %eip. Thus, exactly as for arg2, we must push and pop.
  18 *
  19 * Arg6 is different. The caller puts arg6 in %ebp. Since the sysenter
  20 * instruction clobbers %esp, the user's %esp won't even survive entry
  21 * into the kernel. We store %esp in %ebp. Code in entry.S must fetch
  22 * arg6 from the stack.
  23 *
  24 * You can not use this vsyscall for the clone() syscall because the
  25 * three words on the parent stack do not get copied to the child.
  26 */
  27        .text
  28        .globl __kernel_vsyscall
  29        .type __kernel_vsyscall,@function
  30        ALIGN
  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        int $0x80
  47        /* 16: System call normal return point is here! */
  48VDSO32_SYSENTER_RETURN: /* Symbol used by sysenter.c via vdso32-syms.h */
  49        pop %ebp
  50.Lpop_ebp:
  51        pop %edx
  52.Lpop_edx:
  53        pop %ecx
  54.Lpop_ecx:
  55        ret
  56.LEND_vsyscall:
  57        .size __kernel_vsyscall,.-.LSTART_vsyscall
  58        .previous
  59
  60        .section .eh_frame,"a",@progbits
  61.LSTARTFRAMEDLSI:
  62        .long .LENDCIEDLSI-.LSTARTCIEDLSI
  63.LSTARTCIEDLSI:
  64        .long 0                 /* CIE ID */
  65        .byte 1                 /* Version number */
  66        .string "zR"            /* NUL-terminated augmentation string */
  67        .uleb128 1              /* Code alignment factor */
  68        .sleb128 -4             /* Data alignment factor */
  69        .byte 8                 /* Return address register column */
  70        .uleb128 1              /* Augmentation value length */
  71        .byte 0x1b              /* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */
  72        .byte 0x0c              /* DW_CFA_def_cfa */
  73        .uleb128 4
  74        .uleb128 4
  75        .byte 0x88              /* DW_CFA_offset, column 0x8 */
  76        .uleb128 1
  77        .align 4
  78.LENDCIEDLSI:
  79        .long .LENDFDEDLSI-.LSTARTFDEDLSI /* Length FDE */
  80.LSTARTFDEDLSI:
  81        .long .LSTARTFDEDLSI-.LSTARTFRAMEDLSI /* CIE pointer */
  82        .long .LSTART_vsyscall-.        /* PC-relative start address */
  83        .long .LEND_vsyscall-.LSTART_vsyscall
  84        .uleb128 0
  85        /* What follows are the instructions for the table generation.
  86           We have to record all changes of the stack pointer.  */
  87        .byte 0x40 + (.Lpush_ecx-.LSTART_vsyscall) /* DW_CFA_advance_loc */
  88        .byte 0x0e              /* DW_CFA_def_cfa_offset */
  89        .byte 0x08              /* RA at offset 8 now */
  90        .byte 0x40 + (.Lpush_edx-.Lpush_ecx) /* DW_CFA_advance_loc */
  91        .byte 0x0e              /* DW_CFA_def_cfa_offset */
  92        .byte 0x0c              /* RA at offset 12 now */
  93        .byte 0x40 + (.Lenter_kernel-.Lpush_edx) /* DW_CFA_advance_loc */
  94        .byte 0x0e              /* DW_CFA_def_cfa_offset */
  95        .byte 0x10              /* RA at offset 16 now */
  96        .byte 0x85, 0x04        /* DW_CFA_offset %ebp -16 */
  97        /* Finally the epilogue.  */
  98        .byte 0x40 + (.Lpop_ebp-.Lenter_kernel) /* DW_CFA_advance_loc */
  99        .byte 0x0e              /* DW_CFA_def_cfa_offset */
 100        .byte 0x0c              /* RA at offset 12 now */
 101        .byte 0xc5              /* DW_CFA_restore %ebp */
 102        .byte 0x40 + (.Lpop_edx-.Lpop_ebp) /* DW_CFA_advance_loc */
 103        .byte 0x0e              /* DW_CFA_def_cfa_offset */
 104        .byte 0x08              /* RA at offset 8 now */
 105        .byte 0x40 + (.Lpop_ecx-.Lpop_edx) /* DW_CFA_advance_loc */
 106        .byte 0x0e              /* DW_CFA_def_cfa_offset */
 107        .byte 0x04              /* RA at offset 4 now */
 108        .align 4
 109.LENDFDEDLSI:
 110        .previous
 111
 112        /*
 113         * Emit a symbol with the size of this .eh_frame data,
 114         * to verify it matches the other versions.
 115         */
 116VDSO32_vsyscall_eh_frame_size = (.LENDFDEDLSI-.LSTARTFRAMEDLSI)
 117
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