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/*
* Code for the vsyscall page. This version uses the sysenter instruction.
*
* NOTE:
* 1) __kernel_vsyscall _must_ be first in this page.
* 2) there are alignment constraints on this stub, see vsyscall-sigreturn.S
* for details.
*/
/*
* The caller puts arg2 in %ecx, which gets pushed. The kernel will use
* %ecx itself for arg2. The pushing is because the sysexit instruction
* (found in entry.S) requires that we clobber %ecx with the desired %esp.
* User code might expect that %ecx is unclobbered though, as it would be
* for returning via the iret instruction, so we must push and pop.
*
* The caller puts arg3 in %edx, which the sysexit instruction requires
* for %eip. Thus, exactly as for arg2, we must push and pop.
*
* Arg6 is different. The caller puts arg6 in %ebp. Since the sysenter
* instruction clobbers %esp, the user's %esp won't even survive entry
* into the kernel. We store %esp in %ebp. Code in entry.S must fetch
* arg6 from the stack.
*
* You can not use this vsyscall for the clone() syscall because the
* three dwords on the parent stack do not get copied to the child.
*/
.text
.globl __kernel_vsyscall
.type __kernel_vsyscall,@function
__kernel_vsyscall:
.LSTART_vsyscall:
push %ecx
.Lpush_ecx:
push %edx
.Lpush_edx:
push %ebp
.Lenter_kernel:
movl %esp,%ebp
sysenter
/* 7: align return point with nop's to make disassembly easier */
.space 7,0x90
/* 14: System call restart point is here! (SYSENTER_RETURN-2) */
jmp .Lenter_kernel
/* 16: System call normal return point is here! */
.globl SYSENTER_RETURN /* Symbol used by sysenter.c */
SYSENTER_RETURN:
pop %ebp
.Lpop_ebp:
pop %edx
.Lpop_edx:
pop %ecx
.Lpop_ecx:
ret
.LEND_vsyscall:
.size __kernel_vsyscall,.-.LSTART_vsyscall
.previous
.section .eh_frame,"a",@progbits
.LSTARTFRAMEDLSI:
.long .LENDCIEDLSI-.LSTARTCIEDLSI
.LSTARTCIEDLSI:
.long 0 /* CIE ID */
.byte 1 /* Version number */
.string "zR" /* NUL-terminated augmentation string */
.uleb128 1 /* Code alignment factor */
.sleb128 -4 /* Data alignment factor */
.byte 8 /* Return address register column */
.uleb128 1 /* Augmentation value length */
.byte 0x1b /* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */
.byte 0x0c /* DW_CFA_def_cfa */
.uleb128 4
.uleb128 4
.byte 0x88 /* DW_CFA_offset, column 0x8 */
.uleb128 1
.align 4
.LENDCIEDLSI:
.long .LENDFDEDLSI-.LSTARTFDEDLSI /* Length FDE */
.LSTARTFDEDLSI:
.long .LSTARTFDEDLSI-.LSTARTFRAMEDLSI /* CIE pointer */
.long .LSTART_vsyscall-. /* PC-relative start address */
.long .LEND_vsyscall-.LSTART_vsyscall
.uleb128 0
/* What follows are the instructions for the table generation.
We have to record all changes of the stack pointer. */
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lpush_ecx-.LSTART_vsyscall
.byte 0x0e /* DW_CFA_def_cfa_offset */
.byte 0x08 /* RA at offset 8 now */
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lpush_edx-.Lpush_ecx
.byte 0x0e /* DW_CFA_def_cfa_offset */
.byte 0x0c /* RA at offset 12 now */
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lenter_kernel-.Lpush_edx
.byte 0x0e /* DW_CFA_def_cfa_offset */
.byte 0x10 /* RA at offset 16 now */
.byte 0x85, 0x04 /* DW_CFA_offset %ebp -16 */
/* Finally the epilogue. */
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lpop_ebp-.Lenter_kernel
.byte 0x0e /* DW_CFA_def_cfa_offset */
.byte 0x0c /* RA at offset 12 now */
.byte 0xc5 /* DW_CFA_restore %ebp */
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lpop_edx-.Lpop_ebp
.byte 0x0e /* DW_CFA_def_cfa_offset */
.byte 0x08 /* RA at offset 8 now */
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lpop_ecx-.Lpop_edx
.byte 0x0e /* DW_CFA_def_cfa_offset */
.byte 0x04 /* RA at offset 4 now */
.align 4
.LENDFDEDLSI:
.previous
/*
* Get the common code for the sigreturn entry points.
*/
#include "vsyscall-sigreturn.S"
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