be0a39120c
Document a limitation of vsyscall-sysenter, since patches to fix it have been rejected. Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
122 lines
3.8 KiB
ArmAsm
122 lines
3.8 KiB
ArmAsm
/*
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* Code for the vsyscall page. This version uses the sysenter instruction.
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*
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* NOTE:
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* 1) __kernel_vsyscall _must_ be first in this page.
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* 2) there are alignment constraints on this stub, see vsyscall-sigreturn.S
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* for details.
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*/
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/*
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* The caller puts arg2 in %ecx, which gets pushed. The kernel will use
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* %ecx itself for arg2. The pushing is because the sysexit instruction
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* (found in entry.S) requires that we clobber %ecx with the desired %esp.
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* User code might expect that %ecx is unclobbered though, as it would be
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* for returning via the iret instruction, so we must push and pop.
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*
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* The caller puts arg3 in %edx, which the sysexit instruction requires
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* for %eip. Thus, exactly as for arg2, we must push and pop.
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*
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* Arg6 is different. The caller puts arg6 in %ebp. Since the sysenter
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* instruction clobbers %esp, the user's %esp won't even survive entry
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* into the kernel. We store %esp in %ebp. Code in entry.S must fetch
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* arg6 from the stack.
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*
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* You can not use this vsyscall for the clone() syscall because the
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* three dwords on the parent stack do not get copied to the child.
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*/
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.text
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.globl __kernel_vsyscall
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.type __kernel_vsyscall,@function
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__kernel_vsyscall:
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.LSTART_vsyscall:
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push %ecx
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.Lpush_ecx:
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push %edx
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.Lpush_edx:
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push %ebp
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.Lenter_kernel:
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movl %esp,%ebp
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sysenter
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/* 7: align return point with nop's to make disassembly easier */
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.space 7,0x90
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/* 14: System call restart point is here! (SYSENTER_RETURN - 2) */
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jmp .Lenter_kernel
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/* 16: System call normal return point is here! */
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.globl SYSENTER_RETURN /* Symbol used by entry.S. */
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SYSENTER_RETURN:
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pop %ebp
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.Lpop_ebp:
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pop %edx
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.Lpop_edx:
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pop %ecx
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.Lpop_ecx:
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ret
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.LEND_vsyscall:
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.size __kernel_vsyscall,.-.LSTART_vsyscall
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.previous
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.section .eh_frame,"a",@progbits
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.LSTARTFRAMEDLSI:
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.long .LENDCIEDLSI-.LSTARTCIEDLSI
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.LSTARTCIEDLSI:
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.long 0 /* CIE ID */
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.byte 1 /* Version number */
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.string "zR" /* NUL-terminated augmentation string */
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.uleb128 1 /* Code alignment factor */
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.sleb128 -4 /* Data alignment factor */
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.byte 8 /* Return address register column */
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.uleb128 1 /* Augmentation value length */
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.byte 0x1b /* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */
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.byte 0x0c /* DW_CFA_def_cfa */
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.uleb128 4
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.uleb128 4
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.byte 0x88 /* DW_CFA_offset, column 0x8 */
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.uleb128 1
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.align 4
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.LENDCIEDLSI:
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.long .LENDFDEDLSI-.LSTARTFDEDLSI /* Length FDE */
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.LSTARTFDEDLSI:
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.long .LSTARTFDEDLSI-.LSTARTFRAMEDLSI /* CIE pointer */
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.long .LSTART_vsyscall-. /* PC-relative start address */
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.long .LEND_vsyscall-.LSTART_vsyscall
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.uleb128 0
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/* What follows are the instructions for the table generation.
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We have to record all changes of the stack pointer. */
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.byte 0x04 /* DW_CFA_advance_loc4 */
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.long .Lpush_ecx-.LSTART_vsyscall
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.byte 0x0e /* DW_CFA_def_cfa_offset */
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.byte 0x08 /* RA at offset 8 now */
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.byte 0x04 /* DW_CFA_advance_loc4 */
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.long .Lpush_edx-.Lpush_ecx
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.byte 0x0e /* DW_CFA_def_cfa_offset */
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.byte 0x0c /* RA at offset 12 now */
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.byte 0x04 /* DW_CFA_advance_loc4 */
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.long .Lenter_kernel-.Lpush_edx
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.byte 0x0e /* DW_CFA_def_cfa_offset */
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.byte 0x10 /* RA at offset 16 now */
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.byte 0x85, 0x04 /* DW_CFA_offset %ebp -16 */
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/* Finally the epilogue. */
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.byte 0x04 /* DW_CFA_advance_loc4 */
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.long .Lpop_ebp-.Lenter_kernel
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.byte 0x0e /* DW_CFA_def_cfa_offset */
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.byte 0x0c /* RA at offset 12 now */
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.byte 0xc5 /* DW_CFA_restore %ebp */
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.byte 0x04 /* DW_CFA_advance_loc4 */
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.long .Lpop_edx-.Lpop_ebp
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.byte 0x0e /* DW_CFA_def_cfa_offset */
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.byte 0x08 /* RA at offset 8 now */
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.byte 0x04 /* DW_CFA_advance_loc4 */
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.long .Lpop_ecx-.Lpop_edx
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.byte 0x0e /* DW_CFA_def_cfa_offset */
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.byte 0x04 /* RA at offset 4 now */
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.align 4
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.LENDFDEDLSI:
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.previous
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/*
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* Get the common code for the sigreturn entry points.
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*/
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#include "vsyscall-sigreturn.S"
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