* 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
/* 7: align return point with nop's to make disassembly easier */
.space 7,0x90
- /* 14: System call restart point is here! (SYSENTER_RETURN - 2) */
+ /* 14: System call restart point is here! (SYSENTER_RETURN_OFFSET-2) */
jmp .Lenter_kernel
/* 16: System call normal return point is here! */
- .globl SYSENTER_RETURN /* Symbol used by entry.S. */
-SYSENTER_RETURN:
+ .globl SYSENTER_RETURN_OFFSET /* Symbol used by sysenter.c */
+SYSENTER_RETURN_OFFSET:
pop %ebp
.Lpop_ebp:
pop %edx
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lpop_ebp-.Lenter_kernel
.byte 0x0e /* DW_CFA_def_cfa_offset */
- .byte 0x12 /* RA at offset 12 now */
+ .byte 0x0c /* RA at offset 12 now */
.byte 0xc5 /* DW_CFA_restore %ebp */
.byte 0x04 /* DW_CFA_advance_loc4 */
.long .Lpop_edx-.Lpop_ebp