Fedora kernel-2.6.17-1.2142_FC4 patched with stable patch-2.6.17.4-vs2.0.2-rc26.diff

[linux-2.6.git] / arch / i386 / kernel / vsyscall-sysenter.S

diff --git a/arch/i386/kernel/vsyscall-sysenter.S b/arch/i386/kernel/vsyscall-sysenter.S
index 4daefb2..6de8365 100644 (file)
--- a/arch/i386/kernel/vsyscall-sysenter.S
+++ b/arch/i386/kernel/vsyscall-sysenter.S
@@ -7,6 +7,24 @@
  *    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
@@ -24,11 +42,11 @@ __kernel_vsyscall:
        /* 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