---

yaml
---
r: 20330
b: refs/heads/master
c: 581141c
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 28baebae73c3ea8b75c7cae225a7db817ab825a9
+refs/heads/master: 581141cb4b10ebd865dcb7b80f5e712e2def5408

trunk/arch/i386/kernel/vsyscall-sysenter.S

@@ -7,6 +7,21 @@
  *    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.
+ */
 	.text
 	.globl __kernel_vsyscall
 	.type __kernel_vsyscall,@function