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authorPaul Mackerras <paulus@samba.org>2006-02-24 14:05:47 +1100
committerPaul Mackerras <paulus@samba.org>2006-02-24 14:05:47 +1100
commita00428f5b149e36b8225b2a0812742a6dfb07b8c (patch)
treea78869cd67cf78a0eb091fb0ea5d397734bd6738 /arch/i386/kernel/vsyscall-sysenter.S
parent774fee58c465ea1c7e9775e347ec307bcf2deeb3 (diff)
parentfb5c594c2acc441f0d2d8f457484a0e0e9285db3 (diff)
downloadlinux-a00428f5b149e36b8225b2a0812742a6dfb07b8c.tar.gz
Merge ../powerpc-merge
Diffstat (limited to 'arch/i386/kernel/vsyscall-sysenter.S')
-rw-r--r--arch/i386/kernel/vsyscall-sysenter.S15
1 files changed, 15 insertions, 0 deletions
diff --git a/arch/i386/kernel/vsyscall-sysenter.S b/arch/i386/kernel/vsyscall-sysenter.S
index 4daefb2ec1b281..76b72815940337 100644
--- a/arch/i386/kernel/vsyscall-sysenter.S
+++ b/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