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From d2ca2ffb15f04aab7210757d7c7dabb33ab720d0 Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Tue, 5 May 2015 20:04:15 +0200
Subject: [PATCH gnumach 07/10] document
---
i386/i386/locore.S | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)
diff --git a/i386/i386/locore.S b/i386/i386/locore.S
index 99fbfb6..4c2a253 100644
--- a/i386/i386/locore.S
+++ b/i386/i386/locore.S
@@ -1184,6 +1184,18 @@ syscall_addr:
/* set error code - read user space */
jmp _take_trap /* treat as a trap */
+/*
+ * SYSENTER-based system calls.
+ *
+ * Calling convention:
+ * %eax - syscall number
+ * %ebx - syscall argument 1
+ * %ecx - syscall argument 2
+ * %edx - syscall argument 3
+ * %esi - syscall argument 4
+ * %edi - userspace return address
+ * %ebp - userspace stack pointer
+ */
/* User stub for calling the kernel using the sysenter instruction. */
.globl user_sysenter_stub_start
@@ -1191,9 +1203,9 @@ user_sysenter_stub_start:
push %ebp
mov %esp, %ebp
pushf
- push %ebx
+ push %ebx /* Store callee-saved registers. */
push %esi
- push %edi /* xxxmore callee-saved registers? */
+ push %edi
mov 8(%ebp), %eax /* Move syscall number into %eax. */
mov 12(%ebp), %ebx /* Move first argument into %ebx. */
mov 16(%ebp), %ecx /* Move second argument into %ecx. */
@@ -1216,14 +1228,9 @@ user_sysenter_stub_end:
/*
* SYSENTER entry point.
*
- * Calling convention:
- * %eax - syscall number
- * %ebx - syscall argument 1
- * %ecx - syscall argument 2
- * %edx - syscall argument 3
- * %esi - syscall argument 4
- * %edi - userspace return address
- * %ebp - userspace stack pointer
+ * Control enters at `sysenter_entry' with %esp pointing to the
+ * per-cpu sysenter stack. We store all arguments here. We keep %ebp
+ * pointing to the top of this structure to copy the arguments.
*
* sysenter stack layout:
*
--
2.1.4
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