/**************************************************************************
* arch/x86/src/qemu/up_saveusercontext.S
*
* Copyright (C) 2011 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
**************************************************************************/
/**************************************************************************
* Conditional Compilation Options
**************************************************************************/
/**************************************************************************
* Included Files
**************************************************************************/
#include <nuttx/config.h>
#include <arch/irq.h>
#include "up_internal.h"
.file "qemu_saveusercontext.S"
/**************************************************************************
* Pre-processor Definitions
**************************************************************************/
/****************************************************************************
* Macros
****************************************************************************/
/* Trace macros, use like trace 'i' to print char to serial port. */
.macro chout, addr, ch
#ifdef CONFIG_DEBUG
mov $\addr, %dx
mov $\ch, %al
out %al, %dx
#endif
.endm
.macro trace, ch
#ifdef CONFIG_DEBUG
push %eax
push %edx
chout 0x3f8, \ch
pop %edx
pop %eax
#endif
.endm
/**************************************************************************
* .text
**************************************************************************/
.text
/**************************************************************************
* Name: up_saveusercontext
*
* Full C prototype:
* int up_saveusercontext(uint32_t *regs);
*
* Description:
* Save the "user" context. It is not necessary to save all of the
* registers because it is acceptable for certain registers to be
* modified upon return from a subroutine call. On a context switch
* back to user mode, it will appear as a return from this function.
*
* According to the Intel ABI, the EAX, EDX, and ECX are to be free for
* use within a procedure or function, and need not be preserved. These
* are the so-called caller-saved registers are EAX, ECX, EDX.
*
* On entry,
* sp points to the return address
* sp+4 points to register save array
*
**************************************************************************/
.globl up_saveusercontext
.type up_saveusercontext, @function
up_saveusercontext:
/* Fetch the pointer to the register save array. %eax is a available
* because it must be modified later to provide the return value.
*/
movl 4(%esp), %eax
/* %ebx, %esi, %edi, and %ebp must be preserved. We can freely used %eax
* because it will be the return value from this function.
*/
movl %ebx, (4*REG_EBX)(%eax)
movl %esi, (4*REG_ESI)(%eax)
movl %edi, (4*REG_EDI)(%eax)
/* Save the segment registers */
mov %ss, (4*REG_SS)(%eax)
mov %cs, (4*REG_CS)(%eax)
mov %ds, (4*REG_DS)(%eax)
/* Save the value of SP as will be at the time of the IRET that will
* appear to be the return from this function.
*
*
* CURRENT STACK IRET STACK
* PRIO CHANGE No PRIO CHANGE
* --------------- --------------- -----------------
* EIP
* CS ...
* EFLAGS EIP
* -> ESP CS
* ESP->Return address SS EFLAGS
* Argument Argument Argument
*
* NOTE: We don't yet know the value for REG_ESP! That depends upon
* if a priority change occurs or not.
*/
leal -4(%esp), %ecx
movl %ecx, (4*REG_SP)(%eax)
/* Fetch the PC from the stack and save it in the save block */
movl 0(%esp), %ecx
movl %ecx, (4*REG_EIP)(%eax)
/* Save the framepointer */
movl %ebp, (4*REG_EBP)(%eax)
/* Save EAX=1. This will be the "apparent" return value from this
* function when context is switch back to this thread. The non-zero
* return value is the indication that we have been resumed.
*/
movl $1, (4*REG_EAX)(%eax)
/* Get and save the interrupt state */
pushf
pop %ecx
movl %ecx, (4*REG_EFLAGS)(%eax)
/* And return 0 -- The zero return value is the indication that that
* this is the original, "true" return from the function.
*
* 'ret' will remove the EIP from the top of the stack.
*/
xorl %eax, %eax
ret
.size up_saveusercontext, . - up_saveusercontext
.end
