/****************************************************************************
 * arch/arm/src/armv7-m/up_svcall.c
 *
 *   Copyright (C) 2009, 2011-2015 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * 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.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdint.h>
#include <string.h>
#include <assert.h>
#include <debug.h>

#include <arch/irq.h>
#include <nuttx/sched.h>
#include <nuttx/userspace.h>

#ifdef CONFIG_LIB_SYSCALL
#  include <syscall.h>
#endif

#include "svcall.h"
#include "exc_return.h"
#include "up_internal.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/
/* Configuration ************************************************************/

/* Debug ********************************************************************/
/* Debug output from this file may interfere with context switching!  To get
 * debug output you must enabled the following in your NuttX configuration:
 *
 * - CONFIG_DEBUG and CONFIG_DEBUG_SYSCALL (shows only syscalls)
 * - CONFIG_DEBUG and CONFIG_DEBUG_SVCALL  (shows everything)
 */

#if defined(CONFIG_DEBUG_SYSCALL) || defined(CONFIG_DEBUG_SVCALL)
# define svcdbg(format, ...) lldbg(format, ##__VA_ARGS__)
#else
# define svcdbg(x...)
#endif

/****************************************************************************
 * Private Data
 ****************************************************************************/

/****************************************************************************
 * Public Data
 ****************************************************************************/

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 *   Call the stub function corresponding to the system call.  NOTE the non-
 *   standard parameter passing:
 *
 *     R0 = SYS_ call number
 *     R1 = parm0
 *     R2 = parm1
 *     R3 = parm2
 *     R4 = parm3
 *     R5 = parm4
 *     R6 = parm5
 *
 *   The values of R4-R5 may be preserved in the proxy called by the user
 *   code if they are used (but otherwise will not be).
 *
 *   Register usage:
 *
 *     R0 - Need not be preserved.
 *     R1-R3 - Need to be preserved until the stub is called.  The values of
 *       R0 and R1 returned by the stub must be preserved.
 *     R4-R11 must be preserved to support the expectations of the user-space
 *       callee.  R4-R6 may have been preserved by the proxy, but don't know
 *       for sure.
 *     R12 - Need not be preserved
 *     R13 - (stack pointer)
 *     R14 - Need not be preserved
 *     R15 - (PC)
 *
 ****************************************************************************/

#ifdef CONFIG_LIB_SYSCALL
static void dispatch_syscall(void) naked_function;
static void dispatch_syscall(void)
{
  __asm__ __volatile__
  (
    " sub sp, sp, #16\n"           /* Create a stack frame to hold 3 parms + lr */
    " str r4, [sp, #0]\n"          /* Move parameter 4 (if any) into position */
    " str r5, [sp, #4]\n"          /* Move parameter 5 (if any) into position */
    " str r6, [sp, #8]\n"          /* Move parameter 6 (if any) into position */
    " str lr, [sp, #12]\n"         /* Save lr in the stack frame */
    " ldr ip, =g_stublookup\n"     /* R12=The base of the stub lookup table */
    " ldr ip, [ip, r0, lsl #2]\n"  /* R12=The address of the stub for this syscall */
    " blx ip\n"                    /* Call the stub (modifies lr) */
    " ldr lr, [sp, #12]\n"         /* Restore lr */
    " add sp, sp, #16\n"           /* Destroy the stack frame */
    " mov r2, r0\n"                /* R2=Save return value in R2 */
    " mov r0, #3\n"                /* R0=SYS_syscall_return */
    " svc 0"                       /* Return from the syscall */
  );
}
#endif

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: up_svcall
 *
 * Description:
 *   This is SVCall exception handler that performs context switching
 *
 ****************************************************************************/

int up_svcall(int irq, FAR void *context)
{
  uint32_t *regs = (uint32_t *)context;
  uint32_t cmd;

  DEBUGASSERT(regs && regs == current_regs);
  cmd = regs[REG_R0];

  /* The SVCall software interrupt is called with R0 = system call command
   * and R1..R7 =  variable number of arguments depending on the system call.
   */

#if defined(CONFIG_DEBUG_SYSCALL) || defined(CONFIG_DEBUG_SVCALL)
# ifndef CONFIG_DEBUG_SVCALL
  if (cmd > SYS_switch_context)
# endif
    {
      svcdbg("SVCALL Entry: regs: %p cmd: %d\n", regs, cmd);
      svcdbg("  R0: %08x %08x %08x %08x %08x %08x %08x %08x\n",
             regs[REG_R0],  regs[REG_R1],  regs[REG_R2],  regs[REG_R3],
             regs[REG_R4],  regs[REG_R5],  regs[REG_R6],  regs[REG_R7]);
      svcdbg("  R8: %08x %08x %08x %08x %08x %08x %08x %08x\n",
             regs[REG_R8],  regs[REG_R9],  regs[REG_R10], regs[REG_R11],
             regs[REG_R12], regs[REG_R13], regs[REG_R14], regs[REG_R15]);
# ifdef REG_EXC_RETURN
      svcdbg(" PSR: %08x EXC_RETURN: %08x\n",
             regs[REG_XPSR], regs[REG_EXC_RETURN]);
# else
      svcdbg(" PSR: %08x\n", regs[REG_XPSR]);
# endif
    }
#endif

  /* Handle the SVCall according to the command in R0 */

  switch (cmd)
    {
      /* R0=SYS_save_context:  This is a save context command:
       *
       *   int up_saveusercontext(uint32_t *saveregs);
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_save_context
       *   R1 = saveregs
       *
       * In this case, we simply need to copy the current regsters to the
       * save register space references in the saved R1 and return.
       */

      case SYS_save_context:
        {
          DEBUGASSERT(regs[REG_R1] != 0);
          memcpy((uint32_t *)regs[REG_R1], regs, XCPTCONTEXT_SIZE);
#if defined(CONFIG_ARCH_FPU) && \
    (!defined(CONFIG_ARMV7M_CMNVECTOR) || defined(CONFIG_ARMV7M_LAZYFPU))
          up_savefpu((uint32_t *)regs[REG_R1]);
#endif
        }
        break;

      /* R0=SYS_restore_context:  This a restore context command:
       *
       *   void up_fullcontextrestore(uint32_t *restoreregs) noreturn_function;
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_restore_context
       *   R1 = restoreregs
       *
       * In this case, we simply need to set current_regs to restore register
       * area referenced in the saved R1. context == current_regs is the normal
       * exception return.  By setting current_regs = context[R1], we force
       * the return to the saved context referenced in R1.
       */

      case SYS_restore_context:
        {
          DEBUGASSERT(regs[REG_R1] != 0);
          current_regs = (uint32_t *)regs[REG_R1];
        }
        break;

      /* R0=SYS_switch_context:  This a switch context command:
       *
       *   void up_switchcontext(uint32_t *saveregs, uint32_t *restoreregs);
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_switch_context
       *   R1 = saveregs
       *   R2 = restoreregs
       *
       * In this case, we do both: We save the context registers to the save
       * register area reference by the saved contents of R1 and then set
       * current_regs to to the save register area referenced by the saved
       * contents of R2.
       */

      case SYS_switch_context:
        {
          DEBUGASSERT(regs[REG_R1] != 0 && regs[REG_R2] != 0);
          memcpy((uint32_t *)regs[REG_R1], regs, XCPTCONTEXT_SIZE);
#if defined(CONFIG_ARCH_FPU) && \
    (!defined(CONFIG_ARMV7M_CMNVECTOR) || defined(CONFIG_ARMV7M_LAZYFPU))
          up_savefpu((uint32_t *)regs[REG_R1]);
#endif
          current_regs = (uint32_t *)regs[REG_R2];
        }
        break;

      /* R0=SYS_syscall_return:  This a syscall return command:
       *
       *   void up_syscall_return(void);
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_syscall_return
       *
       * We need to restore the saved return address and return in
       * unprivileged thread mode.
       */

#ifdef CONFIG_LIB_SYSCALL
      case SYS_syscall_return:
        {
          struct tcb_s *rtcb = sched_self();
          int index = (int)rtcb->xcp.nsyscalls - 1;

          /* Make sure that there is a saved syscall return address. */

          DEBUGASSERT(index >= 0);

          /* Setup to return to the saved syscall return address in
           * the original mode.
           */

          regs[REG_PC]         = rtcb->xcp.syscall[index].sysreturn;
          regs[REG_EXC_RETURN] = rtcb->xcp.syscall[index].excreturn;
          rtcb->xcp.nsyscalls  = index;

          /* The return value must be in R0-R1.  dispatch_syscall() temporarily
           * moved the value for R0 into R2.
           */

          regs[REG_R0]         = regs[REG_R2];
        }
        break;
#endif

      /* R0=SYS_task_start:  This a user task start
       *
       *   void up_task_start(main_t taskentry, int argc, FAR char *argv[]) noreturn_function;
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_task_start
       *   R1 = taskentry
       *   R2 = argc
       *   R3 = argv
       */

#ifdef CONFIG_BUILD_PROTECTED
      case SYS_task_start:
        {
          /* Set up to return to the user-space task start-up function in
           * unprivileged mode.
           */

          regs[REG_PC]         = (uint32_t)USERSPACE->task_startup;
          regs[REG_EXC_RETURN] = EXC_RETURN_UNPRIVTHR;

          /* Change the parameter ordering to match the expectation of struct
           * userpace_s task_startup:
           */

          regs[REG_R0]         = regs[REG_R1]; /* Task entry */
          regs[REG_R1]         = regs[REG_R2]; /* argc */
          regs[REG_R2]         = regs[REG_R3]; /* argv */
        }
        break;
#endif

      /* R0=SYS_pthread_start:  This a user pthread start
       *
       *   void up_pthread_start(pthread_startroutine_t entrypt, pthread_addr_t arg) noreturn_function;
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_pthread_start
       *   R1 = entrypt
       *   R2 = arg
       */

#if defined(CONFIG_BUILD_PROTECTED) && !defined(CONFIG_DISABLE_PTHREAD)
      case SYS_pthread_start:
        {
          /* Set up to return to the user-space pthread start-up function in
           * unprivileged mode.
           */

          regs[REG_PC]         = (uint32_t)USERSPACE->pthread_startup;
          regs[REG_EXC_RETURN] = EXC_RETURN_UNPRIVTHR;

          /* Change the parameter ordering to match the expectation of struct
           * userpace_s pthread_startup:
           */

          regs[REG_R0]         = regs[REG_R1]; /* pthread entry */
          regs[REG_R1]         = regs[REG_R2]; /* arg */
        }
        break;
#endif

      /* R0=SYS_signal_handler:  This a user signal handler callback
       *
       * void signal_handler(_sa_sigaction_t sighand, int signo,
       *                     FAR siginfo_t *info, FAR void *ucontext);
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_signal_handler
       *   R1 = sighand
       *   R2 = signo
       *   R3 = info
       *        ucontext (on the stack)
       */

#if defined(CONFIG_BUILD_PROTECTED) && !defined(CONFIG_DISABLE_SIGNALS)
      case SYS_signal_handler:
        {
          struct tcb_s *rtcb   = sched_self();

          /* Remember the caller's return address */

          DEBUGASSERT(rtcb->xcp.sigreturn == 0);
          rtcb->xcp.sigreturn  = regs[REG_PC];

          /* Set up to return to the user-space pthread start-up function in
           * unprivileged mode.
           */

          regs[REG_PC]         = (uint32_t)USERSPACE->signal_handler;
          regs[REG_EXC_RETURN] = EXC_RETURN_UNPRIVTHR;

          /* Change the parameter ordering to match the expectation of struct
           * userpace_s signal_handler.
           */

          regs[REG_R0]         = regs[REG_R1]; /* sighand */
          regs[REG_R1]         = regs[REG_R2]; /* signal */
          regs[REG_R2]         = regs[REG_R3]; /* info */

          /* The last parameter, ucontext, is trickier.  The ucontext
           * parameter will reside at an offset of 4 from the stack pointer.
           */

          regs[REG_R3]         = *(uint32_t *)(regs[REG_SP]+4);
        }
        break;
#endif

      /* R0=SYS_signal_handler_return:  This a user signal handler callback
       *
       *   void signal_handler_return(void);
       *
       * At this point, the following values are saved in context:
       *
       *   R0 = SYS_signal_handler_return
       */

#if defined(CONFIG_BUILD_PROTECTED) && !defined(CONFIG_DISABLE_SIGNALS)
      case SYS_signal_handler_return:
        {
          struct tcb_s *rtcb   = sched_self();

          /* Set up to return to the kernel-mode signal dispatching logic. */

          DEBUGASSERT(rtcb->xcp.sigreturn != 0);

          regs[REG_PC]         = rtcb->xcp.sigreturn;
          regs[REG_EXC_RETURN] = EXC_RETURN_PRIVTHR;
          rtcb->xcp.sigreturn  = 0;
        }
        break;
#endif

      /* This is not an architecture-specific system call.  If NuttX is built
       * as a standalone kernel with a system call interface, then all of the
       * additional system calls must be handled as in the default case.
       */

      default:
        {
#ifdef CONFIG_LIB_SYSCALL
          FAR struct tcb_s *rtcb = sched_self();
          int index = rtcb->xcp.nsyscalls;

          /* Verify that the SYS call number is within range */

          DEBUGASSERT(cmd >= CONFIG_SYS_RESERVED && cmd < SYS_maxsyscall);

          /* Make sure that there is a no saved syscall return address.  We
           * cannot yet handle nested system calls.
           */

          DEBUGASSERT(index < CONFIG_SYS_NNEST);

          /* Setup to return to dispatch_syscall in privileged mode. */

          rtcb->xcp.syscall[index].sysreturn  = regs[REG_PC];
          rtcb->xcp.syscall[index].excreturn  = regs[REG_EXC_RETURN];
          rtcb->xcp.nsyscalls  = index + 1;

          regs[REG_PC]         = (uint32_t)dispatch_syscall;
          regs[REG_EXC_RETURN] = EXC_RETURN_PRIVTHR;

          /* Offset R0 to account for the reserved values */

          regs[REG_R0] -= CONFIG_SYS_RESERVED;
#else
          slldbg("ERROR: Bad SYS call: %d\n", regs[REG_R0]);
#endif
        }
        break;
    }

  /* Report what happened.  That might difficult in the case of a context switch */

#if defined(CONFIG_DEBUG_SYSCALL) || defined(CONFIG_DEBUG_SVCALL)
# ifndef CONFIG_DEBUG_SVCALL
  if (cmd > SYS_switch_context)
# else
  if (regs != current_regs)
# endif
    {
      svcdbg("SVCall Return:\n");
      svcdbg("  R0: %08x %08x %08x %08x %08x %08x %08x %08x\n",
             current_regs[REG_R0],  current_regs[REG_R1],
             current_regs[REG_R2],  current_regs[REG_R3],
             current_regs[REG_R4],  current_regs[REG_R5],
             current_regs[REG_R6],  current_regs[REG_R7]);
      svcdbg("  R8: %08x %08x %08x %08x %08x %08x %08x %08x\n",
             current_regs[REG_R8],  current_regs[REG_R9],
             current_regs[REG_R10], current_regs[REG_R11],
             current_regs[REG_R12], current_regs[REG_R13],
             current_regs[REG_R14], current_regs[REG_R15]);
# ifdef REG_EXC_RETURN
      svcdbg(" PSR: %08x EXC_RETURN: %08x\n",
             current_regs[REG_XPSR], current_regs[REG_EXC_RETURN]);
# else
      svcdbg(" PSR: %08x\n", current_regs[REG_XPSR]);
# endif
    }
# ifdef CONFIG_DEBUG_SVCALL
  else
    {
      svcdbg("SVCall Return: %d\n", regs[REG_R0]);
    }
# endif
#endif

  return OK;
}
