/* Copyright (C) 2005  David Decotigny
    Copyright (C) 2000-2004, The KOS team
 
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License
    as published by the Free Software Foundation; either version 2
    of the License, or (at your option) any later version.
    
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
    
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
    USA. 
 */
 
 
 #include <sos/assert.h>
 #include <sos/klibc.h>
 #include <drivers/bochs.h>
 #include <drivers/x86_videomem.h>
 #include <hwcore/segment.h>
 #include <hwcore/gdt.h>
 #include <sos/uaccess.h>
 
 #include "cpu_context.h"
 
 
 /**
  * Here is the definition of a CPU context for IA32 processors. This
  * is a SOS convention, not a specification given by the IA32
  * spec. However there is a strong constraint related to the x86
  * interrupt handling specification: the top of the stack MUST be
  * compatible with the 'iret' instruction, ie there must be the
  * err_code (might be 0), eip, cs and eflags of the destination
  * context in that order (see Intel x86 specs vol 3, figure 5-4).
  *
  * @note IMPORTANT: This definition MUST be consistent with the way
  * the registers are stored on the stack in
  * irq_wrappers.S/exception_wrappers.S !!! Hence the constraint above.
  */
 struct sos_cpu_state {
   /* (Lower addresses) */
 
   /* These are SOS convention */
   sos_ui16_t  gs;
   sos_ui16_t  fs;
   sos_ui16_t  es;
   sos_ui16_t  ds;
   sos_ui16_t  cpl0_ss; /* This is ALWAYS the Stack Segment of the
                           Kernel context (CPL0) of the interrupted
                           thread, even for a user thread */
   sos_ui16_t  alignment_padding; /* unused */
   sos_ui32_t  eax;
   sos_ui32_t  ebx;
   sos_ui32_t  ecx;
   sos_ui32_t  edx;
   sos_ui32_t  esi;
   sos_ui32_t  edi;
   sos_ui32_t  ebp;
 
   /* MUST NEVER CHANGE (dependent on the IA32 iret instruction) */
   sos_ui32_t  error_code;
   sos_vaddr_t eip;
   sos_ui32_t  cs; /* 32bits according to the specs ! However, the CS
                      register is really 16bits long */
   sos_ui32_t  eflags;
 
   /* (Higher addresses) */
 } __attribute__((packed));
 
 
 /**
  * The CS value pushed on the stack by the CPU upon interrupt, and
  * needed by the iret instruction, is 32bits long while the real CPU
  * CS register is 16bits only: this macro simply retrieves the CPU
  * "CS" register value from the CS value pushed on the stack by the
  * CPU upon interrupt.
  *
  * The remaining 16bits pushed by the CPU should be considered
  * "reserved" and architecture dependent. IMHO, the specs don't say
  * anything about them. Considering that some architectures generate
  * non-zero values for these 16bits (at least Cyrix), we'd better
  * ignore them.
  */
 #define GET_CPU_CS_REGISTER_VALUE(pushed_ui32_cs_value) \
   ( (pushed_ui32_cs_value) & 0xffff )
 
 
 /**
  * Structure of an interrupted Kernel thread's context
  */
 struct sos_cpu_kstate
 {
   struct sos_cpu_state regs;
 } __attribute__((packed));
 
 
 /**
  * Structure of an interrupted User thread's context. This is almost
  * the same as a kernel context, except that 2 additional values are
  * pushed on the stack before the eflags/cs/eip of the interrupted
  * context: the stack configuration of the interrupted user context.
  *
  * @see Section 6.4.1 of Intel x86 vol 1
  */
 struct sos_cpu_ustate
 {
   struct sos_cpu_state regs;
   struct
   {
     sos_ui32_t cpl3_esp;
     sos_ui16_t cpl3_ss;
   };
 } __attribute__((packed));
 
 
 /*
  * Structure of a Task State Segment on the x86 Architecture.
  *
  * @see Intel x86 spec vol 3, figure 6-2
  *
  * @note Such a data structure should not cross any page boundary (see
  * end of section 6.2.1 of Intel spec vol 3). This is the reason why
  * we tell gcc to align it on a 128B boundary (its size is 104B, which
  * is <= 128).
  */
 struct x86_tss {
 
   /**
    * Intel provides a way for a task to switch to another in an
    * automatic way (call gates). In this case, the back_link field
    * stores the source TSS of the context switch. This allows to
    * easily implement coroutines, task backtracking, ... In SOS we
    * don't use TSS for the context switch purpouse, so we always
    * ignore this field.
    * (+0)
    */
   sos_ui16_t back_link;
 
   sos_ui16_t reserved1;
 
   /* CPL0 saved context. (+4) */
   sos_vaddr_t esp0;
   sos_ui16_t ss0;
 
   sos_ui16_t reserved2;
 
   /* CPL1 saved context. (+12) */
   sos_vaddr_t esp1;
   sos_ui16_t ss1;
 
   sos_ui16_t reserved3;
 
   /* CPL2 saved context. (+20) */
   sos_vaddr_t esp2;
   sos_ui16_t ss2;
 
   sos_ui16_t reserved4;
 
   /* Interrupted context's saved registers. (+28) */
   sos_vaddr_t cr3;
   sos_vaddr_t eip;
   sos_ui32_t eflags;
   sos_ui32_t eax;
   sos_ui32_t ecx;
   sos_ui32_t edx;
   sos_ui32_t ebx;
   sos_ui32_t esp;
   sos_ui32_t ebp;
   sos_ui32_t esi;
   sos_ui32_t edi;
 
   /* +72 */
   sos_ui16_t es;
   sos_ui16_t reserved5;
 
   /* +76 */
   sos_ui16_t cs;
   sos_ui16_t reserved6;
 
   /* +80 */
   sos_ui16_t ss;
   sos_ui16_t reserved7;
 
   /* +84 */
   sos_ui16_t ds;
   sos_ui16_t reserved8;
 
   /* +88 */
   sos_ui16_t fs;
   sos_ui16_t reserved9;
 
   /* +92 */
   sos_ui16_t gs;
   sos_ui16_t reserved10;
 
   /* +96 */
   sos_ui16_t ldtr;
   sos_ui16_t reserved11;
 
   /* +100 */
   sos_ui16_t debug_trap_flag :1;
   sos_ui16_t reserved12      :15;
   sos_ui16_t iomap_base_addr;
 
   /* 104 */
 } __attribute__((packed, aligned(128)));
 
 
 static struct x86_tss kernel_tss;
 
 
 sos_ret_t sos_cpu_context_subsystem_setup()
 {
   /* Reset the kernel TSS */
   memset(&kernel_tss, 0x0, sizeof(kernel_tss));
 
   /**
    * Now setup the kernel TSS.
    *
    * Considering the privilege change method we choose (cpl3 -> cpl0
    * through a software interrupt), we don't need to initialize a
    * full-fledged TSS. See section 6.4.1 of Intel x86 vol 1. Actually,
    * only a correct value for the kernel esp and ss are required (aka
    * "ss0" and "esp0" fields). Since the esp0 will have to be updated
    * at privilege change time, we don't have to set it up now.
    */
   kernel_tss.ss0 = SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KDATA);
 
   /* Register this TSS into the gdt */
   sos_gdt_register_kernel_tss((sos_vaddr_t) &kernel_tss);
 
   return SOS_OK;
 }
 
 
 /**
  * THE main operation of a kernel thread. This routine calls the
  * kernel thread function start_func and calls exit_func when
  * start_func returns.
  */
 static void core_routine (sos_cpu_kstate_function_arg1_t *start_func,
                           sos_ui32_t start_arg,
                           sos_cpu_kstate_function_arg1_t *exit_func,
                           sos_ui32_t exit_arg)
      __attribute__((noreturn));
 
 static void core_routine (sos_cpu_kstate_function_arg1_t *start_func,
                           sos_ui32_t start_arg,
                           sos_cpu_kstate_function_arg1_t *exit_func,
                           sos_ui32_t exit_arg)
 {
   start_func(start_arg);
   exit_func(exit_arg);
 
   SOS_ASSERT_FATAL(! "The exit function of the thread should NOT return !");
   for(;;);
 }
 
 
 sos_ret_t sos_cpu_kstate_init(struct sos_cpu_state **ctxt,
                               sos_cpu_kstate_function_arg1_t *start_func,
                               sos_ui32_t  start_arg,
                               sos_vaddr_t stack_bottom,
                               sos_size_t  stack_size,
                               sos_cpu_kstate_function_arg1_t *exit_func,
                               sos_ui32_t  exit_arg)
 {
   /* We are initializing a Kernel thread's context */
   struct sos_cpu_kstate *kctxt;
 
   /* This is a critical internal function, so that it is assumed that
      the caller knows what he does: we legitimally assume that values
      for ctxt, start_func, stack_* and exit_func are allways VALID ! */
 
   /* Setup the stack.
    *
    * On x86, the stack goes downward. Each frame is configured this
    * way (higher addresses first):
    *
    *  - (optional unused space. As of gcc 3.3, this space is 24 bytes)
    *  - arg n
    *  - arg n-1
    *  - ...
    *  - arg 1
    *  - return instruction address: The address the function returns to
    *    once finished
    *  - local variables
    *
    * The remaining of the code should be read from the end upward to
    * understand how the processor will handle it.
    */
 
   sos_vaddr_t tmp_vaddr = stack_bottom + stack_size;
   sos_ui32_t *stack = (sos_ui32_t*)tmp_vaddr;
 
   /* If needed, poison the stack */
 #ifdef SOS_CPU_STATE_DETECT_UNINIT_KERNEL_VARS
   memset((void*)stack_bottom, SOS_CPU_STATE_STACK_POISON, stack_size);
 #elif defined(SOS_CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW)
   sos_cpu_state_prepare_detect_kernel_stack_overflow(stack_bottom, stack_size);
 #endif
 
   /* Simulate a call to the core_routine() function: prepare its
      arguments */
   *(--stack) = exit_arg;
   *(--stack) = (sos_ui32_t)exit_func;
   *(--stack) = start_arg;
   *(--stack) = (sos_ui32_t)start_func;
   *(--stack) = 0; /* Return address of core_routine => force page fault */
 
   /*
    * Setup the initial context structure, so that the CPU will execute
    * the function core_routine() once this new context has been
    * restored on CPU
    */
 
   /* Compute the base address of the structure, which must be located
      below the previous elements */
   tmp_vaddr  = ((sos_vaddr_t)stack) - sizeof(struct sos_cpu_kstate);
   kctxt = (struct sos_cpu_kstate*)tmp_vaddr;
 
   /* Initialize the CPU context structure */
   memset(kctxt, 0x0, sizeof(struct sos_cpu_kstate));
 
   /* Tell the CPU context structure that the first instruction to
      execute will be that of the core_routine() function */
   kctxt->regs.eip = (sos_ui32_t)core_routine;
 
   /* Setup the segment registers */
   kctxt->regs.cs
     = SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KCODE); /* Code */
   kctxt->regs.ds
     = SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KDATA); /* Data */
   kctxt->regs.es
     = SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KDATA); /* Data */
   kctxt->regs.cpl0_ss
     = SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KDATA); /* Stack */
   /* fs and gs unused for the moment. */
 
   /* The newly created context is initially interruptible */
   kctxt->regs.eflags = (1 << 9); /* set IF bit */
 
   /* Finally, update the generic kernel/user thread context */
   *ctxt = (struct sos_cpu_state*) kctxt;
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_cpu_ustate_init(struct sos_cpu_state **ctxt,
                               sos_uaddr_t  user_start_PC,
                               sos_ui32_t   user_start_arg1,
                               sos_ui32_t   user_start_arg2,
                               sos_uaddr_t  user_initial_SP,
                               sos_vaddr_t  kernel_stack_bottom,
                               sos_size_t   kernel_stack_size)
 {
   /* We are initializing a User thread's context */
   struct sos_cpu_ustate *uctxt;
 
   /* This is a critical internal function, so that it is assumed that
      the caller knows what he does: we legitimally assume that values
      for ctxt, etc. are allways VALID ! */
 
   /* Compute the address of the CPU state to restore on CPU when
      switching to this new user thread */
   sos_vaddr_t uctxt_vaddr = kernel_stack_bottom
                              + kernel_stack_size
                              - sizeof(struct sos_cpu_ustate);
   uctxt = (struct sos_cpu_ustate*)uctxt_vaddr;
 
   /* If needed, poison the kernel stack */
 #ifdef SOS_CPU_STATE_DETECT_UNINIT_KERNEL_VARS
   memset((void*)kernel_stack_bottom,
          SOS_CPU_STATE_STACK_POISON,
          kernel_stack_size);
 #elif defined(SOS_CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW)
   sos_cpu_state_prepare_detect_kernel_stack_overflow(kernel_stack_bottom,
                                                      kernel_stack_size);
 #endif
 
   /*
    * Setup the initial context structure, so that the CPU will restore
    * the initial registers' value for the user thread. The
    * user thread argument is passed in the EAX register.
    */
 
   memset(uctxt, 0x0, sizeof(struct sos_cpu_ustate));
   
   /* Tell the CPU context structure that the first instruction to
      execute will be located at user_start_PC (in user space) */
   uctxt->regs.eip = (sos_ui32_t)user_start_PC;
   
   /* Tell the CPU where will be the user stack */
   uctxt->cpl3_esp = user_initial_SP;
 
   /* The parameter to the start function is not passed by the stack to
      avoid a possible page fault */
   uctxt->regs.eax = user_start_arg1;
   uctxt->regs.ebx = user_start_arg2;
 
   /* Setup the segment registers */
   uctxt->regs.cs
     = SOS_BUILD_SEGMENT_REG_VALUE(3, FALSE, SOS_SEG_UCODE); /* Code */
   uctxt->regs.ds
     = SOS_BUILD_SEGMENT_REG_VALUE(3, FALSE, SOS_SEG_UDATA); /* Data */
   uctxt->regs.es
     = SOS_BUILD_SEGMENT_REG_VALUE(3, FALSE, SOS_SEG_UDATA); /* Data */
   uctxt->cpl3_ss
     = SOS_BUILD_SEGMENT_REG_VALUE(3, FALSE, SOS_SEG_UDATA); /* User Stack */
 
   /* We need also to update the segment for the kernel stack
      segment. It will be used when this context will be restored on
      CPU: initially it will be executing in kernel mode and will
      switch immediatly to user mode */
   uctxt->regs.cpl0_ss
     = SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KDATA); /* Kernel Stack */
 
   /* fs and gs unused for the moment. */
 
   /* The newly created context is initially interruptible */
   uctxt->regs.eflags = (1 << 9); /* set IF bit */
 
   /* Finally, update the generic kernel/user thread context */
   *ctxt = (struct sos_cpu_state*) uctxt;
 
   return SOS_OK;
 }
 
 
 sos_ret_t
 sos_cpu_context_is_in_user_mode(const struct sos_cpu_state *ctxt)
 {
   /* An interrupted user thread has its CS register set to that of the
      User code segment */
   switch (GET_CPU_CS_REGISTER_VALUE(ctxt->cs))
     {
     case SOS_BUILD_SEGMENT_REG_VALUE(3, FALSE, SOS_SEG_UCODE):
       return TRUE;
       break;
 
     case SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KCODE):
       return FALSE;
       break;
 
     default:
       SOS_FATAL_ERROR("Invalid saved context Code segment register: 0x%x (k=%x, u=%x) !",
                       (unsigned) GET_CPU_CS_REGISTER_VALUE(ctxt->cs),
                       SOS_BUILD_SEGMENT_REG_VALUE(0, FALSE, SOS_SEG_KCODE),
                       SOS_BUILD_SEGMENT_REG_VALUE(3, FALSE, SOS_SEG_UCODE));
       break;
     }
 
   /* Should never get here */
   return -SOS_EFATAL;
 }
 
 
 #if defined(SOS_CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW)
 void
 sos_cpu_state_prepare_detect_kernel_stack_overflow(const struct sos_cpu_state *ctxt,
                                                    sos_vaddr_t stack_bottom,
                                                    sos_size_t stack_size)
 {
   sos_size_t poison_size = SOS_CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW;
   if (poison_size > stack_size)
     poison_size = stack_size;
 
   memset((void*)stack_bottom, SOS_CPU_STATE_STACK_POISON, poison_size);
 }
 
 
 void
 sos_cpu_state_detect_kernel_stack_overflow(const struct sos_cpu_state *ctxt,
                                            sos_vaddr_t stack_bottom,
                                            sos_size_t stack_size)
 {
   unsigned char *c;
   int i;
 
   /* On SOS, "ctxt" corresponds to the address of the esp register of
      the saved context in Kernel mode (always, even for the interrupted
      context of a user thread). Here we make sure that this stack
      pointer is within the allowed stack area */
   SOS_ASSERT_FATAL(((sos_vaddr_t)ctxt) >= stack_bottom);
   SOS_ASSERT_FATAL(((sos_vaddr_t)ctxt) + sizeof(struct sos_cpu_kstate)
                    <= stack_bottom + stack_size);
 
   /* Check that the bottom of the stack has not been altered */
   for (c = (unsigned char*) stack_bottom, i = 0 ;
        (i < SOS_CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW) && (i < stack_size) ;
        c++, i++)
     {
       SOS_ASSERT_FATAL(SOS_CPU_STATE_STACK_POISON == *c);
     }
 }
 #endif
 
 
 /* =======================================================================
  * Public Accessor functions
  */
 
 
 sos_vaddr_t sos_cpu_context_get_PC(const struct sos_cpu_state *ctxt)
 {
   SOS_ASSERT_FATAL(NULL != ctxt);
 
   /* This is the PC of the interrupted context (ie kernel or user
      context). */
   return ctxt->eip;
 }
 
 
 sos_vaddr_t sos_cpu_context_get_SP(const struct sos_cpu_state *ctxt)
 {
   SOS_ASSERT_FATAL(NULL != ctxt);
 
   /* 'ctxt' corresponds to the SP of the interrupted context, in Kernel
      mode. We have to test whether the original interrupted context
      was that of a kernel or user thread */
   if (TRUE == sos_cpu_context_is_in_user_mode(ctxt))
     {
       struct sos_cpu_ustate * uctxt = (struct sos_cpu_ustate*)ctxt;
       return uctxt->cpl3_esp;
     }
 
   /* On SOS, "ctxt" corresponds to the address of the esp register of
      the saved context in Kernel mode (always, even for the interrupted
      context of a user thread). */
   return (sos_vaddr_t)ctxt;
 }
 
 
 sos_ret_t
 sos_cpu_context_set_EX_return_address(struct sos_cpu_state *ctxt,
                                       sos_vaddr_t ret_vaddr)
 {
   ctxt->eip = ret_vaddr;
   return SOS_OK;
 }
 
 
 void sos_cpu_context_dump(const struct sos_cpu_state *ctxt)
 {
   char buf[128];
 
   snprintf(buf, sizeof(buf),
            "CPU: eip=%x esp0=%x eflags=%x cs=%x ds=%x ss0=%x err=%x",
            (unsigned)ctxt->eip, (unsigned)ctxt, (unsigned)ctxt->eflags,
            (unsigned)GET_CPU_CS_REGISTER_VALUE(ctxt->cs), (unsigned)ctxt->ds,
            (unsigned)ctxt->cpl0_ss,
            (unsigned)ctxt->error_code);
   if (TRUE == sos_cpu_context_is_in_user_mode(ctxt))
     {
       struct sos_cpu_ustate * uctxt = (struct sos_cpu_ustate*)ctxt;
       snprintf(buf, sizeof(buf),
                "%s esp3=%x ss3=%x",
                buf, (unsigned)uctxt->cpl3_esp, (unsigned)uctxt->cpl3_ss);
     }
   else
     snprintf(buf, sizeof(buf), "%s [KERNEL MODE]", buf);
 
   sos_bochs_putstring(buf); sos_bochs_putstring("\n");
   sos_x86_videomem_putstring(23, 0,
                              SOS_X86_VIDEO_FG_BLACK | SOS_X86_VIDEO_BG_LTGRAY,
                              buf);
 }
 
 
 /* =======================================================================
  * Public Accessor functions TO BE USED ONLY BY Exception handlers
  */
 
 
 sos_ui32_t sos_cpu_context_get_EX_info(const struct sos_cpu_state *ctxt)
 {
   SOS_ASSERT_FATAL(NULL != ctxt);
   return ctxt->error_code;
 }
 
 
 sos_vaddr_t
 sos_cpu_context_get_EX_faulting_vaddr(const struct sos_cpu_state *ctxt)
 {
   sos_ui32_t cr2;
 
   /*
    * See Intel Vol 3 (section 5.14): the address of the faulting
    * virtual address of a page fault is stored in the cr2
    * register.
    *
    * Actually, we do not store the cr2 register in a saved
    * kernel thread's context. So we retrieve the cr2's value directly
    * from the processor. The value we retrieve in an exception handler
    * is actually the correct one because an exception is synchronous
    * with the code causing the fault, and cannot be interrupted since
    * the IDT entries in SOS are "interrupt gates" (ie IRQ are
    * disabled).
    */
   asm volatile ("movl %%cr2, %0"
                 :"=r"(cr2)
                 : );
 
   return cr2;
 }
 
 
 /* =======================================================================
  * Public Accessor functions TO BE USED ONLY BY the SYSCALL handler
  */
 
 
 /*
  * By convention, the USER SOS programs always pass 4 arguments to the
  * kernel syscall handler: in eax/../edx. For less arguments, the
  * unused registers are filled with 0s. For more arguments, the 4th
  * syscall parameter gives the address of the array containing the
  * remaining arguments. In any case, eax corresponds to the syscall
  * IDentifier.
  */
 
 
 inline
 sos_ret_t sos_syscall_get3args(const struct sos_cpu_state *user_ctxt,
                                /* out */unsigned int *arg1,
                                /* out */unsigned int *arg2,
                                /* out */unsigned int *arg3)
 {
   *arg1 = user_ctxt->ebx;
   *arg2 = user_ctxt->ecx;
   *arg3 = user_ctxt->edx; 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_syscall_get1arg(const struct sos_cpu_state *user_ctxt,
                               /* out */unsigned int *arg1)
 {
   unsigned int unused;
   return sos_syscall_get3args(user_ctxt, arg1, & unused, & unused);
 }
 
 
 sos_ret_t sos_syscall_get2args(const struct sos_cpu_state *user_ctxt,
                                /* out */unsigned int *arg1,
                                /* out */unsigned int *arg2)
 {
   unsigned int unused;
   return sos_syscall_get3args(user_ctxt, arg1, arg2, & unused);
 }
 
 
 /*
  * sos_syscall_get3args() is defined in cpu_context.c because it needs
  * to know the structure of a struct spu_state
  */
 
 sos_ret_t sos_syscall_get4args(const struct sos_cpu_state *user_ctxt,
                                /* out */unsigned int *arg1,
                                /* out */unsigned int *arg2,
                                /* out */unsigned int *arg3,
                                /* out */unsigned int *arg4)
 {
   sos_uaddr_t  uaddr_other_args;
   unsigned int other_args[2];
   sos_ret_t    retval;
 
   /* Retrieve the 3 arguments. The last one is an array containing the
      remaining arguments */
   retval = sos_syscall_get3args(user_ctxt, arg1, arg2,
                                 (unsigned int *)& uaddr_other_args);
   if (SOS_OK != retval)
     return retval;
   
   /* Copy the array containing the remaining arguments from user
      space */
   retval = sos_memcpy_from_user((sos_vaddr_t)other_args,
                                 (sos_uaddr_t)uaddr_other_args,
                                 sizeof(other_args));
   if (sizeof(other_args) != retval)
     return -SOS_EFAULT;
 
   *arg3 = other_args[0];
   *arg4 = other_args[1];
   return SOS_OK;
 }
 
 
 sos_ret_t sos_syscall_get5args(const struct sos_cpu_state *user_ctxt,
                                /* out */unsigned int *arg1,
                                /* out */unsigned int *arg2,
                                /* out */unsigned int *arg3,
                                /* out */unsigned int *arg4,
                                /* out */unsigned int *arg5)
 {
   sos_uaddr_t  uaddr_other_args;
   unsigned int other_args[3];
   sos_ret_t    retval;
 
   /* Retrieve the 3 arguments. The last one is an array containing the
      remaining arguments */
   retval = sos_syscall_get3args(user_ctxt, arg1, arg2,
                                 (unsigned int *)& uaddr_other_args);
   if (SOS_OK != retval)
     return retval;
   
   /* Copy the array containing the remaining arguments from user
      space */
   retval = sos_memcpy_from_user((sos_vaddr_t)other_args,
                                 (sos_uaddr_t)uaddr_other_args,
                                 sizeof(other_args));
   if (sizeof(other_args) != retval)
     return -SOS_EFAULT;
 
   *arg3 = other_args[0];
   *arg4 = other_args[1];
   *arg5 = other_args[2];
   return SOS_OK;
 }
 
 
 sos_ret_t sos_syscall_get6args(const struct sos_cpu_state *user_ctxt,
                                /* out */unsigned int *arg1,
                                /* out */unsigned int *arg2,
                                /* out */unsigned int *arg3,
                                /* out */unsigned int *arg4,
                                /* out */unsigned int *arg5,
                                /* out */unsigned int *arg6)
 {
   sos_uaddr_t  uaddr_other_args;
   unsigned int other_args[4];
   sos_ret_t    retval;
 
   /* Retrieve the 3 arguments. The last one is an array containing the
      remaining arguments */
   retval = sos_syscall_get3args(user_ctxt, arg1, arg2,
                                 (unsigned int *)& uaddr_other_args);
   if (SOS_OK != retval)
     return retval;
   
   /* Copy the array containing the remaining arguments from user
      space */
   retval = sos_memcpy_from_user((sos_vaddr_t)other_args,
                                 (sos_uaddr_t)uaddr_other_args,
                                 sizeof(other_args));
   if (sizeof(other_args) != retval)
     return -SOS_EFAULT;
 
   *arg3 = other_args[0];
   *arg4 = other_args[1];
   *arg5 = other_args[2];
   *arg6 = other_args[3];
   return SOS_OK;
 }
 
 
 sos_ret_t sos_syscall_get7args(const struct sos_cpu_state *user_ctxt,
                                /* out */unsigned int *arg1,
                                /* out */unsigned int *arg2,
                                /* out */unsigned int *arg3,
                                /* out */unsigned int *arg4,
                                /* out */unsigned int *arg5,
                                /* out */unsigned int *arg6,
                                /* out */unsigned int *arg7)
 {
   sos_uaddr_t  uaddr_other_args;
   unsigned int other_args[5];
   sos_ret_t    retval;
 
   /* Retrieve the 3 arguments. The last one is an array containing the
      remaining arguments */
   retval = sos_syscall_get3args(user_ctxt, arg1, arg2,
                                 (unsigned int *)& uaddr_other_args);
   if (SOS_OK != retval)
     return retval;
   
   /* Copy the array containing the remaining arguments from user
      space */
   retval = sos_memcpy_from_user((sos_vaddr_t)other_args,
                                 (sos_uaddr_t)uaddr_other_args,
                                 sizeof(other_args));
   if (sizeof(other_args) != retval)
     return -SOS_EFAULT;
 
   *arg3 = other_args[0];
   *arg4 = other_args[1];
   *arg5 = other_args[2];
   *arg6 = other_args[3];
   *arg7 = other_args[4];
   return SOS_OK;
 }
 
 
 sos_ret_t sos_syscall_get8args(const struct sos_cpu_state *user_ctxt,
                                /* out */unsigned int *arg1,
                                /* out */unsigned int *arg2,
                                /* out */unsigned int *arg3,
                                /* out */unsigned int *arg4,
                                /* out */unsigned int *arg5,
                                /* out */unsigned int *arg6,
                                /* out */unsigned int *arg7,
                                /* out */unsigned int *arg8)
 {
   sos_uaddr_t  uaddr_other_args;
   unsigned int other_args[6];
   sos_ret_t    retval;
 
   /* Retrieve the 3 arguments. The last one is an array containing the
      remaining arguments */
   retval = sos_syscall_get3args(user_ctxt, arg1, arg2,
                                 (unsigned int *)& uaddr_other_args);
   if (SOS_OK != retval)
     return retval;
   
   /* Copy the array containing the remaining arguments from user
      space */
   retval = sos_memcpy_from_user((sos_vaddr_t)other_args,
                                 (sos_uaddr_t)uaddr_other_args,
                                 sizeof(other_args));
   if (sizeof(other_args) != retval)
     return -SOS_EFAULT;
 
   *arg3 = other_args[0];
   *arg4 = other_args[1];
   *arg5 = other_args[2];
   *arg6 = other_args[3];
   *arg7 = other_args[4];
   *arg8 = other_args[5];
   return SOS_OK;
 }
 
 
 /* =======================================================================
  * Backtrace facility. To be used for DEBUGging purpose ONLY.
  */
 
 
 sos_ui32_t sos_backtrace(const struct sos_cpu_state *cpu_state,
                          sos_ui32_t max_depth,
                          sos_vaddr_t stack_bottom,
                          sos_size_t stack_size,
                          sos_backtrace_callback_t * backtracer,
                          void *custom_arg)
 {
   int depth;
   sos_vaddr_t callee_PC, caller_frame;
 
   /* Cannot backtrace an interrupted user thread ! */
   if ((NULL != cpu_state)
       &&
       (TRUE == sos_cpu_context_is_in_user_mode(cpu_state)))
     {
       return 0;
     }
   
   /*
    * Layout of a frame on the x86 (compiler=gcc):
    *
    * funcA calls funcB calls funcC
    *
    *         ....
    *         funcB Argument 2
    *         funcB Argument 1
    *         funcA Return eip
    * frameB: funcA ebp (ie previous stack frame)
    *         ....
    *         (funcB local variables)
    *         ....
    *         funcC Argument 2
    *         funcC Argument 1
    *         funcB Return eip
    * frameC: funcB ebp (ie previous stack frame == A0) <---- a frame address
    *         ....
    *         (funcC local variables)
    *         ....
    *
    * The presence of "ebp" on the stack depends on 2 things:
    *   + the compiler is gcc
    *   + the source is compiled WITHOUT the -fomit-frame-pointer option
    * In the absence of "ebp", chances are high that the value pushed
    * at that address is outside the stack boundaries, meaning that the
    * function will return -SOS_ENOSUP.
    */
 
   if (cpu_state)
     {
       callee_PC    = cpu_state->eip;
       caller_frame = cpu_state->ebp;
     }
   else
     {
       /* Skip the sos_backtrace() frame */
       callee_PC    = (sos_vaddr_t)__builtin_return_address(0);
       caller_frame = (sos_vaddr_t)__builtin_frame_address(1);
     }
 
   for(depth=0 ; depth < max_depth ; depth ++)
     {
       /* Call the callback */
       backtracer(callee_PC, caller_frame + 8, depth, custom_arg);
 
       /* If the frame address is funky, don't go further */
       if ( (caller_frame < stack_bottom)
            || (caller_frame + 4 >= stack_bottom + stack_size) )
         return depth;
 
       /* Go to caller frame */
       callee_PC    = *((sos_vaddr_t*) (caller_frame + 4));
       caller_frame = *((sos_vaddr_t*) caller_frame);
     }
   
   return depth;
 }
 
 
 /* *************************************************************
  * Function to manage the TSS.  This function is not really "public":
  * it is reserved to the assembler routines defined in
  * cpu_context_switch.S
  *
  * Update the kernel stack address so that the IRQ, syscalls and
  * exception return in a correct stack location when coming back into
  * kernel mode.
  */
 void
 sos_cpu_context_update_kernel_tss(struct sos_cpu_state *next_ctxt)
 {
   /* next_ctxt corresponds to an interrupted user thread ? */
   if (sos_cpu_context_is_in_user_mode(next_ctxt))
     {
       /*
        * Yes: "next_ctxt" is an interrupted user thread => we are
        * going to switch to user mode ! Setup the stack address so
        * that the user thread "next_ctxt" can come back to the correct
        * stack location when returning in kernel mode.
        *
        * This stack location corresponds to the SP of the next user
        * thread once its context has been transferred on the CPU, ie
        * once the CPU has executed all the pop/iret instruction of the
        * context switch with privilege change.
        */
       kernel_tss.esp0 = ((sos_vaddr_t)next_ctxt)
                         + sizeof(struct sos_cpu_ustate);
       /* Note: no need to protect this agains IRQ because IRQs are not
          allowed to update it by themselves, and they are not allowed
          to block */
     }
   else
     {
       /* No: No need to update kernel TSS when we stay in kernel
          mode */
     }
 }