Makefile

@@ -12,12 +12,13 @@ QEMU_OPT += -hda disk.img
 ARCH?=x86
 SUBDIRS := core drivers tests arch/$(ARCH)
 
-CPPFLAGS += $(foreach dir, $(SUBDIRS), -I$(dir))
+INCDIRS += $(foreach dir, $(SUBDIRS), -I$(dir))
+CPPFLAGS += $(INCDIRS)
 
 asmsrc=$(wildcard arch/$(ARCH)/boot/*.asm)
 asmobj=$(asmsrc:%.asm=%.o)
 csrc=$(shell find $(SUBDIRS) -type f -name "*.c")#   $(wildcard *.c)
-cobj=$(csrc:%.c=%.o) arch/$(ARCH)/cpu_context_switch.o arch/$(ARCH)/irq_pit.o arch/$(ARCH)/irq_wrappers.o arch/$(ARCH)/exception_wrappers.o
+cobj=$(csrc:%.c=%.o) arch/$(ARCH)/cpu_context_switch.o arch/$(ARCH)/irq_pit.o arch/$(ARCH)/irq_wrappers.o arch/$(ARCH)/exception_wrappers.o arch/$(ARCH)/syscall_wrappers.o
 deps = $(csrc:%.c=%.d)
 
 kernel kernel.sym &: $(asmobj) $(cobj) linker.ld
@@ -38,7 +39,7 @@ disk.img:
 	$(AS) $(ASFLAGS) -o $@ $<
 
 %.o: %.S
-	$(CC) "-I$(PWD)" -c "$<" $(CFLAGS) -o "$@"
+	$(CC) $(INCDIRS) -c "$<" $(CFLAGS) -o "$@"
 
 
 test: CFLAGS += -DRUN_TEST

arch/x86/cpu_context.c

@@ -38,12 +38,11 @@ struct cpu_state {
     uint16_t alignment_padding; /* unused */
     uint32_t edi;
     uint32_t esi;
-    uint32_t esp;
-    uint32_t ebp;
     uint32_t ebx;
     uint32_t edx;
     uint32_t ecx;
     uint32_t eax;
+    uint32_t ebp;
 
     /* MUST NEVER CHANGE (dependent on the IA32 iret instruction) */
     uint32_t error_code;

arch/x86/cpu_context_switch.S

@@ -24,7 +24,13 @@ cpu_context_switch:
   pushl %cs          // (cs)         esp+52
   pushl $resume_pc   // (ip)         esp+48
   pushl $0           // (error code) esp+12+8x4
-  pushal             // (general reg) esp+12
+  pushl %ebp
+  pushl %eax
+  pushl %ecx
+  pushl %edx
+  pushl %ebx
+  pushl %esi
+  pushl %edi
   subl $2, %esp      // (alignment)  esp+10
   pushw %ss          //              esp+8
   pushw %ds          //              esp+6
@@ -37,11 +43,11 @@ cpu_context_switch:
    */
 
   /* Store the address of the saved context */
-  movl  64(%esp), %ebx
+  movl  60(%esp), %ebx
   movl  %esp, (%ebx)
 
   /* This is the proper context switch ! We change the stack here */
-  movl 68(%esp), %esp
+  movl 64(%esp), %esp
 
   /* Prepare kernel TSS in case we are switching to a user thread: we
      make sure that we will come back into the kernel at a correct
@@ -49,9 +55,8 @@ cpu_context_switch:
   pushl %esp /* Pass the location of the context we are
                 restoring to the function */
   call cpu_context_update_kernel_tss
-
-
   addl $4, %esp
+
   /* Restore the CPU context */
   popw %gs
   popw %fs
@@ -59,7 +64,13 @@ cpu_context_switch:
   popw %ds
   popw %ss
   addl $2,%esp
-  popal
+  popl %edi
+  popl %esi
+  popl %ebx
+  popl %edx
+  popl %ecx
+  popl %eax
+  popl %ebp
   addl $4, %esp /* Ignore "error code" */
 
   /* This restores the eflags, the cs and the eip registers */
@@ -95,6 +106,14 @@ cpu_context_exit_to:
   call  *8(%eax)
   addl  $4, %esp
 
+  /* Prepare kernel TSS in case we are switching to a user thread: we
+     make sure that we will come back into the kernel at a correct
+     stack location */
+  pushl %esp /* Pass the location of the context we are
+	        restoring to the function */
+  call cpu_context_update_kernel_tss
+  addl $4, %esp
+
   /* Restore the CPU context */
   popw %gs
   popw %fs
@@ -102,7 +121,13 @@ cpu_context_exit_to:
   popw %ds
   popw %ss
   addl $2,%esp
-  popal
+  popl %edi
+  popl %esi
+  popl %ebx
+  popl %edx
+  popl %ecx
+  popl %eax
+  popl %ebp
   addl $4, %esp /* Ignore "error code" */
 
   /* This restores the eflags, the cs and the eip registers */

arch/x86/exception_wrappers.S

@@ -1,10 +1,19 @@
 #define ASM_SOURCE 1
+#include "segment.h"
 .file "irq_wrappers.S"
 .text
 
 .extern exception_handler_wrap
 .globl exception_handler_wrapper_array
 
+/** Update the kernel TSS in case we are switching to a thread in user
+	mode in order to come back into the correct kernel stack */
+.extern cpu_context_update_kernel_tss
+
+/* The address of the function to call to set back the user thread's
+   MMU configuration upon return to user context */
+.extern thread_prepare_exception_switch_back
+
 .altmacro
 
 
@@ -24,12 +33,12 @@
 		pushl %ebp
 		movl %esp, %ebp
 
-		pushl %edi
-		pushl %esi
-		pushl %edx
-		pushl %ecx
-		pushl %ebx
 		pushl %eax
+		pushl %ecx
+		pushl %edx
+		pushl %ebx
+		pushl %esi
+		pushl %edi
 		subl  $2,%esp
 		pushw %ss
 		pushw %ds
@@ -37,11 +46,31 @@
 		pushw %fs
 		pushw %gs
 
+		/* Set correct kernel segment descriptors' value */
+		movw $BUILD_SEGMENT_REG_VALUE(0, 0, SEG_KDATA), %di
+		pushw %di ; popw %ds
+		pushw %di ; popw %es
+		pushw %di ; popw %fs
+		pushw %di ; popw %gs
+
         push %esp
         pushl $\id
         call exception_handler_wrap
         addl $8, %esp
 
+        /* Reconfigure the MMU if needed */
+        pushl %esp /* cpu_ctxt */
+        call thread_prepare_exception_switch_back
+        addl  $4, %esp /* Unallocate the stack */
+
+        /* Prepare kernel TSS in case we are switching to a
+           user thread: we make sure that we will come back
+           into the kernel at a correct stack location */
+        pushl %esp /* Pass the location of the context we are
+                      restoring to the function */
+        call cpu_context_update_kernel_tss
+        addl $4, %esp
+
 		/* Restore the context */
 		popw  %gs
 		popw  %fs
@@ -49,14 +78,13 @@
 	        popw  %ds
 		popw  %ss
 		addl  $2,%esp
-		popl  %eax
+		popl %edi
-		popl  %ebx
+		popl %esi
-		popl  %ecx
+		popl %ebx
-		popl  %edx
+		popl %edx
-		popl  %esi
+		popl %ecx
-		popl  %edi
+		popl %eax
-		popl  %ebp
+		popl %ebp
-
 		/* Remove fake error code */
 		addl  $4, %esp
 

arch/x86/gdt.h

@@ -19,6 +19,7 @@
 */
 #pragma once
 #include "types.h"
+#include "stdarg.h"
 /**
  * @file gdt.h
  *

arch/x86/irq_wrappers.S

@@ -1,9 +1,17 @@
 #define ASM_SOURCE 1
+#include "segment.h"
 .file "irq_wrappers.S"
 .text
 
 .extern interrupt_handler_pic
 .globl irq_handler_wrapper_array
+/** Update the kernel TSS in case we are switching to a thread in user
+	mode in order to come back into the correct kernel stack */
+.extern cpu_context_update_kernel_tss
+
+/* The address of the function to call to set back the user thread's
+   MMU configuration upon return to user context */
+.extern thread_prepare_irq_switch_back
 
 .altmacro
 
@@ -24,12 +32,12 @@
 		pushl %ebp
 		movl %esp, %ebp
 
-		pushl %edi
-		pushl %esi
-		pushl %edx
-		pushl %ecx
-		pushl %ebx
 		pushl %eax
+		pushl %ecx
+		pushl %edx
+		pushl %ebx
+		pushl %esi
+		pushl %edi
 		subl  $2,%esp
 		pushw %ss
 		pushw %ds
@@ -37,25 +45,45 @@
 		pushw %fs
 		pushw %gs
 
+		/* Set correct kernel segment descriptors' value */
+		movw $BUILD_SEGMENT_REG_VALUE(0, 0, SEG_KDATA), %di
+		pushw %di ; popw %ds
+		pushw %di ; popw %es
+		pushw %di ; popw %fs
+		pushw %di ; popw %gs
+
         push %esp
         pushl $\irq
         call interrupt_handler_pic
         addl $8, %esp
 
+		/* Reconfigure the MMU if needed */
+		pushl %esp /* cpu_ctxt */
+		call thread_prepare_irq_switch_back
+		addl  $4, %esp /* Unallocate the stack */
+
+		/* Prepare kernel TSS in case we are switching to a
+		   user thread: we make sure that we will come back
+		   into the kernel at a correct stack location */
+		pushl %esp /* Pass the location of the context we are
+		              restoring to the function */
+		call cpu_context_update_kernel_tss
+		addl $4, %esp
+
 		/* Restore the context */
 		popw  %gs
 		popw  %fs
 		popw  %es
-	        popw  %ds
+		popw  %ds
 		popw  %ss
 		addl  $2,%esp
-		popl  %eax
+		popl %edi
-		popl  %ebx
+		popl %esi
-		popl  %ecx
+		popl %ebx
-		popl  %edx
+		popl %edx
-		popl  %esi
+		popl %ecx
-		popl  %edi
+		popl %eax
-		popl  %ebp
+		popl %ebp
 
 		/* Remove fake error code */
 		addl  $4, %esp

arch/x86/syscall_wrappers.S

@@ -0,0 +1,91 @@
+#define ASM_SOURCE
+#include "segment.h"
+
+.file "syscall_wrappers.S"
+
+.text
+
+/* The address of the real "C" syscall function */
+.extern syscall_execute
+
+/** Update the kernel TSS in case we are switching to a thread in user
+	mode in order to come back into the correct kernel stack */
+.extern cpu_context_update_kernel_tss
+
+/* The address of the function to call to set back the user thread's
+   MMU configuration upon return to user context */
+.extern thread_prepare_syscall_switch_back
+
+.p2align 2, 0x90
+.globl syscallHandler
+syscallHandler:
+.type syscallHandler,@function
+ 
+  /* Fake error code */
+  pushl $0
+  /* Backup the context */
+  pushl %ebp
+  movl %esp, %ebp
+ 
+  pushl %eax
+  pushl %ecx
+  pushl %edx
+  pushl %ebx
+  pushl %esi
+  pushl %edi
+  subl  $2,%esp
+  pushw %ss
+  pushw %ds
+  pushw %es
+  pushw %fs
+  pushw %gs
+
+  /* Set correct kernel segment descriptors' value */
+  movw $BUILD_SEGMENT_REG_VALUE(0, 0, SEG_KDATA), %di
+  pushw %di ; popw %ds
+  pushw %di ; popw %es
+  pushw %di ; popw %fs
+  pushw %di ; popw %gs
+
+  /* Prepare the call to do_syscall */ 
+  pushl %esp /* user_ctxt */
+  pushl %eax /* syscall ID */
+
+  call  syscall_execute
+  /* Unallocate the stack used by the
+     do_syscall arguments */
+  addl  $8, %esp
+
+  /* store the do_syscall return value into interrupted context */
+  movl %eax, 12(%esp)
+
+  /* Set the MMU configuration to that of the user thread's process */
+  pushl %esp /* user_ctxt */
+  call thread_prepare_syscall_switch_back
+  addl  $4, %esp /* Unallocate the stack */
+
+  /* Prepare kernel TSS because we are switching back to a user
+     thread: we make sure that we will come back into the kernel at a
+     correct stack location */
+  pushl %esp /* Pass the location of the context we are
+  	        restoring to the function */
+  call cpu_context_update_kernel_tss
+  addl $4, %esp
+
+  /* Restore the user context */
+  popw  %gs
+  popw  %fs
+  popw  %es
+  popw  %ds
+  popw  %ss
+  addl  $2,%esp
+  popl %edi
+  popl %esi
+  popl %ebx
+  popl %edx
+  popl %ecx
+  popl %eax
+  popl  %ebp
+  /* Remove fake error code */
+  addl $4, %esp
+  iret

core/kthread.c

@@ -258,3 +258,16 @@ int kthreadAddThread(struct kthread *th)
 
     return 0;
 }
+void thread_prepare_syscall_switch_back(struct cpu_state *cpu_state){
+    (void)cpu_state;
+        return;
+}
+
+void thread_prepare_exception_switch_back(struct cpu_state *cpu_state){
+    (void)cpu_state;
+        return;
+}
+void thread_prepare_irq_switch_back(struct cpu_state *cpu_state){
+    (void)cpu_state;
+        return;
+}

core/segment.h

@@ -1,4 +1,5 @@
-/* Copyright (C) 2004  The SOS Team
+/* Copyright (C) 2021  Mathieu Maret
+   Copyright (C) 2004  The SOS Team
    Copyright (C) 1999  Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or
@@ -29,8 +30,6 @@
  * @see Intel x86 doc, vol 3 chapter 3.
  */
 
-#include "stdarg.h"
-
 /*
  * Global segment selectors (GDT) for SOS/x86.
  *
@@ -46,9 +45,16 @@
 /**
  * Helper macro that builds a segment register's value
  */
+#ifdef ASM_SOURCE
+#define BUILD_SEGMENT_REG_VALUE(desc_privilege,in_ldt,seg_index) \
+  (  (((desc_privilege) & 0x3)  << 0) \
+   | ((in_ldt & 1)              << 2) \
+   | ((seg_index)               << 3) )
+
+#else
 #define BUILD_SEGMENT_REG_VALUE(desc_privilege, in_ldt, seg_index)                            \
     ((((desc_privilege)&0x3) << 0) | (((in_ldt) ? 1 : 0) << 2) | ((seg_index) << 3))
-
+#endif
 /*
  * Local segment selectors (LDT) for SOS/x86
  */

core/syscall.c

@@ -0,0 +1,21 @@
+#include "syscall.h"
+#include "irq.h"
+#include "idt.h"
+
+extern void syscallHandler();
+
+int syscallSetup(){
+    uint32_t flags, ret;
+
+    disable_IRQs(flags);
+    ret =  idt_set_handler(SYSCALL_INTR_NB, (vaddr_t)syscallHandler, 3);
+    restore_IRQs(flags);
+
+    return ret;
+}
+
+int syscall_execute(int syscallId, const struct cpu_state *user_ctx){
+    (void)syscallId;
+    (void)user_ctx;
+    return 0;
+}

core/syscall.h

@@ -0,0 +1,5 @@
+#pragma once
+
+#define SYSCALL_INTR_NB  0x42
+
+int syscallSetup();