Allow executables to be mapped to a virtual memory address. Now (finally) multiple executables can share the same logical address, and the GUI shell supports displaying the output of multiple programs.

Author: tthomps

Media/Screenshots/MyOS_GUI_1.png

@@ -6,6 +6,7 @@
 #include "../printf.h"
 #include "../Tasks/Context.h"
 #include "../paging.h"
+#include "../../MyOS_GUI_Shell/GUI_Kernel_Shell.h"
 
 jmp_buf peReturnBuf;
 
@@ -86,23 +87,40 @@ bool loadAndRunPE(uint8_t *executableDestination, DOS_Header *mzAddress, const c
 
     // Get a new page directory for the new task
     PAGE_DIRECTORY_ENTRY *newPageDirectory;
-
-    // GUI.exe shares the kernel's page directory
-    if ((uint32_t)executableDestination != 0xC00000)
+    uint32_t physicalLocation = (uint32_t)executableDestination;
+    
+    // Create a new page directory unless we're loading the GUI, because GUI.exe shares the kernel's page directory and uses a hardcoded address
+    if ((uint32_t)executableDestination != GUI_BASE_ADDRESS)
     {
         newPageDirectory = (PAGE_DIRECTORY_ENTRY *)nextPageDirectory;
         nextPageDirectory += sizeof(PAGE_DIRECTORY_ENTRY) * 1024;
 
         // Copy the kernel's page table to this new page table
         memcpy((void*)newPageDirectory, pageDir, sizeof(PAGE_DIRECTORY_ENTRY) * 1024);
 
+        // Allocate a page of memory for the new application
+        unsigned int pagesAllocated;
+        KPageAllocator(1, &pagesAllocated, &physicalLocation);
+        if (!pagesAllocated)
+        {
+            kprintf("Unable to allocate memory for %s", imageName);
+            _enable();
+            return false;
+        }
+
+        //kprintf("Got a page of memory at 0x%X\n", physicalLocation);
+
+        // Map the page of memory into the process' page directory
+        newPageDirectory[(uint32_t)executableDestination / FOUR_MEGABYTES] = physicalLocation
+                                                            | DIRECTORY_ENTRY_PRESENT | DIRECTORY_ENTRY_WRITABLE | DIRECTORY_ENTRY_4MB | DIRECTORY_ENTRY_USER_ACCESSIBLE;
+
         //Paging_Print_Page_Table(newPageDirectory);
     }
     else
         newPageDirectory = pageDir;
 
     // TEMPTEMP - zero out 5 0x1000 sections of memory (tailored to TestApp1.exe)
-    memset(executableDestination, 0, 0x5000);
+    memset(physicalLocation, 0, 0x5000);
 
     // Get the address of the first section
     IMAGE_SECTION_HEADER *sectionHeader = (IMAGE_SECTION_HEADER*)((uint32_t)directory + sizeof(IMAGE_DATA_DIRECTORY));
@@ -120,7 +138,7 @@ bool loadAndRunPE(uint8_t *executableDestination, DOS_Header *mzAddress, const c
         }
 
         // Determine the destination of the current section
-        uint8_t *sectionDest = (uint8_t*)((uint32_t)executableDestination + sectionHeader->mVirtualAddress);
+        uint8_t *sectionDest = (uint8_t*)((uint32_t)physicalLocation + sectionHeader->mVirtualAddress);
         if (debugLevel)
         {
             terminal_writestring("Virtual address of section: ");

MyOS_1/Executables/PE32.c

@@ -123,7 +123,8 @@ void _declspec(naked) timer_interrupt_handler(void)
             ticksLeftInTask = TICKS_PER_TASK;
 
             // switch to the new task's page tables
-            __writecr3(tasks[currentTask].cr3);
+            if(tasks[currentTask].cr3 != __readcr3())
+                __writecr3(tasks[currentTask].cr3);
 
             // Get the stack pointer of the next waiting task and make that the stack
             espVal = tasks[currentTask].ESP;

MyOS_1/Timers/PIT.c

@@ -118,7 +118,7 @@ void KeStartupPhase2(multiboot_info *multibootInfo)
     tasks[0].inUse = true;
     strncpy(tasks[0].imageName, "KERNEL PROCESS", sizeof("KERNEL PROCESS"));
     tasks[0].PID = nextPID - 1;
-    tasks[0].cr3 = pageDir;
+    tasks[0].cr3 = (uint32_t)pageDir;
 
     // Initialize interrupts
     Interrupts_Init();

MyOS_1/main.c

@@ -72,7 +72,7 @@ void KPageAllocator(unsigned int pages, unsigned int *pPagesAllocated, uint32_t
         {
             for (int i = 0; i < MAX_TASKS; ++i)
             {
-                if (!tasks[i].inUse || tasks[i].cr3 == pageDir)
+                if (!tasks[i].inUse || tasks[i].cr3 == (uint32_t)pageDir)
                     continue;
 
                 PAGE_DIRECTORY_ENTRY *otherPageDir = (PAGE_DIRECTORY_ENTRY *)tasks[i].cr3;

MyOS_1/paging.c

@@ -8,6 +8,9 @@ extern "C" {
 
 // Used to define the interface between the Kernel and the GUI Shell (on the shell side)
 
+#define \
+GUI_BASE_ADDRESS 0xC00000
+
 // Called by the kernel to send messages to the GUI
 void GUI_Kernel_Callback(uint32_t PID, uint32_t messageType, void *pData);
 

MyOS_GUI_Shell/GUI_Kernel_Shell.h

@@ -133,14 +133,15 @@
       <AdditionalDependencies>%(AdditionalDependencies)</AdditionalDependencies>
       <IgnoreAllDefaultLibraries>true</IgnoreAllDefaultLibraries>
       <LinkTimeCodeGeneration>Default</LinkTimeCodeGeneration>
-      <BaseAddress>0xC00000</BaseAddress>
+      <BaseAddress>@GUI_Kernel_Shell.h,GUI_BASE_ADDRESS</BaseAddress>
       <DataExecutionPrevention>false</DataExecutionPrevention>
       <MapFileName>GUI.map</MapFileName>
       <MapExports>true</MapExports>
       <RandomizedBaseAddress>false</RandomizedBaseAddress>
       <EntryPointSymbol>main</EntryPointSymbol>
       <GenerateMapFile>true</GenerateMapFile>
       <ImageHasSafeExceptionHandlers>false</ImageHasSafeExceptionHandlers>
+      <FixedBaseAddress>true</FixedBaseAddress>
     </Link>
     <PostBuildEvent>
       <Message>Copying GUI.exe to TFTP directory</Message>
@@ -294,6 +295,7 @@
     <ClInclude Include="GUI_Taskbar.h" />
     <ClInclude Include="GUI_TerminalWindow.h" />
     <ClInclude Include="GUI_Window.h" />
+    <ClInclude Include="MyOS_GUI_Shell.h" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">

MyOS_GUI_Shell/MyOS_GUI_Shell.vcxproj

@@ -386,5 +386,8 @@
     <ClInclude Include="GUI_TerminalWindow.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="MyOS_GUI_Shell.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>