syscalls: make use of stderr and fix chdir syscall return value

src/drivers/screen.c

@@ -36,6 +36,11 @@ void terminal_setcolor(uint8_t color)
         terminal_color = color;
 }
 
+uint8_t terminal_getcolor()
+{
+        return terminal_color;
+}
+
 void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) 
 {
         const size_t index = y * VGA_WIDTH + x;

src/tasking/syscalls.c

@@ -4,6 +4,7 @@
 #include "../include/liballoc.h"
 #include "../include/paging.h"
 #include "../include/string.h"
+#include "../include/screen.h"
 
 #define STDIN_FILENO 0
 #define STDOUT_FILENO 1
@@ -171,6 +172,14 @@ int sys_write(TrapFrame *tf)
             //debug_log("\n=================END OF THAT SHIT=====================\n");
             return tf->edx;
         }
+        if(tf->ebx == STDERR_FILENO)
+        {
+            uint8_t prev_color = terminal_getcolor();
+            terminal_setcolor(VGA_COLOR_RED);
+            print((char*)tf->ecx, tf->edx);
+            terminal_setcolor(prev_color);
+            return tf->edx;
+        }
     }
     else
     {
@@ -234,7 +243,12 @@ int sys_chdir(TrapFrame *tf)
 {
     strcat(current->cwd->fat->path, "/");
     strcat(current->cwd->fat->path, (char*)tf->ebx);
-    return fat_opendir(current->cwd, (const char*)tf->ebx);
+
+    int result = fat_opendir(current->cwd, (const char*)tf->ebx);
+    if(result == 0)
+        return 0;
+
+    return -1;
 }
 
 int sys_getcwd(TrapFrame *tf)