diff --git a/Makefile b/Makefile
index 083535e..502e94b 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,7 @@ GCC_PREF=riscv32-unknown-elf-
 
 CC=$(GCC_PREF)gcc
 OBJDUMP=$(GCC_PREF)objdump
-CFLAGS=-I$(KLIBDIR) -MD -mcmodel=medany -Wall -Wextra -pedantic-errors
+CFLAGS=-I$(KLIBDIR) -MD -mcmodel=medany -Wall -Wextra -pedantic-errors -Wno-builtin-declaration-mismatch
 KERNEL_CFLAGS=-nostdlib -T linker.ld
 ARCH = rv32im							# here you 
 
diff --git a/kinclude/ecall.c b/kinclude/ecall.c
index 8af3db2..d01ec4f 100644
--- a/kinclude/ecall.c
+++ b/kinclude/ecall.c
@@ -1,12 +1,19 @@
+#include "ktypes.h"
 #include "ecall.h"
 #include "sched.h"
 #include "csr.h"
 #include "io.h"
 
+// this type is only used here, therefore we don't need it in the ktypes header
 typedef int (*ecall_handler)(int*,ProcessControlBlock*);
 
 ecall_handler ecall_table[ECALL_TABLE_LEN] = { 0 };
 
+
+// ignore unused parameter errors only for these functions
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+
 int ecall_handle_spawn_thread(int* args_ptr, ProcessControlBlock* pcb)
 {
     void* entry = (void*) args_ptr[0];
@@ -55,6 +62,8 @@ int ecall_handle_exit(int* args, ProcessControlBlock* pcb)
     return 0;
 }
 
+#pragma GCC diagnostic pop
+
 void trap_handle_ecall() {
     {
         
diff --git a/kinclude/ecall.h b/kinclude/ecall.h
index 242302b..51c1aeb 100644
--- a/kinclude/ecall.h
+++ b/kinclude/ecall.h
@@ -17,12 +17,6 @@ enum ecall_codes {
 
 #define ECALL_TABLE_LEN 16
 
-enum error_code {
-    ENOCODE = -1,   // invalid syscall code
-    EINVAL  = -2,   // invalid argument value
-    ENOMEM  = -3,   // not enough memory
-};
-
 // initializer for ecall lookup table
 void init_ecall_table();
 
diff --git a/kinclude/io.c b/kinclude/io.c
index 590afd2..32f2fd2 100644
--- a/kinclude/io.c
+++ b/kinclude/io.c
@@ -29,13 +29,6 @@ void dbgln(char* text, int len)
     *((char*) TEXT_IO_ADDR) = 1;
 }
 
-#else
-
-/* if no textIO module loaded, dbgln is a noop :( */
-void dbgln(char*, int){}
-
-#endif
-
 
 /* alphabet for itoa */
 char alpha[16] = "0123456789abcdef";
@@ -60,4 +53,15 @@ char* itoa (int value, char* str, int base)
     while (value > 0);
 
     return str;
-}
\ No newline at end of file
+}
+
+#else
+
+/* if no textIO module loaded, dbgln is a noop :( */
+void dbgln(char* text, int len){}
+char* itoa (int value, char* str, int base) {
+    return str;
+}
+
+#endif
+
diff --git a/kinclude/malloc.c b/kinclude/malloc.c
index 97a0342..cb3226c 100644
--- a/kinclude/malloc.c
+++ b/kinclude/malloc.c
@@ -11,9 +11,9 @@ void malloc_init(malloc_info* given_info)
     allocate_memory_end = given_info->allocate_memory_end;
 }
 
-void* malloc(size_t size)
+optional_voidptr malloc(size_t size)
 {
-    return (void*) ENOMEM;
+    return (optional_voidptr) { .error = ENOMEM };
 }
 
 int free(void* ptr)
@@ -22,12 +22,12 @@ int free(void* ptr)
 }
 
 // allocate stack and return a pointer to the *end* of the allocated region
-void* malloc_stack(size_t size)
+optional_voidptr malloc_stack(size_t size)
 {
     void* new_alloc_end = (void*) (((int) allocate_memory_end) - size);
     if (new_alloc_end < global_malloc_info.allocate_memory_start) 
-        return (void*) ENOMEM;
+        return (optional_voidptr) { .error = ENOMEM };
     void* stack_top = allocate_memory_end;
     allocate_memory_end = new_alloc_end;
-    return stack_top;
-}
\ No newline at end of file
+    return (optional_voidptr) { .value = stack_top };
+}
diff --git a/kinclude/malloc.h b/kinclude/malloc.h
index 687efc4..57be51d 100644
--- a/kinclude/malloc.h
+++ b/kinclude/malloc.h
@@ -1,17 +1,17 @@
 #ifndef H_MALLOC
 #define H_MALLOC
 
-typedef unsigned int size_t;
+#include "ktypes.h"
 
 typedef struct malloc_info {
     void* allocate_memory_end;
     void* allocate_memory_start;
 } malloc_info;
 
-void* malloc(size_t size);
+optional_voidptr malloc(size_t size);
 // int free(void* ptr);
 
-void* malloc_stack(size_t size);
+optional_voidptr malloc_stack(size_t size);
 
 void malloc_init(malloc_info* info);
 
diff --git a/kinclude/sched.h b/kinclude/sched.h
index 991f95a..a808c7a 100644
--- a/kinclude/sched.h
+++ b/kinclude/sched.h
@@ -2,26 +2,7 @@
 #define H_SCHED
 
 #include "../kernel.h"
-
-enum process_status {
-    PROC_DEAD       = 0,
-    PROC_RDY        = 1,
-    PROC_WAIT_PROC  = 2,
-    PROC_WAIT_SLEEP = 3,
-};
-
-// process structure:
-typedef struct ProcessControlBlock ProcessControlBlock;
-struct ProcessControlBlock {
-    int pid;
-    int pc;
-    int regs[31];
-    int exit_code;
-    // scheduling information
-    enum process_status status;
-    ProcessControlBlock *waiting_for_process;
-    unsigned long long int asleep_until;
-};
+#include "ktypes.h"
 
 // scheduling data:
 extern ProcessControlBlock processes[PROCESS_COUNT];