added placeholder malloc_stack as malloc precursor

Makefile

@@ -33,10 +33,10 @@ CFLAGS += -DTEXT_IO_ADDR=0xff0000 -DTEXT_IO_BUFLEN=64
 CFLAGS += -march=$(ARCH)
 
 # dependencies that need to be built:
-_DEPS = ecall.c csr.c sched.c io.o
+_DEPS = ecall.c csr.c sched.c io.c malloc.c
 
 # dependencies as object files:
-_OBJ = ecall.o sched.o boot.o csr.o io.o
+_OBJ = ecall.o sched.o boot.o csr.o io.o malloc.o
 
 
 DEPS  = $(patsubst %,$(KLIBDIR)/%,$(_DEPS))

kinclude/malloc.c

@@ -0,0 +1,33 @@
+#include "malloc.h"
+#include "ecall.h"
+
+malloc_info global_malloc_info = { 0 };
+void* allocate_memory_end;
+
+
+void malloc_init(malloc_info* given_info)
+{
+    global_malloc_info = *given_info;
+    allocate_memory_end = given_info->allocate_memory_end;
+}
+
+void* malloc(size_t size)
+{
+    return (void*) ENOMEM;
+}
+
+int free(void* ptr)
+{
+    return EINVAL;
+}
+
+// allocate stack and return a pointer to the *end* of the allocated region
+void* 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;
+    void* stack_top = allocate_memory_end;
+    allocate_memory_end = new_alloc_end;
+    return stack_top;
+}

kinclude/malloc.h

@@ -0,0 +1,18 @@
+#ifndef H_MALLOC
+#define H_MALLOC
+
+typedef unsigned int size_t;
+
+typedef struct malloc_info {
+    void* allocate_memory_end;
+    void* allocate_memory_start;
+} malloc_info;
+
+void* malloc(size_t size);
+// int free(void* ptr);
+
+void* malloc_stack(size_t size);
+
+void malloc_init(malloc_info* info);
+
+#endif