tests/malloc: Allow malloc to fail when out of RAM, add heap test

cases.

Fixes #76.

FreeRTOS/Source/portable/esp8266/port.c

@@ -81,13 +81,16 @@
 unsigned cpu_sr;
 char level1_int_disabled;
 
-/* Supervisor stack pointer entry. This is the "high water mark" of how far the
+/* Supervisor stack pointer entry. On reset, sdk_user_start sets a
-   supervisor stack grew down before task started.
+ * tentative 512 byte supervisor stack size.
+
+ When the scheduler starts, this changes to the "high water mark" of
+ how far the supervisor stack grew down before task started.
 
  After tasks start, task stacks are all allocated from the heap and
  FreeRTOS checks for stack overflow.
 */
-static uint32_t xPortSupervisorStackPointer;
+void *xPortSupervisorStackPointer;
 
 /*
  * Stack initialization
@@ -218,7 +221,7 @@ size_t xPortGetFreeHeapSize( void )
     struct mallinfo mi = mallinfo();
     uint32_t brk_val = (uint32_t) sbrk(0);
 
-    uint32_t sp = xPortSupervisorStackPointer;
+    intptr_t sp = (intptr_t)xPortSupervisorStackPointer;
     if(sp == 0) /* scheduler not started */
         __asm__ __volatile__ ("mov %0, a1\n" : "=a"(sp));
     return sp - brk_val + mi.fordblks;

core/newlib_syscalls.c

@@ -12,6 +12,8 @@
 #include <esp/uart.h>
 #include <stdlib.h>
 
+extern void *xPortSupervisorStackPointer;
+
 IRAM caddr_t _sbrk_r (struct _reent *r, int incr)
 {
     extern char   _heap_start; /* linker script defined */
@@ -21,13 +23,16 @@ IRAM caddr_t _sbrk_r (struct _reent *r, int incr)
     if (heap_end == NULL)
 	heap_end = &_heap_start;
     prev_heap_end = heap_end;
-    /* TODO: Check stack collision
+
-       if (heap_end + incr > stack_ptr)
+    intptr_t sp = (intptr_t)xPortSupervisorStackPointer;
+    if(sp == 0) /* scheduler not started */
+        __asm__ __volatile__ ("mov %0, a1\n" : "=a"(sp));
+
+    if ((intptr_t)heap_end + incr >= sp)
     {
-       _write (1, "_sbrk: Heap collided with stack\n", 32);
+        r->_errno = ENOMEM;
-       while(1) {}
+        return (caddr_t)-1;
     }
-    */
     heap_end += incr;
 
     return (caddr_t) prev_heap_end;

ld/common.ld

@@ -232,7 +232,7 @@ SECTIONS
     _heap_start = ABSOLUTE(.);
 /*    _stack_sentry = ALIGN(0x8); */
   } >dram0_0_seg :dram0_0_bss_phdr
-/* __stack = 0x3ffc8000; */
+/* __stack = 0x3ffc8000; <-- this value seems a bit odd, stack on sdk_user_start is ~0x3ffffce9 */
 
   .lit4 : ALIGN(4)
   {

tests/cases/02_heap.c

@@ -4,6 +4,7 @@
 #include <FreeRTOS.h>
 
 DEFINE_SOLO_TESTCASE(02_heap_simple)
+DEFINE_SOLO_TESTCASE(02_heap_full)
 
 /* Simple heap accounting tests */
 static void a_02_heap_simple()
@@ -35,3 +36,21 @@ static void a_02_heap_simple()
     TEST_ASSERT_UINT32_WITHIN_MESSAGE(100, freeheap, after, "Free heap size after freeing buffer should be close to initial");
     TEST_PASS;
 }
+
+/* Ensure malloc behaves when out of memory */
+static void a_02_heap_full()
+{
+    void *x = malloc(65536);
+    TEST_ASSERT_NULL_MESSAGE(x, "Allocating 64kB should fail and return null");
+
+    void *y = malloc(32768);
+    TEST_ASSERT_NOT_NULL_MESSAGE(y, "Allocating 32kB should succeed");
+
+    void *z = malloc(32768);
+    TEST_ASSERT_NULL_MESSAGE(z, "Allocating second 32kB should fail");
+
+    free(y);
+    z = malloc(32768);
+    TEST_ASSERT_NOT_NULL_MESSAGE(z, "Allocating 32kB should succeed after first block freed");
+    TEST_PASS;
+}