esp8266/modesp: Add malloc() and free() functions.

Useful for testing fragmentation issues in OS heap. E.g. freemem() may
report large amount, but is it possible to actually allocate block of
a given size? Issue malloc() (followed by free()) to find out.

esp8266/etshal.h

@@ -20,4 +20,8 @@ void ets_timer_arm_new(os_timer_t *tim, uint32_t millis, bool repeat, bool is_mi
 void ets_timer_setfn(os_timer_t *tim, ETSTimerFunc callback, void *cb_data);
 void ets_timer_disarm(os_timer_t *tim);
 
+// These prototypes are for recent SDKs with "malloc tracking"
+void *pvPortMalloc(unsigned sz, const char *fname, int line);
+void vPortFree(void *p, const char *fname, int line);
+
 #endif // _INCLUDED_ETSHAL_H_

esp8266/modesp.c

@@ -41,6 +41,7 @@
 #include "user_interface.h"
 #include "espconn.h"
 #include "spi_flash.h"
+#include "mem.h"
 #include "espneopixel.h"
 #include "modpyb.h"
 
@@ -646,6 +647,17 @@ STATIC mp_obj_t esp_meminfo() {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_0(esp_meminfo_obj, esp_meminfo);
 
+STATIC mp_obj_t esp_malloc(mp_obj_t size_in) {
+    return MP_OBJ_NEW_SMALL_INT((mp_uint_t)os_malloc(mp_obj_get_int(size_in)));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(esp_malloc_obj, esp_malloc);
+
+STATIC mp_obj_t esp_free(mp_obj_t addr_in) {
+    os_free((void*)mp_obj_get_int(addr_in));
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(esp_free_obj, esp_free);
+
 STATIC mp_obj_t esp_esf_free_bufs(mp_obj_t idx_in) {
     return MP_OBJ_NEW_SMALL_INT(ets_esf_free_bufs(mp_obj_get_int(idx_in)));
 }
@@ -670,6 +682,8 @@ STATIC const mp_map_elem_t esp_module_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_freemem), (mp_obj_t)&esp_freemem_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_meminfo), (mp_obj_t)&esp_meminfo_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_info), (mp_obj_t)&pyb_info_obj }, // TODO delete/rename/move elsewhere
+    { MP_OBJ_NEW_QSTR(MP_QSTR_malloc), (mp_obj_t)&esp_malloc_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_free), (mp_obj_t)&esp_free_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_esf_free_bufs), (mp_obj_t)&esp_esf_free_bufs_obj },
 
 #if MODESP_INCLUDE_CONSTANTS