fix(heap): avoid stack smash when heap tracing stack depth is 0

On RISC-V without frame pointers, STACK_DEPTH defaults to 0, so
alloced_by[] is empty. Writing callers[0] still ran and overwrote the
caller's cm.push saved ra, causing an illegal-instruction fault after
the first traced malloc (e.g. with HEAP_TRACING on ESP32-S31).

components/heap/include/heap_trace.inc

@@ -85,24 +85,23 @@ static HEAP_IRAM_ATTR __attribute__((noinline)) void get_call_stack(void **calle
 
 #else // !CONFIG_IDF_TARGET_ARCH_XTENSA
 
-extern uint32_t esp_fp_get_callers(uint32_t frame, void** callers, void** stacks, uint32_t depth);
-
 static HEAP_IRAM_ATTR __attribute__((noinline)) void get_call_stack(void **callers)
 {
+#if STACK_DEPTH == 0
+    /* alloced_by[] / freed_by[] are empty — nothing to capture;
+     * writing callers[0] would smash the caller's stack. */
+    (void)callers;
+#else
     uint32_t fp = (uint32_t) __builtin_frame_address(0);
     memset(callers, 0, sizeof(void *) * STACK_DEPTH);
 
-#if CONFIG_ESP_SYSTEM_USE_FRAME_POINTER
     /* We can skip the current return address since this function won't be inlined */
+    uint32_t esp_fp_get_callers(uint32_t, void **, void **, uint32_t);
     esp_fp_get_callers(fp, callers, NULL, STACK_DEPTH);
-#else
-    /* RISC-V compiler doesn't support `__builtin_frame_address` with a parameter bigger than 0 */
-    callers[0] = (void*) fp;
 #endif
 }
 
-#endif
-
+#endif /* CONFIG_IDF_TARGET_ARCH_XTENSA */
 
 ESP_STATIC_ASSERT(STACK_DEPTH >= 0 && STACK_DEPTH <= 32, "CONFIG_HEAP_TRACING_STACK_DEPTH must be in range 0-32");