fix: aiecc --aiesim crashes due to missing define and wrong IO backend

runtime_lib/CMakeLists.txt

@@ -131,8 +131,12 @@ add_aiert_headers(xaienginecdo_static
 )
 add_aiert_library(xaienginecdo_static ${XAIE_SOURCE_DIR} STATIC)
 
+# Weak stubs for ess_* symbols (provided at runtime by aiesimulator via dlopen).
+# Must be linked into the static lib so aiecc resolves these at link time.
+target_sources(xaienginecdo_static PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/ess_stubs.c)
+
 target_link_libraries(xaienginecdo_static PRIVATE cdo_driver_mlir_aie)
-target_compile_definitions(xaienginecdo_static PRIVATE -D__AIECDO__ -D__AIEDEBUG__)
+target_compile_definitions(xaienginecdo_static PRIVATE -D__AIECDO__ -D__AIEDEBUG__ -D__AIESIM__)
 
 # just to make cmake happy since AIETargets will need to re-export
 # make sure not abs path...

runtime_lib/ess_stubs.c

@@ -0,0 +1,64 @@
+/*
+ * Weak stubs for aiesimulator ESS functions.
+ *
+ * xaie_sim.c forward-declares these symbols (ess_Write32, ess_Read32, etc.)
+ * which are provided at runtime by the aiesimulator SystemC process via
+ * dlopen. When linking aiecc statically, these symbols are unresolved.
+ *
+ * These weak definitions satisfy the linker. If aiecc is loaded by
+ * aiesimulator, the real (strong) symbols override them. If someone
+ * calls aiecc --aiesim outside of aiesimulator, the sim backend init
+ * will fail gracefully before these are reached, but the stubs abort()
+ * as a safety net.
+ *
+ * This file is licensed under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+ * (c) Copyright 2026 Advanced Micro Devices, Inc.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef unsigned int uint;
+
+__attribute__((weak)) void ess_Write32(uint64_t Addr, uint Data) {
+  (void)Addr;
+  (void)Data;
+  fprintf(stderr, "FATAL: ess_Write32 called outside aiesimulator\n");
+  abort();
+}
+
+__attribute__((weak)) uint ess_Read32(uint64_t Addr) {
+  (void)Addr;
+  fprintf(stderr, "FATAL: ess_Read32 called outside aiesimulator\n");
+  abort();
+}
+
+__attribute__((weak)) void
+ess_WriteCmd(unsigned char Command, unsigned char ColId, unsigned char RowId,
+             unsigned int CmdWd0, unsigned int CmdWd1, unsigned char *CmdStr) {
+  (void)Command;
+  (void)ColId;
+  (void)RowId;
+  (void)CmdWd0;
+  (void)CmdWd1;
+  (void)CmdStr;
+  fprintf(stderr, "FATAL: ess_WriteCmd called outside aiesimulator\n");
+  abort();
+}
+
+__attribute__((weak)) void ess_NpiWrite32(uint64_t Addr, uint Data) {
+  (void)Addr;
+  (void)Data;
+  fprintf(stderr, "FATAL: ess_NpiWrite32 called outside aiesimulator\n");
+  abort();
+}
+
+__attribute__((weak)) uint ess_NpiRead32(uint64_t Addr) {
+  (void)Addr;
+  fprintf(stderr, "FATAL: ess_NpiRead32 called outside aiesimulator\n");
+  abort();
+}