build: allow application code to opt out of Zephyr stdint convention

Kconfig.zephyr

@@ -1116,6 +1116,23 @@ config ENFORCE_ZEPHYR_STDINT
 	  should be turned off with the caveat that argument type validation
 	  on Zephyr code will be skipped.
 
+config OMIT_ZEPHYR_STDINT_FOR_APPS
+	bool "Omit Zephyr stdint convention for application code"
+	depends on ENFORCE_ZEPHYR_STDINT
+	help
+	  When enabled, the "app" build target (i.e. source files under
+	  APPLICATION_SOURCE_DIR) is compiled with the toolchain's native
+	  integer type definitions instead of Zephyr's enforced convention.
+	  This is useful when application code includes compiler-provided
+	  headers that are incompatible with Zephyr's type mappings.
+
+	  The Zephyr kernel, drivers, subsystems, and any libraries built
+	  via zephyr_library() remain under the enforced convention.
+	  Because Zephyr is C-only, there is no symbol mangling dependency
+	  on the underlying types, and the affected types (e.g. int vs long
+	  on ILP32) share the same size and ABI, so linkage between
+	  application and Zephyr object code remains fully compatible.
+
 endmenu
 
 

cmake/modules/kernel.cmake

@@ -224,6 +224,10 @@ add_custom_target(zephyr_property_target)
 zephyr_library_named(app)
 set_property(TARGET app PROPERTY ARCHIVE_OUTPUT_DIRECTORY app)
 
+if(CONFIG_OMIT_ZEPHYR_STDINT_FOR_APPS)
+  target_compile_definitions(app PRIVATE ZEPHYR_INCLUDE_TOOLCHAIN_STDINT_H_)
+endif()
+
 add_subdirectory(${ZEPHYR_BASE} ${__build_dir})
 
 # Link 'app' with the Zephyr interface libraries.

tests/application_development/omit_zephyr_stdint/CMakeLists.txt

@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(omit_zephyr_stdint)
+
+target_sources(app PRIVATE src/main.c)

tests/application_development/omit_zephyr_stdint/prj.conf

@@ -0,0 +1 @@
+CONFIG_COMPILER_WARNINGS_AS_ERRORS=y

tests/application_development/omit_zephyr_stdint/src/main.c

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2026 BayLibre SAS
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Validate CONFIG_OMIT_ZEPHYR_STDINT_FOR_APPS.
+ *
+ * When the option is enabled, application code gets the toolchain's native
+ * integer type definitions. The correct printf format specifiers then
+ * depend on the data model:
+ *
+ *   ILP32 (32-bit targets): int32_t is "long"      -> %ld
+ *   LP64  (64-bit targets): int64_t is "long"      -> %ld
+ *
+ * Under Zephyr's enforced convention (the default), the mapping is:
+ *
+ *   int32_t is always "int"       -> %d
+ *   int64_t is always "long long" -> %lld
+ *
+ * This test uses the format specifiers matching each convention and
+ * must compile cleanly (no -Wformat warnings, which are errors with
+ * -Werror) to pass.
+ */
+
+#include <zephyr/kernel.h>
+#include <stdint.h>
+
+int main(void)
+{
+	int32_t val32 = 32;
+	int64_t val64 = 64;
+
+#ifdef CONFIG_OMIT_ZEPHYR_STDINT_FOR_APPS
+	/* Native toolchain types */
+#if __SIZEOF_POINTER__ == 4
+	/* ILP32: int32_t is long */
+	printk("int32_t = %ld\n", val32);
+	printk("int64_t = %lld\n", val64);
+#else
+	/* LP64: int64_t is long */
+	printk("int32_t = %d\n", val32);
+	printk("int64_t = %ld\n", val64);
+#endif
+#else
+	/* Zephyr convention: int32_t = int, int64_t = long long */
+	printk("int32_t = %d\n", val32);
+	printk("int64_t = %lld\n", val64);
+#endif
+
+	return 0;
+}

tests/application_development/omit_zephyr_stdint/testcase.yaml

@@ -0,0 +1,17 @@
+common:
+  tags: toolchain
+  build_only: true
+  arch_allow:
+    - arm
+    - arm64
+tests:
+  buildsystem.app_dev.omit_zephyr_stdint.enabled:
+    extra_configs:
+      - CONFIG_OMIT_ZEPHYR_STDINT_FOR_APPS=y
+    platform_allow:
+      - qemu_cortex_m3
+      - qemu_cortex_a53
+  buildsystem.app_dev.omit_zephyr_stdint.disabled:
+    platform_allow:
+      - qemu_cortex_m3
+      - qemu_cortex_a53