From 4fe5ac924854b2bd91bc260fb76a69a3374db078 Mon Sep 17 00:00:00 2001
From: Patryk Duda <patrykd@google.com>
Date: Fri, 26 Apr 2024 18:02:31 +0200
Subject: [PATCH] arch: posix: Undefine operating system specific macros for
 native_sim

Compilers predefine system-specific macros which carry information about
compiler, target architecture and operating system. It provides basic
compiler-dependent information like size of types, their maximal and
minimal values, etc. It allows to write common libc headers for multiple
architectures and operating systems.

These macros allow code to always determine what is the target operating
system. This is a problem when compiling code of modules that supports
multiple operating systems (e.g. cryptography libraries).

To avoid confusion we shouldn't leak host operating system macros (e.g.
__linux__, __linux, linux, etc.) when compiling for native_sim board.

Unfortunately, there is no single universal switch that disables all
operating system macros:
- '-undef' removes also architecture-related macros
- '--target' is only available for Clang compiler

This patch uses '-include' option to include file that undefines all
well-known operating system macros.

Run 'gcc -dM -E - < /dev/null | sort' to get full list of predefined
macros.

Signed-off-by: Patryk Duda <patrykd@google.com>
---
 arch/posix/CMakeLists.txt                 |  4 +++-
 arch/posix/include/undef_system_defines.h | 20 ++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 arch/posix/include/undef_system_defines.h

diff --git a/arch/posix/CMakeLists.txt b/arch/posix/CMakeLists.txt
index bc06cecac27..74a0c9e2617 100644
--- a/arch/posix/CMakeLists.txt
+++ b/arch/posix/CMakeLists.txt
@@ -99,11 +99,13 @@ elseif (CONFIG_NATIVE_LIBRARY)
     get_filename_component(COMPILER_OWN_INCLUDE_PATH "${_OUTPUT}" DIRECTORY)
 
     # Do not use the C library from this compiler/host,
-    # but still use the basic compiler headers
+    # but still use the basic compiler headers,
+    # remove all operating system specific predefined macros,
     # no_builtin to avoid the compiler using builtin replacements for std library functions
     zephyr_compile_options(
       -nostdinc
       -isystem ${COMPILER_OWN_INCLUDE_PATH}
+      "SHELL:-include ${ZEPHYR_BASE}/arch/posix/include/undef_system_defines.h"
       $<TARGET_PROPERTY:compiler,freestanding>
       $<TARGET_PROPERTY:compiler,no_builtin>
     )
diff --git a/arch/posix/include/undef_system_defines.h b/arch/posix/include/undef_system_defines.h
new file mode 100644
index 00000000000..d7384e403a6
--- /dev/null
+++ b/arch/posix/include/undef_system_defines.h
@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2024 Google LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Undefine all system-specific macros defined internally, by the compiler.
+ * Run 'gcc -dM -E - < /dev/null | sort' to get full list of internally
+ * defined macros.
+ */
+
+#undef __gnu_linux__
+#undef __linux
+#undef __linux__
+#undef linux
+
+#undef __unix
+#undef __unix__
+#undef unix