From 9672858c1932adba34e21b3764b44f44a6034687 Mon Sep 17 00:00:00 2001
From: Stephanos Ioannidis <root@stephanos.io>
Date: Thu, 11 Aug 2022 03:06:46 +0900
Subject: [PATCH] cmake: compiler: Add flag template for disabling strict
 aliasing rule

This commit adds a template for specifying the C/C++ compiler flag for
disabling the strict aliasing rule.

It also enables this flag globally because the Zephyr codebase does not
strictly adhere to the aliasing rules specified by the C/C++ standards
and the optimisation strategies that assume these rules may end up
generating invalid code.

For instance, GCC 11 and above tend to optimise more aggressively
assuming the strict adherence to the standard aliasing rules and may
generate invalid code, when compiling Zephyr with `-fstrict-aliasing`,
that results in various run-time failures.

Note that the footprint and performance ramifications of disabling the
strict aliasing rule are negligible.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
---
 CMakeLists.txt                               | 4 ++++
 cmake/compiler/compiler_flags_template.cmake | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index bdf5e0c176f..a7701288975 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -141,6 +141,10 @@ if(TOOLCHAIN_USE_CUSTOM)
   zephyr_compile_definitions(__TOOLCHAIN_CUSTOM__)
 endif()
 
+# @Intent: Set compiler specific flag for disabling strict aliasing rule
+zephyr_compile_options($<$<COMPILE_LANGUAGE:C>:$<TARGET_PROPERTY:compiler,no_strict_aliasing>>)
+zephyr_compile_options($<$<COMPILE_LANGUAGE:CXX>:$<TARGET_PROPERTY:compiler-cpp,no_strict_aliasing>>)
+
 # @Intent: Set compiler flags to enable buffer overflow checks in libc functions
 # @config in CONFIG_NO_OPTIMIZATIONS optional : Optimizations may affect security
 zephyr_compile_definitions($<TARGET_PROPERTY:compiler,security_fortify> )
diff --git a/cmake/compiler/compiler_flags_template.cmake b/cmake/compiler/compiler_flags_template.cmake
index b6fb8eb4d46..28b2e7a805a 100644
--- a/cmake/compiler/compiler_flags_template.cmake
+++ b/cmake/compiler/compiler_flags_template.cmake
@@ -65,6 +65,9 @@ set_property(TARGET compiler-cpp PROPERTY dialect_cpp2a)
 set_property(TARGET compiler-cpp PROPERTY dialect_cpp20)
 set_property(TARGET compiler-cpp PROPERTY dialect_cpp2b)
 
+# Flag for disabling strict aliasing rule in C and C++
+set_compiler_property(PROPERTY no_strict_aliasing)
+
 # Flag for disabling exceptions in C++
 set_property(TARGET compiler-cpp PROPERTY no_exceptions)