build: make Zephyr stdint convention enforcing configurable

There are  few cases where removing this enforcement is desirable:

- linking against binary C++ libs with incompatible type mangling

- linking against system provided headers i.e. native_posix

- compiling with legacy code that assumes a different convention

So let's create a Kconfig symbol for it. This is IMHO a good compromize
compared to using the %"PRId32" abomination everywhere otherwise.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

CMakeLists.txt

@@ -283,10 +283,7 @@ zephyr_compile_options($<$<COMPILE_LANGUAGE:ASM>:$<TARGET_PROPERTY:asm,required>
 
 # @Intent: Enforce standard integer type correspondence to match Zephyr usage.
 # (must be after compiler specific flags)
-if(NOT CONFIG_ARCH_POSIX)
+if(CONFIG_ENFORCE_ZEPHYR_STDINT)
-  # `zephyr_stdint.h` is not included for the POSIX (native) arch because it
-  # compiles with the host toolchain/headers and there can be conflicts if we
-  # arbitrarily redefine our own type system (see #37718).
   zephyr_compile_options("SHELL: $<TARGET_PROPERTY:compiler,imacros> ${ZEPHYR_BASE}/include/zephyr/toolchain/zephyr_stdint.h")
 endif()
 

Kconfig.zephyr

@@ -608,6 +608,22 @@ config WARN_EXPERIMENTAL
 	  Print a warning when the Kconfig tree is parsed if any experimental
 	  features are enabled.
 
+config ENFORCE_ZEPHYR_STDINT
+	bool
+	prompt "Enforce Zephyr convention for stdint"
+	depends on !ARCH_POSIX
+	default y
+	help
+	  This enforces the Zephyr stdint convention where int32_t = int,
+	  int64_t = long long, and intptr_t = long so that short string
+	  format length modifiers can be used universally across ILP32
+	  and LP64 architectures. Sometimes this is not possible e.g. when
+	  linking against a binary-only C++ library whose type mangling
+	  is incompatible with the Zephyr convention, or if the build
+	  environment doesn't allow such enforcement, in which case this
+	  should be turned off with the caveat that argument type validation
+	  on Zephyr code will be skipped.
+
 endmenu
 
 

include/zephyr/kernel.h

@@ -25,6 +25,14 @@
 extern "C" {
 #endif
 
+/*
+ * Zephyr currently assumes the size of a couple standard types to simplify
+ * print string formats. Let's make sure this doesn't change without notice.
+ */
+BUILD_ASSERT(sizeof(int32_t) == sizeof(int));
+BUILD_ASSERT(sizeof(int64_t) == sizeof(long long));
+BUILD_ASSERT(sizeof(intptr_t) == sizeof(long));
+
 /**
  * @brief Kernel APIs
  * @defgroup kernel_apis Kernel APIs

include/zephyr/toolchain/gcc.h

@@ -213,7 +213,20 @@ do {                                                                    \
 #define __may_alias     __attribute__((__may_alias__))
 
 #ifndef __printf_like
+#ifdef CONFIG_ENFORCE_ZEPHYR_STDINT
 #define __printf_like(f, a)   __attribute__((format (printf, f, a)))
+#else
+/*
+ * The Zephyr stdint convention enforces int32_t = int, int64_t = long long,
+ * and intptr_t = long so that short string format length modifiers can be
+ * used universally across ILP32 and LP64 architectures. Without that it
+ * is possible for ILP32 toolchains to have int32_t = long and intptr_t = int
+ * clashing with the Zephyr convention and generating pointless warnings
+ * as they're still the same size. Inhibit the format argument type
+ * validation in that case and let the other configs do it.
+ */
+#define __printf_like(f, a)
+#endif
 #endif
 
 #define __used		__attribute__((__used__))