treewide: Enforce C17 as the minimum required C standard

CMakeLists.txt

@@ -319,12 +319,6 @@ if(CONFIG_STD_C23)
   set(CSTD c2x)
 elseif(CONFIG_STD_C17)
   set(CSTD c17)
-elseif(CONFIG_STD_C11)
-  set(CSTD c11)
-elseif(CONFIG_STD_C99)
-  set(CSTD c99)
-elseif(CONFIG_STD_C90)
-  set(CSTD c90)
 else()
   message(FATAL_ERROR "Unreachable code. Expected C standard to have been chosen.")
 endif()
@@ -409,7 +403,7 @@ if(CONFIG_COMPILER_FREESTANDING)
   zephyr_compile_options($<$<COMPILE_LANGUAGE:ASM>:$<TARGET_PROPERTY:compiler,freestanding>>)
 endif()
 
-if (CONFIG_PICOLIBC AND NOT CONFIG_PICOLIBC_IO_FLOAT)
+if(CONFIG_PICOLIBC AND NOT CONFIG_PICOLIBC_IO_FLOAT)
   # @Intent: Set compiler specific flag to disable printf-related optimizations
   zephyr_compile_options($<$<COMPILE_LANGUAGE:C>:$<TARGET_PROPERTY:compiler,no_printf_return_value>>)
 endif()
@@ -1157,7 +1151,7 @@ endif()
 
 get_property(OUTPUT_FORMAT        GLOBAL PROPERTY PROPERTY_OUTPUT_FORMAT)
 
-if (CONFIG_CODE_DATA_RELOCATION)
+if(CONFIG_CODE_DATA_RELOCATION)
   set(CODE_RELOCATION_DEP code_relocation_source_lib)
 endif() # CONFIG_CODE_DATA_RELOCATION
 
@@ -2134,7 +2128,7 @@ if(CONFIG_BUILD_OUTPUT_INFO_HEADER)
     )
 endif()
 
-if (CONFIG_LLEXT AND CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID)
+if(CONFIG_LLEXT AND CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID)
   #slidgen must be the first post-build command to be executed
   #on the Zephyr ELF to ensure that all other commands, such as
   #binary file generation, are operating on a preparated ELF.
@@ -2200,7 +2194,7 @@ if(signing_script)
 endif()
 
 # Generate USB-C VIF policies in XML format
-if (CONFIG_BUILD_OUTPUT_VIF)
+if(CONFIG_BUILD_OUTPUT_VIF)
   include(${CMAKE_CURRENT_LIST_DIR}/cmake/vif.cmake)
 endif()
 
@@ -2251,7 +2245,7 @@ if(LOG_DICT_DB_NAME_ARG)
       --build-header ${PROJECT_BINARY_DIR}/include/generated/zephyr/version.h
   )
 
-  if (NOT CONFIG_LOG_DICTIONARY_DB_TARGET)
+  if(NOT CONFIG_LOG_DICTIONARY_DB_TARGET)
     # If not using a separate target for generating logging dictionary
     # database, add the generation to post build command to make sure
     # the database is actually being generated.

Kconfig.zephyr

@@ -355,20 +355,8 @@ endmenu
 
 menu "Compiler Options"
 
-config REQUIRES_STD_C99
-	bool
-	help
-	  Hidden option to select compiler support C99 standard or higher.
-
-config REQUIRES_STD_C11
-	bool
-	select REQUIRES_STD_C99
-	help
-	  Hidden option to select compiler support C11 standard or higher.
-
 config REQUIRES_STD_C17
 	bool
-	select REQUIRES_STD_C11
 	help
 	  Hidden option to select compiler support C17 standard or higher.
 
@@ -381,31 +369,10 @@ config REQUIRES_STD_C23
 choice STD_C
 	prompt "C Standard"
 	default STD_C23 if REQUIRES_STD_C23
-	default STD_C17 if REQUIRES_STD_C17
-	default STD_C11 if REQUIRES_STD_C11
-	default STD_C99
+	default STD_C17
 	help
 	  C Standards.
 
-config STD_C90
-	bool "C90"
-	depends on !REQUIRES_STD_C99
-	help
-	  1989 C standard as completed in 1989 and ratified by ISO/IEC
-	  as ISO/IEC 9899:1990. This version is known as "ANSI C".
-
-config STD_C99
-	bool "C99"
-	depends on !REQUIRES_STD_C11
-	help
-	  1999 C standard.
-
-config STD_C11
-	bool "C11"
-	depends on !REQUIRES_STD_C17
-	help
-	  2011 C standard.
-
 config STD_C17
 	bool "C17"
 	depends on !REQUIRES_STD_C23

arch/Kconfig

@@ -152,12 +152,6 @@ config ARCH_POSIX
 	select BARRIER_OPERATIONS_BUILTIN
 	# POSIX arch based targets get their memory cleared on entry by the host OS
 	select SKIP_BSS_CLEAR
-	# Override the C standard used for compilation to C 2011
-	# This is due to some tests using _Static_assert which is a 2011 feature, but
-	# otherwise relying on compilers supporting it also when set to C99.
-	# This was in general ok, but with some host compilers and C library versions
-	# it led to problems. So we override it to 2011 for the native targets.
-	select REQUIRES_STD_C11
 	help
 	  POSIX (native) architecture
 

cmake/compiler/compiler_features.cmake

@@ -1,18 +1,15 @@
-set(c23id c2x gnu2x)
+set(c23id c2x gnu2x "iso9899:2023" "iso9899:2024")
 set(c17id c17 c18 gnu17 gnu18 "iso9899:2017" "iso9899:2018")
-set(c11id c11 gnu11 "iso9899:2011")
-set(c99id c99 gnu99 "iso9899:1999")
-set(c90id c89 c90 gnu89 gnu90 "iso9899:1990" "iso9899:199409")
 
 set(compile_features_list)
 
 # For each id value above a compile_features_${idval} with a list of supported
 # `c_std_XX` values are created for easy lookup.
 # For example, the settings
-# - `compile_feature_c99` will contain `c_std_90;c_std_99`
-# - `compile_feature_iso9899:2011` will contain `c_std_90;c_std_99;c_std_11`
+# - `compile_feature_c23` will contain `c_std_17;c_std_23`
+# - `compile_feature_iso9899:2023` will contain `c_std_17;c_std_23`
 # that can then be used to set CMAKE_C_COMPILE_FEATURES accordingly.
-foreach(standard 90 99 11 17 23)
+foreach(standard 17 23)
   list(APPEND compile_features_list c_std_${standard})
   foreach(id ${c${standard}id})
     set(compile_features_${id} ${compile_features_list})

doc/develop/languages/c/index.rst

@@ -24,27 +24,21 @@ Language Standards
 
 Zephyr does not target a specific version of the C standards; however, the
 Zephyr codebase makes extensive use of the features newly introduced in the
-1999 release of the ISO C standard (ISO/IEC 9899:1999, hereinafter referred to
-as C99) such as those listed below, effectively requiring the use of a compiler
-toolchain that supports the C99 standard and above:
+2017 release of the ISO C standard (ISO/IEC 9899:2017, hereinafter referred to
+as C17) such as those listed below, effectively requiring the use of a compiler
+toolchain that supports the C17 standard and above:
 
 * inline functions
 * standard boolean types (``bool`` in ``<stdbool.h>``)
 * fixed-width integer types (``[u]intN_t`` in ``<stdint.h>``)
 * designated initializers
 * variadic macros
 * ``restrict`` qualification
-
-Some Zephyr components make use of the features newly introduced in the 2011
-release of the ISO C standard (ISO/IEC 9899:2011, hereinafter referred to as
-C11) such as the type-generic expressions using the ``_Generic`` keyword. For
-example, the :c:func:`cbprintf` component, used as the default formatted output
-processor for Zephyr, makes use of the C11 type-generic expressions, and this
-effectively requires most Zephyr applications to be compiled using a compiler
-toolchain that supports the C11 standard and above.
+* _Generic keyword
+* _Static_assert keyword
 
 In summary, it is recommended to use a compiler toolchain that supports at
-least the C11 standard for developing with Zephyr. It is, however, important to
+least the C17 standard for developing with Zephyr. It is, however, important to
 note that some optional Zephyr components and external modules may make use of
 the C language features that have been introduced in more recent versions of
 the standards, in which case it will be necessary to use a more up-to-date

doc/services/formatted_output.rst

@@ -81,9 +81,8 @@ Package can be created using two methods:
   package.
 * static - types of arguments are detected at compile time by the preprocessor
   and package is created as simple assignments to a provided memory. This method
-  is significantly faster than runtime (more than 15 times) but has following
-  limitations: requires ``_Generic`` keyword (C11 feature) to be supported by
-  the compiler and cannot distinguish between ``%p`` and ``%s`` if char pointer
+  is significantly faster than runtime (more than 15 times) but has a
+  significant limitation: it cannot distinguish between ``%p`` and ``%s`` if char pointer
   is used. It treats all (unsigned) char pointers as ``%s`` thus it will attempt
   to append string to a package. It can be handled correctly during conversion
   from **transient** package to **self-contained** package using
@@ -174,7 +173,6 @@ formatting since address changes whenever package is copied.
 Limitations and recommendations
 ===============================
 
-* C11 ``_Generic`` support is required by the compiler to use static (fast) packaging.
 * It is recommended to cast any character pointer used with ``%p`` format specifier to
   other pointer type (e.g. ``void *``). If format string is not accessible then only
   static packaging is possible and it will append all detected strings. Character pointer

doc/services/logging/index.rst

@@ -869,8 +869,6 @@ The are following recommendations:
 
 * Enable :kconfig:option:`CONFIG_LOG_SPEED` to slightly speed up deferred logging at the
   cost of slight increase in memory footprint.
-* Compiler with C11 ``_Generic`` keyword support is recommended. Logging
-  performance is significantly degraded without it. See :ref:`cbprintf_packaging`.
 * It is recommended to cast pointer to ``const char *`` when it is used with ``%s``
   format specifier and it points to a constant string.
 * It is recommended to cast pointer to ``char *`` when it is used with ``%s``

include/zephyr/sys/cbprintf.h

@@ -17,19 +17,6 @@
 #include <stdio.h>
 #endif /* CONFIG_CBPRINTF_LIBC_SUBSTS */
 
-/* Determine if _Generic is supported using macro from toolchain.h.
- *
- * @note Z_C_GENERIC is also set for C++ where functionality is implemented
- * using overloading and templates.
- */
-#ifndef Z_C_GENERIC
-#if defined(__cplusplus) || TOOLCHAIN_HAS_C_GENERIC
-#define Z_C_GENERIC 1
-#else
-#define Z_C_GENERIC 0
-#endif
-#endif
-
 #ifdef __xtensa__
 #define Z_PKG_HDR_EXT_XTENSA_ALIGNMENT 8
 #ifdef CONFIG_CBPRINTF_PACKAGE_HEADER_STORE_CREATION_FLAGS
@@ -120,7 +107,6 @@ BUILD_ASSERT(sizeof(struct cbprintf_package_hdr_ext) % Z_PKG_HDR_EXT_XTENSA_ALIG
  * @endcond
  */
 
-/* Z_C_GENERIC is used there */
 #include <zephyr/sys/cbprintf_internal.h>
 
 #ifdef __cplusplus

include/zephyr/sys/cbprintf_internal.h

@@ -534,7 +534,6 @@ extern "C" {
  * @retval 1 if string must be packaged at runtime.
  * @retval 0 if string can be statically packaged.
  */
-#if Z_C_GENERIC
 #define Z_CBPRINTF_MUST_RUNTIME_PACKAGE(flags, ...) ({\
 	int _rv; \
 	if ((flags) & CBPRINTF_PACKAGE_ADD_RW_STR_POS) { \
@@ -544,9 +543,6 @@ extern "C" {
 	} \
 	_rv; \
 })
-#else
-#define Z_CBPRINTF_MUST_RUNTIME_PACKAGE(flags, ...) 1
-#endif
 
 /** @brief Get storage size for given argument.
  *
@@ -864,23 +860,10 @@ do { \
 	} \
 } while (false)
 
-#if Z_C_GENERIC
 #define Z_CBPRINTF_STATIC_PACKAGE(packaged, inlen, outlen, align_offset, flags, \
 				  ... /* fmt, ... */) \
 	Z_CBPRINTF_STATIC_PACKAGE_GENERIC(packaged, inlen, outlen, \
 					  align_offset, flags, __VA_ARGS__)
-#else
-#define Z_CBPRINTF_STATIC_PACKAGE(packaged, inlen, outlen, align_offset, flags, \
-				  ... /* fmt, ... */) \
-do { \
-	/* Small trick needed to avoid warning on always true */ \
-	if (((uintptr_t)packaged + 1) != 1) { \
-		outlen = cbprintf_package(packaged, inlen, flags, __VA_ARGS__); \
-	} else { \
-		outlen = cbprintf_package(NULL, align_offset, flags, __VA_ARGS__); \
-	} \
-} while (false)
-#endif /* Z_C_GENERIC */
 
 #ifdef __cplusplus
 }

lib/os/cbprintf_packaged.c

@@ -17,12 +17,6 @@
 #include <zephyr/logging/log.h>
 LOG_MODULE_REGISTER(cbprintf_package, CONFIG_CBPRINTF_PACKAGE_LOG_LEVEL);
 
-#if defined(CONFIG_CBPRINTF_PACKAGE_SUPPORT_TAGGED_ARGUMENTS) && \
-	!Z_C_GENERIC
-#error "CONFIG_CBPRINTF_PACKAGE_SUPPORT_TAGGED_ARGUMENTS " \
-	"requires toolchain to support _Generic!"
-#endif
-
 /**
  * @brief Check if address is in read only section.
  *

modules/nanopb/Kconfig

@@ -6,8 +6,6 @@ config ZEPHYR_NANOPB_MODULE
 
 menuconfig NANOPB
 	bool "Nanopb Support"
-	# Nanopb requires c_std_11 compiler features like _Static_assert
-	select REQUIRES_STD_C11
 	help
 	  This option enables the Nanopb library and generator.
 

tests/lib/cbprintf_package/src/main.c

@@ -59,7 +59,6 @@ static void unpack(const char *desc, struct out_buffer *buf,
 
 #define TEST_PACKAGING(flags, fmt, ...) do { \
 	int must_runtime = CBPRINTF_MUST_RUNTIME_PACKAGE(flags, fmt, __VA_ARGS__); \
-	zassert_equal(must_runtime, !Z_C_GENERIC); \
 	snprintfcb(compare_buf, sizeof(compare_buf), fmt, __VA_ARGS__); \
 	printk("-----------------------------------------\n"); \
 	printk("%s\n", compare_buf); \
@@ -683,14 +682,6 @@ ZTEST(cbprintf_package, test_cbprintf_ro_rw_loc_const_char_ptr)
 
 static void cbprintf_rw_loc_const_char_ptr(bool keep_ro_str)
 {
-	/* Test requires that static packaging is applied. Runtime packaging
-	 * cannot be tricked because it checks pointers against read only
-	 * section.
-	 */
-	if (Z_C_GENERIC == 0) {
-		ztest_test_skip();
-	}
-
 	int slen, slen2;
 	int clen, clen2;
 	static const char test_str[] = "test %s %d %s";
@@ -778,10 +769,6 @@ ZTEST(cbprintf_package, test_cbprintf_must_runtime_package)
 {
 	int rv;
 
-	if (Z_C_GENERIC == 0) {
-		ztest_test_skip();
-	}
-
 	rv = CBPRINTF_MUST_RUNTIME_PACKAGE(0, "test");
 	zassert_equal(rv, 0);
 
@@ -1006,7 +993,6 @@ static void *print_size_and_alignment_info(void)
 	printk("alignof: int=%zu long=%zu ptr=%zu long long=%zu double=%zu long double=%zu\n",
 	       __alignof__(int), __alignof__(long), __alignof__(void *), __alignof__(long long),
 	       __alignof__(double), __alignof__(long double));
-	printk("%s C11 _Generic\n", Z_C_GENERIC ? "With" : "Without");
 #endif
 
 	return NULL;