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Compiler Attributes: disable __counted_by for clang < 19.1.3

This patch disables __counted_by for clang versions < 19.1.3 because
of the two issues listed below. It does this by introducing
CONFIG_CC_HAS_COUNTED_BY.

1. clang < 19.1.2 has a bug that can lead to __bdos returning 0:
https://github.com/llvm/llvm-project/pull/110497

2. clang < 19.1.3 has a bug that can lead to __bdos being off by 4:
https://github.com/llvm/llvm-project/pull/112636

Fixes: c8248faf3ca2 ("Compiler Attributes: counted_by: Adjust name and identifier expansion")
Cc: stable@vger.kernel.org # 6.6.x: 16c31dd7fdf6: Compiler Attributes: counted_by: bump min gcc version
Cc: stable@vger.kernel.org # 6.6.x: 2993eb7a8d34: Compiler Attributes: counted_by: fixup clang URL
Cc: stable@vger.kernel.org # 6.6.x: 231dc3f0c936: lkdtm/bugs: Improve warning message for compilers without counted_by support
Cc: stable@vger.kernel.org # 6.6.x
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/all/20240913164630.GA4091534@thelio-3990X/
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202409260949.a1254989-oliver.sang@intel.com
Link: https://lore.kernel.org/all/Zw8iawAF5W2uzGuh@archlinux/T/#m204c09f63c076586a02d194b87dffc7e81b8de7b
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Jan Hendrik Farr <kernel@jfarr.cc>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://lore.kernel.org/r/20241029140036.577804-2-kernel@jfarr.cc
Signed-off-by: Kees Cook <kees@kernel.org>

authored by

Jan Hendrik Farr and committed by
Kees Cook f06e108a d7a516c6

+30 -15
+1 -1
drivers/misc/lkdtm/bugs.c
··· 445 445 446 446 pr_err("FAIL: survived access of invalid flexible array member index!\n"); 447 447 448 - if (!__has_attribute(__counted_by__)) 448 + if (!IS_ENABLED(CONFIG_CC_HAS_COUNTED_BY)) 449 449 pr_warn("This is expected since this %s was built with a compiler that does not support __counted_by\n", 450 450 lkdtm_kernel_info); 451 451 else if (IS_ENABLED(CONFIG_UBSAN_BOUNDS))
-13
include/linux/compiler_attributes.h
··· 95 95 #endif 96 96 97 97 /* 98 - * Optional: only supported since gcc >= 15 99 - * Optional: only supported since clang >= 18 100 - * 101 - * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896 102 - * clang: https://github.com/llvm/llvm-project/pull/76348 103 - */ 104 - #if __has_attribute(__counted_by__) 105 - # define __counted_by(member) __attribute__((__counted_by__(member))) 106 - #else 107 - # define __counted_by(member) 108 - #endif 109 - 110 - /* 111 98 * Optional: not supported by gcc 112 99 * Optional: only supported since clang >= 14.0 113 100 *
+19
include/linux/compiler_types.h
··· 324 324 #endif 325 325 326 326 /* 327 + * Optional: only supported since gcc >= 15 328 + * Optional: only supported since clang >= 18 329 + * 330 + * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896 331 + * clang: https://github.com/llvm/llvm-project/pull/76348 332 + * 333 + * __bdos on clang < 19.1.2 can erroneously return 0: 334 + * https://github.com/llvm/llvm-project/pull/110497 335 + * 336 + * __bdos on clang < 19.1.3 can be off by 4: 337 + * https://github.com/llvm/llvm-project/pull/112636 338 + */ 339 + #ifdef CONFIG_CC_HAS_COUNTED_BY 340 + # define __counted_by(member) __attribute__((__counted_by__(member))) 341 + #else 342 + # define __counted_by(member) 343 + #endif 344 + 345 + /* 327 346 * Apply __counted_by() when the Endianness matches to increase test coverage. 328 347 */ 329 348 #ifdef __LITTLE_ENDIAN
+9
init/Kconfig
··· 116 116 config CC_HAS_NO_PROFILE_FN_ATTR 117 117 def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror) 118 118 119 + config CC_HAS_COUNTED_BY 120 + # TODO: when gcc 15 is released remove the build test and add 121 + # a gcc version check 122 + def_bool $(success,echo 'struct flex { int count; int array[] __attribute__((__counted_by__(count))); };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror) 123 + # clang needs to be at least 19.1.3 to avoid __bdos miscalculations 124 + # https://github.com/llvm/llvm-project/pull/110497 125 + # https://github.com/llvm/llvm-project/pull/112636 126 + depends on !(CC_IS_CLANG && CLANG_VERSION < 190103) 127 + 119 128 config PAHOLE_VERSION 120 129 int 121 130 default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
+1 -1
lib/overflow_kunit.c
··· 1187 1187 { 1188 1188 /* Using _RAW_ on a __counted_by struct will initialize "counter" to zero */ 1189 1189 DEFINE_RAW_FLEX(struct foo, two_but_zero, array, 2); 1190 - #if __has_attribute(__counted_by__) 1190 + #ifdef CONFIG_CC_HAS_COUNTED_BY 1191 1191 int expected_raw_size = sizeof(struct foo); 1192 1192 #else 1193 1193 int expected_raw_size = sizeof(struct foo) + 2 * sizeof(s16);