On 29.10.2024 15:00, Jan Hendrik Farr wrote:

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/#m204c09f63c076586a... 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

---

drivers/misc/lkdtm/bugs.c | 2 +- include/linux/compiler_attributes.h | 13 ------------- include/linux/compiler_types.h | 19 +++++++++++++++++++ init/Kconfig | 9 +++++++++ lib/overflow_kunit.c | 2 +- 5 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 62ba01525479..376047beea3d 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -445,7 +445,7 @@ static void lkdtm_FAM_BOUNDS(void)

pr_err("FAIL: survived access of invalid flexible array member index!\n");

• if (!__has_attribute(__counted_by__))

• if (!IS_ENABLED(CONFIG_CC_HAS_COUNTED_BY)) pr_warn("This is expected since this %s was built with a compiler that does not support __counted_by\n", lkdtm_kernel_info); else if (IS_ENABLED(CONFIG_UBSAN_BOUNDS))

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index 32284cd26d52..c16d4199bf92 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -94,19 +94,6 @@ # define __copy(symbol) #endif

-/*

• • Optional: only supported since gcc >= 15
• • Optional: only supported since clang >= 18
• • gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
• • clang: https://github.com/llvm/llvm-project/pull/76348
• */

-#if __has_attribute(__counted_by__) -# define __counted_by(member) __attribute__((__counted_by__(member))) -#else -# define __counted_by(member) -#endif

Why is the define of __counted_by moved from here (compiler_attributes.h) to a different location (compiler_types.h) ? I am asking this because I try to compile an out of tree kernel module with ofed headers. in the ofed header of compiler_types.h there is an added include of types.h:

#include_next <linux/compiler_attributes.h> #include <linux/types.h>

so what happen is that __counted_by is defined in types.h, and then I get a compilation error:

././include/linux/compiler_types.h:323: error: "__counted_by" redefined [-Werror]

I am not sure yet how this should be fixed. Thank you, Dafna

/*

• Optional: not supported by gcc
• Optional: only supported since clang >= 14.0

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 1a957ea2f4fe..639be0f30b45 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -323,6 +323,25 @@ struct ftrace_likely_data { #define __no_sanitize_or_inline __always_inline #endif

+/*

• • Optional: only supported since gcc >= 15
• • Optional: only supported since clang >= 18
• • gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
• • clang: https://github.com/llvm/llvm-project/pull/76348
• • __bdos on clang < 19.1.2 can erroneously return 0:
• • https://github.com/llvm/llvm-project/pull/110497
• • __bdos on clang < 19.1.3 can be off by 4:
• • https://github.com/llvm/llvm-project/pull/112636
• */

+#ifdef CONFIG_CC_HAS_COUNTED_BY +# define __counted_by(member) __attribute__((__counted_by__(member))) +#else +# define __counted_by(member) +#endif

/*

• Apply __counted_by() when the Endianness matches to increase test coverage.

*/ diff --git a/init/Kconfig b/init/Kconfig index 530a382ee0fe..92f106cf5572 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -116,6 +116,15 @@ config CC_HAS_ASM_INLINE config CC_HAS_NO_PROFILE_FN_ATTR def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)

+config CC_HAS_COUNTED_BY

• # TODO: when gcc 15 is released remove the build test and add
• # a gcc version check
• def_bool $(success,echo 'struct flex { int count; int array[] __attribute__((__counted_by__(count))); };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
• # clang needs to be at least 19.1.3 to avoid __bdos miscalculations
• # https://github.com/llvm/llvm-project/pull/110497
• # https://github.com/llvm/llvm-project/pull/112636
• depends on !(CC_IS_CLANG && CLANG_VERSION < 190103)

config PAHOLE_VERSION int default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE)) diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c index 2abc78367dd1..5222c6393f11 100644 --- a/lib/overflow_kunit.c +++ b/lib/overflow_kunit.c @@ -1187,7 +1187,7 @@ static void DEFINE_FLEX_test(struct kunit *test) { /* Using _RAW_ on a __counted_by struct will initialize "counter" to zero */ DEFINE_RAW_FLEX(struct foo, two_but_zero, array, 2); -#if __has_attribute(__counted_by__) +#ifdef CONFIG_CC_HAS_COUNTED_BY int expected_raw_size = sizeof(struct foo); #else int expected_raw_size = sizeof(struct foo) + 2 * sizeof(s16); -- 2.47.0