From e5d523f1ae8f2cef01f8e071aeee432654166708 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Thu, 14 Jul 2022 13:56:43 -0700 Subject: [PATCH] ubsan: disable UBSAN_DIV_ZERO for clang Building with UBSAN_DIV_ZERO with clang produces numerous fallthrough warnings from objtool. In the case of uncheck division, UBSAN_DIV_ZERO may introduce new control flow to check for division by zero. Because the result of the division is undefined, LLVM may optimize the control flow such that after the call to __ubsan_handle_divrem_overflow doesn't matter. If panic_on_warn was set, __ubsan_handle_divrem_overflow would panic. The problem is is that panic_on_warn is run time configurable. If it's disabled, then we cannot guarantee that we will be able to recover safely. Disable this config for clang until we can come up with a solution in LLVM. Link: https://github.com/ClangBuiltLinux/linux/issues/1657 Link: https://github.com/llvm/llvm-project/issues/56289 Link: https://lore.kernel.org/lkml/CAHk-=wj1qhf7y3VNACEexyp5EbkNpdcu_542k-xZpzmYLOjiCg@mail.gmail.com/ Reported-by: Sudip Mukherjee Suggested-by: Linus Torvalds Signed-off-by: Nick Desaulniers Acked-by: Nathan Chancellor Signed-off-by: Linus Torvalds --- lib/Kconfig.ubsan | 3 +++ 1 file changed, 3 insertions(+) diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index a9f7eb047768..fd15230a703b 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -84,6 +84,9 @@ config UBSAN_SHIFT config UBSAN_DIV_ZERO bool "Perform checking for integer divide-by-zero" depends on $(cc-option,-fsanitize=integer-divide-by-zero) + # https://github.com/ClangBuiltLinux/linux/issues/1657 + # https://github.com/llvm/llvm-project/issues/56289 + depends on !CC_IS_CLANG help This option enables -fsanitize=integer-divide-by-zero which checks for integer division by zero. This is effectively redundant with the -- 2.34.1