From: Nick Desaulniers ndesaulniers@google.com
[ Upstream commit e5d523f1ae8f2cef01f8e071aeee432654166708 ]
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-xZpzmYLO... Reported-by: Sudip Mukherjee sudipm.mukherjee@gmail.com Suggested-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Nick Desaulniers ndesaulniers@google.com Acked-by: Nathan Chancellor nathan@kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- lib/Kconfig.ubsan | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index 236c5cefc4cc..641ac2d0477c 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -96,6 +96,9 @@ 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