From: Anders Roxell <anders.roxell@xxxxxxxxxx> Subject: lib/ubsan: default UBSAN_ALIGNMENT to not set When booting an allmodconfig kernel, there are a lot of false-positives. With a message like this 'UBSAN: Undefined behaviour in...' with a call trace that follows. UBSAN warnings are a result of enabling noisy CONFIG_UBSAN_ALIGNMENT which is disabled by default if HAVE_EFFICIENT_UNALIGNED_ACCESS=y. It's noisy even if don't have efficient unaligned access, e.g. people often add __cacheline_aligned_in_smp in structs, but forget to align allocations of such struct (kmalloc() give 8-byte alignment in worst case). Rework so that when building a allmodconfig kernel that turns everything into '=m' or '=y' will turn off UBSAN_ALIGNMENT. [aryabinin@xxxxxxxxxxxxx: changelog addition] Link: http://lkml.kernel.org/r/20181217150326.30933-1-anders.roxell@xxxxxxxxxx Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx> Suggested-by: Arnd Bergmann <arnd@xxxxxxxx> Acked-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/lib/Kconfig.ubsan~lib-ubsan-default-ubsan_alignment-to-not-set +++ a/lib/Kconfig.ubsan @@ -27,15 +27,19 @@ config UBSAN_SANITIZE_ALL Enabling this option will get kernel image size increased significantly. -config UBSAN_ALIGNMENT - bool "Enable checking of pointers alignment" +config UBSAN_NO_ALIGNMENT + bool "Disable checking of pointers alignment" depends on UBSAN - default y if !HAVE_EFFICIENT_UNALIGNED_ACCESS + default y if HAVE_EFFICIENT_UNALIGNED_ACCESS help - This option enables detection of unaligned memory accesses. - Enabling this option on architectures that support unaligned + This option disables the check of unaligned memory accesses. + This option should be used when building allmodconfig. + Disabling this option on architectures that support unaligned accesses may produce a lot of false positives. +config UBSAN_ALIGNMENT + def_bool !UBSAN_NO_ALIGNMENT + config TEST_UBSAN tristate "Module for testing for undefined behavior detection" depends on m && UBSAN _
