(correcting Andrey's email address)
From: Ding Tianhong <[email protected]> Subject: lib/ubsan.c: don't handle misaligned address when kernel supports unaligned access ubsan reports a warning like: UBSAN: Undefined behaviour in ../include/linux/etherdevice.h:386:9 load of misaligned address ffffffc069ba0482 for type 'long unsigned int' which requires 8 byte alignment CPU: 0 PID: 901 Comm: sshd Not tainted 4.xx+ #1 Hardware name: linux,dummy-virt (DT) Call trace: [<ffffffc000093600>] dump_backtrace+0x0/0x348 [<ffffffc000093968>] show_stack+0x20/0x30 [<ffffffc001651664>] dump_stack+0x144/0x1b4 [<ffffffc0016519b0>] ubsan_epilogue+0x18/0x74 [<ffffffc001651bac>] __ubsan_handle_type_mismatch+0x1a0/0x25c [<ffffffc00125d8a0>] dev_gro_receive+0x17d8/0x1830 [<ffffffc00125d928>] napi_gro_receive+0x30/0x158 [<ffffffc000f4f93c>] virtnet_receive+0xad4/0x1fa8 The reason is that when enabling the CONFIG_UBSAN_ALIGNMENT, ubsan will report the unaligned access even if the system supports it (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). This produces a lot of noise in the log and causes confusion. Prevent the detection of unaligned access when the system support unaligned access. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ding Tianhong <[email protected]> Cc: David Laight <[email protected]> Cc: Andrey Ryabinin <[email protected]> Signed-off-by: Andrew Morton <[email protected]> --- lib/ubsan.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff -puN lib/ubsan.c~ubsan-dont-handle-misaligned-address-when-support-unaligned-access lib/ubsan.c --- a/lib/ubsan.c~ubsan-dont-handle-misaligned-address-when-support-unaligned-access +++ a/lib/ubsan.c @@ -322,7 +322,8 @@ void __ubsan_handle_type_mismatch(struct if (!ptr) handle_null_ptr_deref(data); else if (data->alignment && !IS_ALIGNED(ptr, data->alignment)) - handle_missaligned_access(data, ptr); + if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) + handle_missaligned_access(data, ptr); else handle_object_size_mismatch(data, ptr); } _
