CONFIG_UBSAN_TRAP build failures

[nathanchance]

$ make -skj"$(nproc)" ARCH=s390 CC=clang CROSS_COMPILE=s390x-linux-gnu- O=out distclean allmodconfig vmlinux
s390x-linux-gnu-ld: init/main.o: in function `trace_event_raw_event_initcall_level':
/tmp/s390-ubsan-bisect/out/../include/trace/events/initcall.h:10: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: /tmp/s390-ubsan-bisect/out/../include/trace/events/initcall.h:10: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: init/main.o: in function `trace_event_get_offsets_initcall_level':
/tmp/s390-ubsan-bisect/out/../include/trace/events/initcall.h:10: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: init/main.o: in function `setup_boot_config':
/tmp/s390-ubsan-bisect/out/../init/main.c:394: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: /tmp/s390-ubsan-bisect/out/../init/main.c:393: undefined reference to `__ubsan_handle_sub_overflow'
s390x-linux-gnu-ld: /tmp/s390-ubsan-bisect/out/../init/main.c:447: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: init/main.o: in function `setup_command_line':
/tmp/s390-ubsan-bisect/out/../init/main.c:625: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: /tmp/s390-ubsan-bisect/out/../init/main.c:625: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: /tmp/s390-ubsan-bisect/out/../init/main.c:627: undefined reference to `__ubsan_handle_add_overflow'
s390x-linux-gnu-ld: /tmp/s390-ubsan-bisect/out/../init/main.c:623: undefined reference to `__ubsan_handle_add_overflow'
...

Presumably caused/exposed by https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=186c3e18dba3f035b73149f6356f8c1c439288f4 because the issue is not present if I explicitly disabled CONFIG_UBSAN_SANITIZE_ALL. I do not see any issue with GCC 10.2.0.

cc @kees @uweigand

[kees]

Well that's weird. That should be an internally defined function. I'll see if I can figure it out.

[nathanchance]

Looks like this is related to CONFIG_UBSAN_TRAP, which gets turned on with s390 allmodconfig and allyesconfig because CONFIG_COMPILE_TEST is not selectable after 334ef6e. If I disable CONFIG_UBSAN_TRAP, I just run into #1245, which I already have a fix for.

I can similarly reproduce this on x86_64:

$ cat allmod.config
CONFIG_X86_X32=n
CONFIG_COMPILE_TEST=n
CONFIG_UBSAN_TRAP=y

$ make -skj"$(nproc)" KCONFIG_ALLCONFIG=1 LLVM=1 distclean allmodconfig vmlinux
...
ld.lld: error: undefined symbol: __ubsan_handle_sub_overflow
>>> referenced by head64.c:160 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/kernel/head64.c:160)
>>>               arch/x86/kernel/head64.o:(__startup_64)
>>> referenced by head64.c:180 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/kernel/head64.c:180)
>>>               arch/x86/kernel/head64.o:(__startup_64)
>>> referenced by head64.c:236 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/kernel/head64.c:236)
>>>               arch/x86/kernel/head64.o:(__startup_64)
>>> referenced 13605 more times

ld.lld: error: undefined symbol: __ubsan_handle_add_overflow
>>> referenced by head64.c:236 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/kernel/head64.c:236)
>>>               arch/x86/kernel/head64.o:(__startup_64)
>>> referenced by head64.c:237 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/kernel/head64.c:237)
>>>               arch/x86/kernel/head64.o:(__startup_64)
>>> referenced by head64.c:239 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/kernel/head64.c:239)
>>>               arch/x86/kernel/head64.o:(__startup_64)
>>> referenced 20720 more times

ld.lld: error: undefined symbol: __ubsan_handle_mul_overflow
>>> referenced by head64.c:239 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/kernel/head64.c:239)
>>>               arch/x86/kernel/head64.o:(__startup_64)
>>> referenced by delay.h:65 (/home/nathan/cbl/worktrees/cbl-1245/./include/linux/delay.h:65)
>>>               do_mounts.o:(prepare_namespace) in archive init/built-in.a
>>> referenced by calibrate.c:242 (/home/nathan/cbl/worktrees/cbl-1245/init/calibrate.c:242)
>>>               calibrate.o:(calibrate_delay) in archive init/built-in.a
>>> referenced 2692 more times

ld.lld: error: undefined symbol: __ubsan_handle_negate_overflow
>>> referenced by vsyscall_64.c:89 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/entry/vsyscall/vsyscall_64.c:89)
>>>               entry/vsyscall/vsyscall_64.o:(emulate_vsyscall) in archive arch/x86/built-in.a
>>> referenced by vsyscall_64.c:344 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/entry/vsyscall/vsyscall_64.c:344)
>>>               entry/vsyscall/vsyscall_64.o:(in_gate_area_no_mm) in archive arch/x86/built-in.a
>>> referenced by vsyscall_64.c:364 (/home/nathan/cbl/worktrees/cbl-1245/arch/x86/entry/vsyscall/vsyscall_64.c:364)
>>>               entry/vsyscall/vsyscall_64.o:(set_vsyscall_pgtable_user_bits) in archive arch/x86/built-in.a
>>> referenced 2276 more times
...

How are these functions defined when CONFIG_UBSAN_TRAP prevents lib/ubsan.c from being built and we are not linking against compiler-rt?

[nathanchance]

s390 all{mod,yes}config enables CONFIG_COMPILE_TEST after https://git.kernel.org/linus/ea29b20a828511de3348334e529a3d046a180416 so this is not visible unless CONFIG_USBAN_TRAP is explicitly enabled. Marking as low priority.