Trouble with ASan

[coypu%SDF.ORG@localhost]

Hi,
I wanted to run our tests with asan/ubsan.
I've used the following:

cd /usr/src
./build.sh ... -O /usr/amd64 release

cd /usr/src/lib/libm
env USETOOLS=never CFLAGS="-fsanitize=undefined -fsanitize=address -U_FORTIFY_SOURCE" LDFLAGS="-lasan -pthread -lubsan" make -j20

cd /usr/tests/lib/libm
env LD_PRELOAD="/usr/amd64/destdir.amd64/usr/lib/libpthread.so /usr/amd64/destdir.amd64/usr/lib/libpthread.so /usr/src/lib/libm/libm.so /usr/amd64/destdir.amd64/usr/lib/libc.so /usr/amd64/destdir.amd64/usr/lib/libstdc++.so /usr/amd64/destdir.amd64/usr/lib/libubsan.so /usr/amd64/destdir.amd64/libexec/ld.elf_so" atf-run

However, no matter what I try, it seems to die in some
pthread related stuff, e.g.:

Core was generated by `atf-run'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000070d5b980c4a4 in pthread.init () from /usr/amd64/destdir.amd64/usr/lib/libpthread.so
(gdb) bt
#0  0x000070d5b980c4a4 in pthread.init () from /usr/amd64/destdir.amd64/usr/lib/libpthread.so
#1  0x000070d5b9122d0f in _libc_init () from /usr/amd64/destdir.amd64/usr/lib/libc.so
#2  0x000070d5b903d244 in ?? () from /usr/amd64/destdir.amd64/usr/lib/libc.so
#3  0x000070d5b9ab2420 in ?? ()
#4  0x000070d5b90384c9 in _init () from /usr/amd64/destdir.amd64/usr/lib/libc.so
#5  0x0000000000000000 in ?? ()

Any ideas?
Thanks.