[PATCH] D85082: On FreeBSD, add -pthread to ASan dynamic compile flags for tests

Mon Aug 3 06:25:43 PDT 2020

dim added a comment.

In D85082#2190303 <https://reviews.llvm.org/D85082#2190303>, @arichardson wrote:

> In D85082#2190291 <https://reviews.llvm.org/D85082#2190291>, @arichardson wrote:
>
>> Can we instead add a dependency on libpthread.so/libthr.so to libasan.so?
>
> Never mind, it seems like it's already there:
>
>   File: ./lib/clang/12.0.0/lib/freebsd/libclang_rt.asan-x86_64.so
>   Format: elf64-x86-64
>   Arch: x86_64
>   AddressSize: 64bit
>   LoadName: libclang_rt.asan-x86_64.so
>   NeededLibraries [
>     libc++.so.1
>     libc.so.7
>     libcxxrt.so.1
>     libdl.so.1
>     libgcc_s.so.1
>     libm.so.5
>     librt.so.1
>     libthr.so.3
>   ]

Indeed. However, on FreeBSD we don't call `__asan_init` via `.preinit_array` (see https://github.com/llvm/llvm-project/blob/master/compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h#L101), and so ASan gets initialized only when some function like malloc calls into ASan, e.g.:

  #0  __asan::AsanTSDInit (destructor=0x8002a0430 <__asan::PlatformTSDDtor(void*)>) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_posix.cpp:89
  #1  0x000000080029ef39 in __asan::AsanInitInternal () at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_rtl.cpp:465
  #2  0x000000080029edd7 in __asan::AsanInitFromRtl () at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_rtl.cpp:537
  #3  0x00000008002cb66e in __interceptor_readlink (path=0x800c73203 "/etc/malloc.conf", buf=0x7fffffffd0b0 "\336\003", bufsiz=1024) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc:7009
  #4  0x0000000800d7b106 in obtain_malloc_conf (which_source=2, buf=0x7fffffffd0b0 "\336\003") at jemalloc_jemalloc.c:984
  #5  malloc_conf_init_helper (sc_data=0x0, bin_shard_sizes=0x0, initial_call=true, opts_cache=0x7fffffffd4c0, buf=<optimized out>) at jemalloc_jemalloc.c:1042
  #6  0x0000000800d7ab81 in malloc_conf_init (sc_data=0x7fffffffb700, bin_shard_sizes=0x7fffffffb670) at jemalloc_jemalloc.c:1449
  #7  malloc_init_hard_a0_locked () at jemalloc_jemalloc.c:1509
  #8  0x0000000800d78814 in malloc_init_hard () at jemalloc_jemalloc.c:1754
  #9  malloc_init () at jemalloc_jemalloc.c:227
  #10 0x000000080020cf4d in objlist_call_init (list=<optimized out>, lockstate=<optimized out>) at /usr/src/libexec/rtld-elf/rtld.c:2867
  #11 0x000000080020bc1b in _rtld (sp=0x7fffffffe550, exit_proc=0x7fffffffe520, objp=0x7fffffffe528) at /usr/src/libexec/rtld-elf/rtld.c:847
  #12 0x0000000800209419 in rtld_start () at /usr/src/libexec/rtld-elf/amd64/rtld_start.S:39
  #13 0x0000000000000000 in ?? ()

In an executable, linked dynamically to libasan.so, at this point pthread_key_create() still refers to the stubbed libc function, *iff* the executable itself is not directly linked against the threading library, libthr.so. This can be fixed (or rather worked around) by adding -pthread, as I am proposing.

It also means that *any* executable wanting to make use of dynamic libasan.so should be linked with -pthread. But I think the number of actual users approaches zero, except for the compiler-rt unit tests.

The true solution would be to fold FreeBSD libthr functionality into libc, but I have understood that this is a big piece of technical debt which has been dragged around for years now, so it is not likely to be solved very soon, and certainly not for all existing releases of FreeBSD out there.

> I thought libthr functions should be picked up correctly (at least after https://reviews.freebsd.org/D21088)

Nope, this has never worked, and does not work on very recent FreeBSD -CURRENT either.

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