[sanitizer] Simplify GetTls with dl_iterate_phdr on Linux and use it on…

Authored by MaskRay on Apr 15 2021, 3:34 PM.


[sanitizer] Simplify GetTls with dl_iterate_phdr on Linux and use it on musl/FreeBSD

... so that FreeBSD specific GetTls/glibc specific pthread_self code can be
removed. This also helps FreeBSD arm64/powerpc64 which don't have GetTls
implementation yet.

GetTls is the range of

  • thread control block and optional TLS_PRE_TCB_SIZE
  • static TLS blocks plus static TLS surplus

On glibc, lsan requires the range to include
pthread::{specific_1stblock,specific} so that allocations only referenced by
pthread_setspecific can be scanned.

This patch uses dl_iterate_phdr to collect TLS blocks. Find the one
with dlpi_tls_modid==1 as one of the initially loaded module, then find
consecutive ranges. The boundaries give us addr and size.

This allows us to drop the glibc internal _dl_get_tls_static_info and
InitTlsSize. However, huge glibc x86-64 binaries with numerous shared objects
may observe time complexity penalty, so exclude them for now. Use the simplified
method with non-Android Linux for now, but in theory this can be used with *BSD
and potentially other ELF OSes.

This removal of RISC-V __builtin_thread_pointer makes the code compilable with
more compiler versions (added in Clang in 2020-03, added in GCC in 2020-07).

This simplification enables D99566 for TLS Variant I architectures.

Note: as of musl 1.2.2 and FreeBSD 12.2, dlpi_tls_data returned by
dl_iterate_phdr is not desired: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254774
This can be worked around by using __tls_get_addr({modid,0}) instead
of dlpi_tls_data. The workaround can be shared with the workaround for glibc<2.25.

This fixes some tests on Alpine Linux x86-64 (musl)



and test/lsan/TestCases/many_tls_keys_pthread.cpp on glibc aarch64.

The number of sanitizer test failures does not change on FreeBSD/amd64 12.2.

Differential Revision: https://reviews.llvm.org/D98926