llvm: Backport upstream r229195 to fix arm64 TLS relocations

  As is described at http://llvm.org/bugs/show_bug.cgi?id=22408, the GNU
  linkers ld.bfd and ld.gold currently only support a subset of the
  whole range of AArch64 ELF TLS relocations. Furthermore, they assume
  that some of the code sequences to access thread-local variables are
  produced in a very specific sequence.  When the sequence is not as the
  linker expects, it can silently mis-relaxe/mis-optimize the
  instructions.
  Even if that wouldn't be the case, it's good to produce the exact
  sequence, as that ensures that linkers can perform optimizing
  relaxations.

  This patch:

  * implements support for 16MiB TLS area size instead of 4GiB TLS area
    size. Ideally clang would grow an -mtls-size option to allow support
    for both, but that's not part of this patch.
  * by default doesn't produce local dynamic access patterns, as even
    modern ld.bfd and ld.gold linkers do not support the associated
    relocations. An option (-aarch64-elf-ldtls-generation) is added to
    enable generation of local dynamic code sequence, but is off by
    default.
  * makes sure that the exact expected code sequence for local dynamic
    and general dynamic accesses is produced, by making use of a new
    pseudo instruction. The patch also removes two
    (AArch64ISD::TLSDESC_BLR, AArch64ISD::TLSDESC_CALL) pre-existing
    AArch64-specific pseudo SDNode instructions that are superseded by
    the new one (TLSDESC_CALLSEQ).

Submitted by:	Kristof Beyls
Differential Revision:	https://reviews.freebsd.org/D2175

0 files changed, 0 insertions, 0 deletions