[RISCV] Don't force Local Exec TLS for non-PIC
Summary:
Forcing Local Exec TLS requires the use of copy relocations. Copy
relocations need special handling in the runtime linker when being
used against TLS symbols, which is present in glibc, but not in
FreeBSD nor musl, and so cannot be relied upon. Moreover, copy
relocations are a hack that embed the size of an object in the ABI
when it otherwise wouldn't be, and break protected symbols (which are
expected to be DSO local), whilst also wasting space, thus they
should be avoided whenever possible. As discussed in D70398, RISC-V
should move away from forcing Local Exec, and instead use Initial
Exec like other targets, with possible linker relaxation to follow.
The RISC-V GCC maintainers also intend to adopt this
more-conventional behaviour (see
https://github.com/riscv/riscv-elf-psabi-doc/issues/122).
Reviewers: asb, MaskRay
Reviewed By: MaskRay
Subscribers: emaste, krytarowski, hiraditya, rbar, johnrusso,
simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng,
edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe,
PkmX, jocewei, psnobl, benna, Jim, lenary, s.egerton, pzheng,
sameer.abuasal, apazos, llvm-commits, bsdjhb
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70649
This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.
Requested by: jhb
MFC after: 1 week
X-MFC-With: r353358
5c72868c4c