tree 1362430c79a61bba2ebfa4b2094b844fcee95871
parent 072a2ea8f45dd4a44cc81b1a8f5bc009d393968d
author Fangrui Song <maskray@google.com> 1559210420 +0000
committer Fangrui Song <maskray@google.com> 1559210420 +0000

[ELF] Implement Local Dynamic style TLSDESC for x86-64

For the Local Dynamic case of TLSDESC, _TLS_MODULE_BASE_ is defined as a
special TLS symbol that makes:

1) Without relaxation: it produces a dynamic TLSDESC relocation that
computes 0. Adding @dtpoff to access a TLS symbol.
2) With LD->LE relaxation: _TLS_MODULE_BASE_@tpoff = 0 (lowest address in
the TLS block). Adding @tpoff to access a TLS symbol.

For 1), this saves dynamic relocations and GOT slots as otherwise
(General Dynamic) we would create an R_X86_64_TLSDESC and reserve two
GOT slots for each symbol.

Add ElfSym::TlsModuleBase and change the signature of getTlsTpOffset()
to special case _TLS_MODULE_BASE_.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D62577

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@362078 91177308-0d34-0410-b5e6-96231b3b80d8