[PPC64] Add support for local-exec TLS model

This patch adds the relocations needed support the local-exec TLS model:

R_PPC64_TPREL16
R_PPC64_TPREL16_HA
R_PPC64_TPREL16_LO
R_PPC64_TPREL16_HI
R_PPC64_TPREL16_DS
R_PPC64_TPREL16_LO_DS
R_PPC64_TPREL16_HIGHER
R_PPC64_TPREL16_HIGHERA
R_PPC64_TPREL16_HIGHEST
R_PPC64_TPREL16_HIGHESTA

Differential Revision: https://reviews.llvm.org/D47598

1 files changed, 16 insertions, 1 deletions

diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
index 09bc39eaed1..32f1f4846f7 100644
--- a/lld/ELF/InputSection.cpp
+++ b/lld/ELF/InputSection.cpp
@@ -618,8 +618,23 @@ static uint64_t getRelocTargetVA(RelType Type, int64_t A, uint64_t P,
     // statically to zero.
     if (Sym.isTls() && Sym.isUndefWeak())
       return 0;
-    if (Target->TcbSize)
+
+    // For TLS variant 1 the TCB is a fixed size, whereas for TLS variant 2 the
+    // TCB is on unspecified size and content. Targets that implement variant 1
+    // should set TcbSize.
+    if (Target->TcbSize) {
+      // PPC64 V2 ABI has the thread pointer offset into the middle of the TLS
+      // storage area by TlsTpOffset for efficient addressing TCB and up to
+      // 4KB – 8 B of other thread library information (placed before the TCB).
+      // Subtracting this offset will get the address of the first TLS block.
+      if (Target->TlsTpOffset)
+        return Sym.getVA(A) - Target->TlsTpOffset;
+
+      // If thread pointer is not offset into the middle, the first thing in the
+      // TLS storage area is the TCB. Add the TcbSize to get the address of the
+      // first TLS block.
       return Sym.getVA(A) + alignTo(Target->TcbSize, Out::TlsPhdr->p_align);
+    }
     return Sym.getVA(A) - Out::TlsPhdr->p_memsz;
   case R_RELAX_TLS_GD_TO_LE_NEG:
   case R_NEG_TLS: