[mips] Make TTypeEncoding indirect to allow .eh_frame to be read-only.

Summary:
Following on from r209907 which made personality encodings indirect, do the
same for TType encodings. This fixes the case where a try/catch block needs
to generate references to, for example, std::exception in the
.gcc_except_table.

This commit uses DW_EH_PE_sdata8 for N64 as far as is possible at the moment.
However, it is possible to end up with DW_EH_PE_sdata4 when a TargetMachine is
not available. There's no risk of issues with inconsistency here since the
tables are self describing but it does mean there is a small chance of the
PC-relative offset being out of range for particularly large programs.

Reviewers: petarj

Reviewed By: petarj

Subscribers: srhines, joerg, tberghammer, llvm-commits

Differential Revision: http://reviews.llvm.org/D9669

llvm-svn: 238190

1 files changed, 14 insertions, 3 deletions

diff --git a/llvm/lib/MC/MCObjectFileInfo.cpp b/llvm/lib/MC/MCObjectFileInfo.cpp
index e99f036..c189d19 100644
--- a/llvm/lib/MC/MCObjectFileInfo.cpp
+++ b/llvm/lib/MC/MCObjectFileInfo.cpp
@@ -324,10 +324,13 @@ void MCObjectFileInfo::InitELFMCObjectFileInfo(Triple T) {
   case Triple::mipsel:
   case Triple::mips64:
   case Triple::mips64el:
-    // MIPS uses indirect pointer to refer personality functions, so that the
-    // eh_frame section can be read-only.  DW.ref.personality will be generated
-    // for relocation.
+    // MIPS uses indirect pointer to refer personality functions and types, so
+    // that the eh_frame section can be read-only. DW.ref.personality will be
+    // generated for relocation.
     PersonalityEncoding = dwarf::DW_EH_PE_indirect;
+    TTypeEncoding = SelectMipsTTypeEncoding();
+    // We don't support PC-relative LSDA references in GAS so we use the default
+    // DW_EH_PE_absptr for those.
     break;
   case Triple::ppc64:
   case Triple::ppc64le:
@@ -793,3 +796,11 @@ void MCObjectFileInfo::InitEHFrameSection() {
                           COFF::IMAGE_SCN_MEM_WRITE,
                           SectionKind::getDataRel());
 }
+
+unsigned MCObjectFileInfo::SelectMipsTTypeEncoding() const {
+  // FIXME: The N64 ABI ought to use DW_EH_PE_sdata8 but we can't
+  //        identify N64 from just a triple. We currently fix this by
+  //        overriding this function in MipsTargetObjectFile.
+  return dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
+         dwarf::DW_EH_PE_sdata4;
+}