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

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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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238190 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Daniel Sanders
2015-05-26 10:19:18 +00:00
parent eda9f8aa74
commit bda72d8098
5 changed files with 48 additions and 11 deletions
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17
lib/MC/MCObjectFileInfo.cpp
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@@ -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;
}