dwarfgen: Add support for generating the debug_str_offsets section, take 3

Previous version of this patch failed on darwin targets because of
different handling of cross-debug-section relocations. This fixes the
tests to emit the DW_AT_str_offsets_base attribute correctly in both
cases. Since doing this is a non-trivial amount of code, and I'm going
to need it in more than one test, I've added a helper function to the
dwarfgen DIE class to do it.

Original commit message follows:

The motivation for this is D49493, where we'd like to test details of
debug_str_offsets behavior which is difficult to trigger from a
traditional test.

This adds the plubming necessary for dwarfgen to generate this section.
The more interesting changes are:
- I've moved emitStringOffsetsTableHeader function from DwarfFile to
  DwarfStringPool, so I can generate the section header more easily from
  the unit test.
- added a new addAttribute overload taking an MCExpr*. This is used to
  generate the DW_AT_str_offsets_base, which links a compile unit to the
  offset table.

I've also added a basic test for reading and writing DW_form_strx forms.

Reviewers: dblaikie, JDevlieghere, probinson

Subscribers: llvm-commits, aprantl

Differential Revision: https://reviews.llvm.org/D49670

llvm-svn: 338031

1 files changed, 0 insertions, 20 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp
index f3a3cbdbc74..c90bd568162 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp
@@ -28,26 +28,6 @@ void DwarfFile::addUnit(std::unique_ptr<DwarfCompileUnit> U) {
   CUs.push_back(std::move(U));
 }
 
-void DwarfFile::emitStringOffsetsTableHeader(MCSection *Section) {
-  if (StrPool.empty())
-    return;
-  Asm->OutStreamer->SwitchSection(Section);
-  unsigned EntrySize = 4;
-  // FIXME: DWARF64
-  // We are emitting the header for a contribution to the string offsets
-  // table. The header consists of an entry with the contribution's
-  // size (not including the size of the length field), the DWARF version and
-  // 2 bytes of padding.
-  Asm->emitInt32(StrPool.size() * EntrySize + 4);
-  Asm->emitInt16(Asm->getDwarfVersion());
-  Asm->emitInt16(0);
-  // Define the symbol that marks the start of the contribution. It is
-  // referenced by most unit headers via DW_AT_str_offsets_base.
-  // Split units do not use the attribute.
-  if (StringOffsetsStartSym)
-    Asm->OutStreamer->EmitLabel(StringOffsetsStartSym);
-}
-
 // Emit the various dwarf units to the unit section USection with
 // the abbreviations going into ASection.
 void DwarfFile::emitUnits(bool UseOffsets) {