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, 6 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index f1e61b488a2..d2f123ce78e 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1506,8 +1506,9 @@ void DwarfDebug::emitAbbreviations() {
 
 void DwarfDebug::emitStringOffsetsTableHeader() {
   DwarfFile &Holder = useSplitDwarf() ? SkeletonHolder : InfoHolder;
-  Holder.emitStringOffsetsTableHeader(
-      Asm->getObjFileLowering().getDwarfStrOffSection());
+  Holder.getStringPool().emitStringOffsetsTableHeader(
+      *Asm, Asm->getObjFileLowering().getDwarfStrOffSection(),
+      Holder.getStringOffsetsStartSym());
 }
 
 template <typename AccelTableT>
@@ -2292,8 +2293,9 @@ void DwarfDebug::emitDebugLineDWO() {
 
 void DwarfDebug::emitStringOffsetsTableHeaderDWO() {
   assert(useSplitDwarf() && "No split dwarf?");
-  InfoHolder.emitStringOffsetsTableHeader(
-      Asm->getObjFileLowering().getDwarfStrOffDWOSection());
+  InfoHolder.getStringPool().emitStringOffsetsTableHeader(
+      *Asm, Asm->getObjFileLowering().getDwarfStrOffDWOSection(),
+      InfoHolder.getStringOffsetsStartSym());
 }
 
 // Emit the .debug_str.dwo section for separated dwarf. This contains the