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, 4 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfStringPool.h b/llvm/lib/CodeGen/AsmPrinter/DwarfStringPool.h
index 069c124d1a7..6e6988ea4ad 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfStringPool.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfStringPool.h
@@ -19,6 +19,7 @@ namespace llvm {
 
 class AsmPrinter;
 class MCSection;
+class MCSymbol;
 
 // Collection of strings for this unit and assorted symbols.
 // A String->Symbol mapping of strings used by indirect
@@ -36,6 +37,9 @@ public:
 
   DwarfStringPool(BumpPtrAllocator &A, AsmPrinter &Asm, StringRef Prefix);
 
+  void emitStringOffsetsTableHeader(AsmPrinter &Asm, MCSection *OffsetSection,
+                                    MCSymbol *StartSym);
+
   void emit(AsmPrinter &Asm, MCSection *StrSection,
             MCSection *OffsetSection = nullptr,
             bool UseRelativeOffsets = false);