DWARF: Fix debug_info references to the abbreviations section (#2997)

The previous code assumed that each compile unit had its own
abbreviation section, and they are all in order. That's normally how
LLVM emits things, but in #2992 there is a testcase in which linking
of object files with IR files somehow ends up with a different order.

The proper fix is to track the binary offsets of abbreviations in the
abbreviation section. That section is comprised of null-terminated
lists, which each CU has an offset to the beginning of. With those
offsets, we can match things properly.

Add a testcase that crashes without this, to prevent regressions.

Fixes #2992
Fixes #3007

1 files changed, 10 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/ObjectYAML/DWARFYAML.h b/third_party/llvm-project/include/llvm/ObjectYAML/DWARFYAML.h
index bd4aa2007..818bddede 100644
--- a/third_party/llvm-project/include/llvm/ObjectYAML/DWARFYAML.h
+++ b/third_party/llvm-project/include/llvm/ObjectYAML/DWARFYAML.h
@@ -55,6 +55,16 @@ struct Abbrev {
   llvm::dwarf::Tag Tag;
   llvm::dwarf::Constants Children;
   std::vector<AttributeAbbrev> Attributes;
+  // XXX BINARYEN: Represent the binary offset in the abbreviation section for
+  // this abbreviation's list. The abbreviation section has multiple lists,
+  // each null-terminated, and those lists are what are referred to by compile
+  // units by offset. We need to match the offset in a compile unit to the
+  // abbreviation at that offset (which must be the beginning of an
+  // abbreviation list, that is, either the very first element, or after a null
+  // terminator). All abbreviations in the same list have the same offset
+  // (DWARFAbbreviationDeclarationSet does not track anything else, and we don't
+  // need it).
+  uint64_t ListOffset;
 };
 
 struct ARangeDescriptor {