Emit unwind information in .debug_frame section when .cfi_sections .debug_frame intrinsic is used

The .cfi_sections .debug_frame intrinsic is used to emit .debug_frame
section. This directive tells the assembler to write out a section of
debug frame data. AArch64 is a platform where eh_frame is not needed for
unwind information. Unfortunately, that means that even when the
.cfi_sections .debug_frame intrinsic is used, the compiler skips
emitting the CIE's and FDE's in the debug_frame section. This patch
address that issue by making sure that the emission of CIE's and FDE's
are only skipped if the unwind information does not require a
debug_frame section and is a platform where the eh_frame can be skipped.

Differential Revision: https://reviews.llvm.org/D147980

1 files changed, 12 insertions, 4 deletions

diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index 30b8aad..66984ce 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -1876,7 +1876,11 @@ void MCDwarfFrameEmitter::Emit(MCObjectStreamer &Streamer, MCAsmBackend *MAB,
     }
   }
 
-  if (!NeedsEHFrameSection) return;
+  // Compact unwind information can be emitted in the eh_frame section or the
+  // debug_frame section. Skip emitting FDEs and CIEs when the compact unwind
+  // doesn't need an eh_frame section and the emission location is the eh_frame
+  // section.
+  if (!NeedsEHFrameSection && IsEH) return;
 
   MCSection &Section =
       IsEH ? *const_cast<MCObjectFileInfo *>(MOFI)->getEHFrameSection()
@@ -1903,9 +1907,13 @@ void MCDwarfFrameEmitter::Emit(MCObjectStreamer &Streamer, MCAsmBackend *MAB,
     const MCDwarfFrameInfo &Frame = *I;
     ++I;
     if (CanOmitDwarf && Frame.CompactUnwindEncoding !=
-          MOFI->getCompactUnwindDwarfEHFrameOnly())
-      // Don't generate an EH frame if we don't need one. I.e., it's taken care
-      // of by the compact unwind encoding.
+          MOFI->getCompactUnwindDwarfEHFrameOnly() && IsEH)
+      // CIEs and FDEs can be emitted in either the eh_frame section or the
+      // debug_frame section, on some platforms (e.g. AArch64) the target object
+      // file supports emitting a compact_unwind section without an associated
+      // eh_frame section. If the eh_frame section is not needed, and the
+      // location where the CIEs and FDEs are to be emitted is the eh_frame
+      // section, do not emit anything.
       continue;
 
     CIEKey Key(Frame);