[PATCH] D147980: Emit unwind information in .debug_frame section when .cfi_sections .debug_frame intrinsic is used

[Shubham Sandeep Rastogi via Phabricator via llvm-commits]

rastogishubham created this revision.
rastogishubham added reviewers: aprantl, friss, t.p.northover.
Herald added subscribers: hiraditya, kristof.beyls.
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rastogishubham requested review of this revision.
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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. ARM64 however, 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


https://reviews.llvm.org/D147980

Files:
  llvm/lib/MC/MCDwarf.cpp
  llvm/test/DebugInfo/AArch64/debugframeinfo.s


Index: llvm/test/DebugInfo/AArch64/debugframeinfo.s
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/AArch64/debugframeinfo.s
@@ -0,0 +1,43 @@
+# RUN: llvm-mc -filetype=obj --triple=arm64-apple-darwin22.1.0 %s -o %t.o
+# RUN: llvm-dwarfdump -debug-frame %t.o | FileCheck %s
+
+# CHECK: .debug_frame contents:
+# CHECK-EMPTY: 
+# CHECK-NEXT: 00000000 00000014 ffffffff CIE
+# CHECK-NEXT: Format:                DWARF32
+# CHECK-NEXT: Version:               4
+# CHECK-NEXT: Augmentation:          ""
+# CHECK-NEXT: Address size:          8
+# CHECK-NEXT: Segment desc size:     0
+# CHECK-NEXT: Code alignment factor: 1
+# CHECK-NEXT: Data alignment factor: -8
+# CHECK-NEXT: Return address column: 30
+# CHECK-EMPTY: 
+# CHECK-NEXT: DW_CFA_def_cfa: WSP +0
+# CHECK-NEXT: DW_CFA_nop:
+# CHECK-NEXT: DW_CFA_nop:
+# CHECK-NEXT: DW_CFA_nop:
+# CHECK-NEXT: DW_CFA_nop:
+# CHECK-NEXT: DW_CFA_nop:
+# CHECK-NEXT: DW_CFA_nop:
+# CHECK-EMPTY: 
+# CHECK-NEXT: CFA=WSP
+# CHECK-EMPTY: 
+# CHECK-NEXT: 00000018 00000014 00000000 FDE cie=00000000 pc=00000000...00000000
+# CHECK-NEXT: Format:       DWARF32
+# CHECK-EMPTY: 
+# CHECK-NEXT: 0x0: CFA=WSP
+
+# CHECK: .eh_frame contents:
+# CHECK-EMPTY:
+# CHECK-EMPTY:
+
+        .cfi_sections .debug_frame
+        .cfi_startproc
+        .cfi_personality 0x9b, g
+        .cfi_lsda 0x1b, h
+        .cfi_endproc
+        .global g
+g:
+        .global h
+h:
Index: llvm/lib/MC/MCDwarf.cpp
===================================================================
--- llvm/lib/MC/MCDwarf.cpp
+++ llvm/lib/MC/MCDwarf.cpp
@@ -1856,7 +1856,6 @@
   const MCAsmInfo *AsmInfo = Context.getAsmInfo();
   FrameEmitterImpl Emitter(IsEH, Streamer);
   ArrayRef<MCDwarfFrameInfo> FrameArray = Streamer.getDwarfFrameInfos();
-
   // Emit the compact unwind info if available.
   bool NeedsEHFrameSection = !MOFI->getSupportsCompactUnwindWithoutEHFrame();
   if (IsEH && MOFI->getCompactUnwindSection()) {
@@ -1876,7 +1875,7 @@
     }
   }
 
-  if (!NeedsEHFrameSection) return;
+  if (!NeedsEHFrameSection && IsEH) return;
 
   MCSection &Section =
       IsEH ? *const_cast<MCObjectFileInfo *>(MOFI)->getEHFrameSection()
@@ -1903,7 +1902,7 @@
     const MCDwarfFrameInfo &Frame = *I;
     ++I;
     if (CanOmitDwarf && Frame.CompactUnwindEncoding !=
-          MOFI->getCompactUnwindDwarfEHFrameOnly())
+          MOFI->getCompactUnwindDwarfEHFrameOnly() && IsEH)
       // Don't generate an EH frame if we don't need one. I.e., it's taken care
       // of by the compact unwind encoding.
       continue;


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