[DebugInfo/llvm-objdump] - Print "ZERO terminator" for terminator entries when dumping .eh_frame.

[grimar]

Summary

A CIE with the Length == 0 is a terminator:
https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html

And GNU objdump recognizes them and prints the following for such entries:

"00000000 ZERO terminator"

This patch teaches llvm-objdump to do the same. I had to update tests to use
"CHECK-NEXT" too.

(Note: it looks perhaps not right that printing is done inside the DebugInfo library,
I'd expect to see the change in the llvm-objdump's code somewhere instead,
but that is how it done atm).

[MaskRay]

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

307

typo: section

308

binutils-gdb/binutils/dwarf.c:display_debug_frames displays ZERO terminator for both .eh_frame and .debug_frame. We can be consistent here.

[grimar]

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

308

This is something I am not sure in. I've not found in DWARF5 specification anything that says the length can be 0 for .debug_frame (e,g http://www.dwarfstd.org/doc/DWARF5.pdf, p174).

Being consistent is perhaps OK here, but it doesn't seem that .debug_frame is supposed to have a terminator? Probably we should not print "ZERO terminator" for .debug_frame (at least in this patch) then.

[MaskRay]

Thanks!

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

308

OK

[jhenderson]

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

307

Looks like this typo was never fixed?

[grimar]

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

307

Right, sorry. Fixed in https://github.com/llvm/llvm-project/commit/84c643358691b8057199e8c8597428ad0d960786. Thanks for catching!

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

constexpr uint64_t getCIEId(bool IsDWARF64, bool IsEH) {
   if (IsEH)
     return 0;
   if (IsDWARF64)
     return DW64_CIE_ID;
   return DW_CIE_ID;
 }
 
 void CIE::dump(raw_ostream &OS, const MCRegisterInfo *MRI, bool IsEH) const {
+  // A CIE with a zero length is a terminator entry in the .eh_frame sextion.
+  if (IsEH && Length == 0) {
+    OS << format("%08" PRIx64, Offset) << " ZERO terminator\n";
+    return;
+  }
+
   OS << format("%08" PRIx64, Offset)
      << format(" %0*" PRIx64, IsDWARF64 ? 16 : 8, Length)
      << format(" %0*" PRIx64, IsDWARF64 && !IsEH ? 16 : 8,
                getCIEId(IsDWARF64, IsEH))
      << " CIE\n";
   OS << format("  Version:               %d\n", Version);
   OS << "  Augmentation:          \"" << Augmentation << "\"\n";
   if (Version >= 4) {

llvm/test/tools/llvm-objdump/eh_frame-mipsel.test

 # RUN: llvm-objdump --dwarf=frames %p/Inputs/eh_frame.elf-mipsel | FileCheck %s
 
-# CHECK: .eh_frame contents:
-
-# CHECK: 00000000 00000018 00000000 CIE
-# CHECK:   Version:               1
-# CHECK:   Augmentation:          "zPLR"
-# CHECK:   Code alignment factor: 1
-# CHECK:   Data alignment factor: -4
-# CHECK:   Return address column: 31
-# CHECK:   Augmentation data:     80 90 0B 41 00 00 0B
-
-# CHECK:   DW_CFA_def_cfa: reg29 +0
-
-# CHECK: 0000001c 00000018 00000020 FDE cie=00000000 pc=00400890...004008dc
-# CHECK:   DW_CFA_advance_loc: 4
-# CHECK:   DW_CFA_def_cfa_offset: +24
-# CHECK:   DW_CFA_advance_loc: 4
-# CHECK:   DW_CFA_offset: reg31 -4
-# CHECK:   DW_CFA_nop:
-
-## FIXME: GNU objdump prints "00000038 ZERO terminator" instead.
-# CHECK: 00000038 00000000 00000000 CIE
-# CHECK:   Version:               0
-# CHECK:   Augmentation:          ""
-# CHECK:   Code alignment factor: 0
-# CHECK:   Data alignment factor: 0
-# CHECK:   Return address column: 0
+# CHECK:       .eh_frame contents:
+# CHECK-EMPTY:
+# CHECK-NEXT:  00000000 00000018 00000000 CIE
+# CHECK-NEXT:    Version:               1
+# CHECK-NEXT:    Augmentation:          "zPLR"
+# CHECK-NEXT:    Code alignment factor: 1
+# CHECK-NEXT:    Data alignment factor: -4
+# CHECK-NEXT:    Return address column: 31
+# CHECK-NEXT:    Personality Address: 0000000000410b90
+# CHECK-NEXT:    Augmentation data:     80 90 0B 41 00 00 0B
+# CHECK-EMPTY:
+# CHECK-NEXT:  DW_CFA_def_cfa: reg29 +0
+# CHECK-EMPTY:
+# CHECK-NEXT:  0000001c 00000018 00000020 FDE cie=00000000 pc=00400890...004008dc
+# CHECK-NEXT:    LSDA Address: 0000000000400a90
+# CHECK-NEXT:    DW_CFA_advance_loc: 4
+# CHECK-NEXT:    DW_CFA_def_cfa_offset: +24
+# CHECK-NEXT:    DW_CFA_advance_loc: 4
+# CHECK-NEXT:    DW_CFA_offset: reg31 -4
+# CHECK-NEXT:    DW_CFA_nop:
+# CHECK-EMPTY:
+# CHECK-NEXT:  00000038 ZERO terminator
+# CHECK-NOT: {{.}}

llvm/test/tools/llvm-objdump/eh_frame_zero_cie.test

 # RUN: llvm-objdump --dwarf=frames %p/Inputs/eh_frame_zero_cie.o 2>/dev/null | FileCheck %s
 
-# CHECK: .eh_frame contents:
-
-## FIXME: GNU objdump prints "00000000 ZERO terminator" instead.
-# CHECK: 00000000 00000000 00000000 CIE
-# CHECK:   Version:               0
-# CHECK:   Augmentation:          ""
-# CHECK:   Code alignment factor: 0
-# CHECK:   Data alignment factor: 0
-# CHECK:   Return address column: 0
+# CHECK:       .eh_frame contents:
+# CHECK-EMPTY:
+# CHECK-NEXT:  00000000 ZERO terminator
+# CHECK-NOT:   {{.}}