[DebugInfo] Fix printing CIE offsets in EH FDEs.

[ikudrin]

Summary

While in .debug_frame a value of the CIE pointer field is an offset to a corresponding CIE record from the beginning of the section, in .eh_frame it is relative to the current offset. Previously, when we dumped FDE records, we just printed the same value for both the CIE pointer field and the CIE offset, which worked for .debug_frame sections but was wrong for .eh_frame ones. This patch fixes the issue by printing the kept offset of the linked CIE object.

[jhenderson]

Just making sure I understand: in .debug_frame, the cie_pointer field is always an absolute offset, whereas in .eh_frame, it is a relative value from the field, but we weren't making this distinction before, right? What does e.g. classic dwarfdump or GNU readelf display?

llvm/include/llvm/DebugInfo/DWARF/DWARFDebugFrame.h

225–226

Could you fix the second sentence of this comment (possibly as a separate commit). I think the "contains" needs deleting.

It might also be worth saying whether the offset is relative or from the start of the section.

248–249

It may be worth making a note of the eh_frame/debug_frame difference here.

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

317

I'm confused by the casting to 32-bits. I take it this code isn't DWARF64 ready yet?

Also, I'm not sure CIEPointer should be an unsigned type for .eh_frame at least. In the Ian Lance Taylor blog on the topic (https://www.airs.com/blog/archives/460), which I use as my .eh_frame "standard", it talks about how this value can be negative or positive. Do we have examples in tests which show the behaviour for positive and negative values?

[ikudrin]

llvm/include/llvm/DebugInfo/DWARF/DWARFDebugFrame.h

225–226

The comment is about the laziness of acquiring the CIE, but it looks like that was never true, even from the beginning. I guess it is better to remove this comment altogether.

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

317

I'm confused by the casting to 32-bits. I take it this code isn't DWARF64 ready yet?

Right, not supporting 64-bit values yet. The truncation is fixed in D73887, which is the final patch of this set.

Also, I'm not sure CIEPointer should be an unsigned type for .eh_frame at least. In the Ian Lance Taylor blog on the topic (https://www.airs.com/blog/archives/460), which I use as my .eh_frame "standard", it talks about how this value can be negative or positive.

He does not talk about negative values, only that "A positive value goes backward; that is, you have to subtract the value of the ID field from the current byte position to get the CIE position." Also, note that in https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html the value of the CIE pointer is explicitly described as an unsigned value.

[ikudrin]

• Added a comment for CIEPointer describing the difference in EH and debug FDEs.

[ikudrin]

llvm/include/llvm/DebugInfo/DWARF/DWARFDebugFrame.h

225–226

I've added D74761 to remove the comment. What do you think?

[jhenderson]

LGTM, with one nit.

llvm/include/llvm/DebugInfo/DWARF/DWARFDebugFrame.h

250

Strictly speaking, the DWARF standard doesn't define the eh_frame format, so I think I'd replace "debug" here with "DWARF" to emphasise that difference.

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

317

Yeah, my bad. I misread.

lld/test/ELF/eh-frame-hdr-augmentation.s

 // CHECK-NEXT:   Personality Address: 0000000000001029
 // CHECK-NEXT:   Augmentation data:
 
 // CHECK:      DW_CFA_def_cfa:  reg7 +8
 // CHECK-NEXT: DW_CFA_offset:   reg16 -8
 // CHECK-NEXT: DW_CFA_nop:
 // CHECK-NEXT: DW_CFA_nop:
 
-// CHECK:      00000020 00000014 00000024 FDE cie=00000024 pc=00001014...00001014
+// CHECK:      00000020 00000014 00000024 FDE cie=00000000 pc=00001014...00001014
 // CHECK-NEXT:   LSDA Address: 000000000000100b
 // CHECK-NEXT:   DW_CFA_nop:
 // CHECK-NEXT:   DW_CFA_nop:
 // CHECK-NEXT:   DW_CFA_nop:
 
         .cfi_startproc
         .cfi_personality 0x9b, g
         .cfi_lsda 0x1b, h

llvm/include/llvm/DebugInfo/DWARF/DWARFDebugFrame.h

private:
   const uint32_t FDEPointerEncoding;
   const uint32_t LSDAPointerEncoding;
   const Optional<uint64_t> Personality;
   const Optional<uint32_t> PersonalityEnc;
 };
 
 /// DWARF Frame Description Entry (FDE)
 class FDE : public FrameEntry {
 public:
-  FDE(uint64_t Offset, uint64_t Length, int64_t LinkedCIEOffset,
+  FDE(uint64_t Offset, uint64_t Length, uint64_t CIEPointer,
       uint64_t InitialLocation, uint64_t AddressRange, CIE *Cie,
       Optional<uint64_t> LSDAAddress, Triple::ArchType Arch)
       : FrameEntry(FK_FDE, Offset, Length,
                    Cie ? Cie->getCodeAlignmentFactor() : 0,
                    Cie ? Cie->getDataAlignmentFactor() : 0,
                    Arch),
-        LinkedCIEOffset(LinkedCIEOffset), InitialLocation(InitialLocation),
+        CIEPointer(CIEPointer), InitialLocation(InitialLocation),
         AddressRange(AddressRange), LinkedCIE(Cie), LSDAAddress(LSDAAddress) {}
 
   ~FDE() override = default;
 
   const CIE *getLinkedCIE() const { return LinkedCIE; }
   uint64_t getInitialLocation() const { return InitialLocation; }
   uint64_t getAddressRange() const { return AddressRange; }
   Optional<uint64_t> getLSDAAddress() const { return LSDAAddress; }
 
   void dump(raw_ostream &OS, const MCRegisterInfo *MRI,
             bool IsEH) const override;
 
   static bool classof(const FrameEntry *FE) { return FE->getKind() == FK_FDE; }
 
 private:
-  /// The following fields are defined in section 6.4.1 of the DWARF standard v3
-  const uint64_t LinkedCIEOffset;
+  /// The following fields are defined in section 6.4.1 of the DWARFv3 standard.
+  /// Note that CIE pointers in EH FDEs, unlike DWARF FDEs, contain relative
+  /// offsets to the linked CIEs. See the following link for more info:
+  /// https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html
+  const uint64_t CIEPointer;
   const uint64_t InitialLocation;
   const uint64_t AddressRange;
   const CIE *LinkedCIE;
   const Optional<uint64_t> LSDAAddress;
 };
 
 } // end namespace dwarf
 

llvm/lib/DebugInfo/DWARF/DWARFDebugFrame.cpp

if (!AugmentationData.empty()) {
     OS << "\n";
   }
   OS << "\n";
   CFIs.dump(OS, MRI, IsEH);
   OS << "\n";
 }
 
 void FDE::dump(raw_ostream &OS, const MCRegisterInfo *MRI, bool IsEH) const {
-  OS << format("%08x %08x %08x FDE ", (uint32_t)Offset, (uint32_t)Length,
-               (int32_t)LinkedCIEOffset);
-  OS << format("cie=%08x pc=%08x...%08x\n", (int32_t)LinkedCIEOffset,
-               (uint32_t)InitialLocation,
+  OS << format("%08x %08x %08x", (uint32_t)Offset, (uint32_t)Length,
+               (uint32_t)CIEPointer)
+     << " FDE cie=";
+  if (LinkedCIE)
+    OS << format("%08x", (uint32_t)(LinkedCIE->getOffset()));
+  else
+    OS << "<invalid offset>";
+  OS << format(" pc=%08x...%08x\n", (uint32_t)InitialLocation,
                (uint32_t)InitialLocation + (uint32_t)AddressRange);
   if (LSDAAddress)
     OS << format("  LSDA Address: %016" PRIx64 "\n", *LSDAAddress);
   CFIs.dump(OS, MRI, IsEH);
   OS << "\n";
 }
 
 DWARFDebugFrame::DWARFDebugFrame(Triple::ArchType Arch,

llvm/test/DebugInfo/RISCV/eh-frame.s

 # CHECK:   Return address column: 1
 
 # Check the pointer encoding for address pointers used in FDE. This is set by
 # FDECFIEncoding and should be DW_EH_PE_pcrel | DW_EH_PE_sdata4 (0x1b).
 
 # CHECK:   Augmentation data:     1B
 # CHECK:   DW_CFA_def_cfa: reg2 +0
 #
-# CHECK: 00000014 00000010 00000018 FDE cie=00000018 pc=00000000...00000004
+# CHECK: 00000014 00000010 00000018 FDE cie=00000000 pc=00000000...00000004
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:

llvm/test/DebugInfo/X86/debug_frame-invalid-cie-offset.s

+# RUN: llvm-mc -triple i386-unknown-linux %s -filetype=obj -o - | \
+# RUN:  llvm-dwarfdump -debug-frame - | \
+# RUN:  FileCheck %s
+
+# CHECK: .debug_frame contents:
+# CHECK: 00000000 0000000c 12345678 FDE cie=<invalid offset> pc=00010000...00010010
+
+    .section .debug_frame,"",@progbits
+    .long   .LFDE0end-.LFDE0id  # Length
+.LFDE0id:
+    .long   0x12345678          # CIE pointer (invalid)
+    .long   0x00010000          # Initial location
+    .long   0x00000010          # Address range
+.LFDE0end:

llvm/test/MC/Mips/eh-frame.s

 // DWARF32-NEXT:     Return address column: 31
 // DWARF32_ABS-NEXT: Augmentation data: 0B
 //                                      ^^ fde pointer encoding: DW_EH_PE_sdata4
 // DWARF32_PIC-NEXT: Augmentation data: 1B
 //                                      ^^ fde pointer encoding: DW_EH_PE_pcrel | DW_EH_PE_sdata4
 // DWARF32-EMPTY:
 // DWARF32-NEXT:     DW_CFA_def_cfa_register: reg29
 //
-// DWARF32: 00000014 00000010 00000018 FDE cie=00000018 pc=00000000...00000000
+// DWARF32: 00000014 00000010 00000018 FDE cie=00000000 pc=00000000...00000000
 // DWARF32-NEXT:     DW_CFA_nop:
 // DWARF32-NEXT:     DW_CFA_nop:
 // DWARF32-NEXT:     DW_CFA_nop:
 
 
 // DWARF64: 00000000 00000010 00000000 CIE
 // DWARF64-NEXT:     Version:               1
 // DWARF64-NEXT:     Augmentation:          "zR"
 // DWARF64-NEXT:     Code alignment factor: 1
 // DWARF64-NEXT:     Data alignment factor: -8
 //                                          ^^ GAS uses -4. Should be ok as long as
 //                                             all offsets we need are a multiple of 8.
 // DWARF64-NEXT:     Return address column: 31
 // DWARF64_ABS-NEXT: Augmentation data: 0C
 //                                      ^^ fde pointer encoding: DW_EH_PE_sdata8
 // DWARF64_PIC:      Augmentation data: 1B
 //                                      ^^ fde pointer encoding: DW_EH_PE_pcrel | DW_EH_PE_sdata4
 // DWARF64-EMPTY:
 // DWARF64-NEXT:     DW_CFA_def_cfa_register: reg29
 // DWARF64_PIC-NEXT: DW_CFA_nop:
 //
-// DWARF64_ABS:      00000014 00000018 00000018 FDE cie=00000018 pc=00000000...00000000
-// DWARF64_PIC:      00000014 00000010 00000018 FDE cie=00000018 pc=00000000...00000000
+// DWARF64_ABS:      00000014 00000018 00000018 FDE cie=00000000 pc=00000000...00000000
+// DWARF64_PIC:      00000014 00000010 00000018 FDE cie=00000000 pc=00000000...00000000
 // DWARF64-NEXT:     DW_CFA_nop:
 // DWARF64-NEXT:     DW_CFA_nop:
 // DWARF64-NEXT:     DW_CFA_nop:

llvm/test/tools/llvm-dwarfdump/X86/debug_frame_GNU_args_size.s

 # RUN: llvm-mc %s -filetype=obj -triple=i686-pc-linux -o %t
 # RUN: llvm-dwarfdump -v %t | FileCheck %s
 
 # CHECK:      .eh_frame contents:
-# CHECK:        00000018 00000010 0000001c FDE cie=0000001c pc=00000000...00000000
+# CHECK:        00000018 00000010 0000001c FDE cie=00000000 pc=00000000...00000000
 # CHECK-NEXT:     DW_CFA_GNU_args_size: +16
 # CHECK-NEXT:     DW_CFA_nop:
 
 .text
 .globl foo
 .type  foo,@function
 foo:
  .cfi_startproc
  .cfi_escape 0x2e, 0x10
  .cfi_endproc

llvm/test/tools/llvm-dwarfdump/X86/debug_frame_offset.test

 RUN: llc -filetype=obj %p/../../dsymutil/Inputs/frame-dw2.ll -o - \
 RUN:   | llvm-dwarfdump -debug-frame=0x00000014 - | FileCheck %s
 CHECK: .debug_frame contents:
 CHECK-NEXT: 00000014 00000014 00000000 FDE cie=00000000 pc=00000000...0000001d
 CHECK-NEXT:   DW_CFA_advance_loc: 1
 CHECK-NOT: pc
 
 RUN: llvm-dwarfdump %p/../../dsymutil/Inputs/basic1.macho.x86_64.o \
 RUN:   -eh-frame=0x00000018 | FileCheck %s --check-prefix=EH
 EH: .eh_frame contents:
-EH-NEXT: 00000018 00000024 0000001c FDE cie=0000001c pc=fffffd00...fffffd24
+EH-NEXT: 00000018 00000024 0000001c FDE cie=00000000 pc=fffffd00...fffffd24
 EH-NEXT:   DW_CFA_advance_loc: 1
 EH-NOT: pc
 EH-NOT: CIE

llvm/test/tools/llvm-objdump/eh_frame-arm64.test

 # RUN: llvm-objdump -dwarf=frames %p/Inputs/eh_frame.macho-arm64 2>/dev/null | FileCheck %s
 
 # CHECK: .eh_frame contents:
 
 # CHECK: 00000000 00000010 00000000 CIE
 # CHECK:   Version:               1
 # CHECK:   Augmentation:          "zR"
 # CHECK:   Code alignment factor: 1
 # CHECK:   Data alignment factor: -8
 # CHECK:   Return address column: 30
 # CHECK:   Augmentation data:     10
 
 # CHECK:   DW_CFA_def_cfa: reg31 +0
 
-# CHECK: 00000014 00000020 00000018 FDE cie=00000018 pc=ffffffe4...00000004
+# CHECK: 00000014 00000020 00000018 FDE cie=00000000 pc=ffffffe4...00000004
 # CHECK:   DW_CFA_advance_loc: 8
 # CHECK:   DW_CFA_def_cfa_offset: +16
 # CHECK:   DW_CFA_offset: reg30 -8
 # CHECK:   DW_CFA_offset: reg29 -16
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:

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

 # CHECK:   Personality Address: 00000000004025d7
 # CHECK:   Augmentation data:     00 D7 25 40 00 00 00
 
 # CHECK:   DW_CFA_def_cfa: reg4 +4
 # CHECK:   DW_CFA_offset: reg8 -4
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:
 
-# CHECK: 00000020 0000001c 00000024 FDE cie=00000024 pc=00401410...00401488
+# CHECK: 00000020 0000001c 00000024 FDE cie=00000000 pc=00401410...00401488
 # CHECK:   LSDA Address: 0000000000406000
 # CHECK:   DW_CFA_advance_loc: 1
 # CHECK:   DW_CFA_def_cfa_offset: +8
 # CHECK:   DW_CFA_offset: reg5 -8
 # CHECK:   DW_CFA_advance_loc: 2
 # CHECK:   DW_CFA_def_cfa_register: reg5
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:
 # CHECK:   DW_CFA_nop:

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=00000020 pc=00400890...004008dc
+# 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:
 
 # 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