Ensures that GDB prints stacktraces correctly for x64 builds when debugging t...

src/gdb-jit.cc

Index: src/gdb-jit.cc
===================================================================
--- src/gdb-jit.cc	(revision 6445)
+++ src/gdb-jit.cc	(working copy)
@@ -201,6 +201,7 @@
     TYPE_SHLIB = 10,
     TYPE_DYNSYM = 11,
     TYPE_LOPROC = 0x70000000,
+    TYPE_X86_64_UNWIND = 0x70000001,
     TYPE_HIPROC = 0x7fffffff,
     TYPE_LOUSER = 0x80000000,
     TYPE_HIUSER = 0xffffffff
@@ -1166,5 +1167,264 @@
 }
 
 
+#ifdef V8_TARGET_ARCH_X64
+
+
+class UnwindInfoSection : public ELFSection {
+ public:
+  explicit UnwindInfoSection(UnwindInfoInterface::UnwindInformation *);
+  explicit UnwindInfoSection(uintptr_t begin, uintptr_t end);

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

2 argument constructors don't need explicit.

+  virtual bool WriteBody(Writer *w);
+
+ private:
+  UnwindInfoInterface::UnwindInformation *info_;
+  uintptr_t begin_, length_;

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

uintptr_t begin_;
uintptr_t length_;

+  bool is_code_stub_;
+
+  // DWARF3 Specification, Table 7.23
+  enum CFIInstructions {
+    DW_CFA_ADVANCE_LOC = 0X40,

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

style nit: 0X -> 0x

+    DW_CFA_OFFSET = 0X80,
+    DW_CFA_RESTORE = 0XC0,
+    DW_CFA_NOP = 0X00,
+    DW_CFA_SET_LOC = 0X01,
+    DW_CFA_ADVANCE_LOC1 = 0X02,
+    DW_CFA_ADVANCE_LOC2 = 0X03,
+    DW_CFA_ADVANCE_LOC4 = 0X04,
+    DW_CFA_OFFSET_EXTENDED = 0X05,
+    DW_CFA_RESTORE_EXTENDED = 0X06,
+    DW_CFA_UNDEFINED = 0X07,
+    DW_CFA_SAME_VALUE = 0X08,
+    DW_CFA_REGISTER = 0X09,
+    DW_CFA_REMEMBER_STATE = 0X0A,
+    DW_CFA_RESTORE_STATE = 0X0B,
+    DW_CFA_DEF_CFA = 0X0C,
+    DW_CFA_DEF_CFA_REGISTER = 0X0D,
+    DW_CFA_DEF_CFA_OFFSET = 0X0E,
+
+    DW_CFA_DEF_CFA_EXPRESSION = 0X0F,
+    DW_CFA_EXPRESSION = 0X10,
+    DW_CFA_OFFSET_EXTENDED_SF = 0X11,
+    DW_CFA_DEF_CFA_SF = 0X12,
+    DW_CFA_DEF_CFA_OFFSET_SF = 0X13,
+    DW_CFA_VAL_OFFSET = 0X14,
+    DW_CFA_VAL_OFFSET_SF = 0X15,
+    DW_CFA_VAL_EXPRESSION = 0X16
+  };
+
+  // System V ABI, AMD64 Supplement, Version 0.99.5, Figure 3.36
+  enum RegisterMapping {
+    // Only the relevant ones have been added to reduce clutter.
+    AMD64_RBP = 6,
+    AMD64_RSP = 7,
+    AMD64_RA = 16
+  };
+
+  enum CFIConstants {
+    CIE_ID = 0,
+    CIE_VERSION = 1,
+    CODE_ALIGN_FACTOR = 1,
+    DATA_ALIGN_FACTOR = 1,
+    RETURN_ADDRESS_REGISTER = AMD64_RA
+  };
+};
+
+
+UnwindInfoSection::UnwindInfoSection(UnwindInfoInterface::UnwindInformation

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

I think the right way to format this will be 

UnwindInfoSection::UnwindInfoSection(
  UnwindInfoInterface::UnwindInformation* info)  

+                                     *info)
+    : ELFSection(".eh_frame", TYPE_X86_64_UNWIND, 1), info_(info),

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

either all on a single line or each initializer on it's own line

+      is_code_stub_(false) { }
+
+
+UnwindInfoSection::UnwindInfoSection(uintptr_t begin, uintptr_t length)
+    : ELFSection(".eh_frame", TYPE_X86_64_UNWIND, 1), begin_(begin),

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

ditto

+      length_(length), is_code_stub_(true) { }
+
+
+bool UnwindInfoSection::WriteBody(Writer *w) {
+  Writer::Slot<uint32_t> cie_length_slot = w->CreateSlotHere<uint32_t>();
+  uint32_t cie_position = w->position(), align;
+
+  // Write out the CIE header. Currently no 'common instructions' are
+  // emitted onto the CIE; every FDE has its own set of instructions.
+
+  w->Write<uint32_t>(CIE_ID);
+  w->Write<uint8_t>(CIE_VERSION);
+  w->Write<uint8_t>(0);  // Augmentation string.
+  w->WriteSLEB128(CODE_ALIGN_FACTOR);
+  w->WriteSLEB128(DATA_ALIGN_FACTOR);
+  w->Write<uint8_t>(RETURN_ADDRESS_REGISTER);
+
+  align = (w->position() - cie_position) % kPointerSize;
+  if (align) {

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

We don't rely on implicit int->bool convertions, so instead of if (align) -> if
(align == 0) 

+    for (uint32_t i = 0; i < (kPointerSize - align); i++) {
+      w->Write<uint8_t>(DW_CFA_NOP);
+    }
+  }
+  ASSERT((w->position() - cie_position) % kPointerSize == 0);
+  cie_length_slot.set(w->position() - cie_position);
+
+  Writer::Slot<uint32_t> fde_length_slot = w->CreateSlotHere<uint32_t>();
+  int fde_position = w->position();
+  w->Write<int32_t>(fde_position - cie_position + 4);  // Pointer to CIE
+
+  // The (only) FDE for this function
+
+  if (!is_code_stub_) {
+    w->Write<uintptr_t>(info_->begin_);
+    w->Write<uintptr_t>
+        (info_->state_offsets_[UnwindInfoInterface::UNWIND_STATE_AFTER_RETURN]);
+
+    // The CFA is the frame-pointer of the current function. This seemed the
+    // most straightforward since (it seems) both the full-codegen and the
+    // classic codegen maintain the frame-pointer.
+
+    // -- The first state, just after the control has been transferred to the

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

Can you split this into four different functions for each state?

Also remove -- from the comments. 

+    // -- the function.
+
+    // RBP for this function will be the value of RSP after pushing the RBP
+    // for the previous function. The previous RBP has not been pushed yet.
+    w->Write<uint8_t>(DW_CFA_DEF_CFA_SF);
+    w->WriteULEB128(AMD64_RSP);
+    w->WriteSLEB128(-kPointerSize);
+
+    // The RA is stored at location CFA + kCallerPCOffset. This is an invariant,
+    // and hence omitted from the next states.
+    w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
+    w->WriteULEB128(AMD64_RA);
+    w->WriteSLEB128(StandardFrameConstants::kCallerPCOffset);
+
+    // The RBP of the previous function is still in RBP.
+    w->Write<uint8_t>(DW_CFA_SAME_VALUE);
+    w->WriteULEB128(AMD64_RBP);
+
+    // Last location described by this entry.
+    w->Write<uint8_t>(DW_CFA_SET_LOC);
+    w->Write<uint64_t>
+        (info_->begin_ + info_->state_offsets_
+         [UnwindInfoInterface::UNWIND_STATE_AFTER_RBP_PUSH]);
+
+    // -- The second state, just after RBP has been pushed.
+
+    // RBP / CFA for this function is now the current RSP, so just set the
+    // offset from the previous rule (from -8) to 0.
+    w->Write<uint8_t>(DW_CFA_DEF_CFA_OFFSET);
+    w->WriteULEB128(0);
+
+    // The previous RBP is stored at CFA + kCallerFPOffset. This is an invariant
+    // in this and the next state, and hence omitted in the next state.
+    w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
+    w->WriteULEB128(AMD64_RBP);
+    w->WriteSLEB128(StandardFrameConstants::kCallerFPOffset);
+
+    // Last location described by this entry.
+    w->Write<uint8_t>(DW_CFA_SET_LOC);
+    w->Write<uint64_t>
+        (info_->begin_ + info_->state_offsets_
+         [UnwindInfoInterface::UNWIND_STATE_AFTER_RBP_SET]);
+
+    // -- The third state, after the RBP has been set.
+
+    // The CFA can now directly be set to RBP.
+    w->Write<uint8_t>(DW_CFA_DEF_CFA);
+    w->WriteULEB128(AMD64_RBP);
+    w->WriteULEB128(0);
+
+    // Last location described by this entry.
+    w->Write<uint8_t>(DW_CFA_SET_LOC);
+    w->Write<uint64_t>
+        (info_->begin_ + info_->state_offsets_
+         [UnwindInfoInterface::UNWIND_STATE_AFTER_RBP_POP]);
+
+    // -- The fourth (final) state. The RBP has been popped (just before issuing
+    // a return.
+
+    // The CFA can is now calculated in the same way as in the first state.
+    w->Write<uint8_t>(DW_CFA_DEF_CFA_SF);
+    w->WriteULEB128(AMD64_RSP);
+    w->WriteSLEB128(-kPointerSize);
+
+    // The RBP
+    w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
+    w->WriteULEB128(AMD64_RBP);
+    w->WriteSLEB128(StandardFrameConstants::kCallerFPOffset);
+
+    // Last location described by this entry.
+    w->Write<uint8_t>(DW_CFA_SET_LOC);
+    w->Write<uint64_t>
+        (info_->begin_ +
+         info_->state_offsets_[UnwindInfoInterface::UNWIND_STATE_AFTER_RETURN]);
+  } else {
+    // This is a code-stub. Unwind information for code-stubs is not divided
+    // into stages, we just tell GDB to unwind using the frame pointer.
+    w->Write<uintptr_t>(begin_);
+    w->Write<uintptr_t>(length_);
+
+    // The CFA is the current function's RBP
+    w->Write<uint8_t>(DW_CFA_DEF_CFA);
+    w->WriteULEB128(AMD64_RBP);
+    w->WriteULEB128(0);
+
+    // These assumptions are not true at the code-stub entry and exit. However,
+    // we are assuming that the debugger will halt code-stubs only at their
+    // call sites.
+    w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
+    w->WriteULEB128(AMD64_RA);
+    w->WriteSLEB128(StandardFrameConstants::kCallerPCOffset);
+
+    w->Write<uint8_t>(DW_CFA_OFFSET_EXTENDED);
+    w->WriteULEB128(AMD64_RBP);
+    w->WriteSLEB128(StandardFrameConstants::kCallerFPOffset);
+
+    // The last location described by this entry.
+    w->Write<uint8_t>(DW_CFA_SET_LOC);
+    w->Write<uint64_t>(begin_ + length_);
+  }
+
+  if ((align = (w->position() - fde_position) % kPointerSize)) {

[Vyacheslav Egorov (Chromium), 2011/01/25 12:50:11]

I think we usually avoid assignments in expressions. So

align = ...
if (...)

Also I see code duplication. Does it make sense to create a separate function?

+    for (uint32_t i = 0; i < (kPointerSize - align); i++)
+      w->Write<uint8_t>(DW_CFA_NOP);
+  }
+
+  ASSERT((w->position() - fde_position) % kPointerSize == 0);
+  fde_length_slot.set(w->position() - fde_position);
+
+  return true;
+}
+
+
+UnwindInfoInterface::UnwindInformationList *UnwindInfoInterface::info_ = NULL;
+
+
+static void SaveUnwindInfo(UnwindInfoSection *section) {
+  ELF elf;
+  elf.AddSection(section);
+  Writer w(&elf);
+  elf.Write(&w);
+  JITCodeEntry *entry = CreateCodeEntry(w.buffer(), w.position());
+  RegisterCodeEntry(entry);
+}
+
+
+UnwindInfoInterface::~UnwindInfoInterface() {
+  ASSERT(info_ != NULL);
+
+  UnwindInfoSection unwind_section(&info_->data_);
+  SaveUnwindInfo(&unwind_section);
+  UnwindInformationList *tmp = info_->next_;
+  delete info_;
+  info_ = tmp;
+}
+
+
+void UnwindInfoInterface::SetCodeStub(uintptr_t b, uintptr_t l) {
+  UnwindInfoSection unwind_section(b, l);
+  SaveUnwindInfo(&unwind_section);
+}
+
+
+#endif  // V8_TARGET_ARCH_X64
+
+
 } }  // namespace v8::internal
 #endif