[CPU/XThread] Add DWARF .eh_frame unwind info for JIT code on Linux

Generate per-function CIE+FDE records and register them via
__register_frame so the C++ exception unwinder can propagate through
JIT frames. Replace setjmp/longjmp fiber reentry with throw/catch
on Linux to ensure destructors and RAII guards run during fiber
stack switches.

Author: has207

src/xenia/cpu/backend/x64/x64_code_cache_posix.cc

@@ -9,11 +9,74 @@
 
 #include "xenia/cpu/backend/x64/x64_code_cache.h"
 
+#include <cstring>
+#include <vector>
+
+#include "xenia/base/assert.h"
+#include "xenia/base/logging.h"
+#include "xenia/base/math.h"
+#include "xenia/cpu/backend/x64/x64_stack_layout.h"
+
+// libgcc/libunwind APIs for registering DWARF .eh_frame unwind info.
+extern "C" void __register_frame(void*);
+extern "C" void __deregister_frame(void*);
+
 namespace xe {
 namespace cpu {
 namespace backend {
 namespace x64 {
 
+// Maximum size of DWARF .eh_frame data per function (CIE + FDE + terminator).
+static constexpr uint32_t kMaxUnwindInfoSize = 96;
+
+// DWARF register numbers for x86-64.
+static constexpr uint8_t kDwarfRegRBX = 3;
+static constexpr uint8_t kDwarfRegRBP = 6;
+static constexpr uint8_t kDwarfRegRSP = 7;
+static constexpr uint8_t kDwarfRegR12 = 12;
+static constexpr uint8_t kDwarfRegR13 = 13;
+static constexpr uint8_t kDwarfRegR14 = 14;
+static constexpr uint8_t kDwarfRegR15 = 15;
+static constexpr uint8_t kDwarfRegRA = 16;
+
+// DWARF CFA opcodes.
+static constexpr uint8_t kDW_CFA_advance_loc1 = 0x02;
+static constexpr uint8_t kDW_CFA_advance_loc2 = 0x03;
+static constexpr uint8_t kDW_CFA_def_cfa = 0x0c;
+static constexpr uint8_t kDW_CFA_def_cfa_offset = 0x0e;
+static constexpr uint8_t kDW_CFA_nop = 0x00;
+
+// DWARF pointer encoding constants.
+static constexpr uint8_t kDW_EH_PE_pcrel = 0x10;
+static constexpr uint8_t kDW_EH_PE_sdata4 = 0x0b;
+
+static size_t WriteULEB128(uint8_t* p, uint64_t value) {
+  size_t count = 0;
+  do {
+    uint8_t byte = value & 0x7F;
+    value >>= 7;
+    if (value) byte |= 0x80;
+    p[count++] = byte;
+  } while (value);
+  return count;
+}
+
+static size_t WriteSLEB128(uint8_t* p, int64_t value) {
+  size_t count = 0;
+  bool more = true;
+  while (more) {
+    uint8_t byte = value & 0x7F;
+    value >>= 7;
+    if ((value == 0 && !(byte & 0x40)) || (value == -1 && (byte & 0x40))) {
+      more = false;
+    } else {
+      byte |= 0x80;
+    }
+    p[count++] = byte;
+  }
+  return count;
+}
+
 class PosixX64CodeCache : public X64CodeCache {
  public:
   PosixX64CodeCache();
@@ -24,26 +87,240 @@ class PosixX64CodeCache : public X64CodeCache {
   void* LookupUnwindInfo(uint64_t host_pc) override { return nullptr; }
 
  private:
-  /*
   UnwindReservation RequestUnwindReservation(uint8_t* entry_address) override;
-  void PlaceCode(uint32_t guest_address, void* machine_code, size_t code_size,
-                 size_t stack_size, void* code_execute_address,
+  void PlaceCode(uint32_t guest_address, void* machine_code,
+                 const EmitFunctionInfo& func_info, void* code_execute_address,
                  UnwindReservation unwind_reservation) override;
 
   void InitializeUnwindEntry(uint8_t* unwind_entry_address,
-                             size_t unwind_table_slot, void* code_address,
-                             size_t code_size, size_t stack_size);
-  */
+                             void* code_execute_address,
+                             const EmitFunctionInfo& func_info);
+
+  // Pointers registered with __register_frame, for cleanup.
+  std::vector<void*> registered_frames_;
+  // Current number of unwind table entries.
+  uint32_t unwind_table_count_ = 0;
 };
 
 std::unique_ptr<X64CodeCache> X64CodeCache::Create() {
   return std::make_unique<PosixX64CodeCache>();
 }
 
 PosixX64CodeCache::PosixX64CodeCache() = default;
-PosixX64CodeCache::~PosixX64CodeCache() = default;
 
-bool PosixX64CodeCache::Initialize() { return X64CodeCache::Initialize(); }
+PosixX64CodeCache::~PosixX64CodeCache() {
+  for (auto frame : registered_frames_) {
+    __deregister_frame(frame);
+  }
+}
+
+bool PosixX64CodeCache::Initialize() {
+  if (!X64CodeCache::Initialize()) {
+    return false;
+  }
+  registered_frames_.reserve(kMaximumFunctionCount);
+  return true;
+}
+
+X64CodeCache::UnwindReservation PosixX64CodeCache::RequestUnwindReservation(
+    uint8_t* entry_address) {
+#if defined(NDEBUG)
+  if (unwind_table_count_ >= kMaximumFunctionCount) {
+    xe::FatalError(
+        "Unwind table count exceeded maximum! Please report this to "
+        "Xenia developers");
+  }
+#else
+  assert_false(unwind_table_count_ >= kMaximumFunctionCount);
+#endif
+  UnwindReservation unwind_reservation;
+  unwind_reservation.data_size = xe::round_up(kMaxUnwindInfoSize, 16);
+  unwind_reservation.table_slot = unwind_table_count_++;
+  unwind_reservation.entry_address = entry_address;
+  return unwind_reservation;
+}
+
+void PosixX64CodeCache::PlaceCode(uint32_t guest_address, void* machine_code,
+                                  const EmitFunctionInfo& func_info,
+                                  void* code_execute_address,
+                                  UnwindReservation unwind_reservation) {
+  // Write the DWARF .eh_frame data into the reserved unwind space.
+  InitializeUnwindEntry(unwind_reservation.entry_address, code_execute_address,
+                        func_info);
+
+  // Register with the runtime unwinder using the execute-side address.
+  // The execute mapping is readable (kExecuteReadOnly = PROT_EXEC|PROT_READ),
+  // so the unwinder can read the .eh_frame data at runtime.
+  void* unwind_execute_address = unwind_reservation.entry_address -
+                                 generated_code_write_base_ +
+                                 generated_code_execute_base_;
+  __register_frame(unwind_execute_address);
+  registered_frames_.push_back(unwind_execute_address);
+}
+
+void PosixX64CodeCache::InitializeUnwindEntry(
+    uint8_t* unwind_entry_address, void* code_execute_address,
+    const EmitFunctionInfo& func_info) {
+  // Compute execute-side base address of the unwind buffer.
+  // We write via the write mapping but pc-relative offsets must be relative
+  // to the execute mapping (which is what __register_frame sees).
+  uint8_t* unwind_execute_base = unwind_entry_address -
+                                 generated_code_write_base_ +
+                                 generated_code_execute_base_;
+
+  uint8_t* p = unwind_entry_address;
+  uint8_t* cie_start = p;
+
+  // === CIE (Common Information Entry) ===
+  uint8_t* cie_length_ptr = p;
+  p += 4;  // placeholder for length
+
+  uint8_t* cie_content_start = p;
+
+  // CIE ID = 0 (distinguishes CIE from FDE in .eh_frame format).
+  *reinterpret_cast<uint32_t*>(p) = 0;
+  p += 4;
+
+  // Version = 1.
+  *p++ = 1;
+
+  // Augmentation string "zR" - indicates augmentation data with FDE encoding.
+  *p++ = 'z';
+  *p++ = 'R';
+  *p++ = '\0';
+
+  // Code alignment factor = 1.
+  p += WriteULEB128(p, 1);
+
+  // Data alignment factor = -8.
+  p += WriteSLEB128(p, -8);
+
+  // Return address register column = 16 (x86-64 RA).
+  p += WriteULEB128(p, kDwarfRegRA);
+
+  // Augmentation data length = 1 (just the FDE encoding byte).
+  p += WriteULEB128(p, 1);
+
+  // FDE pointer encoding: pc-relative, signed 32-bit.
+  *p++ = kDW_EH_PE_pcrel | kDW_EH_PE_sdata4;
+
+  // Initial instructions:
+  // DW_CFA_def_cfa RSP, 8 — at function entry, CFA = RSP + 8.
+  *p++ = kDW_CFA_def_cfa;
+  p += WriteULEB128(p, kDwarfRegRSP);
+  p += WriteULEB128(p, 8);
+
+  // DW_CFA_offset RA, 1 — return address at CFA - 8 (factored: 1 * 8).
+  *p++ = 0x80 | kDwarfRegRA;
+  p += WriteULEB128(p, 1);
+
+  // Pad CIE to pointer-size (8-byte) alignment.
+  size_t cie_content_len = static_cast<size_t>(p - cie_content_start);
+  size_t cie_padded_len = xe::round_up(cie_content_len, sizeof(void*));
+  while (p < cie_content_start + cie_padded_len) {
+    *p++ = kDW_CFA_nop;
+  }
+
+  // Write CIE length (excludes the length field itself).
+  *reinterpret_cast<uint32_t*>(cie_length_ptr) =
+      static_cast<uint32_t>(p - cie_content_start);
+
+  // === FDE (Frame Description Entry) ===
+  uint8_t* fde_length_ptr = p;
+  p += 4;  // placeholder for length
+
+  uint8_t* fde_content_start = p;
+
+  // CIE pointer: offset from this field back to the start of the CIE.
+  *reinterpret_cast<uint32_t*>(p) = static_cast<uint32_t>(p - cie_start);
+  p += 4;
+
+  // PC begin: pc-relative offset to the start of the function code.
+  // Computed relative to the execute-side address of this field.
+  uint8_t* pc_begin_execute_addr =
+      unwind_execute_base + (p - unwind_entry_address);
+  *reinterpret_cast<int32_t*>(p) =
+      static_cast<int32_t>(reinterpret_cast<intptr_t>(code_execute_address) -
+                           reinterpret_cast<intptr_t>(pc_begin_execute_addr));
+  p += 4;
+
+  // PC range: size of the function code.
+  *reinterpret_cast<uint32_t*>(p) =
+      static_cast<uint32_t>(func_info.code_size.total);
+  p += 4;
+
+  // Augmentation data length = 0 (no LSDA pointer).
+  p += WriteULEB128(p, 0);
+
+  // FDE instructions: describe how the stack frame changes during the prolog.
+  if (func_info.stack_size > 0) {
+    // Advance location to the instruction after the stack allocation.
+    size_t alloc_offset = func_info.prolog_stack_alloc_offset;
+    assert_true(alloc_offset > 0);
+    if (alloc_offset < 64) {
+      *p++ = 0x40 | static_cast<uint8_t>(alloc_offset);
+    } else if (alloc_offset < 256) {
+      *p++ = kDW_CFA_advance_loc1;
+      *p++ = static_cast<uint8_t>(alloc_offset);
+    } else {
+      *p++ = kDW_CFA_advance_loc2;
+      *reinterpret_cast<uint16_t*>(p) = static_cast<uint16_t>(alloc_offset);
+      p += 2;
+    }
+
+    // DW_CFA_def_cfa_offset: CFA = RSP + 8 + stack_size after stack alloc.
+    *p++ = kDW_CFA_def_cfa_offset;
+    p += WriteULEB128(p, 8 + func_info.stack_size);
+
+    // For thunk functions, encode callee-saved register save locations.
+    // The thunk saves non-volatile registers at known offsets from RSP.
+    if (func_info.stack_size == StackLayout::THUNK_STACK_SIZE) {
+      size_t cfa = 8 + func_info.stack_size;  // 272
+
+      // RBX at rsp+0x18 → CFA-248, factored offset = 31
+      *p++ = 0x80 | kDwarfRegRBX;
+      p += WriteULEB128(p, (cfa - 0x18) / 8);
+
+      // RBP at rsp+0x20 → CFA-240, factored offset = 30
+      *p++ = 0x80 | kDwarfRegRBP;
+      p += WriteULEB128(p, (cfa - 0x20) / 8);
+
+      // R12 at rsp+0x40 → CFA-208, factored offset = 26
+      *p++ = 0x80 | kDwarfRegR12;
+      p += WriteULEB128(p, (cfa - 0x40) / 8);
+
+      // R13 at rsp+0x48 → CFA-200, factored offset = 25
+      *p++ = 0x80 | kDwarfRegR13;
+      p += WriteULEB128(p, (cfa - 0x48) / 8);
+
+      // R14 at rsp+0x50 → CFA-192, factored offset = 24
+      *p++ = 0x80 | kDwarfRegR14;
+      p += WriteULEB128(p, (cfa - 0x50) / 8);
+
+      // R15 at rsp+0x58 → CFA-184, factored offset = 23
+      *p++ = 0x80 | kDwarfRegR15;
+      p += WriteULEB128(p, (cfa - 0x58) / 8);
+    }
+  }
+
+  // Pad FDE to pointer-size (8-byte) alignment.
+  size_t fde_content_len = static_cast<size_t>(p - fde_content_start);
+  size_t fde_padded_len = xe::round_up(fde_content_len, sizeof(void*));
+  while (p < fde_content_start + fde_padded_len) {
+    *p++ = kDW_CFA_nop;
+  }
+
+  // Write FDE length.
+  *reinterpret_cast<uint32_t*>(fde_length_ptr) =
+      static_cast<uint32_t>(p - fde_content_start);
+
+  // === Terminator (zero-length entry) ===
+  *reinterpret_cast<uint32_t*>(p) = 0;
+  p += 4;
+
+  assert_true(static_cast<size_t>(p - unwind_entry_address) <=
+              kMaxUnwindInfoSize);
+}
 
 }  // namespace x64
 }  // namespace backend