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Re: [RFA] Add Windows x64 SEH unwinder


On Jun 16, 2012, at 12:39 PM, Mark Kettenis wrote:

>> From: Tristan Gingold <gingold@adacore.com>
>> Date: Fri, 15 Jun 2012 10:09:56 +0200
>> 
>> Hi,
>> 
>> the Windows x64 ABI specifies unwind data info in order to unwind
>> frames for propagating exceptions or getting back traces.  GCC emits
>> this infos since version 4.7
>> 
>> This patch adds an unwinder that reads these data.  The main
>> advantage is that gdb is now able to unwind through code compiled
>> with other compilers (and through system libraries).
>> 
>> I haven't run the gdb testsuite on Windows x64 (I don't know if this
>> is doable), but I have manually tested it on a few executables,
>> including gdb itself.
>> 
>> Comments are welcome.
> 
> The amd64 codebase consistently uses the amd64_-prefix for structures,
> variables and functions.  If this is effectively *the* unwinder for
> 64-bit windows, I'd recommend "amd64_windows_".  If you expect more
> Windows-specfic unwinders (or think amd64_windows_ is too long)
> "amd64_seh_" might be a good alternative.

Thanks for the comments.  Here is the new version.

Tristan.

2012-06-15  Tristan Gingold  <gingold@adacore.com>

	* amd64-windows-tdep.c (struct x64_frame_cache): Declare.
	(x64_w2gdb_regnum): New array.
	(x64_frame_decode_epilogue,	x64_frame_decode_insns)
	(x64_frame_cache, x64_frame_prev_register, x64_frame_this_id): New
	functions.
	(x64_frame_unwind): New variable.
	(amd64_windows_init_abi): Register this unwinder.
	* NEWS: Mention it.



diff --git a/gdb/NEWS b/gdb/NEWS
index 2384489..34903a2 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -117,6 +117,8 @@
 * GDB can now support 'breakpoint always-inserted mode' in 'record'
   target.
 
+* GDB can now use Windows x64 unwinding data.
+
 * MI changes
 
   ** New command -info-os is the MI equivalent of "info os".
diff --git a/gdb/amd64-windows-tdep.c b/gdb/amd64-windows-tdep.c
index 4a40f47..a16cf42 100644
--- a/gdb/amd64-windows-tdep.c
+++ b/gdb/amd64-windows-tdep.c
@@ -23,6 +23,12 @@
 #include "gdbtypes.h"
 #include "gdbcore.h"
 #include "regcache.h"
+#include "objfiles.h"
+#include "frame-unwind.h"
+#include "coff/internal.h"
+#include "coff/i386.h"
+#include "coff/pe.h"
+#include "libcoff.h"
 
 /* The registers used to pass integer arguments during a function call.  */
 static int amd64_windows_dummy_call_integer_regs[] =
@@ -153,6 +159,620 @@ amd64_skip_main_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
   return pc;
 }
 
+struct amd64_windows_frame_cache
+{
+  /* ImageBase for the module.  */
+  CORE_ADDR image_base;
+
+  /* Function start rva.  */
+  CORE_ADDR start_address;
+
+  /* Next instruction to be executed.  */
+  CORE_ADDR pc;
+
+  /* Current sp.  */
+  CORE_ADDR sp;
+
+  /* Address of saved integer and xmm registers.  */
+  CORE_ADDR prev_reg_addr[16];
+  CORE_ADDR prev_xmm_addr[16];
+
+  /* These two next fields are set only for machine info frames.  */
+
+  /* Likewise for RIP.  */
+  CORE_ADDR prev_rip_addr;
+
+  /* Likewise for RSP.  */
+  CORE_ADDR prev_rsp_addr;
+
+  /* Address of the previous frame.  */
+  CORE_ADDR prev_sp;
+};
+
+/* Convert a Windows register number to gdb.  */
+static const enum amd64_regnum amd64_windows_w2gdb_regnum[] =
+{
+  AMD64_RAX_REGNUM,
+  AMD64_RCX_REGNUM,
+  AMD64_RDX_REGNUM,
+  AMD64_RBX_REGNUM,
+  AMD64_RSP_REGNUM,
+  AMD64_RBP_REGNUM,
+  AMD64_RSI_REGNUM,
+  AMD64_RDI_REGNUM,
+  AMD64_R8_REGNUM,
+  AMD64_R9_REGNUM,
+  AMD64_R10_REGNUM,
+  AMD64_R11_REGNUM,
+  AMD64_R12_REGNUM,
+  AMD64_R13_REGNUM,
+  AMD64_R14_REGNUM,
+  AMD64_R15_REGNUM
+};
+
+/* Try to recognize and decode an epilogue sequence.  */
+
+static int
+amd64_windows_frame_decode_epilogue (struct frame_info *this_frame,
+				     struct amd64_windows_frame_cache *cache)
+{
+  /* Not in a prologue, so maybe in an epilogue.  For the rules, cf
+     http://msdn.microsoft.com/en-us/library/tawsa7cb.aspx
+     Furthermore, according to RtlVirtualUnwind, the complete list of
+     epilog marker is:
+     - ret                      [c3]
+     - ret n                    [c2 imm16]
+     - rep ret                  [f3 c3]
+     - jmp imm8 | imm32         [eb rel8] or [e9 rel32]
+     - jmp qword ptr imm32                 - not handled
+     - rex jmp reg              [4X ff eY]
+     I would add:
+     -  pop reg                 [41 58-5f] or [58-5f]
+
+     We don't care about the instruction that deallocate the frame:
+     if it hasn't been executed, we can safely decode the insns,
+     if it has been executed, the following epilog decoding will
+     work.  */
+  CORE_ADDR pc = cache->pc;
+  CORE_ADDR cur_sp = cache->sp;
+  struct gdbarch *gdbarch = get_frame_arch (this_frame);
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+
+  while (1)
+    {
+      gdb_byte op;
+      gdb_byte rex;
+
+      if (target_read_memory (pc, &op, 1) != 0)
+	return -1;
+
+      if (op == 0xc3)
+	{
+	  /* Ret.  */
+	  cache->prev_rip_addr = cur_sp;
+	  cache->prev_sp = cur_sp + 8;
+	  return 1;
+	}
+      else if (op == 0xeb)
+	{
+	  /* jmp rel8  */
+	  gdb_byte rel8;
+
+	  if (target_read_memory (pc + 1, &rel8, 1) != 0)
+	    return -1;
+	  pc = pc + 2 + (signed char)rel8;
+	}
+      else if (op == 0xec)
+	{
+	  /* jmp rel32  */
+	  gdb_byte rel32[4];
+
+	  if (target_read_memory (pc + 1, rel32, 4) != 0)
+	    return -1;
+	  pc = pc + 5 + extract_signed_integer (rel32, 4, byte_order);
+	}
+      else if (op >= 0x58 && op <= 0x5f)
+	{
+	  /* pop reg  */
+	  cache->prev_reg_addr[amd64_windows_w2gdb_regnum[op & 0x0f]] = cur_sp;
+	  cur_sp += 8;
+	}
+      else if (op == 0xc2)
+	{
+	  /* ret n  */
+	  gdb_byte imm16[2];
+
+	  if (target_read_memory (pc + 1, imm16, 2) != 0)
+	    return -1;
+	  cache->prev_rip_addr = cur_sp;
+	  cache->prev_sp = cur_sp
+	    + extract_unsigned_integer (imm16, 4, byte_order);
+	  return 1;
+	}
+      else if (op == 0xf3)
+	{
+	  /* rep; ret  */
+	  gdb_byte op1;
+
+	  if (target_read_memory (pc + 2, &op1, 1) != 0)
+	    return -1;
+	  if (op1 != 0xc3)
+	    return 0;
+
+	  cache->prev_rip_addr = cur_sp;
+	  cache->prev_sp = cur_sp + 8;
+	  return 1;
+	}
+      else if (op < 0x40 || op > 0x4f)
+	{
+	  /* Not REX, so unknown.  */
+	  return 0;
+	}
+
+      /* Got a REX prefix, read next byte.  */
+      rex = op;
+      if (target_read_memory (pc + 1, &op, 1) != 0)
+	return -1;
+
+      if (op >= 0x58 && op <= 0x5f)
+	{
+	  /* pop reg  */
+	  unsigned int reg;
+
+	  reg = (op & 0x0f) | ((rex & 1) << 3);
+	  cache->prev_reg_addr[amd64_windows_w2gdb_regnum[reg]] = cur_sp;
+	  cur_sp += 8;
+	}
+      else if (op == 0xff)
+	{
+	  /* rex jmp reg  */
+	  gdb_byte op1;
+	  unsigned int reg;
+	  gdb_byte buf[8];
+
+	  if (target_read_memory (pc + 2, &op1, 1) != 0)
+	    return -1;
+	  if ((op1 & 0xf8) != 0xe0)
+	    return 0;
+	  reg = (op1 & 0x0f) | ((rex & 1) << 3);
+
+	  get_frame_register (this_frame,
+			      amd64_windows_w2gdb_regnum[reg], buf);
+	  pc = extract_unsigned_integer (buf, 8, byte_order);
+	}
+      else
+	return 0;
+
+      /* Allow the user to break this loop.  */
+      QUIT;
+    }
+}
+
+/* Decode and execute unwind insns at UNWIND_INFO.  */
+
+static void
+amd64_windows_frame_decode_insns (struct frame_info *this_frame,
+				  struct amd64_windows_frame_cache *cache,
+				  CORE_ADDR unwind_info)
+{
+  CORE_ADDR save_addr = 0;
+  CORE_ADDR cur_sp = cache->sp;
+  struct gdbarch *gdbarch = get_frame_arch (this_frame);
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  int j;
+
+  for (j = 0; ; j++)
+    {
+      struct external_pex64_unwind_info ex_ui;
+      /* There are at most 256 16-bit unwind insns.  */
+      gdb_byte insns[2 * 256];
+      gdb_byte *p;
+      gdb_byte *end_insns;
+      unsigned char codes_count;
+      unsigned char frame_reg;
+      unsigned char frame_off;
+
+      /* Read and decode header.  */
+      if (target_read_memory (cache->image_base + unwind_info,
+			      (gdb_byte *) &ex_ui, sizeof (ex_ui)) != 0)
+	return;
+
+      if (unwind_debug)
+	fprintf_unfiltered
+	  (gdb_stdlog,
+	   "amd64_windows_frame_play_insn: "
+	   "%s: ver: %02x, plgsz: %02x, cnt: %02x, frame: %02x\n",
+	   paddress (gdbarch, unwind_info),
+	   ex_ui.Version_Flags, ex_ui.SizeOfPrologue,
+	   ex_ui.CountOfCodes, ex_ui.FrameRegisterOffset);
+
+      /* Check version.  */
+      if (PEX64_UWI_VERSION (ex_ui.Version_Flags) != 1)
+	return;
+
+      if (j == 0
+	  && (cache->pc >=
+	      cache->image_base + cache->start_address + ex_ui.SizeOfPrologue))
+	{
+	  /* Not in the prologue; try to decode an epilog.  */
+	  if (amd64_windows_frame_decode_epilogue (this_frame, cache) == 1)
+	    return;
+
+	  /* Not in an epilog.  Clear possible side effects.  */
+	  memset (cache->prev_reg_addr, 0, sizeof (cache->prev_reg_addr));
+	}
+
+      codes_count = ex_ui.CountOfCodes;
+      frame_reg = PEX64_UWI_FRAMEREG (ex_ui.FrameRegisterOffset);
+
+      if (frame_reg != 0)
+	{
+	  /* According to msdn:
+	     If an FP reg is used, then any unwind code taking an offset must
+	     only be used after the FP reg is established in the prolog.  */
+	  gdb_byte buf[8];
+	  int frreg = amd64_windows_w2gdb_regnum[frame_reg];
+
+	  get_frame_register (this_frame, frreg, buf);
+	  save_addr = extract_unsigned_integer (buf, 8, byte_order);
+
+	  if (unwind_debug)
+	    fprintf_unfiltered (gdb_stdlog, "   frame_reg=%s, val=%s\n",
+				gdbarch_register_name (gdbarch, frreg),
+				paddress (gdbarch, save_addr));
+	}
+
+      /* Read opcodes.  */
+      if (codes_count != 0
+	  && target_read_memory (cache->image_base + unwind_info
+				 + sizeof (ex_ui),
+				 insns, codes_count * 2) != 0)
+	return;
+
+      end_insns = &insns[codes_count * 2];
+      for (p = insns; p < end_insns; p += 2)
+	{
+	  int reg;
+
+	  if (unwind_debug)
+	    fprintf_unfiltered
+	      (gdb_stdlog, "   op #%u: off=0x%02x, insn=0x%02x\n",
+	       (unsigned) (p - insns), p[0], p[1]);
+
+	  /* Virtually execute the operation.  */
+	  if (cache->pc >= cache->image_base + cache->start_address + p[0])
+	    {
+	      /* If there is no frame registers defined, the current value of
+		 rsp is used instead.  */
+	      if (frame_reg == 0)
+		save_addr = cur_sp;
+
+	      switch (PEX64_UNWCODE_CODE (p[1]))
+		{
+		case UWOP_PUSH_NONVOL:
+		  /* Push pre-decrements RSP.  */
+		  reg = amd64_windows_w2gdb_regnum[PEX64_UNWCODE_INFO (p[1])];
+		  cache->prev_reg_addr[reg] = cur_sp;
+		  cur_sp += 8;
+		  break;
+		case UWOP_ALLOC_LARGE:
+		  if (PEX64_UNWCODE_INFO (p[1]) == 0)
+		    cur_sp +=
+		      8 * extract_unsigned_integer (p + 2, 2, byte_order);
+		  else if (PEX64_UNWCODE_INFO (p[1]) == 1)
+		    cur_sp += extract_unsigned_integer (p + 2, 4, byte_order);
+		  else
+		    return;
+		  break;
+		case UWOP_ALLOC_SMALL:
+		  cur_sp += 8 + 8 * PEX64_UNWCODE_INFO (p[1]);
+		  break;
+		case UWOP_SET_FPREG:
+		  cur_sp = save_addr
+		    - PEX64_UWI_FRAMEOFF (ex_ui.FrameRegisterOffset) * 16;
+		  break;
+		case UWOP_SAVE_NONVOL:
+		  reg = amd64_windows_w2gdb_regnum[PEX64_UNWCODE_INFO (p[1])];
+		  cache->prev_reg_addr[reg] = save_addr
+		    + 8 * extract_unsigned_integer (p + 2, 2, byte_order);
+		  break;
+		case UWOP_SAVE_NONVOL_FAR:
+		  reg = amd64_windows_w2gdb_regnum[PEX64_UNWCODE_INFO (p[1])];
+		  cache->prev_reg_addr[reg] = save_addr
+		    + 8 * extract_unsigned_integer (p + 2, 4, byte_order);
+		  break;
+		case UWOP_SAVE_XMM128:
+		  cache->prev_xmm_addr[PEX64_UNWCODE_INFO (p[1])] =
+		    save_addr
+		    + 8 * extract_unsigned_integer (p + 2, 2, byte_order);
+		  break;
+		case UWOP_SAVE_XMM128_FAR:
+		  cache->prev_xmm_addr[PEX64_UNWCODE_INFO (p[1])] =
+		    save_addr
+		    + 8 * extract_unsigned_integer (p + 2, 4, byte_order);
+		  break;
+		case UWOP_PUSH_MACHFRAME:
+		  if (PEX64_UNWCODE_INFO (p[1]) == 0)
+		    {
+		      cache->prev_rip_addr = cur_sp + 0;
+		      cache->prev_rsp_addr = cur_sp + 24;
+		      cur_sp += 40;
+		    }
+		  else if (PEX64_UNWCODE_INFO (p[1]) == 1)
+		    {
+		      cache->prev_rip_addr = cur_sp + 8;
+		      cache->prev_rsp_addr = cur_sp + 32;
+		      cur_sp += 48;
+		    }
+		  else
+		    return;
+		  break;
+		default:
+		  return;
+		}
+	    }
+
+	  /* Adjust with the length of the opcode.  */
+	  switch (PEX64_UNWCODE_CODE (p[1]))
+	    {
+	    case UWOP_PUSH_NONVOL:
+	    case UWOP_ALLOC_SMALL:
+	    case UWOP_SET_FPREG:
+	    case UWOP_PUSH_MACHFRAME:
+	      break;
+	    case UWOP_ALLOC_LARGE:
+	      if (PEX64_UNWCODE_INFO (p[1]) == 0)
+		p += 2;
+	      else if (PEX64_UNWCODE_INFO (p[1]) == 1)
+		p += 4;
+	      else
+		return;
+	      break;
+	    case UWOP_SAVE_NONVOL:
+	    case UWOP_SAVE_XMM128:
+	      p += 2;
+	      break;
+	    case UWOP_SAVE_NONVOL_FAR:
+	    case UWOP_SAVE_XMM128_FAR:
+	      p += 4;
+	      break;
+	    default:
+	      return;
+	    }
+	}
+      if (PEX64_UWI_FLAGS (ex_ui.Version_Flags) != UNW_FLAG_CHAININFO)
+	break;
+      else
+	{
+	  /* Read the chained unwind info.  */
+	  struct external_pex64_runtime_function d;
+	  CORE_ADDR chain_vma;
+
+	  chain_vma = cache->image_base + unwind_info
+	    + sizeof (ex_ui) + ((codes_count + 1) & ~1) * 2 + 8;
+
+	  if (target_read_memory (chain_vma, (gdb_byte *) &d, sizeof (d)) != 0)
+	    return;
+
+	  cache->start_address =
+	    extract_unsigned_integer (d.rva_BeginAddress, 4, byte_order);
+	  unwind_info =
+	    extract_unsigned_integer (d.rva_EndAddress, 4, byte_order);
+	}
+
+      /* Allow the user to break this loop.  */
+      QUIT;
+    }
+  /* PC is saved by the call.  */
+  if (cache->prev_rip_addr == 0)
+    cache->prev_rip_addr = cur_sp;
+  cache->prev_sp = cur_sp + 8;
+
+  if (unwind_debug)
+    fprintf_unfiltered (gdb_stdlog, "   prev_sp: %s, prev_pc @%s\n",
+			paddress (gdbarch, cache->prev_sp),
+			paddress (gdbarch, cache->prev_rip_addr));
+}
+
+/* Do all the work: fill THIS_CACHE with unwinding data for THIS_FRAME.  */
+
+static struct amd64_windows_frame_cache *
+amd64_windows_frame_cache (struct frame_info *this_frame, void **this_cache)
+{
+  struct gdbarch *gdbarch = get_frame_arch (this_frame);
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  struct amd64_windows_frame_cache *cache;
+  char buf[8];
+  struct obj_section *sec;
+  pe_data_type *pe;
+  IMAGE_DATA_DIRECTORY *dir;
+  CORE_ADDR image_base;
+  CORE_ADDR pc;
+  struct objfile *objfile;
+  unsigned long lo, hi;
+  CORE_ADDR unwind_info;
+
+  if (*this_cache)
+    return *this_cache;
+
+  cache = FRAME_OBSTACK_ZALLOC (struct amd64_windows_frame_cache);
+  *this_cache = cache;
+
+  /* Get current PC and SP.  */
+  pc = get_frame_pc (this_frame);
+  get_frame_register (this_frame, AMD64_RSP_REGNUM, buf);
+  cache->sp = extract_unsigned_integer (buf, 8, byte_order);
+  cache->pc = pc;
+
+  /* Get the corresponding exception directory.  */
+  sec = find_pc_section (pc);
+  if (unwind_debug)
+    fprintf_unfiltered (gdb_stdlog,
+			"amd64_windows_frame_cache: pc=%s, sp=%s, sec=%p\n",
+			paddress (gdbarch, pc),
+			paddress (gdbarch, cache->sp), sec);
+  if (sec == NULL)
+    return cache;
+  objfile = sec->objfile;
+  pe = pe_data (sec->objfile->obfd);
+  dir = &pe->pe_opthdr.DataDirectory[PE_EXCEPTION_TABLE];
+
+  image_base = pe->pe_opthdr.ImageBase
+    + ANOFFSET (objfile->section_offsets, SECT_OFF_TEXT (objfile));
+  cache->image_base = image_base;
+
+  if (unwind_debug)
+    fprintf_unfiltered (gdb_stdlog,
+			"amd64_windows_frame_cache:  file:%s, image_base=%s\n",
+			objfile->name, paddress (gdbarch, image_base));
+
+  /* Find the entry.
+     Note: it might be a better idea to ask directly to the kernel.  This
+     will handle dynamically added entries (for JIT engines).  */
+  lo = 0;
+  hi = dir->Size / sizeof (struct external_pex64_runtime_function);
+  unwind_info = 0;
+  while (lo <= hi)
+    {
+      unsigned long mid = lo + (hi - lo) / 2;
+      struct external_pex64_runtime_function d;
+      CORE_ADDR sa, ea;
+
+      if (target_read_memory
+	  (image_base + dir->VirtualAddress + mid * sizeof (d),
+	   (char *) &d, sizeof (d)) != 0)
+	return cache;
+
+      sa = extract_unsigned_integer (d.rva_BeginAddress, 4, byte_order);
+      ea = extract_unsigned_integer (d.rva_EndAddress, 4, byte_order);
+      if (pc < image_base + sa)
+	hi = mid - 1;
+      else if (pc >= image_base + ea)
+	lo = mid + 1;
+      else if (pc >= image_base + sa && pc < image_base + ea)
+	{
+	  /* Got it.  */
+	  cache->start_address = sa;
+	  unwind_info =
+	    extract_unsigned_integer (d.rva_UnwindData, 4, byte_order);
+	  break;
+	}
+      else
+	break;
+    }
+
+  if (unwind_debug)
+    fprintf_unfiltered
+      (gdb_stdlog,
+       "amd64_windows_frame_cache:  image_base=%s, unwind_data=%s\n",
+       paddress (gdbarch, cache->image_base), paddress (gdbarch, unwind_info));
+
+  if (unwind_info == 0)
+    {
+      /* Assume a leaf function.  */
+      cache->prev_sp = cache->sp + 8;
+      cache->prev_rip_addr = cache->sp;
+    }
+  else
+    {
+      if (unwind_info & 1)
+	{
+	  /* Unofficially documented unwind info redirection.  */
+	  struct external_pex64_runtime_function d;
+	  CORE_ADDR sa, ea;
+
+	  if (target_read_memory (image_base + (unwind_info & ~1),
+				  (char *) &d, sizeof (d)) != 0)
+	    return cache;
+
+	  cache->start_address =
+	    extract_unsigned_integer (d.rva_BeginAddress, 4, byte_order);
+	  unwind_info =
+	    extract_unsigned_integer (d.rva_EndAddress, 4, byte_order);
+	}
+
+      /* Decode unwind insns to compute saved addresses.  */
+      amd64_windows_frame_decode_insns (this_frame, cache, unwind_info);
+    }
+  return cache;
+}
+
+/* Get the value of register REGNUM before the execution of code for
+   THIS_FRAME, using THIS_CACHE data.  */
+
+static struct value *
+amd64_windows_frame_prev_register (struct frame_info *this_frame,
+				   void **this_cache, int regnum)
+{
+  struct gdbarch *gdbarch = get_frame_arch (this_frame);
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  struct amd64_windows_frame_cache *cache =
+    amd64_windows_frame_cache (this_frame, this_cache);
+  struct value *val;
+  CORE_ADDR prev;
+
+  if (unwind_debug)
+    fprintf_unfiltered (gdb_stdlog,
+			"amd64_windows_frame_prev_register %s for sp=%s\n",
+			gdbarch_register_name (gdbarch, regnum),
+			paddress (gdbarch, cache->prev_sp));
+
+  if (regnum >= AMD64_XMM0_REGNUM && regnum <= AMD64_XMM0_REGNUM + 15)
+      prev = cache->prev_xmm_addr[regnum - AMD64_XMM0_REGNUM];
+  else if (regnum == AMD64_RSP_REGNUM)
+    {
+      prev = cache->prev_rsp_addr;
+      if (prev == 0)
+	return frame_unwind_got_constant (this_frame, regnum, cache->prev_sp);
+    }
+  else if (regnum >= AMD64_RAX_REGNUM && regnum <= AMD64_R15_REGNUM)
+    prev = cache->prev_reg_addr[regnum - AMD64_RAX_REGNUM];
+  else if (regnum == AMD64_RIP_REGNUM)
+    prev = cache->prev_rip_addr;
+  else
+    prev = 0;
+
+  if (prev && unwind_debug)
+    fprintf_unfiltered (gdb_stdlog, "  -> at %s\n", paddress (gdbarch, prev));
+
+  if (prev)
+    {
+      /* Register was saved.  */
+      return frame_unwind_got_memory (this_frame, regnum, prev);
+    }
+  else
+    {
+      /* Register is either volatile or not modified.  */
+      return frame_unwind_got_register (this_frame, regnum, regnum);
+    }
+}
+
+/* Compute and store the frame identifier to THIS_ID for THIS_FRAME using
+   cached data in THIS_CACHE.  */
+
+static void
+amd64_windows_frame_this_id (struct frame_info *this_frame, void **this_cache,
+		   struct frame_id *this_id)
+{
+  struct gdbarch *gdbarch = get_frame_arch (this_frame);
+  struct amd64_windows_frame_cache *cache =
+    amd64_windows_frame_cache (this_frame, this_cache);
+
+  *this_id = frame_id_build (cache->prev_sp,
+				     cache->image_base + cache->start_address);
+}
+
+/* Windows x64 SEH unwinder.  */
+
+static const struct frame_unwind amd64_windows_frame_unwind =
+{
+  NORMAL_FRAME,
+  default_frame_unwind_stop_reason,
+  &amd64_windows_frame_this_id,
+  &amd64_windows_frame_prev_register,
+  NULL,
+  default_frame_sniffer
+};
 
 static void
 amd64_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
@@ -174,6 +794,8 @@ amd64_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
   set_gdbarch_return_value (gdbarch, amd64_windows_return_value);
   set_gdbarch_skip_main_prologue (gdbarch, amd64_skip_main_prologue);
 
+  frame_unwind_prepend_unwinder (gdbarch, &amd64_windows_frame_unwind);
+
   set_solib_ops (gdbarch, &solib_target_so_ops);
 }


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