[PATCH v3] Windows x64 SEH unwinder

[Tristan Gingold <gingold at adacore dot com>]

Hello,

after discussion with Roland Schwingel, I have found that the patch
doesn't handle well dwarf3 DW_OP_call_frame_cfa, because the SEH
unwinder is before the dwarf2 one.

So I propose this new patch.  The only change is the position of the
SEH unwinder: it is appended after the dwarf2 one.
As a consequence, old binaries should work too.

I have also added the NEWS chunk.

Ok for the trunk ?

Tristan.

2013-07-08  Tristan Gingold  <gingold@adacore.com>

	* NEWS: Add entry mentioning support for native Windows x64
	SEH data. 

	* amd64-windows-tdep.c: #include "objfiles.h", "frame-unwind.h",
	"coff/internal.h", "coff/i386.h", "coff/pe.h" and "libcoff.h".
	(struct amd64_windows_frame_cache): New struct.
	(amd64_windows_w2gdb_regnum): New global.
	(pc_in_range, amd64_windows_frame_decode_epilogue)
	(amd64_windows_frame_decode_insns, amd64_windows_find_unwind_info)
	(amd64_windows_frame_cache, amd64_windows_frame_prev_register)
	(amd64_windows_frame_this_id): New functions.
	(amd64_windows_frame_unwind): New static global.
	(amd64_windows_skip_prologue): New function.
	(amd64_windows_init_abi): Call frame_unwind_prepend_unwinder
	with amd64_windows_frame_unwind. Call set_gdbarch_skip_prologue
	with amd64_windows_skip_prologue.

diff --git a/gdb/NEWS b/gdb/NEWS
index 6ee82f7..d9588ff 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -134,6 +134,8 @@ qXfer:libraries-svr4:read's annex
 * New 'z' formatter for printing and examining memory, this displays the
   value as hexadecimal zero padded on the left to the size of the type.
 
+* GDB can now use Windows x64 unwinding data.
+
 *** Changes in GDB 7.6
 
 * Target record has been renamed to record-full.
diff --git a/gdb/amd64-windows-tdep.c b/gdb/amd64-windows-tdep.c
index a0fd074..4e750a1 100644
--- a/gdb/amd64-windows-tdep.c
+++ b/gdb/amd64-windows-tdep.c
@@ -25,6 +25,12 @@
 #include "regcache.h"
 #include "windows-tdep.h"
 #include "frame.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[] =
@@ -155,6 +161,752 @@ 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 and end rva.  */
+  CORE_ADDR start_rva;
+  CORE_ADDR end_rva;
+
+  /* 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
+};
+
+/* Return TRUE iff PC is the the range of the function corresponding to
+   CACHE.  */
+
+static int
+pc_in_range (CORE_ADDR pc, const struct amd64_windows_frame_cache *cache)
+{
+  return (pc >= cache->image_base + cache->start_rva
+	  && pc < cache->image_base + cache->end_rva);
+}
+
+/* Try to recognize and decode an epilogue sequence.
+
+   Return -1 if we fail to read the instructions for any reason.
+   Return 1 if an epilogue sequence was recognized, 0 otherwise.  */
+
+static int
+amd64_windows_frame_decode_epilogue (struct frame_info *this_frame,
+				     struct amd64_windows_frame_cache *cache)
+{
+  /* According to MSDN an epilogue "must consist of either an add RSP,constant
+     or lea RSP,constant[FPReg], followed by a series of zero or more 8-byte
+     register pops and a return or a jmp".
+
+     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.w jmp reg            [4X ff eY]
+  */
+
+  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);
+  gdb_byte op;
+  gdb_byte rex;
+
+  /* We don't care about the instruction deallocating the frame:
+     if it hasn't been executed, the pc is still in the body,
+     if it has been executed, the following epilog decoding will work.  */
+
+  /* First decode:
+     -  pop reg                 [41 58-5f] or [58-5f].  */
+
+  while (1)
+    {
+      /* Read opcode. */
+      if (target_read_memory (pc, &op, 1) != 0)
+	return -1;
+
+      if (op >= 0x40 && op <= 0x4f)
+	{
+	  /* REX prefix.  */
+	  rex = op;
+
+	  /* Read opcode. */
+	  if (target_read_memory (pc + 1, &op, 1) != 0)
+	    return -1;
+	}
+      else
+	rex = 0;
+
+      if (op >= 0x58 && op <= 0x5f)
+	{
+	  /* pop reg  */
+	  gdb_byte reg = (op & 0x0f) | ((rex & 1) << 3);
+
+	  cache->prev_reg_addr[amd64_windows_w2gdb_regnum[reg]] = cur_sp;
+	  cur_sp += 8;
+	}
+      else
+	break;
+
+      /* Allow the user to break this loop.  This shouldn't happen as the
+	 number of consecutive pop should be small.  */
+      QUIT;
+    }
+
+  /* Then decode the marker.  */
+
+  /* Read opcode.  */
+  if (target_read_memory (pc, &op, 1) != 0)
+    return -1;
+
+  switch (op)
+    {
+    case 0xc3:
+      /* Ret.  */
+      cache->prev_rip_addr = cur_sp;
+      cache->prev_sp = cur_sp + 8;
+      return 1;
+
+    case 0xeb:
+      {
+	/* jmp rel8  */
+	gdb_byte rel8;
+	CORE_ADDR npc;
+
+	if (target_read_memory (pc + 1, &rel8, 1) != 0)
+	  return -1;
+	npc = pc + 2 + (signed char) rel8;
+
+	/* If the jump is within the function, then this is not a marker,
+	   otherwise this is a tail-call.  */
+	return !pc_in_range (npc, cache);
+      }
+
+    case 0xec:
+      {
+	/* jmp rel32  */
+	gdb_byte rel32[4];
+	CORE_ADDR npc;
+
+	if (target_read_memory (pc + 1, rel32, 4) != 0)
+	  return -1;
+	npc = pc + 5 + extract_signed_integer (rel32, 4, byte_order);
+
+	/* If the jump is within the function, then this is not a marker,
+	   otherwise this is a tail-call.  */
+	return !pc_in_range (npc, cache);
+      }
+
+    case 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;
+      }
+
+    case 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;
+      }
+
+    case 0x40:
+    case 0x41:
+    case 0x42:
+    case 0x43:
+    case 0x44:
+    case 0x45:
+    case 0x46:
+    case 0x47:
+    case 0x48:
+    case 0x49:
+    case 0x4a:
+    case 0x4b:
+    case 0x4c:
+    case 0x4d:
+    case 0x4e:
+    case 0x4f:
+      /* Got a REX prefix, read next byte.  */
+      rex = op;
+      if (target_read_memory (pc + 1, &op, 1) != 0)
+	return -1;
+
+      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;
+	  return (op1 & 0xf8) == 0xe0;
+	}
+      else
+	return 0;
+
+    default:
+      /* Not REX, so unknown.  */
+      return 0;
+    }
+}
+
+/* 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 (frame_debug)
+	fprintf_unfiltered
+	  (gdb_stdlog,
+	   "amd64_windows_frame_decodes_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_rva + ex_ui.SizeOfPrologue))
+	{
+	  /* Not in the prologue.  We want to detect if the PC points to an
+	     epilogue. If so, the epilogue detection+decoding function is
+	     sufficient.  Otherwise, the unwinder will consider that the PC
+	     is in the body of the function and will need to decode unwind
+	     info.  */
+	  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 (frame_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 (frame_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_rva + 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
+		    - 16 * 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
+		    - 16 * 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_rva =
+	    extract_unsigned_integer (d.rva_BeginAddress, 4, byte_order);
+	  cache->end_rva =
+	    extract_unsigned_integer (d.rva_EndAddress, 4, byte_order);
+	  unwind_info =
+	    extract_unsigned_integer (d.rva_UnwindData, 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 (frame_debug)
+    fprintf_unfiltered (gdb_stdlog, "   prev_sp: %s, prev_pc @%s\n",
+			paddress (gdbarch, cache->prev_sp),
+			paddress (gdbarch, cache->prev_rip_addr));
+}
+
+/* Find SEH unwind info for PC, returning 0 on success.
+
+   UNWIND_INFO is set to the rva of unwind info address, IMAGE_BASE
+   to the base address of the corresponding image, and START_RVA
+   to the rva of the function containing PC.  */
+
+static int
+amd64_windows_find_unwind_info (struct gdbarch *gdbarch, CORE_ADDR pc,
+				CORE_ADDR *unwind_info,
+				CORE_ADDR *image_base,
+				CORE_ADDR *start_rva,
+				CORE_ADDR *end_rva)
+{
+  struct obj_section *sec;
+  pe_data_type *pe;
+  IMAGE_DATA_DIRECTORY *dir;
+  struct objfile *objfile;
+  unsigned long lo, hi;
+  CORE_ADDR base;
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+
+  /* Get the corresponding exception directory.  */
+  sec = find_pc_section (pc);
+  if (sec == NULL)
+    return -1;
+  objfile = sec->objfile;
+  pe = pe_data (sec->objfile->obfd);
+  dir = &pe->pe_opthdr.DataDirectory[PE_EXCEPTION_TABLE];
+
+  base = pe->pe_opthdr.ImageBase
+    + ANOFFSET (objfile->section_offsets, SECT_OFF_TEXT (objfile));
+  *image_base = base;
+
+  /* Find the entry.
+
+     Note: This does not handle dynamically added entries (for JIT
+     engines).  For this, we would need to ask the kernel directly,
+     which means getting some info from the native layer.  For the
+     rest of the code, however, it's probably faster to search
+     the entry ourselves.  */
+  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 (base + dir->VirtualAddress + mid * sizeof (d),
+			      (gdb_byte *) &d, sizeof (d)) != 0)
+	return -1;
+
+      sa = extract_unsigned_integer (d.rva_BeginAddress, 4, byte_order);
+      ea = extract_unsigned_integer (d.rva_EndAddress, 4, byte_order);
+      if (pc < base + sa)
+	hi = mid - 1;
+      else if (pc >= base + ea)
+	lo = mid + 1;
+      else if (pc >= base + sa && pc < base + ea)
+	{
+	  /* Got it.  */
+	  *start_rva = sa;
+	  *end_rva = ea;
+	  *unwind_info =
+	    extract_unsigned_integer (d.rva_UnwindData, 4, byte_order);
+	  break;
+	}
+      else
+	break;
+    }
+
+  if (frame_debug)
+    fprintf_unfiltered
+      (gdb_stdlog,
+       "amd64_windows_find_unwind_data:  image_base=%s, unwind_data=%s\n",
+       paddress (gdbarch, base), paddress (gdbarch, *unwind_info));
+
+  if (*unwind_info & 1)
+    {
+      /* Unofficially documented unwind info redirection, when UNWIND_INFO
+	 address is odd (http://www.codemachine.com/article_x64deepdive.html).
+      */
+      struct external_pex64_runtime_function d;
+      CORE_ADDR sa, ea;
+
+      if (target_read_memory (base + (*unwind_info & ~1),
+			      (gdb_byte *) &d, sizeof (d)) != 0)
+	return -1;
+
+      *start_rva =
+	extract_unsigned_integer (d.rva_BeginAddress, 4, byte_order);
+      *end_rva = extract_unsigned_integer (d.rva_EndAddress, 4, byte_order);
+      *unwind_info =
+	extract_unsigned_integer (d.rva_UnwindData, 4, byte_order);
+
+    }
+  return 0;
+}
+
+/* Fill THIS_CACHE using the native amd64-windows 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;
+  gdb_byte 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 = 0;
+
+  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;
+
+  if (amd64_windows_find_unwind_info (gdbarch, pc, &unwind_info,
+				      &cache->image_base,
+				      &cache->start_rva,
+				      &cache->end_rva))
+    return cache;
+
+  if (unwind_info == 0)
+    {
+      /* Assume a leaf function.  */
+      cache->prev_sp = cache->sp + 8;
+      cache->prev_rip_addr = cache->sp;
+    }
+  else
+    {
+      /* Decode unwind insns to compute saved addresses.  */
+      amd64_windows_frame_decode_insns (this_frame, cache, unwind_info);
+    }
+  return cache;
+}
+
+/* Implement the "prev_register" method of struct frame_unwind
+   using the standard Windows x64 SEH info.  */
+
+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 (frame_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 && frame_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);
+    }
+}
+
+/* Implement the "this_id" method of struct frame_unwind using
+   the standard Windows x64 SEH info.  */
+
+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_rva);
+}
+
+/* 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
+};
+
+/* Implement the "skip_prologue" gdbarch method.  */
+
+static CORE_ADDR
+amd64_windows_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
+{
+  CORE_ADDR func_addr;
+  CORE_ADDR unwind_info = 0;
+  CORE_ADDR image_base, start_rva, end_rva;
+  struct external_pex64_unwind_info ex_ui;
+
+  /* Use prologue size from unwind info.  */
+  if (amd64_windows_find_unwind_info (gdbarch, pc, &unwind_info,
+				      &image_base, &start_rva, &end_rva) == 0)
+    {
+      if (unwind_info == 0)
+	{
+	  /* Leaf function.  */
+	  return pc;
+	}
+      else if (target_read_memory (image_base + unwind_info,
+				   (gdb_byte *) &ex_ui, sizeof (ex_ui)) == 0
+	       && PEX64_UWI_VERSION (ex_ui.Version_Flags) == 1)
+	return max (pc, image_base + start_rva + ex_ui.SizeOfPrologue);
+    }
+
+  /* See if we can determine the end of the prologue via the symbol
+     table.  If so, then return either the PC, or the PC after
+     the prologue, whichever is greater.  */
+  if (find_pc_partial_function (pc, NULL, &func_addr, NULL))
+    {
+      CORE_ADDR post_prologue_pc
+	= skip_prologue_using_sal (gdbarch, func_addr);
+
+      if (post_prologue_pc != 0)
+	return max (pc, post_prologue_pc);
+    }
+
+  return pc;
+}
+
 /* Check Win64 DLL jmp trampolines and find jump destination.  */
 
 static CORE_ADDR
@@ -205,6 +957,19 @@ amd64_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 
+  /* The dwarf2 unwinder (appended very early by i386_gdbarch_init) is
+     preferred over the SEH one.  The reasons are:
+     - binaries without SEH but with dwarf2 debug info are correcly handled
+       (although they aren't ABI compliant, gcc before 4.7 didn't emit SEH
+       info).
+     - dwarf3 DW_OP_call_frame_cfa is correctly handled (it can only be
+       handled if the dwarf2 unwinder is used).
+
+    The call to amd64_init_abi appends default unwinders, that aren't
+    compatible with the SEH one.
+  */
+  frame_unwind_append_unwinder (gdbarch, &amd64_windows_frame_unwind);
+
   amd64_init_abi (info, gdbarch);
 
   /* On Windows, "long"s are only 32bit.  */
@@ -225,6 +990,8 @@ amd64_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
   set_gdbarch_iterate_over_objfiles_in_search_order
     (gdbarch, windows_iterate_over_objfiles_in_search_order);
 
+  set_gdbarch_skip_prologue (gdbarch, amd64_windows_skip_prologue);
+
   set_gdbarch_auto_wide_charset (gdbarch, amd64_windows_auto_wide_charset);
 
   set_solib_ops (gdbarch, &solib_target_so_ops);
@@ -239,4 +1006,3 @@ _initialize_amd64_windows_tdep (void)
   gdbarch_register_osabi (bfd_arch_i386, bfd_mach_x86_64, GDB_OSABI_CYGWIN,
                           amd64_windows_init_abi);
 }
-