gdb/

Recognize virtual tail call frames.
	* Makefile.in (SFILES): Add dwarf2-frame-tailcall.c.
	(HFILES_NO_SRCDIR): Add dwarf2-frame-tailcall.h.
	(COMMON_OBS): Add dwarf2-frame-tailcall.o.
	* dwarf2-frame-tailcall.c: New file.
	* dwarf2-frame-tailcall.h: New file.
	* dwarf2-frame.c: Include dwarf2-frame-tailcall.h.
	(execute_cfa_program): New function comment.  Return INSN_PTR.  Reset
	REGS.PREV only after CIE execution.
	(struct dwarf2_frame_cache): New field tailcall_cache.
	(dwarf2_frame_cache): New variables entry_pc, entry_cfa_sp_offset,
	entry_cfa_sp_offset_p and instr.  Execute FDE instructions in two
	parts, try to find entry_cfa_sp_offset.  Call
	dwarf2_tailcall_sniffer_first.
	(dwarf2_frame_prev_register): Call dwarf2_tailcall_prev_register_first
	when appropriate.
	(dwarf2_frame_dealloc_cache): New function.
	(dwarf2_frame_sniffer): Preinitialize cache by dwarf2_frame_cache.
	(dwarf2_frame_unwind): Install dwarf2_frame_dealloc_cache.
	(dwarf2_signal_frame_unwind): Do not install dwarf2_frame_dealloc_cache.
	(dwarf2_append_unwinders): Add dwarf2_tailcall_frame_unwind.
	(dwarf2_frame_cfa): Support also dwarf2_tailcall_frame_unwind.
	* dwarf2loc.c (func_addr_to_tail_call_list)
	(tailcall_dump, call_sitep, VEC (call_sitep), chain_candidate)
	(call_site_find_chain_1, call_site_find_chain): New.
	* dwarf2loc.h (struct call_site_chain): New.
	(call_site_find_chain): New declaration.
	* frame.c (get_frame_address_in_block): Support also TAILCALL_FRAME.
	* frame.h (enum frame_type): New entry TAILCALL_FRAME.
	* python/py-frame.c (gdbpy_initialize_frames): Add TAILCALL_FRAME.
	* stack.c (frame_info): Support also TAILCALL_FRAME.

gdb/doc/
	Recognize virtual tail call frames.
	* gdb.texinfo (Optimized Code): Add reference to Tail Call Frames.
	(Tail Call Frames): New node.
	(Frames In Python): Add gdb.TAILCALL_FRAME.

gdb/testsuite/
	Recognize virtual tail call frames.
	* gdb.arch/amd64-entry-value.cc (c, a, b, amb_z, amb_y, amb_x, amb)
	(amb_b, amb_a): New.
	(main): Call a and b.
	* gdb.arch/amd64-entry-value.exp (tailcall: breakhere, tailcall: bt)
	(tailcall: p i, tailcall: p j, set $sp0=$sp, up, p $sp0 == $sp, frame 3)
	(p $sp0 + sizeof (void *) == $sp, ambiguous: breakhere, ambiguous: bt):
	New tests.

gdb/dwarf2-frame.c

@@ -41,6 +41,7 @@
 #include "ax.h"
 #include "dwarf2loc.h"
 #include "exceptions.h"
+#include "dwarf2-frame-tailcall.h"
 
 struct comp_unit;
 
@@ -399,7 +400,11 @@ Not implemented: computing unwound register using explicit value operator"));
 }
 
 
-static void
+/* Execute FDE program from INSN_PTR possibly up to INSN_END or up to inferior
+   PC.  Modify FS state accordingly.  Return current INSN_PTR where the
+   execution has stopped, one can resume it on the next call.  */
+
+static const gdb_byte *
 execute_cfa_program (struct dwarf2_fde *fde, const gdb_byte *insn_ptr,
 		     const gdb_byte *insn_end, struct gdbarch *gdbarch,
 		     CORE_ADDR pc, struct dwarf2_frame_state *fs)
@@ -682,9 +687,14 @@ bad CFI data; mismatched DW_CFA_restore_state at %s"),
 	}
     }
 
-  /* Don't allow remember/restore between CIE and FDE programs.  */
-  dwarf2_frame_state_free_regs (fs->regs.prev);
-  fs->regs.prev = NULL;
+  if (fs->initial.reg == NULL)
+    {
+      /* Don't allow remember/restore between CIE and FDE programs.  */
+      dwarf2_frame_state_free_regs (fs->regs.prev);
+      fs->regs.prev = NULL;
+    }
+
+  return insn_ptr;
 }
 
 
@@ -976,6 +986,13 @@ struct dwarf2_frame_cache
 
   /* The .text offset.  */
   CORE_ADDR text_offset;
+
+  /* If not NULL then this frame is the bottom frame of a TAILCALL_FRAME
+     sequence.  If NULL then it is a normal case with no TAILCALL_FRAME
+     involved.  Non-bottom frames of a virtual tail call frames chain use
+     dwarf2_tailcall_frame_unwind unwinder so this field does not apply for
+     them.  */
+  void *tailcall_cache;
 };
 
 static struct dwarf2_frame_cache *
@@ -989,6 +1006,10 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   struct dwarf2_frame_state *fs;
   struct dwarf2_fde *fde;
   volatile struct gdb_exception ex;
+  CORE_ADDR entry_pc;
+  LONGEST entry_cfa_sp_offset;
+  int entry_cfa_sp_offset_p = 0;
+  const gdb_byte *instr;
 
   if (*this_cache)
     return *this_cache;
@@ -1040,8 +1061,25 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   fs->initial = fs->regs;
   fs->initial.reg = dwarf2_frame_state_copy_regs (&fs->regs);
 
+  if (get_frame_func_if_available (this_frame, &entry_pc))
+    {
+      /* Decode the insns in the FDE up to the entry PC.  */
+      instr = execute_cfa_program (fde, fde->instructions, fde->end, gdbarch,
+				   entry_pc, fs);
+
+      if (fs->regs.cfa_how == CFA_REG_OFFSET
+	  && (gdbarch_dwarf2_reg_to_regnum (gdbarch, fs->regs.cfa_reg)
+	      == gdbarch_sp_regnum (gdbarch)))
+	{
+	  entry_cfa_sp_offset = fs->regs.cfa_offset;
+	  entry_cfa_sp_offset_p = 1;
+	}
+    }
+  else
+    instr = fde->instructions;
+
   /* Then decode the insns in the FDE up to our target PC.  */
-  execute_cfa_program (fde, fde->instructions, fde->end, gdbarch,
+  execute_cfa_program (fde, instr, fde->end, gdbarch,
 		       get_frame_pc (this_frame), fs);
 
   TRY_CATCH (ex, RETURN_MASK_ERROR)
@@ -1182,6 +1220,12 @@ incomplete CFI data; unspecified registers (e.g., %s) at %s"),
 
   do_cleanups (old_chain);
 
+  /* Try to find a virtual tail call frames chain with bottom (callee) frame
+     starting at THIS_FRAME.  */
+  dwarf2_tailcall_sniffer_first (this_frame, &cache->tailcall_cache,
+				 (entry_cfa_sp_offset_p
+				  ? &entry_cfa_sp_offset : NULL));
+
   return cache;
 }
 
@@ -1227,6 +1271,22 @@ dwarf2_frame_prev_register (struct frame_info *this_frame, void **this_cache,
   CORE_ADDR addr;
   int realnum;
 
+  /* Non-bottom frames of a virtual tail call frames chain use
+     dwarf2_tailcall_frame_unwind unwinder so this code does not apply for
+     them.  If dwarf2_tailcall_prev_register_first does not have specific value
+     unwind the register, tail call frames are assumed to have the register set
+     of the top caller.  */
+  if (cache->tailcall_cache)
+    {
+      struct value *val;
+      
+      val = dwarf2_tailcall_prev_register_first (this_frame,
+						 &cache->tailcall_cache,
+						 regnum);
+      if (val)
+	return val;
+    }
+
   switch (cache->reg[regnum].how)
     {
     case DWARF2_FRAME_REG_UNDEFINED:
@@ -1296,6 +1356,18 @@ dwarf2_frame_prev_register (struct frame_info *this_frame, void **this_cache,
     }
 }
 
+/* Proxy for tailcall_frame_dealloc_cache for bottom frame of a virtual tail
+   call frames chain.  */
+
+static void
+dwarf2_frame_dealloc_cache (struct frame_info *self, void *this_cache)
+{
+  struct dwarf2_frame_cache *cache = dwarf2_frame_cache (self, &this_cache);
+
+  if (cache->tailcall_cache)
+    dwarf2_tailcall_frame_unwind.dealloc_cache (self, cache->tailcall_cache);
+}
+
 static int
 dwarf2_frame_sniffer (const struct frame_unwind *self,
 		      struct frame_info *this_frame, void **this_cache)
@@ -1322,7 +1394,14 @@ dwarf2_frame_sniffer (const struct frame_unwind *self,
 				      this_frame))
     return self->type == SIGTRAMP_FRAME;
 
-  return self->type != SIGTRAMP_FRAME;
+  if (self->type != NORMAL_FRAME)
+    return 0;
+
+  /* Preinitializa the cache so that TAILCALL_FRAME can find the record by
+     dwarf2_tailcall_sniffer_first.  */
+  dwarf2_frame_cache (this_frame, this_cache);
+
+  return 1;
 }
 
 static const struct frame_unwind dwarf2_frame_unwind =
@@ -1332,7 +1411,8 @@ static const struct frame_unwind dwarf2_frame_unwind =
   dwarf2_frame_this_id,
   dwarf2_frame_prev_register,
   NULL,
-  dwarf2_frame_sniffer
+  dwarf2_frame_sniffer,
+  dwarf2_frame_dealloc_cache
 };
 
 static const struct frame_unwind dwarf2_signal_frame_unwind =
@@ -1342,7 +1422,10 @@ static const struct frame_unwind dwarf2_signal_frame_unwind =
   dwarf2_frame_this_id,
   dwarf2_frame_prev_register,
   NULL,
-  dwarf2_frame_sniffer
+  dwarf2_frame_sniffer,
+
+  /* TAILCALL_CACHE can never be in such frame to need dealloc_cache.  */
+  NULL
 };
 
 /* Append the DWARF-2 frame unwinders to GDBARCH's list.  */
@@ -1350,6 +1433,10 @@ static const struct frame_unwind dwarf2_signal_frame_unwind =
 void
 dwarf2_append_unwinders (struct gdbarch *gdbarch)
 {
+  /* TAILCALL_FRAME must be first to find the record by
+     dwarf2_tailcall_sniffer_first.  */
+  frame_unwind_append_unwinder (gdbarch, &dwarf2_tailcall_frame_unwind);
+
   frame_unwind_append_unwinder (gdbarch, &dwarf2_frame_unwind);
   frame_unwind_append_unwinder (gdbarch, &dwarf2_signal_frame_unwind);
 }
@@ -1401,7 +1488,8 @@ dwarf2_frame_cfa (struct frame_info *this_frame)
   /* This restriction could be lifted if other unwinders are known to
      compute the frame base in a way compatible with the DWARF
      unwinder.  */
-  if (! frame_unwinder_is (this_frame, &dwarf2_frame_unwind))
+  if (!frame_unwinder_is (this_frame, &dwarf2_frame_unwind)
+      && !frame_unwinder_is (this_frame, &dwarf2_tailcall_frame_unwind))
     error (_("can't compute CFA for this frame"));
   return get_frame_base (this_frame);
 }