diff --git a/include/dwarf.h b/include/dwarf.h
index 82d1f9f8..334aaadc 100644
--- a/include/dwarf.h
+++ b/include/dwarf.h
@@ -296,6 +296,7 @@ typedef struct dwarf_cursor
 
     dwarf_loc_t loc[DWARF_NUM_PRESERVED_REGS];
 
+    unsigned int stash_frames :1; /* stash frames for fast lookup */
     unsigned int use_prev_instr :1; /* use previous (= call) or current (= signal) instruction? */
     unsigned int pi_valid :1;	/* is proc_info valid? */
     unsigned int pi_is_dynamic :1; /* proc_info found via dynamic proc info? */
diff --git a/include/libunwind-arm.h b/include/libunwind-arm.h
index 492331e4..5cbfe860 100644
--- a/include/libunwind-arm.h
+++ b/include/libunwind-arm.h
@@ -286,11 +286,21 @@ typedef struct
   }
 unw_tdep_proc_info_t;
 
+typedef struct
+  {
+    /* no arm-specific fast trace */
+  }
+unw_tdep_frame_t;
+
 #include "libunwind-common.h"
 
 #define unw_tdep_is_fpreg		UNW_ARCH_OBJ(is_fpreg)
 extern int unw_tdep_is_fpreg (int);
 
+#define unw_tdep_make_frame_cache(n)	(0)
+#define unw_tdep_free_frame_cache(p)	do {} while(0)
+#define unw_tdep_trace(cur,addr,n,c)	(-UNW_ENOINFO)
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/libunwind-hppa.h b/include/libunwind-hppa.h
index 74ea70da..e28fcaaf 100644
--- a/include/libunwind-hppa.h
+++ b/include/libunwind-hppa.h
@@ -103,6 +103,12 @@ unw_tdep_save_loc_t;
 /* On PA-RISC, we can directly use ucontext_t as the unwind context.  */
 typedef ucontext_t unw_tdep_context_t;
 
+typedef struct
+  {
+    /* no hppa-specific fast trace */
+  }
+unw_tdep_frame_t;
+
 #define unw_tdep_is_fpreg(r)		((unsigned) ((r) - UNW_HPPA_FR) < 32)
 
 #include "libunwind-dynamic.h"
@@ -118,6 +124,10 @@ unw_tdep_proc_info_t;
 #define unw_tdep_getcontext		UNW_ARCH_OBJ (getcontext)
 extern int unw_tdep_getcontext (unw_tdep_context_t *);
 
+#define unw_tdep_make_frame_cache(n)	(0)
+#define unw_tdep_free_frame_cache(p)	do {} while(0)
+#define unw_tdep_trace(cur,addr,n,c)	(-UNW_ENOINFO)
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/libunwind-ia64.h b/include/libunwind-ia64.h
index fb2fbfe5..e4ac85c2 100644
--- a/include/libunwind-ia64.h
+++ b/include/libunwind-ia64.h
@@ -150,6 +150,12 @@ unw_tdep_save_loc_t;
 /* On IA-64, we can directly use ucontext_t as the unwind context.  */
 typedef ucontext_t unw_tdep_context_t;
 
+typedef struct
+  {
+    /* no ia64-specific fast trace */
+  }
+unw_tdep_frame_t;
+
 #define unw_tdep_is_fpreg(r)		((unsigned) ((r) - UNW_IA64_FR) < 128)
 
 #include "libunwind-dynamic.h"
@@ -187,6 +193,10 @@ extern unw_word_t _Uia64_find_dyn_list (unw_addr_space_t, unw_dyn_info_t *,
    signal-safe.  */
 extern int _Uia64_get_kernel_table (unw_dyn_info_t *);
 
+#define unw_tdep_make_frame_cache(n)	(0)
+#define unw_tdep_free_frame_cache(p)	do {} while(0)
+#define unw_tdep_trace(cur,addr,n,c)	(-UNW_ENOINFO)
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/libunwind-mips.h b/include/libunwind-mips.h
index 91f70015..cbaa5dd1 100644
--- a/include/libunwind-mips.h
+++ b/include/libunwind-mips.h
@@ -137,6 +137,12 @@ typedef struct
   }
 unw_tdep_proc_info_t;
 
+typedef struct
+  {
+    /* no mips-specific fast trace */
+  }
+unw_tdep_frame_t;
+
 #include "libunwind-common.h"
 
 /* There is no getcontext() on MIPS.  Use a stub version which only saves GP
@@ -148,6 +154,10 @@ extern int unw_tdep_getcontext (ucontext_t *uc);
 #define unw_tdep_is_fpreg		UNW_ARCH_OBJ(is_fpreg)
 extern int unw_tdep_is_fpreg (int);
 
+#define unw_tdep_make_frame_cache(n)	(0)
+#define unw_tdep_free_frame_cache(p)	do {} while(0)
+#define unw_tdep_trace(cur,addr,n,c)	(-UNW_ENOINFO)
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/libunwind-ppc32.h b/include/libunwind-ppc32.h
index b40a84ef..b22c2793 100644
--- a/include/libunwind-ppc32.h
+++ b/include/libunwind-ppc32.h
@@ -195,11 +195,21 @@ typedef struct
   }
 unw_tdep_proc_info_t;
 
+typedef struct
+  {
+    /* no ppc32-specific fast trace */
+  }
+unw_tdep_frame_t;
+
 #include "libunwind-common.h"
 
 #define unw_tdep_is_fpreg		UNW_ARCH_OBJ(is_fpreg)
 extern int unw_tdep_is_fpreg (int);
 
+#define unw_tdep_make_frame_cache(n)	(0)
+#define unw_tdep_free_frame_cache(p)	do {} while(0)
+#define unw_tdep_trace(cur,addr,n,c)	(-UNW_ENOINFO)
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/libunwind-ppc64.h b/include/libunwind-ppc64.h
index 66420b33..b1c2b072 100644
--- a/include/libunwind-ppc64.h
+++ b/include/libunwind-ppc64.h
@@ -252,11 +252,21 @@ typedef struct
   }
 unw_tdep_proc_info_t;
 
+typedef struct
+  {
+    /* no ppc64-specific fast trace */
+  }
+unw_tdep_frame_t;
+
 #include "libunwind-common.h"
 
 #define unw_tdep_is_fpreg		UNW_ARCH_OBJ(is_fpreg)
 extern int unw_tdep_is_fpreg (int);
 
+#define unw_tdep_make_frame_cache(n)	(0)
+#define unw_tdep_free_frame_cache(p)	do {} while(0)
+#define unw_tdep_trace(cur,addr,n,c)	(-UNW_ENOINFO)
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/libunwind-x86.h b/include/libunwind-x86.h
index 32533df9..e1f2ba4d 100644
--- a/include/libunwind-x86.h
+++ b/include/libunwind-x86.h
@@ -172,6 +172,12 @@ typedef struct
   }
 unw_tdep_proc_info_t;
 
+typedef struct
+  {
+    /* no x86-specific fast trace */
+  }
+unw_tdep_frame_t;
+
 #include "libunwind-common.h"
 
 #define unw_tdep_getcontext		UNW_ARCH_OBJ(getcontext)
@@ -180,6 +186,10 @@ extern int unw_tdep_getcontext (unw_tdep_context_t *);
 #define unw_tdep_is_fpreg		UNW_ARCH_OBJ(is_fpreg)
 extern int unw_tdep_is_fpreg (int);
 
+#define unw_tdep_make_frame_cache(n)	(0)
+#define unw_tdep_free_frame_cache(p)	do {} while(0)
+#define unw_tdep_trace(cur,addr,n,c)	(-UNW_ENOINFO)
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/libunwind-x86_64.h b/include/libunwind-x86_64.h
index 53789cc3..cdde5579 100644
--- a/include/libunwind-x86_64.h
+++ b/include/libunwind-x86_64.h
@@ -104,15 +104,44 @@ typedef struct
   }
 unw_tdep_proc_info_t;
 
+typedef enum
+  {
+    UNW_X86_64_FRAME_STANDARD = -2,     /* regular rbp, rsp +/- offset */
+    UNW_X86_64_FRAME_SIGRETURN = -1,    /* special sigreturn frame */
+    UNW_X86_64_FRAME_OTHER = 0,         /* not cacheable (special or unrecognised) */
+    UNW_X86_64_FRAME_GUESSED = 1        /* guessed it was regular, but not known */
+  }
+unw_tdep_frame_type_t;
+
+typedef struct
+  {
+    uint64_t virtual_address;
+    int64_t frame_type     : 2;  /* unw_tdep_frame_type_t classification */
+    int64_t last_frame     : 1;  /* non-zero if last frame in chain */
+    int64_t cfa_reg_rsp    : 1;  /* cfa dwarf base register is rsp vs. rbp */
+    int64_t cfa_reg_offset : 30; /* cfa is at this offset from base register value */
+    int64_t rbp_cfa_offset : 15; /* rbp saved at this offset from cfa (-1 = not saved) */
+    int64_t rsp_cfa_offset : 15; /* rsp saved at this offset from cfa (-1 = not saved) */
+  }
+unw_tdep_frame_t;
+
 #include "libunwind-dynamic.h"
 #include "libunwind-common.h"
 
 #define unw_tdep_getcontext		UNW_ARCH_OBJ(getcontext)
-extern int unw_tdep_getcontext (unw_tdep_context_t *);
-
 #define unw_tdep_is_fpreg		UNW_ARCH_OBJ(is_fpreg)
+#define unw_tdep_make_frame_cache	UNW_OBJ(make_frame_cache)
+#define unw_tdep_free_frame_cache	UNW_OBJ(free_frame_cache)
+#define unw_tdep_trace			UNW_OBJ(trace)
+
+extern int unw_tdep_getcontext (unw_tdep_context_t *);
 extern int unw_tdep_is_fpreg (int);
 
+extern unw_tdep_frame_t *unw_tdep_make_frame_cache (size_t n);
+extern int unw_tdep_free_frame_cache (unw_tdep_frame_t *p);
+extern int unw_tdep_trace (unw_cursor_t *cursor, void **addresses,
+			   int *n, unw_tdep_frame_t *cache);
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
diff --git a/include/tdep-arm/libunwind_i.h b/include/tdep-arm/libunwind_i.h
index acaf6d71..0cb4a719 100644
--- a/include/tdep-arm/libunwind_i.h
+++ b/include/tdep-arm/libunwind_i.h
@@ -221,6 +221,7 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 #define tdep_fetch_frame(c,ip,n)	do {} while(0)
 #define tdep_cache_frame(c,rs)		do {} while(0)
 #define tdep_reuse_frame(c,rs)		do {} while(0)
+#define tdep_stash_frame(c,rs)		do {} while(0)
 
 #ifdef UNW_LOCAL_ONLY
 # define tdep_find_proc_info(c,ip,n)				\
diff --git a/include/tdep-hppa/libunwind_i.h b/include/tdep-hppa/libunwind_i.h
index 50d1aabd..4e6c1c3a 100644
--- a/include/tdep-hppa/libunwind_i.h
+++ b/include/tdep-hppa/libunwind_i.h
@@ -227,6 +227,7 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 #define tdep_fetch_frame(c,ip,n)	do {} while(0)
 #define tdep_cache_frame(c,rs)		do {} while(0)
 #define tdep_reuse_frame(c,rs)		do {} while(0)
+#define tdep_stash_frame(c,rs)		do {} while(0)
 
 #ifdef UNW_LOCAL_ONLY
 # define tdep_find_proc_info(c,ip,n)				\
diff --git a/include/tdep-ia64/libunwind_i.h b/include/tdep-ia64/libunwind_i.h
index 75cc220d..3193a646 100644
--- a/include/tdep-ia64/libunwind_i.h
+++ b/include/tdep-ia64/libunwind_i.h
@@ -223,6 +223,7 @@ struct ia64_global_unwind_state
 #define tdep_fetch_frame(c,ip,n)	do {} while(0)
 #define tdep_cache_frame(c,rs)		do {} while(0)
 #define tdep_reuse_frame(c,rs)		do {} while(0)
+#define tdep_stash_frame(c,rs)		do {} while(0)
 #define tdep_get_as(c)			((c)->as)
 #define tdep_get_as_arg(c)		((c)->as_arg)
 #define tdep_get_ip(c)			((c)->ip)
diff --git a/include/tdep-mips/libunwind_i.h b/include/tdep-mips/libunwind_i.h
index 160a6372..2e6fc4fd 100644
--- a/include/tdep-mips/libunwind_i.h
+++ b/include/tdep-mips/libunwind_i.h
@@ -282,6 +282,7 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 #define tdep_fetch_frame(c,ip,n)	do {} while(0)
 #define tdep_cache_frame(c,rs)		do {} while(0)
 #define tdep_reuse_frame(c,rs)		do {} while(0)
+#define tdep_stash_frame(c,rs)		do {} while(0)
 
 #ifdef UNW_LOCAL_ONLY
 # define tdep_find_proc_info(c,ip,n)				\
diff --git a/include/tdep-ppc32/libunwind_i.h b/include/tdep-ppc32/libunwind_i.h
index e775dd64..7db2b393 100644
--- a/include/tdep-ppc32/libunwind_i.h
+++ b/include/tdep-ppc32/libunwind_i.h
@@ -245,8 +245,6 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 				     1, c->as_arg);
 }
 
-
-
 #define tdep_needs_initialization	UNW_OBJ(needs_initialization)
 #define tdep_init			UNW_OBJ(init)
 /* Platforms that support UNW_INFO_FORMAT_TABLE need to define
@@ -259,6 +257,7 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 #define tdep_fetch_frame(c,ip,n)	do {} while(0)
 #define tdep_cache_frame(c,rs)		do {} while(0)
 #define tdep_reuse_frame(c,rs)		do {} while(0)
+#define tdep_stash_frame(c,rs)		do {} while(0)
 #define tdep_get_func_addr		UNW_OBJ(get_func_addr)
 
 #ifdef UNW_LOCAL_ONLY
diff --git a/include/tdep-ppc64/libunwind_i.h b/include/tdep-ppc64/libunwind_i.h
index bb6c977b..6c46e1a7 100644
--- a/include/tdep-ppc64/libunwind_i.h
+++ b/include/tdep-ppc64/libunwind_i.h
@@ -245,8 +245,6 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 				     1, c->as_arg);
 }
 
-
-
 #define tdep_needs_initialization	UNW_OBJ(needs_initialization)
 #define tdep_init			UNW_OBJ(init)
 /* Platforms that support UNW_INFO_FORMAT_TABLE need to define
@@ -259,6 +257,7 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 #define tdep_fetch_frame(c,ip,n)	do {} while(0)
 #define tdep_cache_frame(c,rs)		do {} while(0)
 #define tdep_reuse_frame(c,rs)		do {} while(0)
+#define tdep_stash_frame(c,rs)		do {} while(0)
 #define tdep_get_func_addr		UNW_OBJ(get_func_addr)
 
 #ifdef UNW_LOCAL_ONLY
diff --git a/include/tdep-x86/libunwind_i.h b/include/tdep-x86/libunwind_i.h
index bc381e91..88ab2467 100644
--- a/include/tdep-x86/libunwind_i.h
+++ b/include/tdep-x86/libunwind_i.h
@@ -243,6 +243,7 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 #define tdep_fetch_frame(c,ip,n)	do {} while(0)
 #define tdep_cache_frame(c,rs)		do {} while(0)
 #define tdep_reuse_frame(c,rs)		do {} while(0)
+#define tdep_stash_frame(c,rs)		do {} while(0)
 
 #ifdef UNW_LOCAL_ONLY
 # define tdep_find_proc_info(c,ip,n)				\
diff --git a/include/tdep-x86_64/libunwind_i.h b/include/tdep-x86_64/libunwind_i.h
index fa5ebe97..b076bd18 100644
--- a/include/tdep-x86_64/libunwind_i.h
+++ b/include/tdep-x86_64/libunwind_i.h
@@ -57,6 +57,8 @@ struct cursor
   {
     struct dwarf_cursor dwarf;		/* must be first */
 
+    unw_tdep_frame_t frame_info;	/* quick tracing assist info */
+
     /* Format of sigcontext structure and address at which it is
        stored: */
     enum
@@ -173,6 +175,7 @@ dwarf_put (struct dwarf_cursor *c, dwarf_loc_t loc, unw_word_t val)
 # define tdep_cache_frame(c,rs)		do {} while(0)
 # define tdep_reuse_frame(c,rs)		do {} while(0)
 #endif
+#define tdep_stash_frame		UNW_OBJ(stash_frame)
 
 #ifdef UNW_LOCAL_ONLY
 # define tdep_find_proc_info(c,ip,n)				\
@@ -215,7 +218,8 @@ extern void tdep_cache_frame (struct dwarf_cursor *c,
 			      struct dwarf_reg_state *rs);
 extern void tdep_reuse_frame (struct dwarf_cursor *c,
 			      struct dwarf_reg_state *rs);
+extern void tdep_stash_frame (struct dwarf_cursor *c,
+			      struct dwarf_reg_state *rs);
 #endif
 
-
 #endif /* X86_64_LIBUNWIND_I_H */
diff --git a/src/Makefile.am b/src/Makefile.am
index 68470eab..9703724e 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -258,8 +258,8 @@ libunwind_la_SOURCES_x86_64 = $(libunwind_la_SOURCES_x86_64_common)	    \
 	x86_64/setcontext.S						    \
 	x86_64/Lcreate_addr_space.c x86_64/Lget_save_loc.c x86_64/Lglobal.c \
 	x86_64/Linit.c x86_64/Linit_local.c x86_64/Linit_remote.c	    \
-	x86_64/Lget_proc_info.c x86_64/Lregs.c    			    \
-	x86_64/Lresume.c x86_64/Lstep.c x86_64/getcontext.S
+	x86_64/Lget_proc_info.c x86_64/Lregs.c x86_64/Lresume.c		    \
+	x86_64/Lstash_frame.c x86_64/Lstep.c x86_64/Ltrace.c x86_64/getcontext.S
 
 # The list of files that go into libunwind-x86_64:
 libunwind_x86_64_la_SOURCES_x86_64 = $(libunwind_la_SOURCES_x86_64_common)  \
@@ -267,8 +267,8 @@ libunwind_x86_64_la_SOURCES_x86_64 = $(libunwind_la_SOURCES_x86_64_common)  \
 	$(libunwind_la_SOURCES_generic)					    \
 	x86_64/Gcreate_addr_space.c x86_64/Gget_save_loc.c x86_64/Gglobal.c \
 	x86_64/Ginit.c x86_64/Ginit_local.c x86_64/Ginit_remote.c	    \
-	x86_64/Gget_proc_info.c x86_64/Gregs.c    			    \
-	x86_64/Gresume.c x86_64/Gstep.c
+	x86_64/Gget_proc_info.c x86_64/Gregs.c x86_64/Gresume.c		    \
+	x86_64/Gstash_frame.c x86_64/Gstep.c x86_64/Gtrace.c
 
 # The list of local files that go to Power 64 and 32:
 libunwind_la_SOURCES_ppc = ppc/Lcreate_addr_space.c 			\
diff --git a/src/arm/init.h b/src/arm/init.h
index a3025698..1f8d7c11 100644
--- a/src/arm/init.h
+++ b/src/arm/init.h
@@ -62,6 +62,7 @@ common_init (struct cursor *c, unsigned use_prev_instr)
 
   c->dwarf.args_size = 0;
   c->dwarf.ret_addr_column = 0;
+  c->dwarf.stash_frames = 0;
   c->dwarf.use_prev_instr = use_prev_instr;
   c->dwarf.pi_valid = 0;
   c->dwarf.pi_is_dynamic = 0;
diff --git a/src/dwarf/Gparser.c b/src/dwarf/Gparser.c
index 13bd9a27..1db15461 100644
--- a/src/dwarf/Gparser.c
+++ b/src/dwarf/Gparser.c
@@ -803,6 +803,10 @@ apply_reg_state (struct dwarf_cursor *c, struct dwarf_reg_state *rs)
 	       __FUNCTION__, (long) c->ip);
       return -UNW_EBADFRAME;
     }
+
+  if (c->stash_frames)
+    tdep_stash_frame (c, rs);
+
   return 0;
 }
 
diff --git a/src/hppa/init.h b/src/hppa/init.h
index d14354f6..6fabb154 100644
--- a/src/hppa/init.h
+++ b/src/hppa/init.h
@@ -41,6 +41,7 @@ common_init (struct cursor *c, unsigned use_prev_instr)
   if (ret < 0)
     return ret;
 
+  c->dwarf.stash_frames = 0;
   c->dwarf.use_prev_instr = use_prev_instr;
   return 0;
 }
diff --git a/src/mips/init.h b/src/mips/init.h
index e32e3c9e..3a4bb008 100644
--- a/src/mips/init.h
+++ b/src/mips/init.h
@@ -47,6 +47,7 @@ common_init (struct cursor *c, unsigned use_prev_instr)
 
   c->dwarf.args_size = 0;
   c->dwarf.ret_addr_column = 0;
+  c->dwarf.stash_frames = 0;
   c->dwarf.use_prev_instr = use_prev_instr;
   c->dwarf.pi_valid = 0;
   c->dwarf.pi_is_dynamic = 0;
diff --git a/src/ppc32/init.h b/src/ppc32/init.h
index c2208ad9..4cb91920 100644
--- a/src/ppc32/init.h
+++ b/src/ppc32/init.h
@@ -62,6 +62,7 @@ common_init_ppc32 (struct cursor *c, unsigned use_prev_instr)
 
   c->dwarf.args_size = 0;
   c->dwarf.ret_addr_column = 0;
+  c->dwarf.stash_frames = 0;
   c->dwarf.use_prev_instr = use_prev_instr;
   c->dwarf.pi_valid = 0;
   c->dwarf.pi_is_dynamic = 0;
diff --git a/src/ppc64/init.h b/src/ppc64/init.h
index 64847b84..7503a7c7 100644
--- a/src/ppc64/init.h
+++ b/src/ppc64/init.h
@@ -72,6 +72,7 @@ common_init_ppc64 (struct cursor *c, unsigned use_prev_instr)
 
   c->dwarf.args_size = 0;
   c->dwarf.ret_addr_column = 0;
+  c->dwarf.stash_frames = 0;
   c->dwarf.use_prev_instr = use_prev_instr;
   c->dwarf.pi_valid = 0;
   c->dwarf.pi_is_dynamic = 0;
diff --git a/src/x86/init.h b/src/x86/init.h
index b59ad842..f35387d4 100644
--- a/src/x86/init.h
+++ b/src/x86/init.h
@@ -59,6 +59,7 @@ common_init (struct cursor *c, unsigned use_prev_instr)
 
   c->dwarf.args_size = 0;
   c->dwarf.ret_addr_column = 0;
+  c->dwarf.stash_frames = 0;
   c->dwarf.use_prev_instr = use_prev_instr;
   c->dwarf.pi_valid = 0;
   c->dwarf.pi_is_dynamic = 0;
diff --git a/src/x86_64/Ginit_local.c b/src/x86_64/Ginit_local.c
index 18b3d989..70bef3e1 100644
--- a/src/x86_64/Ginit_local.c
+++ b/src/x86_64/Ginit_local.c
@@ -51,11 +51,7 @@ unw_init_local (unw_cursor_t *cursor, ucontext_t *uc)
   c->dwarf.as = unw_local_addr_space;
   c->dwarf.as_arg = c;
   c->uc = uc;
-#if CONSERVATIVE_CHECKS
-  c->validate = 1;
-#else
   c->validate = 0;
-#endif
   return common_init (c, 1);
 }
 
diff --git a/src/x86_64/Gos-linux.c b/src/x86_64/Gos-linux.c
index b7f832ca..c0278881 100644
--- a/src/x86_64/Gos-linux.c
+++ b/src/x86_64/Gos-linux.c
@@ -39,18 +39,12 @@ tdep_fetch_frame (struct dwarf_cursor *dw, unw_word_t ip, int need_unwind_info)
   if (dw->pi_valid
       && dw->pi.unwind_info
       && ((struct dwarf_cie_info *) dw->pi.unwind_info)->signal_frame)
-  {
     c->sigcontext_format = X86_64_SCF_LINUX_RT_SIGFRAME;
-    c->sigcontext_addr = dw->cfa;
-  }
   else
-  {
     c->sigcontext_format = X86_64_SCF_NONE;
-    c->sigcontext_addr = 0;
-  }
 
-  Debug(15, "fetch frame ip=0x%lx cfa=0x%lx format=%d addr=0x%lx\n",
-        dw->ip, dw->cfa, c->sigcontext_format, c->sigcontext_addr);
+  Debug(5, "fetch frame ip=0x%lx cfa=0x%lx format=%d\n",
+        dw->ip, dw->cfa, c->sigcontext_format);
 }
 
 HIDDEN void
@@ -59,8 +53,8 @@ tdep_cache_frame (struct dwarf_cursor *dw, struct dwarf_reg_state *rs)
   struct cursor *c = (struct cursor *) dw;
   rs->signal_frame = c->sigcontext_format;
 
-  Debug(15, "cache frame ip=0x%lx cfa=0x%lx format=%d addr=0x%lx\n",
-        dw->ip, dw->cfa, c->sigcontext_format, c->sigcontext_addr);
+  Debug(5, "cache frame ip=0x%lx cfa=0x%lx format=%d\n",
+        dw->ip, dw->cfa, c->sigcontext_format);
 }
 
 HIDDEN void
@@ -69,12 +63,20 @@ tdep_reuse_frame (struct dwarf_cursor *dw, struct dwarf_reg_state *rs)
   struct cursor *c = (struct cursor *) dw;
   c->sigcontext_format = rs->signal_frame;
   if (c->sigcontext_format == X86_64_SCF_LINUX_RT_SIGFRAME)
+  {
+    /* Rest will be filled by tdep_stash_frame(), save what it needs. */
+    c->frame_info.frame_type = UNW_X86_64_FRAME_SIGRETURN;
+    c->frame_info.cfa_reg_offset = -1;
+    c->frame_info.cfa_reg_rsp = -1;
     c->sigcontext_addr = dw->cfa;
+  }
   else
     c->sigcontext_addr = 0;
 
-  Debug(15, "reuse frame ip=0x%lx cfa=0x%lx format=%d addr=0x%lx\n",
-        dw->ip, dw->cfa, c->sigcontext_format, c->sigcontext_addr);
+  Debug(5, "reuse frame ip=0x%lx cfa=0x%lx format=%d addr=0x%lx offset=%+d\n",
+        dw->ip, dw->cfa, c->sigcontext_format, c->sigcontext_addr,
+	(c->sigcontext_format == X86_64_SCF_LINUX_RT_SIGFRAME
+	 ? c->frame_info.cfa_reg_offset : 0));
 }
 
 PROTECTED int
@@ -90,17 +92,14 @@ unw_handle_signal_frame (unw_cursor_t *cursor)
 #if UNW_DEBUG /* To silence compiler warnings */
   /* Should not get here because we now use kernel-provided dwarf
      information for the signal trampoline and dwarf_step() works.
-     Hence dwarf_step() should never call this function. Maybe
+     Hence unw_step() should never call this function. Maybe
      restore old non-dwarf signal handling here, but then the
      gating on unw_is_signal_frame() needs to be removed. */
   struct cursor *c = (struct cursor *) cursor;
   Debug(1, "old format signal frame? format=%d addr=0x%lx cfa=0x%lx\n",
 	c->sigcontext_format, c->sigcontext_addr, c->dwarf.cfa);
-  assert(c->sigcontext_format == X86_64_SCF_LINUX_RT_SIGFRAME);
-  assert(c->sigcontext_addr == c->dwarf.cfa);
-  assert(0);
 #endif
-  return 1;
+  return -UNW_EBADFRAME;
 }
 
 #ifndef UNW_REMOTE_ONLY
diff --git a/src/x86_64/Gstash_frame.c b/src/x86_64/Gstash_frame.c
new file mode 100644
index 00000000..8cbc947f
--- /dev/null
+++ b/src/x86_64/Gstash_frame.c
@@ -0,0 +1,95 @@
+/* libunwind - a platform-independent unwind library
+   Copyright (C) 2010 by Lassi Tuura <lat@iki.fi>
+
+This file is part of libunwind.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#include "unwind_i.h"
+#include "ucontext_i.h"
+
+HIDDEN void
+tdep_stash_frame (struct dwarf_cursor *d, struct dwarf_reg_state *rs)
+{
+  struct cursor *c = (struct cursor *) dwarf_to_cursor (d);
+  unw_tdep_frame_t *f = &c->frame_info;
+
+  Debug (4, "ip=0x%lx cfa=0x%lx type %d cfa [where=%d val=%ld] cfaoff=%ld"
+	 " ra=0x%lx rbp [where=%d val=%ld @0x%lx] rsp [where=%d val=%ld @0x%lx]\n",
+	 d->ip, d->cfa, f->frame_type,
+	 rs->reg[DWARF_CFA_REG_COLUMN].where,
+	 rs->reg[DWARF_CFA_REG_COLUMN].val,
+	 rs->reg[DWARF_CFA_OFF_COLUMN].val,
+	 DWARF_GET_LOC(d->loc[d->ret_addr_column]),
+	 rs->reg[RBP].where, rs->reg[RBP].val, DWARF_GET_LOC(d->loc[RBP]),
+	 rs->reg[RSP].where, rs->reg[RSP].val, DWARF_GET_LOC(d->loc[RSP]));
+
+  /* A standard frame is defined as:
+      - CFA is register-relative offset off RBP or RSP;
+      - Return address is saved at CFA-8;
+      - RBP is unsaved or saved at CFA+offset, offset != -1;
+      - RSP is unsaved or saved at CFA+offset, offset != -1.  */
+  if (f->frame_type == UNW_X86_64_FRAME_OTHER
+      && (rs->reg[DWARF_CFA_REG_COLUMN].where == DWARF_WHERE_REG)
+      && (rs->reg[DWARF_CFA_REG_COLUMN].val == RBP
+	  || rs->reg[DWARF_CFA_REG_COLUMN].val == RSP)
+      && labs(rs->reg[DWARF_CFA_OFF_COLUMN].val) < (1 << 29)
+      && DWARF_GET_LOC(d->loc[d->ret_addr_column]) == d->cfa-8
+      && (rs->reg[RBP].where == DWARF_WHERE_UNDEF
+	  || rs->reg[RBP].where == DWARF_WHERE_SAME
+	  || (rs->reg[RBP].where == DWARF_WHERE_CFAREL
+	      && labs(rs->reg[RBP].val) < (1 << 14)
+	      && rs->reg[RBP].val+1 != 0))
+      && (rs->reg[RSP].where == DWARF_WHERE_UNDEF
+	  || rs->reg[RSP].where == DWARF_WHERE_SAME
+	  || (rs->reg[RSP].where == DWARF_WHERE_CFAREL
+	      && labs(rs->reg[RSP].val) < (1 << 14)
+	      && rs->reg[RSP].val+1 != 0)))
+  {
+    /* Save information for a standard frame. */
+    f->frame_type = UNW_X86_64_FRAME_STANDARD;
+    f->cfa_reg_rsp = (rs->reg[DWARF_CFA_REG_COLUMN].val == RSP);
+    f->cfa_reg_offset = rs->reg[DWARF_CFA_OFF_COLUMN].val;
+    if (rs->reg[RBP].where == DWARF_WHERE_CFAREL)
+      f->rbp_cfa_offset = rs->reg[RBP].val;
+    if (rs->reg[RSP].where == DWARF_WHERE_CFAREL)
+      f->rsp_cfa_offset = rs->reg[RSP].val;
+    Debug (4, " standard frame\n");
+  }
+
+  /* Signal frame was detected via augmentation in tdep_fetch_frame()
+     and partially filled in tdep_reuse_frame().  Now that we have
+     the delta between inner and outer CFAs available to use, fill in
+     the offsets for CFA and stored registers.  We don't have space
+     for RIP, it's location is calculated relative to RBP location. */
+  else if (f->frame_type == UNW_X86_64_FRAME_SIGRETURN)
+  {
+    assert (f->cfa_reg_offset == -1);
+    f->cfa_reg_offset = d->cfa - c->sigcontext_addr;
+    f->rbp_cfa_offset = DWARF_GET_LOC(d->loc[RBP]) - d->cfa;
+    f->rsp_cfa_offset = DWARF_GET_LOC(d->loc[RSP]) - d->cfa;
+    Debug (4, " sigreturn frame rbpoff %d rspoff %d\n",
+	   f->rbp_cfa_offset, f->rsp_cfa_offset);
+  }
+
+  /* PLT and guessed RBP-walked frames are handled in unw_step(). */
+  else
+    Debug (4, " unusual frame\n");
+}
diff --git a/src/x86_64/Gstep.c b/src/x86_64/Gstep.c
index 85e3989a..0d2eef80 100644
--- a/src/x86_64/Gstep.c
+++ b/src/x86_64/Gstep.c
@@ -58,6 +58,11 @@ unw_step (unw_cursor_t *cursor)
   struct cursor *c = (struct cursor *) cursor;
   int ret, i;
 
+#if CONSERVATIVE_CHECKS
+  int val = c->validate;
+  c->validate = 1;
+#endif
+
   Debug (1, "(cursor=%p, ip=0x%016lx, cfa=0x%016lx)\n",
 	 c, c->dwarf.ip, c->dwarf.cfa);
 
@@ -65,6 +70,10 @@ unw_step (unw_cursor_t *cursor)
   c->sigcontext_format = X86_64_SCF_NONE;
   ret = dwarf_step (&c->dwarf);
 
+#if CONSERVATIVE_CHECKS
+  c->validate = val;
+#endif
+
   if (ret < 0 && ret != -UNW_ENOINFO)
     {
       Debug (2, "returning %d\n", ret);
@@ -112,7 +121,11 @@ unw_step (unw_cursor_t *cursor)
 	}
       else if (is_plt_entry (&c->dwarf))
 	{
+          /* Like regular frame, CFA = RSP+8, RA = [CFA-8], no regs saved. */
 	  Debug (2, "found plt entry\n");
+          c->frame_info.cfa_reg_offset = 8;
+          c->frame_info.cfa_reg_rsp = -1;
+          c->frame_info.frame_type = UNW_X86_64_FRAME_STANDARD;
           c->dwarf.loc[RIP] = DWARF_LOC (c->dwarf.cfa, 0);
           c->dwarf.cfa += 8;
 	}
@@ -142,19 +155,32 @@ unw_step (unw_cursor_t *cursor)
 	    }
 	  else
 	    {
-	      unw_word_t rbp1;
-	      Debug (1, "[RBP=0x%Lx] = 0x%Lx (cfa = 0x%Lx)\n",
-		     (unsigned long long) DWARF_GET_LOC (c->dwarf.loc[RBP]),
-		     (unsigned long long) rbp,
-		     (unsigned long long) c->dwarf.cfa);
-
+	      unw_word_t rbp1 = 0;
 	      rbp_loc = DWARF_LOC(rbp, 0);
 	      rsp_loc = DWARF_NULL_LOC;
 	      rip_loc = DWARF_LOC (rbp + 8, 0);
-              /* Heuristic to recognize a bogus frame pointer */
 	      ret = dwarf_get (&c->dwarf, rbp_loc, &rbp1);
-              if (ret || ((rbp1 - rbp) > 0x4000))
-                rbp_loc = DWARF_NULL_LOC;
+	      Debug (1, "[RBP=0x%lx] = 0x%lx (cfa = 0x%lx) -> 0x%lx\n",
+		     (unsigned long) DWARF_GET_LOC (c->dwarf.loc[RBP]),
+		     rbp, c->dwarf.cfa, rbp1);
+
+	      /* Heuristic to determine incorrect guess.  For RBP to be a
+	         valid frame it needs to be above current CFA, but don't
+		 let it go more than a little.  Note that we can't deduce
+		 anything about new RBP (rbp1) since it may not be a frame
+		 pointer in the frame above.  Just check we get the value. */
+              if (ret < 0
+		  || rbp <= c->dwarf.cfa
+		  || (rbp - c->dwarf.cfa) > 0x4000)
+	        {
+                  rip_loc = DWARF_NULL_LOC;
+                  rbp_loc = DWARF_NULL_LOC;
+		}
+
+              c->frame_info.frame_type = UNW_X86_64_FRAME_GUESSED;
+              c->frame_info.cfa_reg_rsp = 0;
+              c->frame_info.cfa_reg_offset = 16;
+              c->frame_info.rbp_cfa_offset = -16;
 	      c->dwarf.cfa += 16;
 	    }
 
diff --git a/src/x86_64/Gtrace.c b/src/x86_64/Gtrace.c
new file mode 100644
index 00000000..24087443
--- /dev/null
+++ b/src/x86_64/Gtrace.c
@@ -0,0 +1,401 @@
+/* libunwind - a platform-independent unwind library
+   Copyright (C) 2010 by Lassi Tuura <lat@iki.fi>
+
+This file is part of libunwind.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#include "unwind_i.h"
+#include "ucontext_i.h"
+#include <signal.h>
+
+/* Utility for timing in debug mode.  You'll probably want to
+   comment out all unnecessary debugging in this file if you
+   use this, otherwise the timings printed will not make sense. */
+#if UNW_DEBUG
+#define rdtsc(v)				 		\
+  do { unsigned lo, hi;						\
+    __asm__ volatile ("rdtsc" : "=a" (lo), "=d" (hi));		\
+    (v) = ((unsigned long) lo) | ((unsigned long) hi << 32);	\
+  } while (0)
+#endif
+
+/* There's not enough space to store RIP's location in a signal
+   frame, but we can calculate it relative to RBP's (or RSP's)
+   position in mcontext structure.  Note we don't want to use
+   the UC_MCONTEXT_GREGS_* directly since we rely on DWARF info. */
+#define dRIP (UC_MCONTEXT_GREGS_RIP - UC_MCONTEXT_GREGS_RBP)
+
+/* Allocate and initialise hash table for frame cache lookups.
+   Client requests size N, which should be 5 to 10 more than expected
+   number of unique addresses to trace.  Minimum size of 10000 is
+   forced.  Returns the cache, or NULL if there was a memory
+   allocation problem. */
+unw_tdep_frame_t *
+unw_tdep_make_frame_cache (size_t n)
+{
+  size_t i;
+  unw_tdep_frame_t *cache;
+
+  if (n < 10000)
+    n = 10000;
+
+  if (! (cache = malloc((n+1) * sizeof(unw_tdep_frame_t))))
+    return 0;
+
+  unw_tdep_frame_t empty = { 0, UNW_X86_64_FRAME_OTHER, -1, -1, 0, -1, -1 };
+  for (i = 0; i < n; ++i)
+    cache[i] = empty;
+
+  cache[0].virtual_address = n;
+  return cache+1;
+}
+
+/* Free the address cache allocated by unw_tdep_make_frame_cache().
+   Returns 0 on success, or -UNW_EINVAL if cache was NULL. */
+int
+unw_tdep_free_frame_cache (unw_tdep_frame_t *cache)
+{
+  if (! cache)
+    return -UNW_EINVAL;
+
+  free(cache-1);
+  return 0;
+}
+
+/* Initialise frame properties for address cache slot F at address
+   RIP using current CFA, RBP and RSP values.  Modifies CURSOR to
+   that location, performs one unw_step(), and fills F with what
+   was discovered about the location.  Returns F.
+
+   FIXME: This probably should tell DWARF handling to never evaluate
+   or use registers other than RBP, RSP and RIP in case there is
+   highly unusual unwind info which uses these creatively. */
+static unw_tdep_frame_t *
+trace_init_addr (unw_tdep_frame_t *f,
+		 unw_cursor_t *cursor,
+		 unw_word_t cfa,
+		 unw_word_t rip,
+		 unw_word_t rbp,
+		 unw_word_t rsp)
+{
+  struct cursor *c = (struct cursor *) cursor;
+  struct dwarf_cursor *d = &c->dwarf;
+  int ret = -UNW_EINVAL;
+
+  /* Initialise frame properties: unknown, not last. */
+  f->virtual_address = rip;
+  f->frame_type = UNW_X86_64_FRAME_OTHER;
+  f->last_frame = 0;
+  f->cfa_reg_rsp = -1;
+  f->cfa_reg_offset = 0;
+  f->rbp_cfa_offset = -1;
+  f->rsp_cfa_offset = -1;
+
+  /* Reinitialise cursor to this instruction - but undo next/prev RIP
+     adjustment because unw_step will redo it - and force RIP, RBP
+     RSP into register locations (=~ ucontext we keep), then set
+     their desired values. Then perform the step. */
+  d->ip = rip + d->use_prev_instr;
+  d->cfa = cfa;
+  d->loc[UNW_X86_64_RIP] = DWARF_REG_LOC (d, UNW_X86_64_RIP);
+  d->loc[UNW_X86_64_RBP] = DWARF_REG_LOC (d, UNW_X86_64_RBP);
+  d->loc[UNW_X86_64_RSP] = DWARF_REG_LOC (d, UNW_X86_64_RSP);
+  c->frame_info = *f;
+
+  if (dwarf_put (d, d->loc[UNW_X86_64_RIP], rip) >= 0
+      && dwarf_put (d, d->loc[UNW_X86_64_RBP], rbp) >= 0
+      && dwarf_put (d, d->loc[UNW_X86_64_RSP], rsp) >= 0
+      && (ret = unw_step (cursor)) >= 0)
+    *f = c->frame_info;
+
+  /* If unw_step() stopped voluntarily, remember that, even if it
+     otherwise could not determine anything useful.  This avoids
+     failing trace if we hit frames without unwind info, which is
+     common for the outermost frame (CRT stuff) on many systems.
+     This avoids failing trace in very common circumstances; failing
+     to unw_step() loop wouldn't produce any better result. */
+  if (ret == 0)
+    f->last_frame = -1;
+
+  Debug (3, "frame va %lx type %d last %d cfa %s+%d rbp @ cfa%+d rsp @ cfa%+d\n",
+	 f->virtual_address, f->frame_type, f->last_frame,
+	 f->cfa_reg_rsp ? "rsp" : "rbp", f->cfa_reg_offset,
+	 f->rbp_cfa_offset, f->rsp_cfa_offset);
+
+  return f;
+}
+
+/* Look up and if necessary fill in frame attributes for address RIP
+   in CACHE using current CFA, RBP and RSP values.  Uses CURSOR to
+   perform any unwind steps necessary to fill the cache.  Returns the
+   frame cache slot which describes RIP. */
+static unw_tdep_frame_t *
+trace_lookup (unw_cursor_t *cursor,
+	      unw_tdep_frame_t *cache,
+	      unw_word_t cfa,
+	      unw_word_t rip,
+	      unw_word_t rbp,
+	      unw_word_t rsp)
+{
+  /* First look up for previously cached information using cache as
+     linear probing hash table with probe step of 1.  Majority of
+     lookups should be completed within few steps, but it is very
+     important the hash table does not fill up, or performance falls
+     off the cliff. */
+  uint64_t cache_size = cache[-1].virtual_address;
+  uint64_t probe_steps = (cache_size >> 5);
+  uint64_t slot = ((rip * 0x9e3779b97f4a7c16) >> 43) % cache_size;
+  uint64_t i;
+
+  for (i = 0; i < probe_steps; ++i)
+  {
+    uint64_t addr = cache[slot].virtual_address;
+
+    /* Return if we found the address. */
+    if (addr == rip)
+    {
+      Debug (4, "found address after %ld steps\n", i);
+      return &cache[slot];
+    }
+
+    /* If slot is empty, reuse it. */
+    if (! addr)
+      break;
+
+    /* Linear probe to next slot candidate, step = 1. */
+    if (++slot > cache_size)
+      slot -= cache_size;
+  }
+
+  /* Fill this slot, whether it's free or hash collision. */
+  Debug (4, "updating slot after %ld steps\n", i);
+  return trace_init_addr (&cache[slot], cursor, cfa, rip, rbp, rsp);
+}
+
+/* Fast stack backtrace for x86-64.
+
+   Intended for use when the application makes frequent queries to the
+   current call stack without any desire to unwind.  Somewhat like the
+   GLIBC backtrace() function: fills BUFFER with the call tree from
+   CURSOR upwards, and SIZE with the number of stack levels so found.
+   When called, SIZE should tell the maximum number of entries that
+   can be stored in BUFFER.  CACHE is used to accelerate the stack
+   queries; no other thread may use the same cache concurrently.
+
+   The caller should fall back to a unw_step() loop if this function
+   fails by returning -UNW_ESTOPUNWIND, meaning the routine hit a
+   stack frame that is too complex to be traced in the fast path.
+
+   This function is tuned for clients which only need to walk the
+   stack to get the call tree as fast as possible but without any
+   other details, for example profilers sampling the stack thousands
+   to millions of times per second.  The routine handles the most
+   common x86-64 ABI stack layouts: CFA is RBP or RSP plus/minus
+   constant offset, return address is at CFA-8, and RBP and RSP are
+   either unchanged or saved on stack at constant offset from the CFA;
+   the signal return frame; and frames without unwind info provided
+   they are at the outermost (final) frame or can conservatively be
+   assumed to be frame-pointer based.
+
+   Any other stack layout will cause the routine to give up.  There
+   are only a handful of relatively rarely used functions which do
+   not have a stack in the standard form: vfork, longjmp, setcontext
+   and _dl_runtime_profile on common linux systems for example.
+
+   On success BUFFER and *SIZE reflect the trace progress up to *SIZE
+   stack levels or the outermost frame, which ever is less.  It may
+   stop short of outermost frame if unw_step() loop would also do so,
+   e.g. if there is no more unwind information; this is not reported
+   as an error.
+
+   The function returns a negative value for errors, -UNW_ESTOPUNWIND
+   if tracing stopped because of an unusual frame unwind info.  The
+   BUFFER and *SIZE reflect tracing progress up to the error frame.
+
+   Callers of this function would normally look like this:
+
+     unw_cursor_t     cur;
+     unw_context_t    ctx, saved;
+     unw_tdep_frame_t *cache = ...;
+     void             addrs[128];
+     int              depth = 128;
+     int              ret;
+
+     unw_getcontext(&ctx);
+     memcpy(&saved, &ctx, sizeof(ctx));
+
+     unw_init_local(&cur, &ctx);
+     if (! cache || (ret = unw_tdep_trace(&cur, addrs, &depth, cache)) < 0)
+     {
+       depth = 0;
+       unw_init_local(&cur, &saved);
+       while (depth < 128)
+       {
+         unw_word_t ip;
+         unw_get_reg(&cur, UNW_REG_IP, &ip);
+         addresses[depth++] = (void *) ip;
+         if ((ret = unw_step(&cur)) <= 0)
+           break;
+       }
+     }
+*/
+int
+unw_tdep_trace (unw_cursor_t *cursor,
+		void **buffer,
+		int *size,
+		unw_tdep_frame_t *cache)
+{
+  struct cursor *c = (struct cursor *) cursor;
+  struct dwarf_cursor *d = &c->dwarf;
+  unw_word_t rbp, rsp, rip, cfa;
+  int maxdepth = 0;
+  int depth = 0;
+  int ret;
+#if UNW_DEBUG
+  unsigned long start, end;
+  rdtsc(start);
+#endif
+
+  /* Check input parametres. */
+  if (! cursor || ! buffer || ! size || ! cache || (maxdepth = *size) <= 0)
+    return -UNW_EINVAL;
+
+  Debug (1, "begin ip 0x%lx cfa 0x%lx\n", d->ip, d->cfa);
+
+  /* Tell core dwarf routines to call back to us. */
+  d->stash_frames = 1;
+
+  /* Determine initial register values. */
+  rip = d->ip;
+  rsp = cfa = d->cfa;
+  if ((ret = dwarf_get (d, d->loc[UNW_X86_64_RBP], &rbp)) < 0)
+  {
+    *size = 0;
+    return ret;
+  }
+
+  /* Trace the stack upwards, starting from current RIP.  Adjust
+     the RIP address for previous/next instruction as the main
+     unwinding logic would also do.  We undo this before calling
+     back into unw_step(). */
+  while (depth < maxdepth)
+  {
+    rip -= d->use_prev_instr;
+    Debug (2, "depth %d cfa 0x%lx rip 0x%lx rsp 0x%lx rbp 0x%lx\n",
+	   depth, cfa, rip, rsp, rbp);
+
+    /* See if we have this address cached.  If not, evaluate enough of
+       the dwarf unwind information to fill the cache line data, or to
+       decide this frame cannot be handled in fast trace mode.  We
+       cache negative results too to prevent unnecessary dwarf parsing
+       for common failures. */
+    unw_tdep_frame_t *f = trace_lookup (cursor, cache, cfa, rip, rbp, rsp);
+
+    /* Record this address in stack trace. */
+    buffer[depth++] = (void *) rip;
+
+    /* If we don't have information for this frame, give up. */
+    if (! f)
+    {
+      ret = -UNW_ENOINFO;
+      break;
+    }
+
+    Debug (3, "frame va %lx type %d last %d cfa %s+%d rbp @ cfa%+d rsp @ cfa%+d\n",
+           f->virtual_address, f->frame_type, f->last_frame,
+           f->cfa_reg_rsp ? "rsp" : "rbp", f->cfa_reg_offset,
+           f->rbp_cfa_offset, f->rsp_cfa_offset);
+
+    assert (f->virtual_address == rip);
+
+    /* Stop if this was the last frame.  In particular don't evaluate
+       new register values as it may not be safe - we don't normally
+       run with full validation on, and do not want to - and there's
+       enough bad unwind info floating around that we need to trust
+       what unw_step() previously said, in potentially bogus frames. */
+    if (f->last_frame)
+      break;
+
+    /* Evaluate CFA and registers for the next frame. */
+    switch (f->frame_type)
+    {
+    case UNW_X86_64_FRAME_GUESSED:
+      /* Fall thru to standard processing after forcing validation. */
+      c->validate = 1;
+
+    case UNW_X86_64_FRAME_STANDARD:
+      /* Advance standard traceable frame. */
+      cfa = (f->cfa_reg_rsp ? rsp : rbp) + f->cfa_reg_offset;
+      ret = dwarf_get (d, DWARF_MEM_LOC (d, cfa - 8), &rip);
+      if (ret >= 0 && f->rbp_cfa_offset != -1)
+	ret = dwarf_get (d, DWARF_MEM_LOC (d, cfa + f->rbp_cfa_offset), &rbp);
+
+      /* Don't bother reading RSP from DWARF, CFA becomes new RSP. */
+      rsp = cfa;
+
+      /* Next frame needs to back up for unwind info lookup. */
+      d->use_prev_instr = 1;
+      break;
+
+    case UNW_X86_64_FRAME_SIGRETURN:
+      /* Advance standard signal frame, whose CFA points above saved
+         registers (ucontext) among other things.  We know the info
+	 is stored at some unknown constant offset off inner frame's
+	 CFA.  We determine the actual offset from DWARF unwind info. */
+      d->use_prev_instr = 0;
+      cfa = cfa + f->cfa_reg_offset;
+      ret = dwarf_get (d, DWARF_MEM_LOC (d, cfa + f->rbp_cfa_offset + dRIP), &rip);
+      if (ret >= 0)
+	ret = dwarf_get (d, DWARF_MEM_LOC (d, cfa + f->rbp_cfa_offset), &rbp);
+      if (ret >= 0)
+	ret = dwarf_get (d, DWARF_MEM_LOC (d, cfa + f->rsp_cfa_offset), &rsp);
+
+      /* Resume stack at signal restoration point. The stack is not
+         necessarily continuous here, especially with sigaltstack(). */
+      cfa = rsp;
+
+      /* Next frame should not back up. */
+      d->use_prev_instr = 0;
+      break;
+
+    default:
+      /* We cannot trace through this frame, give up and tell the
+	 caller we had to stop.  Data collected so far may still be
+	 useful to the caller, so let it know how far we got.  */
+      ret = -UNW_ESTOPUNWIND;
+      break;
+    }
+
+    Debug (4, "new cfa 0x%lx rip 0x%lx rsp 0x%lx rbp 0x%lx\n",
+	   cfa, rip, rsp, rbp);
+
+    /* If we failed on ended up somewhere bogus, stop. */
+    if (ret < 0 || rip < 0x4000)
+      break;
+  }
+
+#if UNW_DEBUG
+  rdtsc(end);
+  Debug (1, "returning %d depth %d, dt=%ld\n", ret, depth, end - start);
+#endif
+  *size = depth;
+  return ret;
+}
diff --git a/src/x86_64/Lstash_frame.c b/src/x86_64/Lstash_frame.c
new file mode 100644
index 00000000..77587803
--- /dev/null
+++ b/src/x86_64/Lstash_frame.c
@@ -0,0 +1,5 @@
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+#if defined(UNW_LOCAL_ONLY) && !defined(UNW_REMOTE_ONLY)
+#include "Gstash_frame.c"
+#endif
diff --git a/src/x86_64/Ltrace.c b/src/x86_64/Ltrace.c
new file mode 100644
index 00000000..fcd3f239
--- /dev/null
+++ b/src/x86_64/Ltrace.c
@@ -0,0 +1,5 @@
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+#if defined(UNW_LOCAL_ONLY) && !defined(UNW_REMOTE_ONLY)
+#include "Gtrace.c"
+#endif
diff --git a/src/x86_64/init.h b/src/x86_64/init.h
index dcd4aea2..f04ecda3 100644
--- a/src/x86_64/init.h
+++ b/src/x86_64/init.h
@@ -64,6 +64,7 @@ common_init (struct cursor *c, unsigned use_prev_instr)
 
   c->dwarf.args_size = 0;
   c->dwarf.ret_addr_column = RIP;
+  c->dwarf.stash_frames = 0;
   c->dwarf.use_prev_instr = use_prev_instr;
   c->dwarf.pi_valid = 0;
   c->dwarf.pi_is_dynamic = 0;
diff --git a/tests/Gtest-trace.c b/tests/Gtest-trace.c
new file mode 100644
index 00000000..90452be6
--- /dev/null
+++ b/tests/Gtest-trace.c
@@ -0,0 +1,265 @@
+/* libunwind - a platform-independent unwind library
+   Copyright (C) 2010 by Lassi Tuura <lat@iki.fi>
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <errno.h>
+#if HAVE_EXECINFO_H
+# include <execinfo.h>
+#else
+  extern int backtrace (void **, int);
+#endif
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <libunwind.h>
+
+#define panic(args...)				\
+	{ fprintf (stderr, args); exit (-1); }
+
+#ifndef HAVE_SIGHANDLER_T
+typedef RETSIGTYPE (*sighandler_t) (int);
+#endif
+
+int verbose;
+int num_errors;
+
+/* These variables are global because they
+ * cause the signal stack to overflow */
+char buf[512], name[256];
+void *addresses[2][128];
+unw_cursor_t cursor;
+ucontext_t uc;
+#if UNW_TARGET_X86_64
+unw_tdep_frame_t *cache;
+#endif
+
+static void
+do_backtrace (void)
+{
+  unw_word_t ip;
+  int ret = -UNW_ENOINFO;
+  int depth = 128;
+  int i, n;
+
+  if (verbose)
+    printf ("\tfast backtrace:\n");
+
+  unw_getcontext (&uc);
+  if (unw_init_local (&cursor, &uc) < 0)
+    panic ("unw_init_local failed!\n");
+
+#if UNW_TARGET_X86_64
+  if ((ret = unw_tdep_trace (&cursor, addresses[0], &depth, cache)) < 0)
+    {
+      unw_get_reg (&cursor, UNW_REG_IP, &ip);
+      printf ("FAILURE: unw_tdep_trace() returned %d for ip=%lx\n", ret, (long) ip);
+      ++num_errors;
+    }
+#endif
+
+  if (ret < 0)
+    {
+      i = 0;
+      do
+        {
+	  unw_get_reg (&cursor, UNW_REG_IP, &ip);
+	  addresses[0][i] = (void *) ip;
+        }
+      while ((ret = unw_step (&cursor)) >= 0 && ++i < 128);
+
+      if (ret < 0)
+        {
+	  unw_get_reg (&cursor, UNW_REG_IP, &ip);
+          printf ("FAILURE: unw_step() returned %d for ip=%lx\n", ret, (long) ip);
+          ++num_errors;
+	}
+    }
+
+  if (verbose)
+    for (i = 0; i < depth; ++i)
+      printf ("\t #%-3d ip=%p\n", i, addresses[0][i]);
+
+  if (verbose)
+    printf ("\n\tvia backtrace():\n");
+
+  n = backtrace (addresses[1], 128);
+
+  if (verbose)
+    for (i = 0; i < n; ++i)
+	printf ("\t #%-3d ip=%p\n", i, addresses[1][i]);
+
+  if (n != depth)
+    {
+      printf ("FAILURE: unw_tdep_trace() and backtrace() depths differ: %d vs. %d\n", depth, n);
+      ++num_errors;
+    }
+  else
+    for (i = 1; i < depth; ++i)
+      /* Allow one in difference in comparison, trace returns adjusted addresses. */
+      if (labs((unw_word_t) addresses[0][i] - (unw_word_t) addresses[1][i]) > 1)
+	{
+          printf ("FAILURE: unw_tdep_trace() and backtrace() addresses differ at %d: %p vs. %p\n",
+		  i, addresses[0][n], addresses[1][n]);
+          ++num_errors;
+	}
+}
+
+void
+foo (long val)
+{
+  do_backtrace ();
+}
+
+void
+bar (long v)
+{
+  extern long f (long);
+  int arr[v];
+
+  /* This is a vain attempt to use up lots of registers to force
+     the frame-chain info to be saved on the memory stack on ia64.
+     It happens to work with gcc v3.3.4 and gcc v3.4.1 but perhaps
+     not with any other compiler.  */
+  foo (f (arr[0]) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v)
+       + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + (f (v) + f (v))
+       ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
+       )))))))))))))))))))))))))))))))))))))))))))))))))))))));
+}
+
+void
+sighandler (int signal, void *siginfo, void *context)
+{
+  ucontext_t *uc = context;
+  int sp;
+
+  if (verbose)
+    {
+      printf ("sighandler: got signal %d, sp=%p", signal, &sp);
+#if UNW_TARGET_IA64
+# if defined(__linux__)
+      printf (" @ %lx", uc->uc_mcontext.sc_ip);
+# else
+      {
+	uint16_t reason;
+	uint64_t ip;
+
+	__uc_get_reason (uc, &reason);
+	__uc_get_ip (uc, &ip);
+	printf (" @ %lx (reason=%d)", ip, reason);
+      }
+# endif
+#elif UNW_TARGET_X86
+#if defined __linux__
+      printf (" @ %lx", (unsigned long) uc->uc_mcontext.gregs[REG_EIP]);
+#elif defined __FreeBSD__
+      printf (" @ %lx", (unsigned long) uc->uc_mcontext.mc_eip);
+#endif
+#elif UNW_TARGET_X86_64
+#if defined __linux__
+      printf (" @ %lx", (unsigned long) uc->uc_mcontext.gregs[REG_RIP]);
+#elif defined __FreeBSD__
+      printf (" @ %lx", (unsigned long) uc->uc_mcontext.mc_rip);
+#endif
+#endif
+      printf ("\n");
+    }
+  do_backtrace();
+}
+
+int
+main (int argc, char **argv)
+{
+  struct sigaction act;
+  stack_t stk;
+
+#if UNW_TARGET_X86_64
+  cache = unw_tdep_make_frame_cache (0);
+#endif
+
+  verbose = (argc > 1);
+
+  if (verbose)
+    printf ("Normal backtrace:\n");
+
+  bar (1);
+
+  memset (&act, 0, sizeof (act));
+  act.sa_handler = (void (*)(int)) sighandler;
+  act.sa_flags = SA_SIGINFO;
+  if (sigaction (SIGTERM, &act, NULL) < 0)
+    panic ("sigaction: %s\n", strerror (errno));
+
+  if (verbose)
+    printf ("\nBacktrace across signal handler:\n");
+  kill (getpid (), SIGTERM);
+
+  if (verbose)
+    printf ("\nBacktrace across signal handler on alternate stack:\n");
+  stk.ss_sp = malloc (SIGSTKSZ);
+  if (!stk.ss_sp)
+    panic ("failed to allocate SIGSTKSZ (%u) bytes\n", SIGSTKSZ);
+  stk.ss_size = SIGSTKSZ;
+  stk.ss_flags = 0;
+  if (sigaltstack (&stk, NULL) < 0)
+    panic ("sigaltstack: %s\n", strerror (errno));
+
+  memset (&act, 0, sizeof (act));
+  act.sa_handler = (void (*)(int)) sighandler;
+  act.sa_flags = SA_ONSTACK | SA_SIGINFO;
+  if (sigaction (SIGTERM, &act, NULL) < 0)
+    panic ("sigaction: %s\n", strerror (errno));
+  kill (getpid (), SIGTERM);
+
+  if (num_errors > 0)
+    {
+      fprintf (stderr, "FAILURE: detected %d errors\n", num_errors);
+      exit (-1);
+    }
+
+#if UNW_TARGET_X86_64
+  unw_tdep_free_frame_cache (cache);
+#endif
+
+  if (verbose)
+    printf ("SUCCESS.\n");
+  return 0;
+}
diff --git a/tests/Ltest-trace.c b/tests/Ltest-trace.c
new file mode 100644
index 00000000..fb0e9c10
--- /dev/null
+++ b/tests/Ltest-trace.c
@@ -0,0 +1,5 @@
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+#if !defined(UNW_REMOTE_ONLY)
+#include "Gtest-trace.c"
+#endif
diff --git a/tests/Makefile.am b/tests/Makefile.am
index fe4a1afe..a981d635 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -41,6 +41,7 @@ endif #ARCH_IA64
 			Gtest-concurrent Ltest-concurrent		 \
 			Gtest-resume-sig Ltest-resume-sig		 \
 			Gtest-dyn1 Ltest-dyn1				 \
+			Gtest-trace Ltest-trace				 \
 			test-async-sig test-flush-cache test-init-remote \
 			test-mem test-setjmp test-ptrace		 \
 			Ltest-nomalloc rs-race
@@ -98,6 +99,8 @@ Gtest_bt_SOURCES = Gtest-bt.c ident.c
 Ltest_bt_SOURCES = Ltest-bt.c ident.c
 test_ptrace_misc_SOURCES = test-ptrace-misc.c ident.c
 Ltest_nomalloc_SOURCES = Ltest-nomalloc.c
+Gtest_trace_SOURCES = Gtest-trace.c ident.c
+Ltest_trace_SOURCES = Ltest-trace.c ident.c
 
 LIBUNWIND = $(top_builddir)/src/libunwind-$(arch).la $(LIBUNWIND_local)
 LIBUNWIND_ptrace = $(top_builddir)/src/libunwind-ptrace.a
diff --git a/tests/check-namespace.sh.in b/tests/check-namespace.sh.in
index 9c6b12dc..9d9fb974 100644
--- a/tests/check-namespace.sh.in
+++ b/tests/check-namespace.sh.in
@@ -123,6 +123,9 @@ check_local_unw_abi () {
 	    match _U${plat}_is_fpreg
 	    match _UL${plat}_dwarf_search_unwind_table
 	    match _U${plat}_setcontext
+            match _UL${plat}_free_frame_cache
+            match _UL${plat}_make_frame_cache
+            match _UL${plat}_trace
 	    ;;
 	*)
 	    match _U${plat}_is_fpreg
@@ -186,6 +189,9 @@ check_generic_unw_abi () {
 	    match _U${plat}_get_elf_image
 	    match _U${plat}_is_fpreg
 	    match _U${plat}_dwarf_search_unwind_table
+            match _U${plat}_free_frame_cache
+            match _U${plat}_make_frame_cache
+            match _U${plat}_trace
 	    ;;
 	*)
 	    match _U${plat}_is_fpreg