(unw_step): If dwarf_step() fails and the frame doesn't look like

a signal-trampoline, assume that it's a PLT stub.
	If non-DWARF stepping fails to change IP and CFA, declare
	it a bad frame.

2004/11/23 16:59:56-08:00 mostang.com!davidm
(unw_step): Also print IP as part of the function-trace.

2004/11/23 16:17:37-08:00 mostang.com!davidm
(unw_step): When dwarf_step() fails on a signal-frame, fill in all
	the known locations because dwarf_step() fails on older
	kernels which don't export the kernel vDSO even though every-
	thing else may be providing proper DWARF unwind-info.

2004/10/25 17:43:57+02:00 homeip.net!davidm
Add Debug statement for return-value.

(Logical change 1.290)

src/x86_64/Gstep.c

@@ -1,5 +1,5 @@
 /* libunwind - a platform-independent unwind library
-   Copyright (C) 2002-2003 Hewlett-Packard Co
+   Copyright (C) 2002-2004 Hewlett-Packard Co
 	Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
 
    Modified for x86_64 by Max Asbock <masbock@us.ibm.com>
@@ -35,11 +35,17 @@ unw_step (unw_cursor_t *cursor)
   struct cursor *c = (struct cursor *) cursor;
   int ret, i;
 
+  Debug (1, "(cursor=%p, ip=0x%016llx)\n",
+	 c, (unsigned long long) c->dwarf.ip);
+
   /* Try DWARF-based unwinding... */
   ret = dwarf_step (&c->dwarf);
 
-  if (unlikely (ret == -UNW_ESTOPUNWIND))
+  if (ret < 0 && ret != -UNW_ENOINFO)
-    return ret;
+    {
+      Debug (2, "returning %d\n", ret);
+      return ret;
+    }
 
   if (likely (ret >= 0))
     {
@@ -50,8 +56,19 @@ unw_step (unw_cursor_t *cursor)
     }
   else
     {
-      /* DWARF failed, let's see if we can follow the frame-chain
+      /* DWARF failed.  There isn't much of a usable frame-chain on x86-64,
-	 or skip over the signal trampoline.  */
+	 but we do need to handle two special-cases:
+
+	  (i) signal trampoline: Old kernels and older libcs don't
+	      export the vDSO needed to get proper unwind info for the
+	      trampoline.  Recognize that case by looking at the code
+	      and filling in things by hand.
+
+	  (ii) PLT (shared-library) call-stubs: PLT stubs are invoked
+	      via CALLQ.  Try this for all non-signal trampoline
+	      code.  */
+
+      unw_word_t prev_ip = c->dwarf.ip, prev_cfa = c->dwarf.cfa;
       struct dwarf_loc rbp_loc, rsp_loc, rip_loc;
 
       Debug (13, "dwarf_step() failed (ret=%d), trying frame-chain\n", ret);
@@ -71,28 +88,64 @@ unw_step (unw_cursor_t *cursor)
 
 	  ret = dwarf_get (&c->dwarf, rsp_loc, &c->dwarf.cfa);
 	  if (ret < 0)
-	    return ret;
+	    {
+	      Debug (2, "returning %d\n", ret);
+	      return ret;
+	    }
+
+	  c->dwarf.loc[RAX] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RAX, 0);
+	  c->dwarf.loc[RDX] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RDX, 0);
+	  c->dwarf.loc[RCX] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RCX, 0);
+	  c->dwarf.loc[RBX] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RBX, 0);
+	  c->dwarf.loc[RSI] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RSI, 0);
+	  c->dwarf.loc[RDI] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RDI, 0);
+	  c->dwarf.loc[RBP] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RBP, 0);
+	  c->dwarf.loc[ R8] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R8, 0);
+	  c->dwarf.loc[ R9] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R9, 0);
+	  c->dwarf.loc[R10] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R10, 0);
+	  c->dwarf.loc[R11] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R11, 0);
+	  c->dwarf.loc[R12] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R12, 0);
+	  c->dwarf.loc[R13] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R13, 0);
+	  c->dwarf.loc[R14] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R14, 0);
+	  c->dwarf.loc[R15] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_R15, 0);
+	  c->dwarf.loc[RIP] = DWARF_LOC (ucontext + UC_MCONTEXT_GREGS_RIP, 0);
 	}
       else
 	{
-	  ret = dwarf_get (&c->dwarf, c->dwarf.loc[RBP], &c->dwarf.cfa);
+	  unw_word_t rbp;
+
+	  ret = dwarf_get (&c->dwarf, c->dwarf.loc[RBP], &rbp);
 	  if (ret < 0)
-	    return ret;
+	    {
+	      Debug (2, "returning %d\n", ret);
+	      return ret;
+	    }
 
-	  Debug (13, "[RBP=0x%Lx] = 0x%Lx\n",
+	  if (!rbp)
-		 (unsigned long long) DWARF_GET_LOC (c->dwarf.loc[RBP]),
+	    {
-		 (unsigned long long) c->dwarf.cfa);
+	      /* Looks like we may have reached the end of the call-chain.  */
+	      rbp_loc = DWARF_NULL_LOC;
+	      rsp_loc = DWARF_NULL_LOC;
+	      rip_loc = DWARF_NULL_LOC;
+	    }
+	  else
+	    {
+	      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);
 
-	  rbp_loc = DWARF_LOC (c->dwarf.cfa, 0);
+	      rbp_loc = c->dwarf.loc[RBP];
-	  rsp_loc = DWARF_NULL_LOC;
+	      rsp_loc = DWARF_NULL_LOC;
-	  rip_loc = DWARF_LOC (c->dwarf.cfa + 8, 0);
+	      rip_loc = DWARF_LOC (c->dwarf.cfa + 8, 0);
-	  c->dwarf.cfa += 16;
+	      c->dwarf.cfa += 8;
+	    }
+
+	  /* Mark all registers unsaved */
+	  for (i = 0; i < DWARF_NUM_PRESERVED_REGS; ++i)
+	    c->dwarf.loc[i] = DWARF_NULL_LOC;
 	}
 
-      /* Mark all registers unsaved */
-      for (i = 0; i < DWARF_NUM_PRESERVED_REGS; ++i)
-	c->dwarf.loc[i] = DWARF_NULL_LOC;
-
       c->dwarf.loc[RBP] = rbp_loc;
       c->dwarf.loc[RSP] = rsp_loc;
       c->dwarf.loc[RIP] = rip_loc;
@@ -102,10 +155,18 @@ unw_step (unw_cursor_t *cursor)
 	{
 	  ret = dwarf_get (&c->dwarf, c->dwarf.loc[RIP], &c->dwarf.ip);
 	  if (ret < 0)
-	    return ret;
+	    {
+	      Debug (2, "returning %d\n", ret);
+	      return ret;
+	    }
 	}
       else
 	c->dwarf.ip = 0;
+
+      if (c->dwarf.ip == prev_ip && c->dwarf.cfa == prev_cfa)
+	return -UNW_EBADFRAME;
     }
-  return (c->dwarf.ip == 0) ? 0 : 1;
+  ret = (c->dwarf.ip == 0) ? 0 : 1;
+  Debug (2, "returning %d\n", ret);
+  return ret;
 }