Fix strict-aliasing warnings from unwind-dw2-fde.c

["Joseph S. Myers" <joseph at codesourcery dot com>]

On platforms with SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2_5), such as
x86 and MIPS, there are several "dereferencing type-punned pointer
will break strict-aliasing rules" warnings from unwind-dw2-fde.c
(accessing _Unwind_Ptr and pointer types through a char[] array, when
only the other way round is valid under C aliasing rules).

This patch fixes these warnings by using memcpy in an inline function
to extract the values from the array.  Tested x86, and tested on MIPS
(all three ABIs) that it also eliminates the warnings there.

2012-11-21  Joseph Myers  <joseph@codesourcery.com>

	* sysdeps/generic/unwind-dw2-fde.c (get_pc_begin): New function.
	(fde_unencoded_compare): Use get_pc_begin instead of type-punning.
	(add_fdes): Likewise.
	(linear_search_fdes): Likewise.
	(binary_search_unencoded_fdes): Likewise.

diff --git a/sysdeps/generic/unwind-dw2-fde.c b/sysdeps/generic/unwind-dw2-fde.c
index d47f2b1..6dcca1d 100644
--- a/sysdeps/generic/unwind-dw2-fde.c
+++ b/sysdeps/generic/unwind-dw2-fde.c
@@ -1,6 +1,5 @@
 /* Subroutines needed for unwinding stack frames for exception handling.  */
-/* Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2006, 2007
-   Free Software Foundation, Inc.
+/* Copyright (C) 1997-2012 Free Software Foundation, Inc.
    Contributed by Jason Merrill <jason@cygnus.com>.
 
    This file is part of the GNU C Library.
@@ -342,14 +341,24 @@ get_fde_encoding (struct dwarf_fde *f)
    (Ideally we would have the linker sort the FDEs so we don't have to do
    it at run time. But the linkers are not yet prepared for this.)  */
 
+/* Return the Nth pc_begin value from FDE x.  */
+
+static inline _Unwind_Ptr
+get_pc_begin (fde *x, size_t n)
+{
+  _Unwind_Ptr p;
+  memcpy (&p, x->pc_begin + n * sizeof (_Unwind_Ptr), sizeof (_Unwind_Ptr));
+  return p;
+}
+
 /* Comparison routines.  Three variants of increasing complexity.  */
 
 static int
 fde_unencoded_compare (struct object *ob __attribute__((unused)),
 		       fde *x, fde *y)
 {
-  _Unwind_Ptr x_ptr = *(_Unwind_Ptr *) x->pc_begin;
-  _Unwind_Ptr y_ptr = *(_Unwind_Ptr *) y->pc_begin;
+  _Unwind_Ptr x_ptr = get_pc_begin (x, 0);
+  _Unwind_Ptr y_ptr = get_pc_begin (y, 0);
 
   if (x_ptr > y_ptr)
     return 1;
@@ -712,7 +721,7 @@ add_fdes (struct object *ob, struct fde_accumulator *accu, fde *this_fde)
 
       if (encoding == DW_EH_PE_absptr)
 	{
-	  if (*(_Unwind_Ptr *) this_fde->pc_begin == 0)
+	  if (get_pc_begin (this_fde, 0) == 0)
 	    continue;
 	}
       else
@@ -830,8 +839,8 @@ linear_search_fdes (struct object *ob, fde *this_fde, void *pc)
 
       if (encoding == DW_EH_PE_absptr)
 	{
-	  pc_begin = ((_Unwind_Ptr *) this_fde->pc_begin)[0];
-	  pc_range = ((_Unwind_Ptr *) this_fde->pc_begin)[1];
+	  pc_begin = get_pc_begin (this_fde, 0);
+	  pc_range = get_pc_begin (this_fde, 1);
 	  if (pc_begin == 0)
 	    continue;
 	}
@@ -881,8 +890,8 @@ binary_search_unencoded_fdes (struct object *ob, void *pc)
       void *pc_begin;
       uaddr pc_range;
 
-      pc_begin = ((void **) f->pc_begin)[0];
-      pc_range = ((uaddr *) f->pc_begin)[1];
+      pc_begin = (void *) get_pc_begin (f, 0);
+      pc_range = (uaddr) get_pc_begin (f, 1);
 
       if (pc < pc_begin)
 	hi = i;

-- 
Joseph S. Myers
joseph@codesourcery.com