Aliasing troubles in dwarf_getaranges with gcc 4.4

[Mark Wielaard <mjw at redhat dot com>]

Hi,

Current git master has the following aliasing issue with gcc 4.4:

gcc -D_GNU_SOURCE -DHAVE_CONFIG_H -DIS_LIBDW -I. -I.. -I. -I. -I./../libelf -I.. -I./../lib    -Wall -Werror -Wshadow -Wunused -Wformat=2 -Wextra -std=gnu99 -g -O2 -MT dwarf_getaranges.o -MD -MP -MF .deps/dwarf_getaranges.Tpo -c -o dwarf_getaranges.o dwarf_getaranges.c
cc1: warnings being treated as errors
dwarf_getaranges.c: In function ‘dwarf_getaranges’:
libdwP.h:540: error: dereferencing pointer ‘readp.44’ does break strict-aliasing rules
dwarf_getaranges.c:152: note: initialized from here
libdwP.h:519: error: dereferencing pointer ‘readp.44’ does break strict-aliasing rules
dwarf_getaranges.c:174: note: initialized from here

I think the fix (attached) is to not threat readp as a const char, but
as unsigned char in this function since __libdw_read_offset_inc function
needs a non-const char**.

Or maybe the signature of the __libdw_read_offset_inc is wrong?
I couldn't directly tell since the function uses some macros which uses
some functions that actually seem to ignores all its arguments at the
moment

Cheers,

Mark

diff --git a/libdw/dwarf_getaranges.c b/libdw/dwarf_getaranges.c
index 74f04ea..7b930ec 100644
--- a/libdw/dwarf_getaranges.c
+++ b/libdw/dwarf_getaranges.c
@@ -104,13 +104,14 @@ dwarf_getaranges (dbg, aranges, naranges)
   struct arangelist *arangelist = NULL;
   unsigned int narangelist = 0;
 
-  const char *readp
-    = (const char *) dbg->sectiondata[IDX_debug_aranges]->d_buf;
-  const char *readendp = readp + dbg->sectiondata[IDX_debug_aranges]->d_size;
+  unsigned char *readp
+    = dbg->sectiondata[IDX_debug_aranges]->d_buf;
+  unsigned char *readendp
+    = readp + dbg->sectiondata[IDX_debug_aranges]->d_size;
 
   while (readp < readendp)
     {
-      const char *hdrstart = readp;
+      const unsigned char *hdrstart = readp;
 
       /* Each entry starts with a header:
 
@@ -150,7 +151,7 @@ dwarf_getaranges (dbg, aranges, naranges)
 
       Dwarf_Word offset;
       if (__libdw_read_offset_inc (dbg,
-				   IDX_debug_aranges, (unsigned char **)&readp,
+				   IDX_debug_aranges, &readp,
 				   length_bytes, &offset, IDX_debug_info, 4))
 	return -1;
 
@@ -172,7 +173,7 @@ dwarf_getaranges (dbg, aranges, naranges)
 	  Dwarf_Word range_length;
 
 	  if (__libdw_read_address_inc (dbg, IDX_debug_aranges,
-					(unsigned char **)&readp,
+					&readp,
 					address_size, &range_address))
 	    return -1;