[rfc] Fix bitfield regressions on 64-bit big-endian targets

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Daniel Jacobowitz wrote:

> value_offset for a bitfield is an offset to be added into the parent's
> contents.  So including the parent's offset is incorrect; the attached
> test shows that we were reading the wrong location.  With large enough
> offsets, we could wander off to another page of memory and fault.

This changes the value_offset for a bitfield, but does not adapt all
places where the offset is used; in particular value_assign still does
not take the parent's offset into account.

This causes a significant number of store.exp testsuite failures on
s390x-linux and ppc64-linux (and presumably other 64-bit big-endian
platforms).

The following patch updates value_assign to respect the parent offset,
which fixes all those failures.

Tested on s390(x)-linux and ppc(64)-linux with no regressions.

Does this look OK to you?

Bye,
Ulrich


ChangeLog:

	* valops.c (value_assign): Respect parent offset when
	assigning to a bitfield.


Index: gdb/valops.c
===================================================================
RCS file: /cvs/src/src/gdb/valops.c,v
retrieving revision 1.225
diff -c -p -r1.225 valops.c
*** gdb/valops.c	31 Aug 2009 20:18:45 -0000	1.225
--- gdb/valops.c	25 Sep 2009 18:37:40 -0000
*************** value_assign (struct value *toval, struc
*** 827,832 ****
--- 827,835 ----
  
  	if (value_bitsize (toval))
  	  {
+ 	    struct value *parent = value_parent (toval);
+ 	    changed_addr = value_address (parent) + value_offset (toval);
+ 
  	    changed_len = (value_bitpos (toval)
  			   + value_bitsize (toval)
  			   + HOST_CHAR_BIT - 1)
*************** value_assign (struct value *toval, struc
*** 838,854 ****
  	       registers.  */
  	    if (changed_len < TYPE_LENGTH (type)
  		&& TYPE_LENGTH (type) <= (int) sizeof (LONGEST)
! 		&& ((LONGEST) value_address (toval) % TYPE_LENGTH (type)) == 0)
  	      changed_len = TYPE_LENGTH (type);
  
  	    if (changed_len > (int) sizeof (LONGEST))
  	      error (_("Can't handle bitfields which don't fit in a %d bit word."),
  		     (int) sizeof (LONGEST) * HOST_CHAR_BIT);
  
! 	    read_memory (value_address (toval), buffer, changed_len);
  	    modify_field (type, buffer, value_as_long (fromval),
  			  value_bitpos (toval), value_bitsize (toval));
- 	    changed_addr = value_address (toval);
  	    dest_buffer = buffer;
  	  }
  	else
--- 841,856 ----
  	       registers.  */
  	    if (changed_len < TYPE_LENGTH (type)
  		&& TYPE_LENGTH (type) <= (int) sizeof (LONGEST)
! 		&& ((LONGEST) changed_addr % TYPE_LENGTH (type)) == 0)
  	      changed_len = TYPE_LENGTH (type);
  
  	    if (changed_len > (int) sizeof (LONGEST))
  	      error (_("Can't handle bitfields which don't fit in a %d bit word."),
  		     (int) sizeof (LONGEST) * HOST_CHAR_BIT);
  
! 	    read_memory (changed_addr, buffer, changed_len);
  	    modify_field (type, buffer, value_as_long (fromval),
  			  value_bitpos (toval), value_bitsize (toval));
  	    dest_buffer = buffer;
  	  }
  	else
*************** value_assign (struct value *toval, struc
*** 891,896 ****
--- 893,900 ----
  	  {
  	    if (value_bitsize (toval))
  	      {
+ 		struct value *parent = value_parent (toval);
+ 		int offset = value_offset (parent) + value_offset (toval);
  		int changed_len;
  		gdb_byte buffer[sizeof (LONGEST)];
  
*************** value_assign (struct value *toval, struc
*** 903,917 ****
  		  error (_("Can't handle bitfields which don't fit in a %d bit word."),
  			 (int) sizeof (LONGEST) * HOST_CHAR_BIT);
  
! 		get_frame_register_bytes (frame, value_reg,
! 					  value_offset (toval),
  					  changed_len, buffer);
  
  		modify_field (type, buffer, value_as_long (fromval),
  			      value_bitpos (toval), value_bitsize (toval));
  
! 		put_frame_register_bytes (frame, value_reg,
! 					  value_offset (toval),
  					  changed_len, buffer);
  	      }
  	    else
--- 907,919 ----
  		  error (_("Can't handle bitfields which don't fit in a %d bit word."),
  			 (int) sizeof (LONGEST) * HOST_CHAR_BIT);
  
! 		get_frame_register_bytes (frame, value_reg, offset,
  					  changed_len, buffer);
  
  		modify_field (type, buffer, value_as_long (fromval),
  			      value_bitpos (toval), value_bitsize (toval));
  
! 		put_frame_register_bytes (frame, value_reg, offset,
  					  changed_len, buffer);
  	      }
  	    else

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com