Re: [RFA] dwarf2-frame.c sign extension patch

["Martin M. Hunt" <hunt@redhat.com>]

Mark,

Yes, I like your patch and it works fine.  Please check it in. 

Martin
  
On Thu, 2004-07-22 at 13:45, Mark Kettenis wrote:
>    Date: Wed, 21 Jul 2004 20:46:21 -0400
>    From: Daniel Jacobowitz <drow@false.org>
> 
>    On Wed, Jul 21, 2004 at 05:41:36PM -0700, Kevin Buettner wrote:
>    > > Any use of bits_per_address, IMO, is a bug.  Take a look at how this
>    > > field is set on MIPS; it's based on the architecture, not the ABI or
>    > > the pointer size or the dwarf address size or anything like that.
>    > 
>    > I agree.
>    > 
>    > > TYPE_LENGTH doesn't seem like an ideal replacement.  Can we use the
>    > > value in the compilation unit header here?
>    > 
>    > I considered doing this, but was told that the information in
>    > .debug_frame should be independent of the CU header.  I really
>    > don't know what the "right" solution is.
> 
>    Oh, right, we're in .debug_frame here.  I care very much about being
>    .able to use .debug_frame without .debug_info.  Debian distributes
>    library images with only .debug_frame, to provide backtraces.
> 
> Ah yes, the standard explicitly says that .debug_frame is
> self-contained.
> 
>    .debug_frame doesn't provide this information.  That's a known defect;
>    I think that Jim proposed correcting it on the dwarf2 list.
> 
> Hmm, I'm starting to wonder why we set unit->addr_size at all.  It's
> only used in decode_frame_entry_1().  I suppose it makes sense to
> cache this value, although I have no data to support that.
> 
>    Does anyone know if .eh_frame solves this problem somehow?
> 
> In many cases it directly encodes the size of pointers.
> 
>    Otherwise, I think that using TYPE_LENGTH (with a big comment
>    explaining the issue) may be the best we can do.
> 
> Actually, it would make things more symmetric if we'd use TYPE_LENGTH.
> Even better, avoid the issue completely by initializing the CIE
> encoding to DW_EH_PE_absptr.  How about the attached patch?  Does it
> solve your problems Martin?
> 
> Mark
> 
> 
> Index: ChangeLog
> from  Mark Kettenis  <kettenis@gnu.org>
> 
> 	* dwarf2-frame.c (struct dwarf2_cie): Delete `addr_size' member.
> 	(decode_frame_entry_1): Use DW_EH_PE_absptr as default for CIE
> 	encoding.
> 	(dwarf2_build_frame_info): Adjust for removal of `addr_size'
> 	member of `struct comp_unit'.
> 
> Index: dwarf2-frame.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/dwarf2-frame.c,v
> retrieving revision 1.36
> diff -u -p -r1.36 dwarf2-frame.c
> --- dwarf2-frame.c 15 Jun 2004 01:04:19 -0000 1.36
> +++ dwarf2-frame.c 22 Jul 2004 20:45:28 -0000
> @@ -890,9 +890,6 @@ struct comp_unit
>    /* Linked list of CIEs for this object.  */
>    struct dwarf2_cie *cie;
>  
> -  /* Address size for this unit - from unit header.  */
> -  unsigned char addr_size;
> -
>    /* Pointer to the .debug_frame section loaded into memory.  */
>    char *dwarf_frame_buffer;
>  
> @@ -1284,9 +1281,8 @@ decode_frame_entry_1 (struct comp_unit *
>        cie->cie_pointer = cie_pointer;
>  
>        /* The encoding for FDE's in a normal .debug_frame section
> -         depends on the target address size as specified in the
> -         Compilation Unit Header.  */
> -      cie->encoding = encoding_for_size (unit->addr_size);
> +         depends on the target address size.  */
> +      cie->encoding = DW_EH_PE_absptr;
>  
>        /* Check version number.  */
>        cie_version = read_1_byte (unit->abfd, buf);
> @@ -1557,7 +1553,6 @@ dwarf2_build_frame_info (struct objfile 
>    /* Build a minimal decoding of the DWARF2 compilation unit.  */
>    unit.abfd = objfile->obfd;
>    unit.objfile = objfile;
> -  unit.addr_size = objfile->obfd->arch_info->bits_per_address / 8;
>    unit.dbase = 0;
>    unit.tbase = 0;
>