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Re: DWARF 2 sections and padding ?
- From: Brian Ford <ford at vss dot fsi dot com>
- To: binutils at sources dot redhat dot com
- Cc: gdb at sources dot redhat dot com
- Date: Fri, 21 Feb 2003 12:59:54 -0600 (CST)
- Subject: Re: DWARF 2 sections and padding ?
On Fri, 21 Feb 2003, Daniel Jacobowitz wrote:
> On Fri, Feb 21, 2003 at 10:16:49AM -0600, Brian Ford wrote:
> > I am trying to add DWARF 2 support for PE/COFF on Cygwin. PE/COFF
> > sections must be aligned to 512 byte boundaries. This extra padding
> > confuses the DWARF 2 parsing routines because they use the sections
> > raw_size, thus parsing an invalid compilation unit header (all
> > zeros).
> > The actual, smaller size is available in the section header. I am
> > confused about what the cooked_size is supposed to mean. It is currently
> > zero, but I think it could contain the smaller virtual size.
> > I have read the DWARF spec several times, and although it discusses this
> > issue briefly for some debugging sections, it is unclear to me how this
> > should really work. Unless I try to arrange for the producer (gcc) to
> > pad the compilation units with zeros instead of having bfd pad the end of
> > the sections, I don't know how to proceed.
> > I would like to just use an alternate size instead of the raw size (cooked
> > maybe?) but I don't know how this would affect other targets and I don't
> > want a PE specific hack in DWARF parsing code.
> > Any ideas? Thanks.
> I don't see why the raw size should include the padding; that should
> just be used when _placing_ sections. But this is a binutils/bfd
> issue; redirected to that list.
The raw size appears to translate directly to the size in the section
header. The PE/COFF format states this must be a multiple of the page
Other COFF targets that define ALIGN_SECTIONS_IN_FILE do the same thing,
in separate code, though. There is one case where these other targets do
what you suggest, if COFF_PAGE_SIZE is defined:
/* In demand paged files the low order bits of the file offset
must match the low order bits of the virtual address. */
if ((abfd->flags & D_PAGED) != 0
&& (current->flags & SEC_ALLOC) != 0)
sofar += (current->vma - sofar) % page_size;
I modified the PE/COFF code to do this instead and, although it violates
the format, a simple test appeared valid and runable on Windows XP. What
do the binutils maintainers think about making this change?
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems