ack/util/led/WRONG

This file contains a summary of the bugs/features/inconsistencies
Robbert and Ed found while making the linker usable for the 68000 and amoeba.

There is something wrong with the way the combination of
assembler and linker handle bss.
In the original (Duk's) the assembler translated .space and, worse, .align
to a sequence of zero's. If this sequence was at the end of a segment
within a module the assembler didn't put zero in the segment but sets
os_flen to the amount of space initialized before the zero space
and os_size to the segements size. (os_size - os_flen) is then the
size of the space filled by zeroes.
For the sake of clarity, let us call 0...os_flen-1 initialized space
and os_flen..os_size-1 uninitialized space.
Now the linker, it does a nasty trick. It gathers the uninitialized space
of all modules within a segment and puts it consequtively at the end
of the segment. I think that I understand the reason: This way you can keep
your resultant a.out smaller and you don't need a special bss segment
(a la unix). But it is incorrect, the net effect is that the .align's
at the end of segments within a module do have the desired effect,
the space thus allocated is removed to 'higher spheres' thereby
leaving the first items of that segment in the inmediatly following
modules at unaligned boundaries.
What should be done is that the linker leaves the initialized and
the unitialized code alone and regards the whole a a chunk that can be
relocated. Only producing a difference of os_size and os_flen for
the zeroes at the very end of the segment. Thereby collapsing all
.space (and .align) commands into zero space only if they
are in consequtive modules at the end of the segment, with modules
NOT containing any initialized data.
I already, ad-hoc, changed the code of the assembler to producing 'hard'
zeroes when aligning. The trick could also be done for .space
but is a bit harder here.
The reason: .space is also used to allocate space in the BSS segment
if that produced zeroes in the a.out file (0..bss_size) we would
have a.out files that are far too large.
This feature of the linker also caused weird effects for names that
are defined as the very last in a section within a module, without
any data (initialized or uninitialezed) after it.
The names a regarded as pointing into the uninitialized space and
thus relocated to the end of the section.
The sequence
	.sect .data
begdata:
	.sect ....
in an head_em.s resulted in the relocation of begdata to the END
of the .data segment.

Another problem form the commons:
1 - Local commons are not handled by led and not produced by as.
    using .comm for unitialized data is not correct because (from C)
    two uninitialized static declarations for the same name in
    different modules will be handled as external commons and thus
    be overlayed.
2 - The commons are allocated at the very end of the first pass, after the
    initialezed data has been allocated in the segments. The order on which
    the commons are allocated seems to be random. That way it is impossible
    to produce a label that is guaranteed to point to the last byte (+1)
    of a segment containing commons.
    The currently used trick is to declare an extra segment after the
    segment containing the commons. The first bytre in this segment
    inmediatly follows the commons and can be used as _end or endbss.

The archiver (aal) with the automatic ranlib is buggy.
The only thing that seems to work at the moment is creation of a fresh
archive.
replacing/adding/deleting modules is likely to produce libraries
with incorrect ranlib entries.
The major troublemaker seems to be the extra padding byte at the end
of odd sized modules.

Led should return a non-zero value when it has found Undefined symbols
or has another reason for not being able to produce a correct output file.