On 04-05-2012 01:57, H. S. Teoh wrote:
On Fri, May 04, 2012 at 12:53:02AM +0200, Alex Rønne Petersen wrote:
On 04-05-2012 00:47, Pierre LeMoine wrote:
[...]
Anyway, the project would aim to be a replacement or alternative to
optlink on windows. I've personally encountered quite a few seemingly
random problems with optlink, and the error messages are not exactly
friendly. My vision is to create a linker in a relatively modern
language (D) and to release the project as open source.
Sounds like a good idea to me. Though in my personal opinion, you
should try to make the linker as platform-agnostic as possible, so
it's easy to adapt for new platforms / file formats.
[...]
The problem with writing linkers is that they are usually closely tied
to implementation details on the host OS. At the very least, they must
play nice with the OS's runtime dynamic linker (or *be* the dynamic
linker themselves, like ld on the *nixes). They must also play nice with
object files produced by other compilers on that platform, since
otherwise it sorta defeats the purpose of rewriting optlink in the first
place. This means that they must understand all the intimate details of
every common object file and executable format on that OS.
I know, but that doesn't mean you can't write the linker so that it
actually *is* portable at *all* (unlike a certain other linker ;).
The basic concept behind a linker is very simple, really, but it's the
implementation where details get ugly.
To be frank, I question the wisdom of not just using ld on Posix
systems... but OTOH, the world *needs* better linker technology than we
currently have, so this projects like this one is a good thing.
Well, there's currently an LLVM linker in the works. If anything, that's
probably the way forward. But seeing as DMD is not using LLVM...
Linkers date from several decades ago, where programs can be broken up
into separate, self-contained source files in a simple way. Things have
changed a lot since then. Nowadays, we have template functions, virtual
functions, dynamic libraries, etc., which require hacks like weak
symbols to work properly. And we're *still* missing a sound conceptual
framework for things like cross-module dead code elimination,
cross-module template instantiation, duplicate code merging (like
overlapping immutable arrays), etc.. These things _sorta_ work right
now, but they're sorta hacked on top of basic 30-year-old linker
technology, rather than being part of a sound, conceptual linker
paradigm.
T
--
- Alex
