repost: why doesn't i686-pc-mingw32-ld offer gc-sections?

[Adam Megacz <adam at megacz dot com>]

Hey, does anybody have any idea about this? Short form of the question
is: if BFD abstracts the internal structure of binary files, why will
gc-sections work on ELF but not on PE (win32)? How much effort would
be required to make it work (if it's only a few days, I might be able
to do it).

 - a

Adam Megacz <adam@megacz.com> writes:
> Hey, all.
> 
> I'm sort of desperately in need of a really tiny statically linked
> binary that uses parts of libjava (which is huge). -ffunction-sections
> and gc-sections are likely my only salvation. I have some ugly
> post-processing hacks to simulate vtable-gc, which mingw does not
> directly support.
> 
> I noticed that the i686-gnu-linux-ld does gc-sections, yet
> i686-pc-mingw32-ld does not. This confuses me. My understanding (which
> is probably incorrect) is that ld manipulates binaries via the BFD
> abstraction layer, so the concept of a "relocation" and a "section"
> should be independent of which platform you're targeting.
> 
> If this is the case, shouldn't the mark-sweep algorithm to find
> unreachable sections be totally independent of which backend (PE / ELF
> / A.OUT) is in use? I understand why vtable-gc doesn't work this way
> (it requires special markers to be added to the binary), but it seems
> that gc-sections shouldn't need any extra special magic.
> 
> If there is some extra work to be done to get this feature into ld, I
> may be able to throw a few days at adding the feature. Can anybody
> give me an idea of what would be involved? I already have FSF
> paperwork on file.
> 
> One other idea -- I noticed this in objcopy's man page:
> 
>   objcopy uses the GNU BFD Library to read and write the object files.
>   It can write the destination object file in a format different from
>   that of the source object file.... Note that objcopy should be able
>   to copy a fully linked file between any two formats.
> 
> This sounds pretty amazing -- does it mean that I could generate ELF
> .o's, link them into an ELF executable (performing section-gc along
> the way), and then use objcopy to turn that into a PE executable?
> Somehow that sounds like it should be impossible...
> 
> Thanks for any advice...
> 
>   - a
> 

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