[MLton-commit] r6675

[Adam Goode]

Wesley Terpstra wrote:
> This patch adds support for shared and static libraries to MLton. So far,
> the shared libraries probably only work on *nix. I have yet to make DLLs or
> dylibs for windows and mac osx respectively. However, the patch has already
> grown large enough and seems stable enough that I think this is a good
> check-point for committing it. I have tested all the codegens with all three
> compile modes (executable, archive, library) and they all work except
> amd64+shared. The problem here is that the output amd64 assembly code is not
> PIC. The amd64 codegen needs to be changed to use relocatable symbols, which
> shouldn't be too hard. In any case, both C and bytecode work on amd64. The
> x86 codegen also is not PIC, but x86 shared libraries work even when not
> relocatable. Nevertheless, when the amd64 codegen is updated, the x86 should
> be as well.


Actually, I believe that on Fedora, non-PIC x86 shared libraries will
also fail, because the tricks that the linker has to use to fix up the
non-PIC binary are forbidden at runtime (at least by default). This is
for security reasons (this kind of operation is often used by exploits
to generate code in memory), and I believe wastes extra pages of memory
as well (because of copy on write).

Gory details and plenty of commentary are here for the interested:
http://people.redhat.com/drepper/textrelocs.html
http://people.redhat.com/drepper/selinux-mem.html
http://people.redhat.com/drepper/dsohowto.pdf


Adam



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