Mach-O GHCi linker lacks support for a range of relocation entries
The Mach-O code of the GHCi linker rts/Linker.c
lacks support for a range of relocation entries. It used to silently ignore many of them. The following patch makes it barf() when it encounters an unsupported entry:
Wed Nov 11 13:07:12 EST 2009 Manuel M T Chakravarty <chak@cse.unsw.edu.au>
* Barf on unhandled Mach-O relocations in the ghci linker
- It might be worthwhile to MERGE this to 6.12, BUT somebody should validate
it on PPC/Mac OS X first.
Moreover, at least one entry type —i.e., GENERIC_RELOC_LOCAL_SECTDIFF
— is not correctly implemented.
This is an unsatisfactory situation as the transition from Mac OS X 10.5 (Leopard) to 10.6 (Snow Leopard) showed. In that case, changes in ld
suddenly created a so far unsupported entry type. This was before the above patch; so, the ignored entry led to an incorrectly relocated image, which crashed GHCi with a SIGBUS.
Instead of trying to improve the dynamic linker, IMHO, GHC should use dynamic libraries with dlopen()
and leave the implementation of dynamic linking to the OS vendor. This has a number of advantages:
- The RTS gets smaller & simpler, and we eliminate a whole category of potentially tricky bugs.
- Dynamically loaded code can use dtrace probes (and other features requiring linker trickery).
- Packages that GHC links to, don't need to be in memory twice (once statically and once dynamically linked).
- Potential performance advantage due to optimisations in the OS' dynamic linker.
The main obstacle with using dynamic libraries and dlopen()
appears to be the required on-the-fly conversion of GHC-generated object files into dynamic libraries. Otherwise, SimonM says that it is already possible to compile GHC itself dynamically-linked at the moment that the linker will then use dlopen()
for loading packages.
More details are in the following thread on cvs-ghc@haskell.org
:
http://www.haskell.org/pipermail/cvs-ghc/2009-November/050941.html http://www.haskell.org/pipermail/cvs-ghc/2009-October/050893.html
Trac metadata
Trac field | Value |
---|---|
Version | 6.13 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Runtime System |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |