On Wed, Aug 29, 2007 at 10:40:41PM +0400, Alexander Vodomerov wrote: > On Wed, Aug 29, 2007 at 08:41:12AM -0700, Bryan O'Sullivan wrote: > > > The underlying problem is harder to fix: the default SELinux policy doesn't > > allow PROT_EXEC pages to be mapped with PROT_WRITE, for obvious reasons. > > The solution is expensive in terms of address space and TLB entries: map > > the same pages twice, once only with PROT_EXEC, and once only with > > PROT_WRITE. > Just for experiment I've removed PROT_EXEC from my_mmap function in > rts/MBlock.c and recompiled GHC. The resulting GHC was able to compile > itself and my code. Binaries, produced by it worked fine with SELinux. > However, another problem related to GHCi ocurred. More details are > available at the 738 ticket you mentioned. > > So it is not clear if GHC does really need this PROT_EXEC. Can someone > familiar with GHC internals answer why PROT_EXEC is used in getMBlocks?
It's not possible to correctly implement 'foreign import ccall
"wrapper"' without self-modifying code on any mainstream computer
architecture. Does this program work on your no-PROT_EXEC ghc? :
{-# OPTIONS_GHC -ffi #-}
import Foreign
foreign import ccall "wrapper" wrap :: IO () -> IO (FunPtr (IO ()))
foreign import ccall "dynamic" call :: FunPtr (IO ()) -> IO ()
main = call =<< wrap (print "hi!")
Stefan
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