On 13.06.2017 14:44, Peter Maydell wrote: > On 13 June 2017 at 12:54, Antonio Groza <antoniogr...@gmail.com> wrote: >> Hello, i am trying to emulate x86 on a platform that won't allow me to map >> memory pages as RWX(Apple's iOS) and i was wondering if there was any way >> of running qemu without doing that. I've had a brief look at your >> documentation and it looks like you are transpiling between 2 different >> instruction sets and i don't know how that would be possible without a rwx >> page. > > It's certainly possible in theory -- you'd just need to be more > careful than we are currently about mapping the memory RW when > writing or patching code and then R-X when executing. (Now we're > multithreaded this is probably trickier than when we only had > a single thread, though.) But we don't do it currently and it > would require (possibly complicated) code changes to do it. > > thanks > -- PMM >
MacOSX and NetBSD both have this RWX MPROTECT restriction and both have option to relax it on per-page basis. Example code inspiration is in LLVM's: Memory::AllocateRWX (llvm/lib/Support/Unix/Memory.inc). [NetBSD code is still pending upstream in review] Proper PaX MPROTECT is not about toggling RW-RX memory region, as once a memory page was allocated with W mode, it won't in regular circumstances mapped to X anymore.
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