On Thu, 9 Dec 2010, Jay K wrote:
Most Linux kernel based systems will give you an executable stack if you
ask for it by setting the GNU executable stack attribute on your executable.
I really don't want to make the entire stack executable just for the
sake of a relatively small amount of code. It seems like overkill.
I don't even like the use I've seen of mprotect as needed that makes
entire pages executable. Also overkill and slow.
I think I will look into what various JITers do (Java, Mono).
e.g. maybe mmap over file -1 with protection flags that allow execution?
I believe I have known/nested lifetimes, so I can use a per-thread LIFO discipline,
rather than, e.g. something garbage collected.
This is how I allocate temporary executable memory for JIT compilation,
FWIW:
// POSIX:
void* p = mmap(0, sizeInBytes, PROT_EXEC | PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON, -1, 0);
if (p != MAP_FAILED) {
doSomething(p);
munmap(const_cast<void*>(p), sizeInBytes);
}
// Windows:
void* p = VirtualAlloc(0, sizeInBytes, MEM_COMMIT | MEM_RESERVE,
PAGE_EXECUTE_READWRITE);
if (p) {
doSomething(p);
VirtualFree(const_cast<void*>(p), 0, MEM_RELEASE);
}
We also support far more than Linux: Solaris, MacOSX, Open/Net/FreeBSD, NT.
sort of: Tru64, HP-UX (they were running recently)
theoretically: Irix, AIX (should be easy given what we have), maybe even VMS (I
did some investigation/work on it)
Obviously there is a solution involving writing out little temporary .so files,
since all systems can run executable code out of files, but that I definitely don't want to do.
