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Re: Executable memory: some apps that work on RH9 don't on FC1



On Mon, 2003-11-17 at 20:12, Roland McGrath wrote:
> > The official binary of mit-scheme 7.7.1 (http://www.gnu.org/software/mit-scheme)
> > segfaults if called with 'scheme -compiler'. In this case the scheme main
> > program load a 'band' called compiler.com, which contains executable code.
> > Could somebody investigate this issue? I am not that familiar with problems
> > like this.
> 
> If this binary was created with old tools and has no PT_GNU_STACK marker,
> then it should get executable stack by default.  More likely the issue is
> that it calls malloc and expects the memory returned to be executable.
> The Scheme runtime needs to be changed to use mmap when executability matters.

I further investigated problem using scheme-7.7.90 and found the
following. When loading a band (the runtime image), the following is
called:

static void *
mmap_heap_malloc_1 (unsigned long requested_length, int fixedp)
{
  unsigned long ps = (UX_getpagesize ());
  void * addr
    = (mmap (((void *) MMAP_BASE_ADDRESS),
	     (((requested_length + (ps - 1)) / ps) * ps),
	     (PROT_EXEC | PROT_READ | PROT_WRITE),
	     (MAP_PRIVATE | MAP_ANONYMOUS | (fixedp ? MAP_FIXED : 0)),
	     /* Ignored by GNU/Linux, required by FreeBSD and Solaris.  */
	     (-1),
	     0));
  return ((addr == MAP_FAILED) ? 0 : addr);
}

Now for the default runtime (runtime.com), requested_length == 5726028,
and the function proceeds without fault. However when the "-compiler"
switch is used to load the compiler, the all.com runtime is loaded and
then requested_length == 18563072 (this image is much bigger) and the
mmap call results in a segfault. ps is 4096, fixedp is 1 and
MMAP_BASE_ADDRESS == 4096.
Why does mmap segfault at all? Shouldn't it at worst return an error?

Hope this helps...

-- 
Gérard Milmeister
Tannenrauchstrasse 35
8038 Zürich
gemi bluewin ch




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