----- Original Message -----
> From: "Paul Moore" <paul@xxxxxxxxxxxxxx>
> To: "Jan Stancek" <jstancek@xxxxxxxxxx>
> Cc: selinux@xxxxxxxxxxxxx, sds@xxxxxxxxxxxxx
> Sent: Friday, 6 November, 2015 7:14:54 PM
> Subject: Re: [selinux-testsuite PATCH 3/4] mmap/mprotect_heap: make sure memory is allocated from heap
>
> On Friday, November 06, 2015 02:07:23 PM Jan Stancek wrote:
> > This test failed on ppc64 with 64k pagesize because memory
> > allocation used mmap() instead of advancing heap.
> >
> > Use mallopt(M_MMAP_THRESHOLD,..) with large enough value
> > to discourage use of mmap().
> >
> > Also set length in mprotect to pagesize, kernel silently aligns
> > it to pagesize anyway.
> >
> > Signed-off-by: Jan Stancek <jstancek@xxxxxxxxxx>
> > Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
> > Cc: Stephen Smalley <sds@xxxxxxxxxxxxx>
> > ---
> > tests/mmap/mprotect_heap.c | 9 ++++++++-
> > 1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/tests/mmap/mprotect_heap.c b/tests/mmap/mprotect_heap.c
> > index 691299493c3f..8b4321d6fc0b 100644
> > --- a/tests/mmap/mprotect_heap.c
> > +++ b/tests/mmap/mprotect_heap.c
> > @@ -3,6 +3,7 @@
> > #include <stdlib.h>
> > #include <errno.h>
> > #include <sys/mman.h>
> > +#include <malloc.h>
> >
> > int main(void)
> > {
> > @@ -10,13 +11,19 @@ int main(void)
> > int rc;
> > int pagesize = getpagesize();
> >
> > + rc = mallopt(M_MMAP_THRESHOLD, pagesize * 16);
> > + if (rc != 1) {
> > + fprintf(stderr, "mallopt failed: %d\n", rc);
> > + exit(1);
> > + }
>
> Can you explain how you arrived at 16? It looks a bit like a magic number to
> me, which always gives me pause. Based on a quick read of the man page, it
> would seem like any value greater than "pagesize" would work, yes?
I thought 2 would be enough - as you can find aligned page sized block within.
But when I tried it, it failed. It started working with 3 * pagesize.
I picked 16 as rule of thumb. Now, that I'm looking at man page I guess
we can as well use DEFAULT_MMAP_THRESHOLD_MAX.
Regards,
Jan
>
> > rc = posix_memalign(&ptr, pagesize, pagesize);
> > if (rc) {
> > fprintf(stderr, "posix_memalign failed: %d\n", rc);
> > exit(1);
> > }
> >
> > - rc = mprotect(ptr, 4096, PROT_READ | PROT_EXEC);
> > + rc = mprotect(ptr, pagesize, PROT_READ | PROT_EXEC);
> > if (rc < 0) {
> > perror("mprotect");
> > exit(1);
>
> --
> paul moore
> www.paul-moore.com
>
>
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