[LTP] LTP release

[Cyril Hrubis]

Hi!
> > Sounds reasonable. I tried to reserve more space for the mapping grows,
> > and that works for me:).
> >
> 
> To precisely, we could reserve 256 pages size at the end of the free-range
> memory to let the stack keep away from a preceding mapping in its growing
> then.
> (my only concern is the stack_guard_gap can be changed via kernel command
> line, but I assume that happen rarely, so here use the default 256 pages)
> 
> If there is no objection, I'd make these changes in patch V4.
> 
> --------
> 
> static void *find_free_range(size_t size)
> {
>     void *mem;
>     long stack_guard_gap = 256 * getpageszie();
> 
>     /*
>     * Since the newer kernel does not allow a MAP_GROWSDOWN mapping to grow
>     * closer than stack_guard_gap pages away from a preceding mapping.
>     * The guard then ensures that the next-highest mapped page remains more
>     * than stack_guard_gap below the lowest stack address, and if not then
>     * it will trigger a segfault. So, here let's reserve 256 pages memory
>     * spacing for stack growing safely.
>     */
>     mem = SAFE_MMAP(NULL, size + stack_guard_gap, PROT_READ | PROT_WRITE,
>                       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>     SAFE_MUNMAP(mem, size + stack_guard_gap);
> 
>     return mem;
> }
> 
> static void split_unmapped_plus_stack(void *start, size_t size)
> {
>     /* start           start + size
>     * +---------------------+----------------------+-----------+
>     * + unmapped            | mapped               | 256 pages |
>     * +---------------------+----------------------+-----------+
>     *                       stack
>     */

Shouldn't the 256 pages follow the unmapped part?

If I'm not mistaken if stack grows down the address decreases with stack
allocations, so it should be as:

| 256 pages | unmapped | mapped |


That would also mean that we should map the stack at address start +
total_size - size if I'm not mistaken. I guess that we can put all the
mess into a single function as well and have just allocate_stack() that
will find a suitable address, mmap the stack together, splitting this
into two functions is unnecessary confusing.

>     stack = SAFE_MMAP(start + size, size, PROT_READ | PROT_WRITE,
>                              MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS |
> MAP_GROWSDOWN,
>                              -1, 0);
> }

Also I would like to get rid of the -fno-optimize-sibling-calls in the
Makefile, this makes the test a bit fragile and less portable.

-- 
Cyril Hrubis
chrubis@suse.cz