[ANNOUNCEMENT] TEST RELEASE: Cygwin 2.1.0-0.1
Ken Brown
kbrown@cornell.edu
Fri Jun 26 16:55:00 GMT 2015
Hi Corinna,
On 6/26/2015 11:36 AM, Corinna Vinschen wrote:
> Hi Ken,
>
> On Jun 26 10:33, Ken Brown wrote:
>> On 6/26/2015 10:14 AM, Corinna Vinschen wrote:
>>> On Jun 26 08:02, Ken Brown wrote:
>>>> On 6/26/2015 7:12 AM, Corinna Vinschen wrote:
>>> Thank you. I'll try to test this in the next couple of days. One hint
>>> and one question:
>>>
>>>> The signal handler:
>>>>
>>>> /* Attempt to recover from SIGSEGV caused by C stack overflow. */
>>>> static void
>>>> handle_sigsegv (int sig, siginfo_t *siginfo, void *arg)
>>>> {
>>>> /* Hard GC error may lead to stack overflow caused by
>>>> too nested calls to mark_object. No way to survive. */
>>>> if (!gc_in_progress)
>>>> {
>>>> struct rlimit rlim;
>>>>
>>>> if (!getrlimit (RLIMIT_STACK, &rlim))
>>>
>>> This getrlimit probably won't work as desired. I just had a quick look
>>> how this request is handled. It will return the size of the alternate
>>> stack while running the signal handler, rather than the size of the
>>> initial thread's stack as required by POSIX. This definitely needs
>>> fixing.
>>>
>>>> {
>>>> enum { STACK_DANGER_ZONE = 16 * 1024 };
>>>> char *beg, *end, *addr;
>>>>
>>>> beg = stack_bottom;
>>>> end = stack_bottom + stack_direction * rlim.rlim_cur;
>>>> if (beg > end)
>>>> addr = beg, beg = end, end = addr;
>>>> addr = (char *) siginfo->si_addr;
>>>> /* If we're somewhere on stack and too close to
>>>> one of its boundaries, most likely this is it. */
>>>> if (beg < addr && addr < end
>>>> && (addr - beg < STACK_DANGER_ZONE
>>>> || end - addr < STACK_DANGER_ZONE))
>>>> siglongjmp (return_to_command_loop, 1);
>>>> }
>>>> }
>>>>
>>>> /* Otherwise we can't do anything with this. */
>>>> deliver_fatal_thread_signal (sig);
>>>> }
>>>>
>>>> The code to set up the signal handler on the alternate stack:
>>>>
>>>> static bool
>>>> init_sigsegv (void)
>>>> {
>>>> struct sigaction sa;
>>>> stack_t ss;
>>>>
>>>> stack_direction = ((char *) &ss < stack_bottom) ? -1 : 1;
>>>>
>>>> ss.ss_sp = sigsegv_stack;
>>>> ss.ss_size = sizeof (sigsegv_stack);
>>> ^^^^^^^^^^^^^^^^^^^^^^^
>>>
>>> What's that size in bytes?
>>
>> SIGSTKSZ
>
> Thanks. Another question: How does emacs compute stack_bottom?
Very near the beginning of main() it does the following:
char stack_bottom_variable;
[...]
/* Record (approximately) where the stack begins. */
stack_bottom = &stack_bottom_variable;
Ken
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