Hi John,
On Tue, Sep 10, 2019 at 4:58 AM John David Anglin <dave.ang...@bell.net> wrote:
>
> I added some printfs to the code.
>
> thr_wrapper: stacksize=0x0
> thr_wrapper: stacksize=0x0
> thr_wrapper: stacksize=0x0
> thr_wrapper: stacksize=0x10000
> thr_wrapper: stacksize=0x10000
> thr_wrapper: stacksize=0x10000
> erts_init_bif_re: &c=0xf9730748 ERTS STACK LIMIT=0x0
> erts_init_bif_re: &c=0xf9df6748 ERTS STACK LIMIT=0x0
> erts_init_bif_re: &c=0xf90b0748 ERTS STACK LIMIT=0x0
> erts_init_bif_re: &c=0xf908c748 ERTS STACK LIMIT=0x0
This seems to cause the issue since stack limit 0x0 means that it's still
uninitialized, but it's used in a comparison which determines the
direction of stack.
>
> It would seem to me that ERTS_STACK_LIMIT is incorrect. As a result,
> stack_guard_downwards
> is called instead of stack_guard_upwards.
>
> It's also a bit odd that twd->stacksize in thr_wrapper is sometimes 0.
> Think ethr_thr_create
> needs looking at.
May be. As a quick fix I can suggest a separate check for the stack
direction in erl_bif_re.c, here's a patch.
--- a/erts/emulator/beam/erl_bif_re.c
+++ b/erts/emulator/beam/erl_bif_re.c
@@ -90,6 +90,15 @@
return erts_check_above_limit(&c, limit - ERTS_PCRE_STACK_MARGIN);
}
+__attribute__((noinline)) static int stack_grows_downwards(char *prev_c)
+{
+ char c;
+ if (&c < prev_c)
+ return 1;
+ else
+ return 0;
+}
+
void erts_init_bif_re(void)
{
char c;
@@ -97,7 +106,7 @@
erts_pcre_free = &erts_erts_pcre_free;
erts_pcre_stack_malloc = &erts_erts_pcre_stack_malloc;
erts_pcre_stack_free = &erts_erts_pcre_stack_free;
- if ((char *) erts_ptr_id(&c) > ERTS_STACK_LIMIT)
+ if (stack_grows_downwards(&c))
erts_pcre_stack_guard = stack_guard_downwards;
else
erts_pcre_stack_guard = stack_guard_upwards;
I don't think it can be accepted upstream as a permanent fix though. I
think it'd
be better to fix the stack limit initialization somehow.
Cheers!
--
Sergei Golovan
