[Pkg-erlang-devel] Bug#939804: Bug#939804: erlang: FTBFS on hppa - escript: exception error: bad argument

[Sergei Golovan]

Hi John,

On Mon, Sep 9, 2019 at 2:13 PM John David Anglin <dave.anglin at bell.net> wrote:
>
> If you know how to reduce one of these regexp problems, I could look again.  Debugging
> across forks is problematic (i.e., the error doesn't occur in escript).

I seem to find the problematic code. If you look into
erts/emulator/beam/erl_bif_re.c then
you'll find the following lines after line 66:

#define ERTS_PCRE_STACK_MARGIN (10*1024)

#  define ERTS_STACK_LIMIT ((char *) ethr_get_stacklimit())

static int
stack_guard_downwards(void)
{
    char *limit = ERTS_STACK_LIMIT;
    char c;

    ASSERT(limit);

    return erts_check_below_limit(&c, limit + ERTS_PCRE_STACK_MARGIN);
}

static int
stack_guard_upwards(void)
{
    char *limit = ERTS_STACK_LIMIT;
    char c;

    ASSERT(limit);

    return erts_check_above_limit(&c, limit - ERTS_PCRE_STACK_MARGIN);
}

void erts_init_bif_re(void)
{
    char c;
    erts_pcre_malloc = &erts_erts_pcre_malloc;
    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)
        erts_pcre_stack_guard = stack_guard_downwards;
    else
        erts_pcre_stack_guard = stack_guard_upwards;
    default_table = NULL; /* ISO8859-1 default, forced into pcre */
    max_loop_limit = CONTEXT_REDS * LOOP_FACTOR;

    erts_init_trap_export(&re_exec_trap_export, am_erlang, am_re_run_trap, 3,
                          &re_exec_trap);

    grun_trap_exportp =  erts_export_put(am_re,am_grun,3);
    urun_trap_exportp =  erts_export_put(am_re,am_urun,3);
    ucompile_trap_exportp =  erts_export_put(am_re,am_ucompile,2);

    return;
}

The code

    if ((char *) erts_ptr_id(&c) > ERTS_STACK_LIMIT)
        erts_pcre_stack_guard = stack_guard_downwards;
    else
        erts_pcre_stack_guard = stack_guard_upwards;

has been introduces in version 20, and it is used to protect stack
during PCRE calls.
It seems that this stack protection doesn't work for hppa and always
fails. As a result,
every call to a regexp routine fails.

After I remove the erts_pcre_stack_guard assignment, Erlang started to
build on hppa
just fine.

Unfortunately, I don't know anything about stack in hppa architecture,
so I can't offer
a proper fix in this case.

I hope this'll help in debugging and developing a fix.

Cheers!
-- 
Sergei Golovan