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Date: Tue, 9 Jan 2018 16:24:06 -0600
From: William Pitcock <nenolod@...eferenced.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] track pthread stack guard sizes

Hi,

On Tue, Jan 9, 2018 at 11:22 AM, Rich Felker <dalias@...c.org> wrote:
> On Sat, Jan 06, 2018 at 04:44:43AM +0000, William Pitcock wrote:
>> some applications (rustc) are dependent on pthread_getattr_np() providing the guard size.
>> ---
>>  src/internal/pthread_impl.h     | 1 +
>>  src/thread/pthread_create.c     | 1 +
>>  src/thread/pthread_getattr_np.c | 1 +
>>  3 files changed, 3 insertions(+)
>>
>> diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
>> index 56e19348..c2cafeaa 100644
>> --- a/src/internal/pthread_impl.h
>> +++ b/src/internal/pthread_impl.h
>> @@ -48,6 +48,7 @@ struct pthread {
>>       void *stdio_locks;
>>       uintptr_t canary_at_end;
>>       void **dtv_copy;
>> +     size_t guard_size;
>>  };
>>
>>  struct __timer {
>> diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
>> index 6cbf85b3..0faad765 100644
>> --- a/src/thread/pthread_create.c
>> +++ b/src/thread/pthread_create.c
>> @@ -265,6 +265,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
>>       new->map_size = size;
>>       new->stack = stack;
>>       new->stack_size = stack - stack_limit;
>> +     new->guard_size = guard;
>>       new->start = entry;
>>       new->start_arg = arg;
>>       new->self = new;
>> diff --git a/src/thread/pthread_getattr_np.c b/src/thread/pthread_getattr_np.c
>> index ae26a5ab..29a209bd 100644
>> --- a/src/thread/pthread_getattr_np.c
>> +++ b/src/thread/pthread_getattr_np.c
>> @@ -7,6 +7,7 @@ int pthread_getattr_np(pthread_t t, pthread_attr_t *a)
>>  {
>>       *a = (pthread_attr_t){0};
>>       a->_a_detach = !!t->detached;
>> +     a->_a_guardsize = t->guard_size;
>>       if (t->stack) {
>>               a->_a_stackaddr = (uintptr_t)t->stack;
>>               a->_a_stacksize = t->stack_size;
>> --
>> 2.15.0
>
> I'm pretty sure there's another bug in this patch: the local variable
> guard is uninitialized where you use it if the application provided a
> stack and TLS was able to be allocated in the app-provided stack.
>
> The line guard = 0; above should probably just be moved down one line
> (and unindented one level).
>
> Does this sound right?

Yes, I would agree that guardsize should be 0 if the app provided a
sufficient stack.
The rustc error had to do with a libc-provided stack, so was trying to
fix it quickly for that case mostly.

William

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