Re: [PATCH] track pthread stack guard sizes

[Rich Felker <dalias@libc.org>]

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?

Rich