Re: [musl] [PATCH] ldso: notify the debugger when we're doing a dlopen

[Rich Felker <dalias@libc.org>]

On Sat, Oct 24, 2020 at 12:31:56AM -0500, rcombs wrote:
> Otherwise lldb doesn't notice the new library and stack traces containing it
> get cut off unhelpfully.
> ---
>  ldso/dynlink.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/ldso/dynlink.c b/ldso/dynlink.c
> index fcc8f6a6..1ab9bf5b 100644
> --- a/ldso/dynlink.c
> +++ b/ldso/dynlink.c
> @@ -1963,7 +1963,7 @@ void __dls3(size_t *sp, size_t *auxv)
>  	debug.bp = dl_debug_state;
>  	debug.head = head;
>  	debug.base = ldso.base;
> -	debug.state = 0;
> +	debug.state = RT_CONSISTENT;
>  	_dl_debug_state();
>  
>  	if (replace_argv0) argv[0] = replace_argv0;
> @@ -2012,6 +2012,10 @@ void *dlopen(const char *file, int mode)
>  	pthread_rwlock_wrlock(&lock);
>  	__inhibit_ptc();
>  
> +	int oldstate = debug.state;
> +	debug.state = RT_ADD;
> +	_dl_debug_state();
> +
>  	p = 0;
>  	if (shutting_down) {
>  		error("Cannot dlopen while program is exiting.");
> @@ -2104,9 +2108,10 @@ void *dlopen(const char *file, int mode)
>  	update_tls_size();
>  	if (tls_cnt != orig_tls_cnt)
>  		install_new_tls();
> -	_dl_debug_state();
>  	orig_tail = tail;
>  end:
> +	debug.state = oldstate;
> +	_dl_debug_state();
>  	__release_ptc();
>  	if (p) gencnt++;
>  	pthread_rwlock_unlock(&lock);
> -- 
> 2.17.1

This looks good, but saving/restoring oldstate isn't necessary and
doesn't make sense logically. The code here is taking place under an
exclusive lock on the state. The initial state being consistent is a
logical precondition to it, and a requirement for releasing the lock
again when finished.

Rich