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

[Ridley Combs <rcombs@rcombs.me>]

> On Oct 24, 2020, at 10:41, Rich Felker <dalias@libc.org> wrote:
> 
> 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

Ah, I'd been thinking that dlopen might get called from within a ctor, but now that I look closer I see those are run after we set the state back anyway, so yeah this isn't needed.